JP7181576B2 - X-ray CT CTDI measurement method, dosimeter holding jig therefor, and X-ray CT CTDI measurement method and apparatus using the same - Google Patents

Description

The present invention relates to a CTDI (Computed Tomography Dose Index) measuring method for X-ray CT (Computed Tomography), a dosimeter holding jig therefor, and a CTDI measuring method and apparatus for X-ray CT using the same. Measure CTDI quickly, easily, and inexpensively by using fluorescent glass dosimeters (hereinafter referred to simply as glass dosimeters), optical (stimulated) luminescence dosimeters (OSLD), thermoluminescence dosimeters (TLD), etc. instead of ionization chambers. The present invention relates to a CTDI measuring method for X-ray CT, a dosimeter holding jig therefor, and a CTDI measuring method and apparatus for X-ray CT using the same.

CTDI is a dose index, which is a dose value for performance evaluation and management of X-ray CT equipment. It is also used as (see Patent Document 1). In recent years, the output function of exposure dose has come to be included in the requirements for equipment certification. Measurements must be made using a dedicated CT dosimetry phantom and dosimeter.

As a CT dosimetry phantom, for example, a cylindrical CT dosimetry phantom 10 made of acrylic resin and having a diameter of 320 mm for the abdomen and a diameter of 160 mm for the head is known, as shown in FIG. It is inserted into a gantry 20 equipped with an X-ray source 22 such as an X-ray tube and a camera 24, and the X-ray source 22 and camera 24 are rotated around the CT dosimetry phantom 10 for measurement. The CT dosimetry phantom 10 has an ionization chamber insertion hole 12 at a depth of, for example, 10 mm from the center and the top, bottom, left, and right surfaces of the phantom 10 for CT dosimetry. and take measurements.

An example of measurement is shown in FIG. The CT dosimetry phantom 10 in which the CT ionization chamber 14 is inserted is placed directly or floated on the patient bed 30, and measurement is performed, for example, by performing a single scan.

On the other hand, in recent years, attempts have been made to use an easy-to-handle glass dosimeter instead of the CT ionization chamber (see Patent Document 2 and Non-Patent Document 1).

JP-A-2006-26417 JP 2016-174863 A

Fumika Hirosawa et al., “Study on the characteristics and usage of fluorescent glass dosimeters for dose evaluation in X-ray CT,” Journal of the Japan Society of Radiological Technology, Vol.71, No.1, January 2015

However, in the past, an appropriate method of attaching a glass dosimeter smaller than the ionization chamber, an optical (stimulation) luminescence dosimeter (OSLD), or a thermoluminescence dosimeter (TLD) other than the ionization chamber to the CT dosimetry phantom was considered. It wasn't done.

The present invention has been made to solve the above-mentioned conventional problems. It is an object of the present invention to enable the CTDI of X-ray CT to be measured quickly, easily, and inexpensively by using a .

The present invention is an X-ray CT CTDI measurement method in which a jig holding a dosimeter smaller than the ionization chamber is inserted into a CT dose measurement phantom to measure CTDI (for example, CTDIvol). The problem is solved by inserting a jig instead of the CT ionization chamber into the hole of the CT dosimetry phantom, which is provided for inserting the CT ionization chamber.

Here , the jig can hold the dosimeter at a predetermined position of the CT dosimetry phantom.

Also, the dosimeter can be a glass dosimeter.

The present invention also provides a portion other than the ionization chamber, which is made of a material that does not interfere with the detection of X-rays due to scattering, and contains a dosimeter smaller than the ionization chamber, and a CT dosimetry phantom formed in the phantom for CT dosimetry. A dosimeter holding jig for CTDI measurement of X-ray CT, characterized by having a tubular outer shape that can be inserted into an ionization chamber insertion hole in place of a CT ionization chamber.

Here, the holding jig can be made of foamed plastic.

Further, the holding jig can be composed of a main body portion having a hole for housing the dosimeter formed in the center thereof, and a cap portion for covering the dosimeter housing hole of the main body portion.

The present invention also provides a dosimetry unit by inserting a dosimeter smaller than the ionization chamber into the dosimeter holding jig, and the dose measurement unit is a CT ionization chamber formed in a CT dosimetry phantom. A CTDI measuring method for X-ray CT characterized by inserting an ionization chamber instead of a CT ionization chamber into an insertion hole , irradiating X-rays, and detecting transmitted X-rays.

The present invention also provides a dosimeter other than the ionization chamber smaller than the ionization chamber, a holding jig into which the dosimeter is inserted, a dosimetry unit in which the dosimeter is inserted into the holding jig, and a CT scanner. An ionization chamber insertion hole is formed, and the dose measurement unit is inserted into the CT ionization chamber insertion hole instead of the CT ionization chamber , and the CT dose measurement phantom is irradiated with X-rays. and means for detecting X-rays transmitted through the CT dosimetry phantom.

According to the present invention, CTDI of X-ray CT (especially CTDIvol ) can be measured quickly, easily and inexpensively.

Schematic showing an example of a CT dosimetry phantom Cross-sectional view showing an example of CTDI measurement arrangement 1 is a perspective view showing the configuration of an embodiment of a holding jig for a CTDI measuring glass dosimeter according to the present invention; FIG. The exploded perspective view which shows an example of the glass dosimeter inserted in the said holding jig. FIG. 2 is a flow chart showing a CTDI measurement procedure in an embodiment of the present invention; FIG. A side view and a perspective view showing a state in which the phantom for CT dose measurement and the gantry are aligned in the measurement procedure. Perspective view showing a state in which the central dosimetry unit is similarly inserted into the CT dosimetry phantom. Side view and perspective view similarly showing the position of the dosimetry unit after insertion of the phantom for CT dosimetry Side view and perspective view similarly showing the arrangement of five dose measurement units after the phantom for CT dose measurement is inserted. Horizontal sectional view showing the imaging range of the phantom for CT dose measurement during imaging.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the present invention is not limited by the contents described in the following embodiments and examples. In addition, the configuration requirements in the embodiments and examples described below include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those that fall within the so-called equivalent range. Furthermore, the constituent elements disclosed in the embodiments and examples described below may be combined as appropriate, or may be selected and used as appropriate.

FIG. 3 shows an embodiment of a holding jig for a CTDI measuring glass dosimeter used in the present invention.

The holding jig 40 is made of a material that does not interfere with the detection of X-rays by causing scattering, such as foamed plastic with a transmittance close to that of air. 44 is formed, and a cylindrical body portion 42 having an outer shape to be inserted into the CT dosimetry phantom 10 illustrated in FIG. and a cap portion 46 for covering.

Positions for identifying the center (C), upper (T), lower (B), right (R), and left (L) insertion positions into the CT dosimetry phantom 10 are provided on the cap portion 46, for example. A seal 48 with an identification number or the like is attached. Instead of the seal 48, the position identification number or the like can be written by hand.

The glass dosimeter 50 housed in the glass dosimeter housing hole 44 of the main body 42 includes, as shown in detail in FIG. 56. An ID 58 for identifying the holder 54 is attached to, for example, the side surface of the holder 54 . The holder 54 may or may not have a filter for correction, and may be used depending on the application.

When measuring CTDI, as shown in FIG. 5, first, in step 100, the glass dosimeter 50 is inserted into the holding jig 40 to form a dose measuring unit 60. As shown in FIG.

Next, at step 110 , the CT dosimetry phantom 10 is set within the gantry 20 .

Specifically, the headrest and extension bed of the X-ray CT are removed, and a towel or the like is laid on the patient bed 30 to create an environment in which the CT dose measurement phantom 10 is fixed. The center of the phantom 10 is the center of the gantry 20, and the peripheral measurement points are positioned at, for example, 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock.

Next, in step 120, confirmation is performed using a projection laser, and in step 130, without inserting the glass dosimeter 50 or the holding jig 40 while the X-ray source 22 is fixed, the front side is used to determine the imaging range of the CT scan. (0°) scout imaging is performed to confirm the position of the CT dosimetry phantom 10 .

Next, in step 200, as shown in FIG. 7, the dosimetry unit 60 is inserted into the ionization chamber insertion hole 12 of the CT dosimetry phantom 10 from the bed side toward the gantry side. At this time, when the main body portion 42 is completely inserted, it naturally stops at the cap portion 46, and the measurement portion of the dose measurement unit 60 is arranged at the center of the CT dose measurement phantom 10 as shown in FIG. Then, as shown in FIG. 9, the dose measurement units 60 are inserted at all five measurement points of the CT dose measurement phantom 10: center C, top T, bottom B, right R, and left L.

Next, proceeding to step 300, CTDI measurement is performed by the dosimetry unit 60 according to the present invention. Specifically, according to FIG. 10, a range of, for example, 10 cm is imaged so that the center of the CT dose measurement phantom 10 is the imaging center. Five sets of similar imaging are performed for each condition, and the measurement is completed.

In this manner, measurements can be performed at five points simultaneously, so that the measurement can be performed in one-fifth of the time required in the conventional method using an ionization chamber.

In the above-described embodiment, the holding jig 40 is a combination of the main body portion 42 and the cap portion 46 and is made of foamed plastic, but the shape and material of the holding jig are not limited to these.

In the above-described embodiment, a glass dosimeter was used as a dosimeter. It is also possible to use other small dosimeters.

The object of measurement is not limited to CTDIvol.

DESCRIPTION OF SYMBOLS 10... Phantom for CT dose measurement 12... Ionization chamber insertion hole 20... Gantry 40... Glass dosimeter holding jig 42... Body part 44... Glass dosimeter accommodation hole 46... Cap part 50... (Fluorescence) glass dosimeter 52... Glass Element 54... Holder 56... Cap 60... Dose measurement unit

Claims (8)

A CTDI measurement method for X-ray CT in which a jig holding a dosimeter smaller than the ionization chamber other than the ionization chamber is inserted into a CT dose measurement phantom to measure CTDI,
A CTDI measurement method for X-ray CT, wherein the jig is inserted in place of the CT ionization chamber into a hole provided in the CT dosimetry phantom for inserting the CT ionization chamber. 2. The CTDI measurement method for X-ray CT according to claim 1, wherein said jig holds said dosimeter at a predetermined position of said CT dosimetry phantom. 3. The CTDI measuring method for X-ray CT according to claim 1, wherein said dosimeter is a glass dosimeter. A portion other than the ionization chamber that is made of a material that does not interfere with the detection of X-rays by causing scattering and that accommodates a dosimeter smaller than the ionization chamber , and the CT ionization chamber insertion hole formed in the CT dosimetry phantom, A dosimeter holding jig for CTDI measurement of X-ray CT, characterized by having a tubular outer shape that can be inserted in place of a CT ionization chamber. 5. The dosimeter holding jig for CTDI measurement of X-ray CT according to claim 4, wherein the dosimeter holding jig is made of foamed plastic. 6. An X-ray CT according to claim 4 or 5, comprising: a main body having a hole for accommodating a dosimeter in the center thereof; and a cap covering the dosimeter-accommodating hole of the main body. Dosimeter holding jig for CTDI measurement. A dosimeter other than the ionization chamber, which is smaller than the ionization chamber, is inserted into the dosimeter holding jig to form a dosimeter unit,
The dosimetry unit is inserted into the CT ionization chamber insertion hole formed in the CT dosimetry phantom,
Insert instead of ionization chamber for CT,
irradiate with X-rays,
A CTDI measuring method for X-ray CT, characterized by detecting transmitted X-rays. a dosimeter, other than the ionization chamber, smaller than the ionization chamber;
a holding jig into which the dosimeter is inserted;
A dose measurement unit in which the dosimeter is inserted into the holding jig;
a CT dosimetry phantom in which a CT ionization chamber insertion hole is formed and the dose measurement unit is inserted into the CT ionization chamber insertion hole instead of the CT ionization chamber;
means for irradiating the CT dosimetry phantom with X-rays;
means for detecting X-rays transmitted through the CT dosimetry phantom;
An X-ray CT CTDI measuring device comprising:

Images