RU2299083C2 - Method for carrying out dosimetric planning intracavitary metastatic vaginal carcinoma brachytherapy - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: method involves arranging active positions of walking source in known way. Dosimetric plan of walking source iridium-192 has fourteen active positions uniformly distributed in regular intervals in pairs 7.5 mm one from another, the source having step size of 2.5 mm, in single ring applicator "Ring Applicator Sets" having ring diameter of 30 mm and active length of 80 mm, of Microselectron HDR device.

EFFECT: reduced malignant tumor recurrence risk.

1 tbl

Description

The invention relates to medicine, in particular oncology, radiation therapy of primary and metastatic vaginal cancer (RV).

Primary vaginal cancer among the total number of female genital tumors ranges from 1% to 3% (Perez CA, Madoc-Jones H. Carcinoma of the vagina. / Eds. Perez CA and Brady LW Principles and Practice of Radiation Oncology. Philadelphia: JBLippincott. - 1987. - Chapter 53. - P.1023-1035.) At the same time, tumor metastases in the vagina (cervical and uterine cancer) are much more common - from 10% to 20% in relation to all tumors of the female genitalia (Bohman I .V. Guide to Oncogynecology. - L. Medicine, 1989 - 464 p.). The widespread development of radiation methods, the low frequency of complications, as well as the possibility of obtaining satisfactory results, make radiation therapy the main method of treating vaginal cancer (Vishnevskaya E.E. Guide to Oncogynecology. / Ed. By N.N. Aleksandrov. - Minsk .: Belarus, - 1980 .-- 223 p.). As previously noted by many researchers involved in the problem of radiation treatment of malignant tumors of the vagina (Perez CA, 1987; Vishnevskaya E.E., 1980; Bohman Ya.V., 1989), the successful outcome of radiotherapy largely depends on the individual approach and the technical means that currently has a radiotherapist. Therefore, it seems important to us to consider and compare the effectiveness of the various capabilities of modern contact exposure and its computer dosimetric planning. In addition, given the anatomical and topometric features of the location in the vagina of both primary and metastatic tumors (similar sizes, spread and localization in the same organ with similar adjacent anatomical structures), it is advisable to use a single technical approach when irradiating these types of malignant tumors . This position is confirmed by a retrospective assessment of the irradiation technology of the patients we observed. In the set of applicators of the Microselectron HDR apparatus, the Ring Applicator Sets is of interest - a combination of a ring post post with metrastat, which in many cases replaces the generally accepted standard metra post post. By us, for the first time in our country (Kanaev S.V., Turkevich V.G. Modern brachytherapy technologies for primary and metastatic cancer of the vagina. // Vopr. Onkol. - 1997. - T 43. - No. 5. - P.528-534 .), for the treatment of malignant formations of the vagina, separately used ring applicators (Ring) with various diameters (26, 30, 34 mm) and an angle of inclination (30, 45, 60 degrees) included in the delivery set of devices were used. The ring applicator was equally successfully used to treat tumors of the upper, middle and lower third of the vagina. In the upper third or dome of the vaginal stump, a ring with an angle of 60 degrees was installed, with brachytherapy of the lower third of the vagina, rings with an angle of 30 degrees are more convenient. To date, the most complex and widely used is the optimization of the location time in a walking source dosimetric system (VSS) (Van der Laarse R, Prins TPE. Introduction to HDR brachytherapy optimization. In: Brachytherapy from Radium to Optimization, ed. Mold RF, Battermann, JJ, Martinez, AA, et al. - Nucletron. Veenendaal, the Netherlands. - 1994. - P.331-351), which can be considered as a prototype of the present invention. In order to discuss the advantages and disadvantages of optimizing the location time (BP) of a walking source, it is necessary to consider the basic mechanisms of how this is done. All methods are divided into fundamental characteristics - BP is changed to maximize (or minimize) a certain function, this is the optimization.

The most important is the concept in which the optimization process will be so useful if the function, being mathematically optimized, is able to solve a clinical problem. One of the possible errors in BP optimization is the inability of the user to mathematically set the required isodose distribution. Optimization of BP allows the formation of a reference isodose that optimally corresponds to the target volume with minimal damage to adjacent tissues. The mathematical apparatus of the planning program uses a geometric algorithm to distribute the source BP along the length of the applicator and, correspondingly, to the optimization points, calculate the BP in each applicator. It should be emphasized that the possibility of the successful use of LSS depends on the mutual spatial arrangement of the applicators and the radiation energy from each source. Since the dose from the source falls in inverse proportion to the square of the distance and grows linearly with respect to the time of application, the effectiveness of manipulation with BP is limited. This can be improved with more implants, however, brachytherapy can never effectively treat tumors located at a distant distance without a high risk of damage to surrounding tissues. Therefore, optimization of the location time of the source will never be as important as optimization of the spatial location of the implants and the position of the source in them.

The modern methodology for calculating the dose load for intracavitary radiation treatment is described in the report of the International Commission on Radiation Units and Measurements, 1985 (International Commission on Radiation Units and Measurements. Dose and Measurements. International Commission on Radiation Units and Measurements (ICPE) N 38). volume specification for reporting intracavitary therapy in gynecology. ICRU Report 38. - 1985. - Bethesda. MD.). The main provisions of this document, devoted to fundamental issues, for a long time determined a systematic approach to planning brachytherapy for most malignant tumors:

- the possibility of stimulating linear sources by several point sources located at equal distances from each other, as well as simulating them by moving a point source, changing the type of movement (continuously or stepwise), the speed and delay time of the source in different positions, which modifies the shape of the isodose surfaces;

- the dose rate of brachytherapy in conventional radium therapy in the range of 0.4-2 Gy / h is usually defined as low dose rate (NMD), the average is 2-12 Gy / h (SMD) and> 12 Gy / h is high (AMD) ;

- the target volume is included in the treatment volume, must be physically measured, described with respect to the anatomical structures of the patient and include a tumor or any other tissue containing the tumor;

- the reference volume is enclosed beneath the surface of the reference isodose.

No less important than ICRE-38 at one time, are the recommendations of the International Commission on Radiation Units and Measurements. Dose and volume specification for reporting interstitial therapy. ICRU Report 51. - 1997. - Bethesda. - MD.) .:

- the treatment volume includes the volume of tissue that the implant occupies, limited by the peripheral isodose, this volume ideally approaches the clinical volume of the target;

- preset dose - the dose determined by the radiotherapist;

- the minimum dose is located on the border of the clinical volume of the target;

- the area of high dose loading is surrounded by an isodose corresponding to 150% of the average central dose in any plan;

- the index of a homogeneous dose distribution is defined as the ratio of the peripheral minimum dose to the central average.

The technical result of the present invention is to significantly reduce the risk of cancer recurrence. This is achieved practically without radiation complications due to summarizing the necessary tumorucidal dose, provided that the optimal dosimetric plan is chosen.

The essence of the invention lies in the selection of an optimal model for positioning a walking source with a step size of 2.5 mm, Iridium-192, the Microselectron HDR apparatus in one 30 mm diameter Ring Applicator Sets, with intracavitary brachytherapy of primary and metastatic vaginal cancer, which provides complete cure of a malignant tumor with a minimum number of radiation complications.

In most cases, for planning intracavitary brachytherapy, we use a stereo reconstruction of the location of the applicator with stereo electroradiographs performed with a focus shift of 80 mm on each side. The selection of patient reference points is based on the use of orthogonal reconstruction, followed by the designation of areas of interest from a digitizer in the x-ray coordinate system.

We have studied many isodose distributions obtained with different positions of the walking source of iridium-192 of the Microselectron HDR apparatus in a ring applicator with a diameter of 30 mm during intracavitary brachytherapy of primary and metastatic vaginal cancer. When using this technique of intracavitary radiation therapy, the location of the reference single dose in the required treatment volume is not a big problem and is almost always achieved using the mathematical apparatus of the brachytherapy planning computer system. At the same time, the main difficulties lie in the selection of such an optimal variant of summing up the tumorucidal dose, in which there is the possibility of minimizing the number and severity of early and late radiation complications. Therefore, we selected the most optimal dosimetric plans used in brachytherapy of various patients with primary and metastatic vaginal cancer, there were 10 of them. The most representative characteristics of these plans are presented in table No. 1. BP in each position is equal to the quotient of the total treatment time divided by the number of source positions . For a more visual comparison of all dosimetric plans, the target volume - the planned tumor volume (RTU) is defined as the standard V0 = 27 cm ³ , and it should be noted that in clinical practice we treated tumors with PTV that are close or smaller in value compared to V0. Comparison of dose plans was carried out with identical activity of the source of iridium-192.

Legend:

The total number of active source positions is N

Total active length (mm) - A

Interval between active positions (mm) - 1

The minimum peripheral dose (% of the set) - D min

High dose loading (% of the set) - D max

Homogeneous Dose Distribution Index - Indx

Reference dose rate - P (Gy / h)

Dose rate at dose maximum - P max (Gy / h)

Dose rate in the dose minimum - P min (Gy / h)

Tumor volume (cm ³ ) - V0 = 27

The volume of 100% isodose (cm ³ ) - V1

The volume of 300% isodose (cm ³ ) - V2

Ratio V1 to V0 - V1 / V0

Ratio V2 to V0 - V2 / V0

Table number 1. No. N BUT I Dmin Dmax Indx R Pmax Pmin V1 V2 V1 / V0 V2 / v0 one 33 82.5 0 fifty one hundred 0.5 16 32 8 41.5 10.7 1.5 0.4 2 24 77.7 2.5 fifty one hundred 0.5 16 32 8 37.6 9.3 1.4 0.3 3 24 84.0 2.5 58 112 0.52 fifteen 29th 8.6 45.1 9.7 1.7 0.4 four 21 82.5 5 58 112 0.52 fifteen thirty 8.8 44.3 9.3 1.6 0.3 5 eighteen 85.0 5 58 117 0.49 14.8 29.6 8.6 44.2 10.7 1.6 0.4 6 eighteen 82.5 7.5 58 108 0.54 14.9 29.8 8.7 45.6 9.7 1.7 0.36 7 17 82.5 2.5 55 one hundred 0.55 15.4 30.8 8.5 41.9 12.4 1.6 0.46 8 fourteen 80.0 7.5 58 103 0.56 15.1 30.2 8.8 43.4 11.7 1.6 0.43 9 12 85.0 5 55 105 0.52 14.8 29.6 8.1 45.2 11.4 1.7 0.42 10 9 82.5 7.5 55 one hundred 0.55 15.5 31 8.5 40.2 11.1 1.5 0.41

We carried out a thorough comparative analysis of the 10 most optimal (from the point of view of uniform correspondence between the reference dose volume and the clinical volume) dosimetric plans (DP) of intracavitary brachytherapy for all the above parameters.

In table No. 1, all plans are ranked by reducing the total number (N) of active source positions, since a larger number of source positions in the endostat causes a large dose load along the entire active length directly next to the applicator, which leads to unjustified radiation damage to healthy tissues. What happens when using the seemingly ideal plan N 1, which we took as a prototype. It is difficult to note in the table the frequency and uniformity of the arrangement of the active positions of the source, therefore this parameter will be described in the text. In plan 2, the active positions are located in 3 with a gap of 2.5 mm, and in DP 3 - in 2 with an empty interval of 2.5 mm. Despite the fact that in each DP active positions in different variants were generally evenly distributed, their grouping was the main distinguishing feature that defines the difference between one or another plan. In plan N1, all 33 positions are located tightly one after another without an empty interval. The source pitch is 2.5 mm in all dose plans. In DP 4, active positions are grouped in 3 by an empty interval of 5 mm, in DP 5 active positions are arranged in pairs after 5 mm, in DP 6 active positions - 3 tightly after 7.5 mm, in DP 7 active positions - one after 2.5 mm , in DP 8 active positions - in pairs through 7.5 mm, in DP 9 active positions - one after 5 mm, in DP 10 active positions - one after 7.5 mm.

It must be emphasized once again that all 10 of the dosimetric plans that we examined almost completely solve the problem - summing the tumorucidal (healing) dose to the tumor, which is proved by the acceptable isodose distribution of all DPs. Therefore, the dosimetric characteristics of all plans are close in value. The main difficulty in choosing one or another plan was to choose the optimal combination of all the above parameters of the isodose distribution, which ultimately allowed us to solve the technical problem - to minimize the number and severity of early and late radiation complications. It is known that the severity of radiation complications is directly proportional to the dose and the dose rate of brachytherapy. In all the presented DPs, we used a single focal dose of 6 Gy, summed up with a 100% reference isodose with a volume of V1. Therefore, it was important to compare dose plans for dose rate at different points.

From Table 1, according to the characteristics presented, we can immediately exclude DP 1 and 2, which differ from others in low Indx, high dose rate of brachytherapy and low values of V1 / V0 and V2 / V0. According to these data, plan N 10 is also close to them, which stands out only with a high Indx = 0.55, which, by the way, determined its clinical use. Unfortunately, DP 5 is very inferior in this parameter, although in general its other characteristics are quite high, which also led to its clinical use. The following plans with a low Indx = 0.52 were DP 3, 4, 9. Among the latter, N 9 differs by higher values of V1 / V0 and V2 / V0 and a low dose rate, which explains its more successful clinical use. Among the remaining dosimetric plans 6, 7, 8, which are the best of all 10 in terms of the Indx parameter, DP 6, which has a relatively low dose rate, but a contradictory ratio of V1 / V0 and V2 / V0, stands out separately, which is obvious and determined it is very rare clinical use. The best according to the analysis of the isodose distribution turned out to be plans N 7 and 8. Obviously, the most simple-to-follow plan N 7, in which all 17 active positions of the iridium-192 source are evenly spaced 2.5 mm and all the characteristics of the isodose distribution are almost optimally balanced, attracts practical brachytherapists. But probably a lower value of the index of homogeneous dose distribution, compared with DP 8, a higher dose rate and a volume of 300% isodoses predetermined in practice a greater number of early and late radiation complications when using DP 7.

The final selection criterion in our case is clinical practice - brachytherapy of malignant tumors located in the vagina. We most often used DP 5, 7, 8, 9, 10 for treatment. But unlike all other dose plans, there were no radiation complications among patients who underwent intracavitary brachytherapy of primary and metastatic vaginal cancer when using dosimetric plan N 8 with the 14th active positions located evenly in pairs through 7.5 mm, of a walking source of iridium-192 with a step size of 2.5 mm in one ring applicator "Ring Applicator Sets" with a ring diameter of 30 mm and an active length of 80 mm, the Microselectron HDR apparatus.

We give examples of a specific implementation of the method

1) Patient K., 71 years old. Was in the hospital of the Radiological Department of the Oncology Research Institute. prof. NN Petrova Ministry of Health of the Russian Federation with a diagnosis of Vaginal cancer T1 N0 M0. Histology: squamous keratinizing cancer. Upon admission, it was found that an exophytic tumor of 20 mm located on the back wall of the middle third of the vagina was subjected to brachytherapy with one ring applicator Ring Applicator Sets with a ring diameter of 30 mm and an active length of 80 mm, Microselectron HDR apparatus, single focal dose (ROD) = 6 Gy (P = 15 Gy / h), total focal dose (SOD) = 36 Gy, dosimetric plan N 8 in accordance with the above methodology of the invention. There were no complications.

2) Patient B., 48 years old. Was in the hospital of the Radiological Department of the Oncology Research Institute. prof. NN Petrova Ministry of Health of the Russian Federation with a diagnosis of metastasis of cervical cancer in the vagina. In the past, surgical treatment for cervical cancer T1 b N0 M0. Histology: squamous non-keratinizing cancer. Upon admission, an exophytic tumor of 25 mm was found in the dome of the vaginal stump. Was subjected to brachytherapy with one ring applicator "Ring Applicator Sets" with a ring diameter of 30 mm and an active length of 80 mm, the apparatus "Microselectron HDR", ROD = 6 Gy (P = 15 Gy / h), SOD = 42 Gy, dosimetric plan N 8 in in accordance with the above methodology of the invention. There were no complications.

3) Patient T., 54 years old. Was in the hospital of the Radiological Department of the Oncology Research Institute. prof. NN Petrova Ministry of Health of the Russian Federation with a diagnosis of metastasis of cancer of the uterus in the vagina. In the past, the surgical treatment of cancer of the uterus is T1 b N0 M0. Histology: highly differentiated endometrial adenocarcinoma. Upon admission, an exophytic tumor of 20 mm was found on the front wall of the lower third of the vagina. Was subjected to brachytherapy with one ring applicator "Ring Applicator Sets" with a ring diameter of 30 mm and an active length of 80 mm, the apparatus "Microselectron HDR", ROD = 6 Gy (R-15 Gy / h), SOD = 42 Gy, dosimetric plan N 8 in in accordance with the above methodology of the invention. There were no complications.

Claims (1)

A method for dosimetric planning of intracavitary brachytherapy of primary and metastatic vaginal cancer by arranging the active positions of a walking source, characterized in that they use a dosimetric plan with 14 active positions located evenly in pairs across 7.5 mm of an iridium-192 walking source with a step size of 2, 5 mm, in one ring applicator "Ring Applicator Sets" with a ring diameter of 30 mm and an active length of 80 mm, the apparatus "Microselectron HDR".