JP3873493B2 - Charged particle beam extraction apparatus and charged particle beam irradiation method - Google Patents

Description

【００１７】
ここで、Ｒ：照射領域の半径，ｍ：層の総数である。
【００１８】
（数１）より、本実施例の層Ｌ９における各照射領域Ａ９ｉの中心位置Ｐ９ｉの間隔Ｄ９は、
【００１９】
【数２】

【００２０】
となる。（数１）に従って、その他の層Ｌ１〜Ｌ８についてもそれぞれに間隔Ｄ１〜Ｄ８が求められる。求められた間隔Ｄｎに基づいて各照射領域Ａｎｉの位置が設定され、その中心位置Ｐｎｉが決定される。なお（数１）によれば、層Ｌｎが浅い位置にあるほど間隔Ｄｎは広くなる。この間隔Ｄｎが最も広い層Ｌ１では、間隔Ｄ１が照射領域Ａｎｉの半径と等しくなる。層Ｌ１における各照射領域Ａ１ｉを図３（ｂ）に示す。このように、各層Ｌｎにおいて照射領域Ａｎｉの間隔Ｄｎを照射領域Ａｎｉの半径Ｒ以下に設定することによって、ガウス分布をもつビームの照射線量の重ね合わせにより、ビームを照射したときの各層Ｌｎにおける照射線量の分布が均一となる。
【００２１】
次に、演算部３１は、各層Ｌｎに照射するビームの照射線量を決定する。まず最初に、層Ｌ９に照射するビームの照射線量を決める。層Ｌ９に照射される照射線量としては、層Ｌ９の各照射領域Ａ９ｉにビームを照射して得られる照射線量の分布（各照射領域Ａ９ｉにおける照射線量を重ね合せた結果）が、演算部３１に入力された患部に照射すべき照射線量と等しくなるように、照射領域の重ね合わせを考慮して、各照射領域Ａ９ｉに照射するビームの照射線量が決定される。当然のことながら、各照射領域Ａ９ｉに照射するビームの照射線量は、演算部３１に入力された患部に照射すべき照射線量よりも小さくなる。
【００２２】
続いて、層Ｌ８における照射線量を決定するが、層Ｌ８はエネルギーＥ９のビームが照射されるときにいくらか照射されるので、その照射線量を考慮しなければならない。ここで図４を用いて、本実施例における、ビームのエネルギーＥｎと照射線量との関係について説明する。図４は、横軸に体表からの深さ位置、縦軸に照射線量を示し、エネルギーＥ６〜Ｅ９のビームによる照射線量の分布と、その総和の分布を表わす。図に示すように、エネルギーＥ９のビームを照射した場合、層Ｌ９位置で最も照射線量が大きくなっているが、層Ｌ８位置でもいくらかは照射される。従って、層Ｌ９位置と層Ｌ８位置とで照射線量を均一にするためには、図に示すように、エネルギーＥ８のビームによる照射線量をエネルギーＥ９のビームの照射線量に比べて低くしなければならない。具体的には、エネルギーＥ９のビームの照射線量分布において、層Ｌ９位置における照射線量（ピーク値）から層Ｌ８位置における照射線量を引いた値を、層Ｌ８に照射される線量とすれば良い。
【００２３】
演算部３１は、この層Ｌ８に照射される線量に基づき、かつ照射領域の重ね合わせを考慮して、各照射領域Ａ８ｉに照射するビームの照射線量、すなわちエネルギーＥ８のビームによる照射線量（ピーク値）を決定する。このようにしてエネルギーＥ８のビームによる照射線量を決定することにより、層Ｌ８位置における照射線量は、層Ｌ９位置における照射線量と等しくなる。その他のエネルギーＥ１〜Ｅ７のビームについてもエネルギーＥ８のビームの場合と同様に、エネルギーの高いビームによる照射線量と、照射領域の重ね合わせとを考慮した上で、照射線量（ピーク値）を決定する。
【００２４】
以上説明したように、各層Ｌｎに照射するビームのエネルギーＥｎ、各層Ｌｎにおける各照射領域Ａｎｉの中心位置Ｐｎｉ、及び各層Ｌｎの照射領域Ａｎｉにおける照射線量を決定する。本実施例によれば、層Ｌｎの位置が浅くなるにしたがって、ビームのエネルギーＥｎ及び照射線量は低く設定され、照射領域Ａｎｉの間隔Ｄｎは広く設定される。
【００２５】
演算部３１で求められたビームのエネルギーＥｎ，各照射領域Ａｎｉの中心位置Ｐｎｉ及び照射線量は、制御部３２に出力され、制御部３２に記憶される。また、制御部３２は、入力されたエネルギーＥｎを制御部３３に出力する。
【００２６】
制御部３２は、入力されたビームのエネルギーＥｎに基づいて、それらのビームを加速器１から出射するために電源１６から高周波印加装置１１に出力する電流値を求める。求めた電流値は、層Ｌ１〜Ｌ９に対応づけた形式で記憶する。また、制御部３２は、入力された各照射領域Ａｎｉの中心位置Ｐｎｉに基づいて、ビームをその中心位置Ｐｎｉに照射するために電源２８から走査電磁石２４，２５それぞれに出力する電流値を求める。この電流値は、各照射領域Ａｎｉに対応づけた形式で記憶される。なお、前述したように、層の位置が浅いほど隣り合う照射領域の間隔Ｄｎは大きくなるので、走査電磁石に供給する電流値の照射領域変更時の変化量も大きくなる。
【００２７】
一方、制御部３３は、入力されたビームのエネルギーＥｎに基づいて、前段加速器４から出射されるビーム（エネルギー一定）をエネルギーＥｎまで加速する際に偏向電磁石１２，四極電磁石１３，六極電磁石１４および高周波加速空胴１５で必要とされる電流値を求める。求められた電流値は、層Ｌ１〜Ｌ９に対応づけた形式で偏向電磁石１２，四極電磁石１３，六極電磁石１４および高周波加速空胴１５毎に記憶される。また、制御部３３は、加速器１から出射したビームを走査電磁石２４，２５に導くために四極電磁石２２及び偏向電磁石２１，２３で必要とされる電流値を求める。求めた電流値は、層Ｌ１〜Ｌ９に対応づけた形式で四極電磁石２２及び偏向電磁石２１，２３毎に記憶される。
【００２８】
なお、制御部３２，３３は、各電流値を求めるために、予めビームのエネルギーや照射領域の中心位置と各電流値とを対応づけたテーブルを用意しておき、そのテーブルを用いて各電流値を求める。
【００２９】
次に、ビームを患部に照射するまでの手順について説明する。なお、本実施例では、体表から最も深い位置にある層Ｌ９から最も浅い位置にある層Ｌ１へと順にビームを照射する。まず、層Ｌ９にビームを照射する手順を説明する。
【００３０】
最初に、制御部３３から前段加速器４に対してビーム出射指令が出力される。前段加速器４は、ビーム出射指令が入力されると、ビームを出射する。前段加速器４から出射されたビームは、加速器１に入射される。
【００３１】
また、制御部３３は、前段加速器４にビーム出射指令を出力すると共に、電源１７に対して層Ｌ９に対応づけて記憶された偏向電磁石１２，四極電磁石１３，六極電磁石１４及び高周波加速空胴１５の各電流値を出力する。電源１７は、入力された値の電流を偏向電磁石１２，四極電磁石１３，六極電磁石１４及び高周波加速空胴１５のそれぞれに供給する。ここで、それぞれに供給される電流は、ビームの加速と共に変化するように設定されている。
【００３２】
ここで、加速器１における各構成の役割を説明する。まず、偏向電磁石１２は、供給された電流に応じた磁場を発生し、ビームが加速器１の周回軌道に沿って周回するように磁場でビームを偏向する。四極電磁石１３は、供給された電流に応じた磁場によりビームの安定限界を制御する。高周波加速空胴１５は、供給された電流に応じてビームに高周波の電場を印加し、ビームを加速する。すなわち、ビームのエネルギーを上昇させる。六極電磁石１４は、供給された電流に応じてビームに磁場を印加することにより、ビームを共鳴させる。この共鳴は、ビームを加速器１から出射するときに用いる。
【００３３】
加速器１においてビームがエネルギーＥ９まで加速されると、制御部３２は層Ｌ９に対応づけて記憶された高周波印加装置１１の電流値を電源１６に出力する。電源１６は入力された値の電流を、高周波印加装置１１に供給する。高周波印加装置１１は、供給された電流に応じた高周波電場を発生し、その高周波電場をビームに印加することより、ビームを加速器１００から出射する。具体的には、本実施例の加速器１では、ビーム出射時に四極電磁石１３により安定限界を一定に保ち、その状態で高周波印加装置１１によりビームに高周波電場を印加する。高周波電場の印加により、ビームが安定限界を超え、安定限界を超えたビームは、六極電磁石１４の磁場により共鳴を起こし、加速器１から出射される。加速器１から出射されたビームは、回転照射装置２に導かれる。
【００３４】
制御部３３は、加速器１においてビームを加速中に、層Ｌ９に対応づけて記憶された四極電磁石２２及び偏向電磁石２１，２３の各電流値を電源２７に出力する。電源２７は入力された値の電流を、四極電磁石２２及び偏向電磁石２１，２３にそれぞれ供給する。回転照射装置２に入力されたビームは、四極電磁石２２及び偏向電磁石２１，２３により予め設定された軌道に沿って走査電磁石２４，２５に導かれる。
【００３５】
また、制御部３２は、制御部３３が電源２７に電流値を出力するのと共に、照射領域Ａ９１の中心位置Ｐ９１に対応づけて記憶された電流値を電源２８に出力する。電源２８は、入力された値の電流を走査電磁石２４，２５それぞれに供給する。走査電磁石２４，２５は、それぞれに供給された電流に応じて磁場を発生し、走査電磁石２４はＸ方向に、走査電磁石２５はＹ方向にビームを偏向する。走査電磁石２４，２５により偏向されたビームは、照射領域Ａ９１の中心位置Ｐ９１に照射される。
【００３６】
線量モニター２６は、患部に照射されるビームの照射線量を計測する。線量モニター２６において計測されたビームの照射線量の実測値は、制御部３２に入力される。制御部３２は、層Ｌ９に対応づけて記憶された照射線量の値（設定値）と、入力された実測値とを比較し、実測値が設定値に達した時点で電源１６に対して出射停止指令を出力する。電源１６は、出射停止指令が入力されると高周波印加装置１１に対する電流の供給を停止する。従って、高周波印加装置１１による高周波電場の発生が停止し、加速器１からのビームの出射も停止する。なお、実測値が設定値に達する前に加速器１を周回するビームがなくなった場合には、新たに前段加速器４からビームを入射し、加速器１においてエネルギーＥ９まで加速した後、再度ビームを加速器１から出射すれば良い。
【００３７】
このようにして照射領域Ａ９１に対するビームの照射が終了したら、次に照射領域Ａ９２にビームを照射する。照射領域Ａ９２にビームを照射する際には、加速器１からのビームの出射を停止した状態で、制御部３２から電源２８に対して、照射領域Ａ９２に対応づけて記憶された走査電磁石２４，２５のそれぞれの電流値が出力される。電源２８は入力された値の電流を走査電磁石２４，２５それぞれに供給し、走査電磁石２４，２５は供給された電流に応じた磁場を発生する。なお、図３(ａ)に示すように、照射領域Ａ９２の位置は、照射領域Ａ９１をＸ方向にＤ９だけずらした位置に相当するので、ビームをＹ方向に偏向する走査電磁石２５に供給される電流は、照射領域Ａ９１を照射するときと照射領域Ａ９２を照射するときとで変化はなく、ビームをＸ方向に偏向する走査電磁石２４に供給される電流のみが変化する。
【００３８】
電源２８から走査電磁石２４，２５に電流が供給された時点で、制御部３２は、層Ｌ９に対応づけて記憶された高周波印加装置１１の電流の値を電源１６に出力する。電源１６は、入力された値の電流を高周波印加装置１１に供給する。高周波印加装置１１は、供給された電流に応じた高周波電場を加速器１を周回中のビームに印加し、ビームを加速器１から出射する。加速器１から出射されたビームは、走査電磁石２４，２５に導かれて走査電磁石２４，２５により偏向された後、照射領域Ａ９２に照射される。照射領域Ａ９１にビームを照射する場合と同様に、照射領域Ａ９２にビームを照射する際にも、線量モニター２６による実測値と制御部３２に記憶された設定値とを比較し、実測値が設定値に達した時点で加速器１からのビームの出射を停止する。
【００３９】
このような手順を繰り返すことにより、層Ｌ９の各照射領域Ａ９１，Ａ９２，…に対して、設定された照射線量のビームが照射される。なお、照射領域Ａ９１から照射領域Ａ９２にビームの照射位置を変更する際には走査電磁石２５に供給する電流に変化はなかったが、ビームの照射位置をＹ方向に移動する場合には走査電磁石２５に供給する電流も変化させる。
【００４０】
層Ｌ９における全ての照射領域Ａ９ｉにビームを照射し終えたら、次に層Ｌ８の各照射領域Ａ８ｉを照射する。層Ｌ８にビームを照射する手順は、層Ｌ９の場合と同様であり、層Ｌ８に対応づけて記憶された各電流値等を各々の装置に供給することにより加速器１，回転照射装置２を制御して、層Ｌ８にビームを照射する。以降、層Ｌ１まで同じ手順を繰り返すことにより患部全体にビームを照射する。
【００４１】
図５は、患部に対してビームを照射する手順をフローチャートで示す。まず、ビームを照射する層Ｌｎとして層Ｌ９を設定し、ビームを照射する照射領域Ａniとして照射領域Ａ９１を設定する（ステップ５０１）。次に、前段加速器４からビームを出射し、加速器１にそのビームを入射する（ステップ５０２）。加速器１は、入射されたビームをエネルギーＥｎまで加速する（ステップ５０３）。またステップ５０２と並行して、走査電磁石２４，２５に対して、照射領域Ａｎｉにビームを照射するための電流を供給する（ステップ５０４）。
【００４２】
次に、加速器１からビームを出射し、照射領域Ａｎｉにそのビームを照射する（ステップ５０５）。続いて、照射されたビームの照射線量の実測値が、層Ｌｎに対して設定された照射線量の設定値に達したかを判定する(ステップ５０６)。ステップ５０６において「Yes」と判定された場合にはステップ５０７へ進み、「No」と判定された場合にはステップ５０８へ進む。ステップ５０８では、加速器１にビームがあるかを判定し、「Yes」と判定した場合にはステップ５０６へ進み、「No」と判定した場合にはステップ５０２へ進む。すなわち、加速器１にビームがなくなった時点で、ステップ５０２，５０３でエネルギーＥｎのビームを生成し、ステップ５０５により再度ビームを照射する。
【００４３】
ステップ５０６においてビームの照射線量の実測値が、設定値に達したと判定されたら、ビームの出射を停止する（ステップ５０７）。次に層Ｌｎの全ての照射領域Ａｎｉを照射したかを判定し、「Yes」と判定した場合にはステップ５１０へ、「No」と判定した場合にはステップ５１１へ進む（ステップ５０９）。ステップ５１１では、ｉに１を加算し、ステップ５１２へ進む。なお、ｉに１が加算されたことによってビームを照射する照射領域Ａｎｉが変更される。ステップ５１２では、加速器１にビームがあるかを判定し、「Yes」と判定した場合にはステップ５０４へ進む。一方「No」と判定した場合には、ステップ５０２へ進む。このようにして、新たな照射領域Ａｎｉにビームが照射される。
【００４４】
ステップ５１０では、層Ｌｎが層Ｌ１かを判定し、「Yes」と判定した場合には患部に対するビームの照射を終了する。「No」と判定した場合には、ステップ５１３へ進む。ステップ５１３では、ｎに１を加算し、ステップ５０２へ進む。ｎに１が加算されたことによってビームを照射する層Ｌｎが変更される。
【００４５】
以上説明したように、本実施例では、予め決定した照射計画に従って、各層Ｌｎにおける各照射領域Ａｎｉ毎にビームを照射する。このような本実施例によっても従来の技術と同様に、ビームの照射位置が照射領域Ａｎｉからずれてしまうことがある。しかしながら、本実施例によれば、照射位置がずれた場合でも、線量の不均一を抑制することができる。なぜならば、本実施例では、前述のように位置が深い層においては各照射領域Ａｎｉの間隔Ｄｎが狭い、すなわち照射領域Ａｎｉが密集しているため、そのうちの１つの位置がずれたとしても、全体の照射線量から見て位置のずれた照射領域の照射線量の割合は非常に小さく、照射線量の分布に大きな影響はない。よって、位置が深い層におけるビームの照射位置のずれは、患部における照射線量の均一性に大きな影響を及ぼさない。また、位置が浅い層ではビームの照射線量が小さいため、照射位置がずれても全体の照射線量に比べればその割合は小さい。よって、位置が浅い層におけるビームの照射位置のずれも、患部における照射線量の均一性に大きな影響を及ぼさない。このように、本実施例では、深い位置にある層ほど照射領域の間隔を狭めること、および浅い位置にある層ほど照射線量を小さくすることにより、照射位置のずれが原因で発生する照射線量の不均一を抑制することができる。
【００４６】
なお、本実施例において、各層毎に照射領域を移動する方向を変えることにより、ビームが照射領域からずれることによって起こる照射線量の不均一を相殺することができる。
【００４７】
また、本実施例では、照射領域を直線状に移動させているが、照射領域の移動のしかたは本実施例に限られるものではなく、例えばうずまき状に移動させても良い。
【００４８】
（実施例２）
本発明の他の実施例である荷電粒子ビーム出射装置について、実施例１と異なる箇所を以下説明する。本実施例の荷電粒子ビーム出射装置は、図６に示すように、各層をＹ方向に複数の領域に分けて、その領域毎にビームを照射する。つまり、実施例１では点であった照射領域を、本実施例ではＸ方向に伸びる線とし、その照射領域ＡｎｉにおいてビームをＸ方向に複数回走査して照射する。なお、本実施例の荷電粒子線ビーム出射装置の装置構成は、実施例１と同様である。
【００４９】
本実施例において、演算部３１は、（数１）によりＹ方向における照射領域Ａｎｉの中心位置Ｐｎｉの間隔Ｄｎを決定し、その間隔Ｄｎに基づいてＹ方向における各照射領域Ａｎｉの中心位置Ｐｎｉを設定する。その後、層Ｌｎ全体を照射領域Ａｎｉで覆うように各照射領域ＡｎｉのＸ方向の長さと位置を決定し、その長さと位置からＸ方向における各照射領域Ａｎｉの両端位置を設定する。演算部３１で設定された各照射領域ＡｎｉのＹ方向における中心位置ＰｎｉとＸ方向における両端位置は、制御部３２に入力される。
【００５０】
制御部３２は、ビームをＹ方向における中心位置Ｐｎｉに照射するために走査電磁石２５で必要とされる電流値と、ビームをＸ方向における両端位置の間で走査して照射するために走査電磁石２４で必要とされる電流値とを求める。求めた各電流値は、照射領域Ａｎｉと対応づけた形で記憶する。なお、Ｘ方向にはビームを走査するため、走査電磁石２４で必要とされる電流値は周期的に正負が反転する交流電流となる。また、Ｙ方向における中心位置Ｐｎｉ及びＸ方向における両端位置と走査電磁石２４、２５で必要とされる電流値とは、その対応関係を予めテーブル化しておき、制御部３２はそのテーブルを用いることにより各電流値を求める。
【００５１】
以上説明した点以外は図１の実施例と同様である。
【００５２】
本実施例によれば、照射領域ＡｎｉにおいてビームはＸ方向に複数回走査され、予め設定された照射線量に達した時点で照射位置がＹ方向に移動されて照射領域Ａｎｉが変更される。このような本実施例でも、Ｙ方向における中心位置の間隔Ｄｎが各層毎に異なり（層の位置が浅いほど間隔Ｄｎは広くなる）、各層における照射線量が異なる（層の位置が浅いほど照射線量は少ない）ので、図１の実施例と同様に、患部における照射線量の不均一を抑制できる。
【００５３】
（実施例３）
本発明の他の実施例である荷電粒子ビーム出射装置について、実施例２と異なる箇所を以下説明する。本実施例の荷電粒子ビーム出射装置は、図９に示すように各層を複数の領域に分けて、その領域毎にビームを出射する。つまり、実施例２では、ビームをＸ方向に伸びる線状に走査したが、本実施例では、Ｘ方向及びＹ方向に斜めに延びる線にそって走査する。即ち、各照射領域Ａｎｉの中心がＸ方向及びＹ方向に斜めに延びる線である。図１０に走査する時のビーム中心の移動を実線で示す。本実施例において、走査電磁石２４と２５の電流は同時に変化させる。各照射領域Ａｎｉのビーム中心の走査角度は、走査電磁石２４と２５の電流変化率の比できまるため、走査ビームサイズに応じ適切に走査電磁石２４と２５の電流変化率を定める。演算部３１は、照射領域ＡｎｉのＸ方向及びＹ方向の中心位置ＰｎｉのＹ方向における間隔Ｄｎを(数１)により決定し、それに基づいて、Ｘ方向，Ｙ方向における各照射領域Ａｎｉの中心位置Ｐｎｉを設定する。その後、層Ｌｎ全体を照射領域Ａｎｉで覆うようにＸ方向，Ｙ方向における各照射領域Ａｎｉの両端位置を設定する。演算部３１で設定された各照射領域Ａｎｉの中心位置ＰｎｉとＸ方向，Ｙ方向における両端位置は、制御部３２に入力される。
【００５４】
制御部３２は、ビームを照射領域ＡｎｉのＸ方向及びＹ方向における両端間で照射するために走査電磁石２４，２５で必要とされる電流値を求め、求めた各電流値は、照射領域Ａｎｉと対応づけた形で記憶する。なお、Ｘ方向，Ｙ方向にビームを走査するため、走査電磁石２４，２５で必要とされる電流値は、周期的に正負が反転する交流電流となる。
【００５５】
以上説明した点以外は実施例２と同様である。
【００５６】
以上説明した各実施例では、照射領域Ａｎｉを変更する際に加速器１からのビームの出射を停止しているが、照射領域Ａｎｉの変更を高速で行うことができる場合には、加速器１からビームを出射しながら照射領域Ａｎｉの変更を行っても良い。なお、ここでいう高速とは、照射領域Ａｎｉを変更する間に照射される照射線量を患部全体に照射される照射線量よりも十分に小さくできる程度の速さである。更に、照射領域Ａｎｉの変更時にビームの照射線量を低下させれば、照射領域Ａｎｉ変更時の照射線量をより小さくすることができる。なお、ビームの照射線量を低下させるには、加速器１において高周波印加装置１１からビームに印加される高周波電場の強度を低下させれば良い。
【００５７】
また、前述の各実施例では患部に照射するビームのエネルギーＥｎを加速器１において変更しているが、加速器１からは常に同じエネルギーのビームを出射し、ビームが加速器１から出射されて患者に照射されるまでに通る経路（ビームの軌道）にビームのエネルギーを変更する手段を設けることによってビームのエネルギーを変更しても良い。図７にその一例として、偏向電磁石２３と走査電磁石２４との間にレンジシフター７を設けた例を示す。
【００５８】
レンジシフター７は、図に示すように、Ｙ方向に厚さが変化する構造物７１，７２からなる。この構造物７１，７２は、ビームのエネルギーをその厚さに応じて減衰させる材料からなり、Ｙ方向に移動させることによりビームが通過する位置における厚さを変えてビームのエネルギーを調節する。
【００５９】
このようなレンジシフター７を用いる場合は、ビームを照射する層によらず加速器１から出射するビームのエネルギーを一定にし、各層に対して求められたビームのエネルギーＥｎをレンジシフター７の駆動装置（図示せず）に与えて、エネルギーＥｎに合わせて駆動装置により構造物７１，７２の位置を調節する。なお、加速器１から出射するビームのエネルギーの値は、層Ｌｎのうち最も深い位置にある層Ｌ９の位置にブラッグピークが来るように設定する。従って、層Ｌ９にビームを照射する場合には構造物７１，７２をビームの軌道上からはずし、層Ｌ８から層Ｌ１へと層の位置が浅くなるのにしたがって、ビーム軌道上の構造物７１，７２の厚さが厚くなるように構造物７１，７２の位置を調節する。このようにして、ビームのエネルギーを変更することもできる。
【００６０】
なお、以上説明した各実施例では層の数を９つとしているが、層の数は９つに限られるものではなく、患部の深さ方向の大きさに応じて適切な数を設定すれば良い。
【００６１】
また、前述の各実施例では、加速器１においてビームの出射及び停止を制御しているが、ビームを完全に遮断する遮蔽物を用いて患部に対するビームの照射を制御しても良い。
【００６２】
【発明の効果】
以上説明したように、本発明によれば、簡単な制御で、照射対象における照射線量の不均一を抑制することができる。
【図面の簡単な説明】
【図１】本発明の好適な一実施例である荷電粒子ビーム出射装置の構成図である。
【図２】患部における層と照射領域の設定例を示す図である。
【図３】図３（ａ）は層Ｌ９における各照射領域の位置を示す図であり、図３（ｂ）は層Ｌ１における各照射領域の位置を示す図である。
【図４】エネルギーＥ６〜Ｅ９のビームの照射線量の分布を示す図である。
【図５】患部にビームを照射する手順を示すフローチャートである。
【図６】患部における層と照射領域の他の設定例を示す図である。
【図７】レンジシフター７の構成図である。
【図８】ガウス分布をもつビームの照射線量分布と、その総和の照射線量分布を示す図である。
【図９】患部における層と照射領域の他の設定例を示す図である。
【図１０】図９におけるビーム中心の移動を示す図である。
【符号の説明】
１…加速器、２…回転照射装置、３…制御装置、４…前段加速器、１１…高周波印加装置、１２，２１，２３…偏向電磁石、１３，２２…四極電磁石、１４…六極電磁石、１５…高周波加速空胴、１６，１７，２７，２８…電源、２４，２５…走査電磁石、２６…線量モニター、３１…演算部、３２，３３…制御部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charged particle beam extraction apparatus that outputs a charged particle beam used for cancer treatment or diagnosis of an affected area, and more particularly, a charged particle beam extraction capable of outputting a charged particle beam so that an irradiation dose on an irradiation target is uniform. Relates to the device.
[0002]
[Prior art]
As a method of irradiating a charged particle beam (hereinafter referred to as a beam) to an irradiation target, a method is known in which the irradiation target is divided into a plurality of regions and the beam is irradiated for each region. As an example, Japanese Patent Laid-Open No. 9-223600 discloses that an irradiation target is divided into a plurality of layered regions in the beam traveling direction, the layered region is further divided into a plurality of small regions, and a beam is divided into each small region. Is described.
[0003]
Moreover, when using a beam for cancer treatment etc., it is desirable that the irradiation dose in an affected part is uniform. In order to make the irradiation dose uniform, there is known an irradiation method in which the beam irradiation ranges are overlapped using the fact that the beam irradiation dose has a Gaussian distribution. FIG. 8 shows an example of an irradiation dose distribution according to the irradiation method. As shown in FIG. 8, since the beam irradiation dose (dotted line) has a Gaussian distribution, the total irradiation dose (solid line) can be made uniform by overlapping a plurality of beam irradiation ranges. .
[0004]
[Problems to be solved by the invention]
From the two conventional techniques described above, the irradiation target is divided into a plurality of layers, the layer is further divided into a plurality of regions, and when the beam is irradiated for each region, the plurality of regions are overlapped and set, It is conceivable to make the radiation dose in the layer uniform.
[0005]
However, with this irradiation method, if the irradiation range of the beam slightly deviates from the target region, the irradiation dose in the layer becomes non-uniform. There must be. Therefore, there is a problem that the control of the beam irradiation range becomes complicated.
[0006]
An object of the present invention is to provide a charged particle beam extraction apparatus capable of suppressing non-uniform irradiation dose in an irradiation target with simple control.
[0007]
[Means for Solving the Problems]
A feature of the present invention that achieves the above object is that irradiation includes outputting an accelerator that emits a charged particle beam after accelerating, and a scanning electromagnet that controls an irradiation position of the charged particle beam emitted from the accelerator. In the charged particle beam extraction apparatus comprising: means; and a power source that supplies the scanning electromagnet with a current that repeats a period in which the value changes over time and a period in which the value does not change over time, When a charged particle beam having a second energy lower than the first energy is output from the irradiation unit, compared to a case where a charged particle beam having a first energy is output from the irradiation unit, The purpose is to increase the amount of current change during a period in which the current supplied to the scanning electromagnet changes.
[0008]
As the energy of the charged particle beam output from the irradiation means decreases, the amount of current change in the period in which the current supplied to the scanning electromagnet changes over time is increased, so that the charged particle beam energy is low. When the charged particle beam energy is high compared to when the irradiation position is shallow, that is, when the irradiation position of the charged particle beam is deep, the current change during the period when the current supplied to the scanning electromagnet changes over time The amount will be increased. In addition, by increasing the amount of current change during the period when the current supplied to the scanning electromagnet changes over time, the irradiation position of the charged particle beam moves greatly in the direction perpendicular to the traveling direction of the charged particle beam, and conversely If the amount of change is small, the amount of movement of the irradiation position is also small.
[0009]
Therefore, according to the present invention having the above characteristics, the deeper the irradiation position of the charged particle beam, the smaller the amount of movement of the irradiation position in the direction perpendicular to the traveling direction of the charged particle beam. Changes in the irradiation dose distribution in the irradiation target when the irradiation region irradiated with the particle beam is dense and the irradiation position is shifted can be reduced. As described above, according to the present invention, it is possible to suppress non-uniformity of the irradiation dose in the irradiation target with simple control.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Example 1
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0011]
FIG. 1 shows a charged particle beam extraction apparatus according to a preferred embodiment of the present invention. Note that the charged particle beam extraction apparatus in FIG. 1 performs cancer treatment by irradiating an affected area of a cancer patient with a charged particle beam (hereinafter referred to as a beam).
[0012]
In the treatment of a cancer patient using the charged particle beam extraction apparatus of FIG. To the arithmetic unit 31. The calculation unit 31 determines the energy of the beam emitted from the accelerator 1, the irradiation position of the beam in the affected area, and the irradiation dose of the beam in the affected area based on the input patient information.
[0013]
Hereinafter, a method for determining the beam energy, the irradiation position, and the irradiation dose in the calculation unit 31 will be described. In this embodiment, as shown in FIG. 2, layered regions L1 to L9 (hereinafter referred to as layer Ln, n = 1 to 9) obtained by dividing the affected part into nine in the beam traveling direction (Z direction). ) Are further divided into a plurality of regions A11, A12,... (Hereinafter referred to as irradiation regions Ani, i = 1, 2,...), And a beam is irradiated for each irradiation region Ani. In addition, the layer Ln in a present Example shows that it is in a position far from a body surface, ie, a deep position, so that n becomes large. Each irradiation area Ani has such a size that irradiation can be performed without moving the irradiation position of the beam, and the sizes are all equal.
[0014]
First, the calculation unit 31 determines how many layers the affected part is divided based on the above-described patient information. In this embodiment, the affected part is divided into nine layers as described above. Next, the depth position of the layer L9 at the deepest position is obtained, and the energy E9 of the beam having the Bragg peak at the depth position is calculated. For the other layers L1 to L8, beam energies E1 to E8 are calculated such that a Bragg peak comes at the depth position of each layer. Hereinafter, the beam of energy E9 is referred to as a beam that irradiates the layer L9, and the beam of energy E8 is referred to as a beam that irradiates the layer L8. In practice, the beam of energy E9 is applied to all of the layers L1 to L9.
[0015]
Next, the calculation unit 31 determines the irradiation position of the beam irradiated to each layer Ln based on the shape of the affected part, that is, the center position of a plurality of irradiation regions Ani (circular shape) in each layer Ln. Fig.3 (a) shows each irradiation area | region A91, A92, ... in the layer L9. In FIG. 3A, only a part of the irradiation area A9i in the layer L9 is shown, but the irradiation area A9i is actually set so as to cover the entire layer L9. In addition, each irradiation area | region A9i of the layer L9 has the center position P9i set with the space | interval of D9 in the X direction and the Y direction. This interval D9 is obtained by (Equation 1).
[0016]
[Expression 1]

[0017]
Here, R: radius of irradiation region, m: total number of layers.
[0018]
From (Equation 1), the distance D9 of the center position P9i of each irradiation region A9i in the layer L9 of the present embodiment is:
[0019]
[Expression 2]

[0020]
It becomes. According to (Equation 1), the distances D1 to D8 are obtained for the other layers L1 to L8, respectively. The position of each irradiation region Ani is set based on the obtained interval Dn, and the center position Pni is determined. According to (Equation 1), the distance Dn becomes wider as the layer Ln is at a shallower position. In the layer L1 having the widest distance Dn, the distance D1 is equal to the radius of the irradiation region Ani. Each irradiation area A1i in the layer L1 is shown in FIG. In this way, by setting the interval Dn between the irradiation regions Ani in each layer Ln to be equal to or less than the radius R of the irradiation region Ani, the irradiation in each layer Ln when the beams are irradiated by superimposing the irradiation doses of the beams having a Gaussian distribution. The dose distribution is uniform.
[0021]
Next, the calculating part 31 determines the irradiation dose of the beam irradiated to each layer Ln. First, the irradiation dose of the beam irradiated on the layer L9 is determined. As the irradiation dose irradiated to the layer L9, the distribution of the irradiation dose obtained by irradiating each irradiation region A9i of the layer L9 (the result of superimposing the irradiation doses in each irradiation region A9i) is sent to the calculation unit 31. The irradiation dose of the beam irradiated to each irradiation region A9i is determined in consideration of the overlapping of the irradiation regions so as to be equal to the input irradiation dose to be irradiated to the affected part. As a matter of course, the irradiation dose of the beam irradiated to each irradiation region A9i is smaller than the irradiation dose to be irradiated to the affected part input to the calculation unit 31.
[0022]
Subsequently, the irradiation dose in the layer L8 is determined. Since the layer L8 is irradiated somewhat when the beam of energy E9 is irradiated, the irradiation dose must be taken into consideration. Here, the relationship between the beam energy En and the irradiation dose in the present embodiment will be described with reference to FIG. FIG. 4 shows the depth position from the body surface on the horizontal axis and the irradiation dose on the vertical axis, and shows the distribution of the irradiation dose by the beams of energy E6 to E9 and the distribution of the sum. As shown in the figure, when the beam of energy E9 is irradiated, the irradiation dose is highest at the position of the layer L9, but some irradiation is also performed at the position of the layer L8. Therefore, in order to make the irradiation dose uniform at the position of the layer L9 and the position of the layer L8, as shown in the figure, the irradiation dose by the beam of energy E8 must be lower than the irradiation dose of the beam of energy E9. . Specifically, in the irradiation dose distribution of the beam of energy E9, a value obtained by subtracting the irradiation dose at the layer L8 position from the irradiation dose (peak value) at the layer L9 position may be set as the dose irradiated to the layer L8.
[0023]
The calculation unit 31 considers the irradiation of the layer L8 and considers the overlapping of the irradiation regions, and the irradiation dose of the beam irradiated to each irradiation region A8i, that is, the irradiation dose (peak value) of the beam of energy E8. ). By determining the irradiation dose by the beam of energy E8 in this way, the irradiation dose at the position of the layer L8 becomes equal to the irradiation dose at the position of the layer L9. For the other energy beams E1 to E7, as in the case of the energy beam E8, the irradiation dose (peak value) is determined in consideration of the irradiation dose by the high-energy beam and the overlapping of the irradiation regions. .
[0024]
As described above, the energy En of the beam irradiated to each layer Ln, the center position Pni of each irradiation region Ani in each layer Ln, and the irradiation dose in the irradiation region Ani of each layer Ln are determined. According to the present embodiment, as the position of the layer Ln becomes shallower, the beam energy En and the irradiation dose are set lower, and the interval Dn between the irradiation areas Ani is set wider.
[0025]
The beam energy En, the center position Pni of each irradiation area Ani, and the irradiation dose obtained by the calculation unit 31 are output to the control unit 32 and stored in the control unit 32. Further, the control unit 32 outputs the input energy En to the control unit 33.
[0026]
Based on the energy En of the input beam, the control unit 32 obtains a current value output from the power supply 16 to the high-frequency applying device 11 in order to emit the beam from the accelerator 1. The obtained current value is stored in a format associated with the layers L1 to L9. Further, the control unit 32 obtains a current value output from the power source 28 to each of the scanning electromagnets 24 and 25 in order to irradiate the center position Pni with the beam, based on the input center position Pni of each irradiation region Ani. This current value is stored in a format associated with each irradiation area Ani. As described above, as the layer position is shallower, the distance Dn between adjacent irradiation regions becomes larger, so that the amount of change in changing the irradiation region of the current value supplied to the scanning electromagnet also increases.
[0027]
On the other hand, the control unit 33, based on the input energy En of the beam, accelerates the beam emitted from the pre-accelerator 4 (constant energy) to the energy En, so that the deflecting electromagnet 12, the quadrupole electromagnet 13, and the hexapole electromagnet 14 are used. And the electric current value required by the high frequency acceleration cavity 15 is calculated | required. The obtained current value is stored for each of the deflecting electromagnet 12, the quadrupole electromagnet 13, the hexapole electromagnet 14 and the high-frequency acceleration cavity 15 in a format corresponding to the layers L1 to L9. In addition, the control unit 33 obtains current values required by the quadrupole electromagnet 22 and the deflection electromagnets 21 and 23 in order to guide the beam emitted from the accelerator 1 to the scanning electromagnets 24 and 25. The obtained current value is stored for each of the quadrupole electromagnet 22 and the deflecting electromagnets 21 and 23 in a format associated with the layers L1 to L9.
[0028]
In addition, in order to obtain | require each electric current value, the control parts 32 and 33 prepare the table which matched each energy value with the energy of a beam, the center position of an irradiation area | region, and each electric current using that table is prepared. Find the value.
[0029]
Next, a procedure until the affected part is irradiated with the beam will be described. In this embodiment, the beam is irradiated in order from the layer L9 at the deepest position to the layer L1 at the shallowest position from the body surface. First, a procedure for irradiating the layer L9 with a beam will be described.
[0030]
First, a beam extraction command is output from the control unit 33 to the pre-stage accelerator 4. The front accelerator 4 emits a beam when a beam emission command is input. The beam emitted from the front stage accelerator 4 is incident on the accelerator 1.
[0031]
Further, the control unit 33 outputs a beam extraction command to the pre-accelerator 4 and stores the deflection electromagnet 12, the quadrupole electromagnet 13, the hexapole electromagnet 14, and the high-frequency acceleration cavity stored in the power supply 17 in association with the layer L 9. 15 current values are output. The power supply 17 supplies the input current value to each of the deflection electromagnet 12, the quadrupole electromagnet 13, the hexapole electromagnet 14, and the high-frequency acceleration cavity 15. Here, the current supplied to each is set so as to change with the acceleration of the beam.
[0032]
Here, the role of each component in the accelerator 1 will be described. First, the deflecting electromagnet 12 generates a magnetic field corresponding to the supplied current, and deflects the beam with the magnetic field so that the beam circulates along the orbit of the accelerator 1. The quadrupole electromagnet 13 controls the beam stability limit by a magnetic field corresponding to the supplied current. The high-frequency acceleration cavity 15 applies a high-frequency electric field to the beam according to the supplied current and accelerates the beam. That is, the energy of the beam is increased. The hexapole magnet 14 resonates the beam by applying a magnetic field to the beam in accordance with the supplied current. This resonance is used when the beam is emitted from the accelerator 1.
[0033]
When the beam is accelerated to energy E9 in the accelerator 1, the control unit 32 outputs the current value of the high-frequency applying device 11 stored in association with the layer L9 to the power supply 16. The power supply 16 supplies the input value of current to the high-frequency application device 11. The high-frequency applying device 11 generates a high-frequency electric field corresponding to the supplied current, and applies the high-frequency electric field to the beam, thereby emitting the beam from the accelerator 100. Specifically, in the accelerator 1 of the present embodiment, the stability limit is kept constant by the quadrupole electromagnet 13 when the beam is emitted, and in this state, a high frequency electric field is applied to the beam by the high frequency application device 11. Due to the application of the high-frequency electric field, the beam exceeds the stability limit, and the beam exceeding the stability limit resonates with the magnetic field of the hexapole electromagnet 14 and is emitted from the accelerator 1. The beam emitted from the accelerator 1 is guided to the rotary irradiation device 2.
[0034]
The control unit 33 outputs the current values of the quadrupole electromagnet 22 and the deflection electromagnets 21 and 23 stored in association with the layer L9 to the power source 27 while accelerating the beam in the accelerator 1. The power supply 27 supplies the input current to the quadrupole electromagnet 22 and the deflection electromagnets 21 and 23, respectively. The beam input to the rotary irradiation device 2 is guided to the scanning electromagnets 24 and 25 along a predetermined trajectory by the quadrupole electromagnet 22 and the deflection electromagnets 21 and 23.
[0035]
In addition, the control unit 32 outputs the current value stored in association with the center position P91 of the irradiation area A91 to the power supply 28 while the control unit 33 outputs the current value to the power supply 27. The power supply 28 supplies the current of the input value to the scanning electromagnets 24 and 25, respectively. The scanning electromagnets 24 and 25 generate magnetic fields according to the currents supplied thereto, the scanning electromagnet 24 deflects the beam in the X direction, and the scanning electromagnet 25 deflects the beam in the Y direction. The beams deflected by the scanning electromagnets 24 and 25 are irradiated to the center position P91 of the irradiation area A91.
[0036]
The dose monitor 26 measures the irradiation dose of the beam irradiated to the affected area. An actual measurement value of the beam irradiation dose measured by the dose monitor 26 is input to the control unit 32. The control unit 32 compares the irradiation dose value (set value) stored in association with the layer L9 and the input measured value, and emits the power to the power source 16 when the measured value reaches the set value. Output a stop command. The power supply 16 stops the supply of current to the high-frequency applying device 11 when an extraction stop command is input. Accordingly, the generation of the high frequency electric field by the high frequency applying device 11 is stopped, and the emission of the beam from the accelerator 1 is also stopped. If there is no beam that goes around the accelerator 1 before the actually measured value reaches the set value, a beam is newly incident from the front stage accelerator 4 and accelerated to the energy E9 in the accelerator 1, and then the beam is accelerated again. The light may be emitted from
[0037]
When the irradiation of the irradiation area A91 is thus completed, the irradiation area A92 is then irradiated with the beam. When irradiating the irradiation area A92 with the beam, the scanning electromagnets 24 and 25 stored in association with the irradiation area A92 from the control unit 32 to the power supply 28 in a state where the emission of the beam from the accelerator 1 is stopped. Each current value is output. The power supply 28 supplies the current of the input value to the scanning electromagnets 24 and 25, respectively, and the scanning electromagnets 24 and 25 generate a magnetic field corresponding to the supplied current. As shown in FIG. 3A, the position of the irradiation area A92 corresponds to a position shifted from the irradiation area A91 by D9 in the X direction, so that the beam is supplied to the scanning electromagnet 25 that deflects the beam in the Y direction. The current does not change between when the irradiation region A91 is irradiated and when the irradiation region A92 is irradiated, and only the current supplied to the scanning electromagnet 24 that deflects the beam in the X direction changes.
[0038]
When a current is supplied from the power supply 28 to the scanning electromagnets 24 and 25, the control unit 32 outputs the current value of the high-frequency applying device 11 stored in association with the layer L9 to the power supply 16. The power supply 16 supplies the input value of current to the high-frequency application device 11. The high-frequency application device 11 applies a high-frequency electric field corresponding to the supplied current to the beam that is circulating around the accelerator 1 and emits the beam from the accelerator 1. The beam emitted from the accelerator 1 is guided to the scanning electromagnets 24 and 25, deflected by the scanning electromagnets 24 and 25, and then irradiated to the irradiation area A92. As in the case of irradiating the irradiation area A91 with the beam, when irradiating the irradiation area A92 with the beam, the actual measurement value by the dose monitor 26 is compared with the set value stored in the control unit 32 to set the actual measurement value. When the value is reached, the beam emission from the accelerator 1 is stopped.
[0039]
By repeating such a procedure, a beam having a set irradiation dose is irradiated to each irradiation region A91, A92,... Of the layer L9. Note that when changing the irradiation position of the beam from the irradiation area A91 to the irradiation area A92, the current supplied to the scanning electromagnet 25 did not change, but when moving the irradiation position of the beam in the Y direction, the scanning electromagnet 25 was changed. The current supplied to is also changed.
[0040]
When all the irradiation areas A9i in the layer L9 have been irradiated with the beam, each irradiation area A8i in the layer L8 is then irradiated. The procedure for irradiating the layer L8 with the beam is the same as that for the layer L9, and the accelerator 1 and the rotary irradiation device 2 are controlled by supplying each device with the current values stored in association with the layer L8. Then, the layer L8 is irradiated with a beam. Thereafter, the same procedure is repeated up to the layer L1 to irradiate the entire affected area with the beam.
[0041]
FIG. 5 is a flowchart showing a procedure for irradiating the affected area with a beam. First, the layer L9 is set as the layer Ln to be irradiated with the beam, and the irradiation region A91 is set as the irradiation region Ani to be irradiated with the beam (step 501). Next, a beam is emitted from the front stage accelerator 4 and incident on the accelerator 1 (step 502). The accelerator 1 accelerates the incident beam to the energy En (step 503). In parallel with step 502, a current for irradiating the irradiation area Ani with a beam is supplied to the scanning electromagnets 24 and 25 (step 504).
[0042]
Next, a beam is emitted from the accelerator 1, and the irradiation region Ani is irradiated with the beam (step 505). Subsequently, it is determined whether or not the actual measurement value of the irradiation dose of the irradiated beam has reached the setting value of the irradiation dose set for the layer Ln (step 506). If “Yes” is determined in step 506, the process proceeds to step 507, and if “No” is determined, the process proceeds to step 508. In step 508, it is determined whether or not the accelerator 1 has a beam. If “Yes” is determined, the process proceeds to step 506, and if “No” is determined, the process proceeds to step 502. That is, when there is no beam in the accelerator 1, a beam of energy En is generated in steps 502 and 503, and the beam is irradiated again in step 505.
[0043]
When it is determined in step 506 that the actual measurement value of the irradiation dose of the beam has reached the set value, the beam emission is stopped (step 507). Next, it is determined whether or not all the irradiation regions Ani of the layer Ln have been irradiated. If “Yes” is determined, the process proceeds to step 510, and if “No” is determined, the process proceeds to step 511 (step 509). In step 511, 1 is added to i, and the process proceeds to step 512. Note that the irradiation region An to be irradiated with the beam is changed by adding 1 to i. In step 512, it is determined whether or not there is a beam in the accelerator 1. If it is determined “Yes”, the process proceeds to step 504. On the other hand, if “No” is determined, the process proceeds to step 502. In this way, the beam is irradiated to the new irradiation area Ani.
[0044]
In step 510, it is determined whether the layer Ln is the layer L1, and when it is determined “Yes”, the irradiation of the beam to the affected part is terminated. If “No” is determined, the process proceeds to step 513. In step 513, 1 is added to n, and the process proceeds to step 502. By adding 1 to n, the layer Ln to be irradiated with the beam is changed.
[0045]
As described above, in this embodiment, a beam is irradiated for each irradiation region Ani in each layer Ln according to a predetermined irradiation plan. Even in this embodiment, the irradiation position of the beam may deviate from the irradiation area Ani as in the conventional technique. However, according to the present embodiment, it is possible to suppress dose non-uniformity even when the irradiation position is shifted. This is because, in the present embodiment, as described above, in the layer where the position is deep, the interval Dn between the irradiation regions Ani is narrow, that is, the irradiation regions Ani are dense, so even if one of them shifts, The ratio of the irradiation dose in the irradiation region whose position is shifted from the whole irradiation dose is very small, and the distribution of the irradiation dose is not greatly affected. Therefore, the deviation of the irradiation position of the beam in the deep layer does not greatly affect the uniformity of the irradiation dose in the affected area. In addition, since the irradiation dose of the beam is small in the shallow layer, even if the irradiation position is shifted, the ratio is small compared to the entire irradiation dose. Therefore, the deviation of the irradiation position of the beam in the shallow layer does not greatly affect the uniformity of the irradiation dose in the affected area. As described above, in this embodiment, the irradiation dose generated due to the shift of the irradiation position is reduced by narrowing the interval between the irradiation regions in the deeper layer and decreasing the irradiation dose in the shallower layer. Nonuniformity can be suppressed.
[0046]
In the present embodiment, by changing the direction in which the irradiation region is moved for each layer, it is possible to cancel out the non-uniformity of the irradiation dose that occurs when the beam deviates from the irradiation region.
[0047]
In this embodiment, the irradiation area is moved linearly. However, the movement of the irradiation area is not limited to this embodiment, and may be moved, for example, in a spiral manner.
[0048]
(Example 2)
The charged particle beam extraction apparatus according to another embodiment of the present invention will be described in the following points different from the first embodiment. As shown in FIG. 6, the charged particle beam emitting apparatus of the present embodiment divides each layer into a plurality of regions in the Y direction, and irradiates a beam for each region. In other words, the irradiation area that was a point in the first embodiment is a line extending in the X direction in the present embodiment, and irradiation is performed by scanning the beam several times in the X direction in the irradiation area Ani. The device configuration of the charged particle beam extraction apparatus of the present embodiment is the same as that of the first embodiment.
[0049]
In the present embodiment, the calculation unit 31 determines the interval Dn of the center position Pni of the irradiation region Ani in the Y direction by (Equation 1), and determines the center position Pni of each irradiation region Ani in the Y direction based on the interval Dn. Set. Thereafter, the length and position in the X direction of each irradiation region Ani are determined so as to cover the entire layer Ln with the irradiation region Ani, and both end positions of each irradiation region Ani in the X direction are set from the length and position. The center position Pni in the Y direction and the both end positions in the X direction of each irradiation region Ani set by the calculation unit 31 are input to the control unit 32.
[0050]
The control unit 32 scans and irradiates the current between a current value required by the scanning electromagnet 25 to irradiate the center position Pni in the Y direction and the beam between both end positions in the X direction. To obtain the current value required. Each obtained current value is stored in a form associated with the irradiation region Ani. Since the beam is scanned in the X direction, the current value required by the scanning electromagnet 24 is an alternating current whose polarity is periodically reversed. The correspondence between the center position Pni in the Y direction and both end positions in the X direction and the current values required by the scanning electromagnets 24 and 25 is tabulated in advance, and the control unit 32 uses the table. Find each current value.
[0051]
Except for the points described above, the embodiment is the same as the embodiment of FIG.
[0052]
According to the present embodiment, the beam is scanned in the X direction a plurality of times in the irradiation area Ani, and when the preset irradiation dose is reached, the irradiation position is moved in the Y direction to change the irradiation area Ani. Also in this embodiment, the distance Dn between the center positions in the Y direction is different for each layer (the distance Dn is wider as the layer position is shallower), and the irradiation dose in each layer is different (the irradiation dose is smaller as the layer position is shallower). Therefore, as in the embodiment of FIG. 1, it is possible to suppress uneven irradiation dose in the affected area.
[0053]
(Example 3)
A charged particle beam extraction apparatus according to another embodiment of the present invention will be described below with respect to points different from the second embodiment. The charged particle beam emitting apparatus of the present embodiment divides each layer into a plurality of regions as shown in FIG. 9, and emits a beam for each region. That is, in the second embodiment, the beam is scanned in a line extending in the X direction, but in the present embodiment, scanning is performed along lines extending obliquely in the X direction and the Y direction. That is, the center of each irradiation area Ani is a line extending obliquely in the X direction and the Y direction. FIG. 10 shows the movement of the beam center during scanning with a solid line. In this embodiment, the currents of the scanning electromagnets 24 and 25 are changed simultaneously. Since the scanning angle of the beam center of each irradiation area Ani can be the ratio of the current change rate of the scanning electromagnets 24 and 25, the current change rate of the scanning electromagnets 24 and 25 is appropriately determined according to the scanning beam size. The calculation unit 31 determines an interval Dn in the Y direction of the center position Pni in the X direction and the Y direction of the irradiation area Ani based on (Equation 1), and based on this, the center position of each irradiation area Ani in the X direction and the Y direction Set Pni. Thereafter, both end positions of each irradiation region Ani in the X direction and the Y direction are set so as to cover the entire layer Ln with the irradiation region Ani. The central position Pni of each irradiation region Ani set by the calculation unit 31 and both end positions in the X direction and the Y direction are input to the control unit 32.
[0054]
The control unit 32 obtains current values required by the scanning electromagnets 24 and 25 to irradiate the beam between both ends in the X direction and the Y direction of the irradiation region Ani, and the obtained current values are the irradiation region Ani. Memorize it in a correlated form. In addition, since the beam is scanned in the X direction and the Y direction, the current value required by the scanning electromagnets 24 and 25 is an alternating current whose polarity is periodically reversed.
[0055]
Except for the points described above, the second embodiment is the same as the second embodiment.
[0056]
In each of the embodiments described above, the emission of the beam from the accelerator 1 is stopped when the irradiation area Ani is changed. However, when the irradiation area Ani can be changed at high speed, the beam is emitted from the accelerator 1. The irradiation area Ani may be changed while emitting the light. The high speed referred to here is a speed at which the irradiation dose irradiated while changing the irradiation region Ani can be made sufficiently smaller than the irradiation dose irradiated to the entire affected area. Furthermore, if the irradiation dose of the beam is reduced at the time of changing the irradiation region Ani, the irradiation dose at the time of changing the irradiation region Ani can be further reduced. In order to reduce the irradiation dose of the beam, the intensity of the high-frequency electric field applied to the beam from the high-frequency applying device 11 in the accelerator 1 may be reduced.
[0057]
In each of the above-described embodiments, the energy En of the beam irradiated to the affected area is changed in the accelerator 1. However, the accelerator 1 always emits a beam having the same energy, and the beam is emitted from the accelerator 1 and irradiated to the patient. The energy of the beam may be changed by providing a means for changing the energy of the beam in the path (beam trajectory) that is taken. FIG. 7 shows an example in which a range shifter 7 is provided between the deflection electromagnet 23 and the scanning electromagnet 24.
[0058]
As shown in the figure, the range shifter 7 is composed of structures 71 and 72 whose thickness changes in the Y direction. The structures 71 and 72 are made of a material that attenuates the energy of the beam in accordance with the thickness thereof, and the beam energy is adjusted by changing the thickness at the position where the beam passes by moving in the Y direction.
[0059]
When such a range shifter 7 is used, the energy of the beam emitted from the accelerator 1 is made constant irrespective of the layer to which the beam is irradiated, and the energy En of the beam obtained for each layer is changed to the driving device ( (Not shown) and the positions of the structures 71 and 72 are adjusted by the driving device in accordance with the energy En. The energy value of the beam emitted from the accelerator 1 is set so that the Bragg peak comes to the position of the layer L9 which is the deepest position in the layer Ln. Therefore, when irradiating the beam to the layer L9, the structures 71 and 72 are removed from the trajectory of the beam, and as the position of the layer becomes shallower from the layer L8 to the layer L1, the structures 71 and 72 on the beam trajectory. The positions of the structures 71 and 72 are adjusted so that the thickness of 72 is increased. In this way, the energy of the beam can be changed.
[0060]
In each of the embodiments described above, the number of layers is nine. However, the number of layers is not limited to nine, and an appropriate number may be set according to the depth direction size of the affected area. good.
[0061]
In each of the above-described embodiments, the emission and stop of the beam are controlled by the accelerator 1. However, the irradiation of the beam to the affected area may be controlled using a shield that completely blocks the beam.
[0062]
【The invention's effect】
As described above, according to the present invention, it is possible to suppress non-uniform irradiation doses in the irradiation target with simple control.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a charged particle beam extraction apparatus according to a preferred embodiment of the present invention.
FIG. 2 is a diagram illustrating a setting example of a layer and an irradiation area in an affected area.
FIG. 3A is a diagram showing the position of each irradiation region in the layer L9, and FIG. 3B is a diagram showing the position of each irradiation region in the layer L1.
FIG. 4 is a diagram showing a distribution of irradiation doses of beams of energy E6 to E9.
FIG. 5 is a flowchart showing a procedure for irradiating an affected area with a beam;
FIG. 6 is a diagram illustrating another setting example of a layer and an irradiation region in an affected area.
7 is a configuration diagram of a range shifter 7. FIG.
FIG. 8 is a diagram showing an irradiation dose distribution of a beam having a Gaussian distribution and a total irradiation dose distribution.
FIG. 9 is a diagram illustrating another setting example of a layer and an irradiation region in an affected area.
10 is a diagram showing the movement of the beam center in FIG. 9. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Accelerator, 2 ... Rotary irradiation apparatus, 3 ... Control apparatus, 4 ... Pre-stage accelerator, 11 ... High frequency application apparatus, 12, 21, 23 ... Deflection electromagnet, 13, 22 ... Quadrupole electromagnet, 14 ... Hexapole electromagnet, 15 ... High-frequency acceleration cavity, 16, 17, 27, 28 ... power source, 24, 25 ... scanning magnet, 26 ... dose monitor, 31 ... calculation unit, 32, 33 ... control unit.

Claims (6)

An accelerator that emits a charged particle beam after being accelerated, an irradiation unit that has a scanning electromagnet that controls the irradiation position of the charged particle beam emitted from the accelerator, and outputs a charged particle beam; a period and a time during which the value changes In a charged particle beam extraction apparatus comprising a power source that supplies a current that repeats a period that does not change to the scanning electromagnet,
The power source outputs a charged particle beam having a second energy lower than the first energy from the irradiation unit as compared with a case where a charged particle beam having a first energy is output from the irradiation unit. In this case, the charged particle beam extraction apparatus is characterized in that the amount of current change during a period in which the current supplied to the scanning electromagnet changes with time is increased.   The charged particle beam extraction apparatus according to claim 1, wherein the accelerator includes a high-frequency acceleration cavity that controls energy of the charged particle beam.   The range shifter which is provided on the track of the charged particle beam output from the irradiation unit and controls the energy of the charged particle beam by attenuating the energy of the charged particle beam is provided. Charged particle beam extraction device.   A dose monitor for measuring the irradiation dose of the charged particle beam output from the irradiation means during a period in which the value of the current supplied from the power supply does not change with time, and an irradiation dose value of the charged particle beam measured by the dose monitor; Comparing with a preset irradiation dose value and controlling the power supply so that the current supplied from the power supply changes when the measured irradiation dose value reaches the set irradiation dose value The charged particle beam extraction apparatus according to claim 1, further comprising a control unit configured to control the charged particle beam.   The stop means for stopping the output of the charged particle beam from the irradiation means, and the stop means outputs the output of the charged particle beam from the irradiation means during a period in which the value of the current supplied from the power source changes over time. The charged particle beam extraction apparatus according to claim 1, wherein the charged particle beam extraction apparatus is stopped.   The said stop means is a high frequency application apparatus which is provided in the said accelerator and applies a high frequency electric field to the charged particle beam which circulates in the said accelerator, and radiate | emits a charged particle beam from an accelerator. Charged particle beam extraction device.

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