RU2299081C2 - Dosimetric method for planning intracavitary brachytherapy of uterine body carcinoma - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: method involves arranging active positions of walking source in double metrastat "Rotte Endometrial Applicator Sets" applicator. Active length of each metrastat is selected to be equal to 50 mm in double metrastat device of "Microselectron HDR" and dosimetric plan having 6 active positions is used. The positions are uniformly spaced in regular intervals from the endostat end, each position being 2.5 mm far from each other and further having 3 active positions 5 mm far from each other in each iridium-192 walking source metrastat with step size equal to 2.5 mm.

EFFECT: reduced risk of malignant tumor relapse.

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Description

The invention relates to medicine, in particular oncology, radiation therapy for cancer of the uterine body (RTM).

Radiotherapy of RTM as an independent method is used only with absolute contraindications to surgery. They are most often caused by severe, uncompensated concomitant diseases and / or the spread of the tumor to the parametric tissue and vagina. Therefore, this category of patients is very difficult for radiotherapy and requires gentle regimes that exclude the use of large volumes of radiation. In this case, the technology of hardware brachytherapy, which provides the maximum dose load on a malignant tumor while maintaining the surrounding healthy tissues for a short period of time, is most suitable. The modern methodology for calculating the dose load for intracavitary radiation treatment in gynecology is described in the report of the International Commission on Radiation Units and Measurements, 1985 (International Commission on Radiation Units and Measurements. Dose and volumespecification for reporting intracavitary therapy in gynecology. ICRU Report 38. - 1985. - Bethesda. MD.). The main provisions of this document on brachytherapy for cervical cancer are also valid in brachytherapy for uterine cancer:

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

- planning of conventional brachytherapy with NMD is carried out according to the reference isodose corresponding to 60 Gy. For intracavitary irradiation with DMD and AMD, the planned focal dose should be biologically equivalent to 60 Gy with NMD;

- the reference volume corresponds to the classical pear-shaped form, and the reference isodose passes through the metering points (points A);

- Dose load registration points are determined relative to the sources (maximum dose) and in the area of risk organs (minimum possible dose);

- the reference point in the bladder is determined on radiographs in the center of the image of the Foley catheter balloon, in the area of its contact with the mucosa of the posterior wall;

- the reference point in the rectum is located 5 mm from the vaginal wall at the location of the vaginal ovoid.

The clinical advantages of using high and medium dose rates in contact radiotherapy equipment are obvious: the possibility of outpatient irradiation, the position of the source is highly reproducible and, if necessary, relatively easily visually controlled during the entire treatment session, the patient is motionless for a short period of time, which reduces the risk of thrombosis and embolism.

In modern brachytherapy units with a high radiation dose rate, iridium-192 sources with an activity of 5-10 Ci become more and more popular, despite the relatively short half-life (74.02 days), which necessitates frequent recharging of the device (3-4 times a year ) With a good organization of maintenance, this drawback can in no way be decisive. The main advantage of iridium-192 is the relatively low average energy of its gamma radiation (0.456 MeV), due to which it is possible to drastically reduce the mass of the storage vault and, most importantly, from a clinical point of view, reduce the number and severity of radiation complications. To modify dose distributions in intracavitary gamma-therapeutic devices, point or linear sources are used which, for irradiating extended targets, line up in a fixed chain or, moving during the irradiation process, imitate such a chain. A significant difference in the optimization of dose distributions when using sources that are stationary and transported during irradiation occurs due to the fact that with stationary sources the dose rate at any point of the irradiated medium remains constant, and the absorbed dose is proportional to time, whereas in the case of a source transferred during exposure, the dose rate at each point of the surrounding space changes as the source moves, so to build up the dose distribution, the accumulation of absorption dose for the entire time the source moves from one extreme position to another. The forms of isodose curves are also different, which, in the case of using a source chain, have a characteristic dip towards the ends of the chain due to attenuation of the radiation of some sources by others, whereas when moving a point source during irradiation, the isodoses in the axial direction are not distorted.

In the Microselectron HDR apparatus manufactured by Nucletron, a source (diameter 1 mm) of iridium-192 (5-10 Ci) with an active length of 3.5 mm, firmly connected to 2.0 meters, is used for endocurotherapy with a high dose rate steel cable. The source, according to the irradiation program, is alternately installed with a step of 2.5 or 5 mm in any of the 48 positions in the endostat, forming a radiating line up to 24 cm long.The variety of figures of the isodose distribution obtained on this device is due to the length of time the source has stood in the selected position. The maximum distance of the source from the apparatus is 1500 mm. The small diameter (1 mm) of the iridium-192 source made it possible to create thin applicators with a diameter of 3 mm. The applicator kit contains a double metrastat "Rotte Endometrial Applicator Sets", consisting of two symmetric applicators, metrastat, bent at an angle of 30 degrees, inserted into the uterus alternately and then firmly fixed together so that in the frontal projection they mimic the letter Y. Previously, this applicator had the name Y-shaped, where each metrastat is located in its corner of the uterine cavity. In K. Rotte's "HDR Brachytherapy for Endometrial Cancer". (In: Mold RF, Battermann JJ, Martinez AA and Speiser, BL eds. Brachytherapy from Radium to Optimization. - 1994. Veenendaal, the Netherlands: Nucletron Corporation. - P.91-100) rightly notes the main difficulties of uterine cancer brachytherapy, are associated with determining the target volume and achieving a homogeneous dose distribution in the target volume. For the first time, this author used a double Y-shaped applicator to treat RTM with AMD brachytherapy, which completely avoided such serious complications as thromboembolism. JAStitt and AAAbitbol in Chapter 28, “Brachytherapy for Endometrial Carcinoma” (In: Subir Nag.eds. Principles and Practice of Brachytherapy. - 1997 - Futura Publishing Company, Inc. - New York. - P.553-567.) fully describe the various technologies of brachytherapy for cancer of the uterus. Of particular interest is the experience of AMD of endocuritherapy of this tumor in the clinic of the University of Miami, where they used a Y-shaped double applicator, which makes it possible to more optimally irradiate tumors located in the bottom of the uterus, in comparison with other standard applicators. A single dose of 6-7 Gy once a week was set at points located 2 cm below the bottom of the uterus and 2 cm lateral to the middle axis of the uterine cavity.

The most detailed in the modern literature is a description of various methods for dosimetric planning of RTM brachytherapy by R. Potter, A. Gerbaulet, C. Haie-Meder "Endometrial Cancer". In: The GEC ESTRO Handbook of Brachytherapy. Ed. A. Gerbaulet at all. - 2002. - P.365-401), which we took as a prototype of the invention. The technology of using the Rotte Y-shaped applicator makes it possible to treat small malignant tumors located in small and medium-sized uterine cavities. Dose distribution is optimized depending on the thickness of the walls of the uterus. The authors summarized the experience of using this technology by various researchers, who used both standard dosimetric plans that take into account the dose load at various reference points, and individual dosimetric planning for special localization of the active positions of the source and different source location times. It is known that the optimization of the location time of the source will never be as important as the optimization of the spatial location of the applicators and the position of the source in them. Therefore, in our invention, it was the latter method that was used. In the technology of dose planning of the prototype, the main attention is paid to the size of the uterine cavity and the treatment volume that provides cure for a malignant tumor of the uterus, and the dose load on critical organs (bladder and rectum) is considered last. In our invention, on the basis of a thorough dosimetric analysis of various optimal dose plans, both of these problems are equally solved.

The technical result of the present invention is to significantly reduce the risk of relapse of a malignant tumor without radiation complications from adjacent risk organs. This is achieved by summarizing the necessary tumorigenic dose to the tumor, provided that the optimal dosimetric plan is selected.

The essence of the invention is to select the optimal positioning model of the positions of a walking source of iridium-192 with a step size of 2.5 mm, in a Rotte Endometrial Applicator Sets double applicator, with an active length of 50 mm each, Microselectron HDR apparatus for intracavitary brachytherapy of uterine body cancer providing a complete cure for a malignant tumor with a minimum number of radiation complications. In most cases, for planning brachytherapy, we use a stereo reconstruction of the location of the applicator from stereo electroradiographs made with a focus shift of 80 mm on each side. Contrasting adjacent pelvic organs is done using radiopaque medical solutions and flexible plastic catheters that have metal marks. 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. The set of points related to the applicator, according to which a focal dose of radiation is planned, is selected in accordance with the Manchester method for the treatment of uterine tumors. The reference isodose has a pear-shaped, corresponding to the shape of the uterus body, and passes through both points A. Thus, the reference treatment volume includes the entire cavity and body of the uterus. The location of the considered points of the risk organs and the reference volume of exposure is determined in accordance with the recommendations of ICRU Report 38. The residence time of the source in all possible preset positions can be optimized in accordance with the required dose at one or more points or the required isodose distributions. These points can be the points of the patient and / or applicator at which the reference single dose is set. An isodose curve is formed along a number of dose points for one or more catheters. Each dose point of the isodose curve can be placed at different distances from the given active positions of the source in the selected catheter. The time spent by the source in one place or another is chosen so as to ensure an identical predetermined dose at each point on the curve.

We have studied many isodose distributions obtained for different positions of the walking source of iridium-192 with a step size of 2.5 mm, a double metrastat applicator "Rotte Endometrial Applicator Set" with an active length of each metrastat 50 mm, the Microselectron HDR apparatus for intracavitary brachytherapy of uterine body cancer . When using this technique of intracavitary radiation therapy, the location of the reference single dose in the required treatment volume is almost always achieved using the mathematical apparatus of the brachytherapy planning system. The main difficulties lie in the selection of such an optimal variant of summing up the tumorigenic dose, at which it is possible to minimize the number and severity of early and late radiation complications from critical organs. We selected 8 of the most optimal dosimetric plans (DP) used in brachytherapy for various patients with cancer of the uterus. The main characteristics of these plans are presented in tables 1 and 2. The location time in each active 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 (planning treatment volume - PTV) is defined as the standard V0 = 48 cm ³ . We have treated tumors with PTVs that are close or less in value compared to V0. Comparison of dose plans was carried out with an identical activity of the source of iridium-192 and a pitch of 2.5 mm.

Legend:

The number of active source positions in both metrastats is N

The number of active source positions in one metrastat is n

Interval between active positions in one metrastat (mm) - i

Active length of one metrastat (mm) - a

Dose load in the bladder (% of the target) - dCyst

Dose load in the rectum (% of target) - dRect

Reference dose rate (Gy / hour) - P

Bladder dose rate (Gy / hour) - pCyst

Rectal dose rate (Gy / hour) - pRect

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

The volume of 200% isodose (cm ³ ) - V2

The volume of 300% isodose (cm ³ ) - V3

Ratio V1 to V0 - V1 / V0

Ratio V2 to V3 - V2 / V3

Table 1. No. N n I BUT dCyst dRect R one 40 twenty 0 fifty 58 67 10.9 2 34 17 2.5 52.5 62 73 10 3 thirty fifteen 2.5 fifty 56 70 10.3 four thirty fifteen 2.5 52.5 57 73 10.4 5 28 fourteen 5.0 55 58 74 8.8 6 22 eleven 2.5 52.5 54 73 10.7 7 22 eleven 5.0 52.5 54 73 10.4 8 eighteen 9 5.0 fifty 55 73 9.9

Table 2. No. pCyst pRect V1 V2 V3 V1 / V0 V2 / v3 one 6.3 7.3 58.5 19.1 9.7 1.22 1.97 2 6.2 7.3 65.4 24.6 11.3 1.36 2.17 3 5.7 7.2 64.4 21.8 11.1 1.34 1.97 four 5.9 7.6 62.4 20.8 10.7 1.30 1.95 5 5.1 6.5 78.4 27.4 13.1 1.63 2.09 6 5.8 7.8 59.7 19.3 9.9 1.24 1.96 7 5.6 7.6 62.6 20.1 9.7 1.30 2.08 8 5.2 7.2 68.8 22.4 11.4 1.43 1.96

We carried out a thorough comparative analysis of the 8 most optimal in terms of uniform correspondence of the reference dose volume and the clinical volume of exposure of the dosimetric plans of intracavitary brachytherapy with double metrastat according to all the above parameters. It should be noted once again that a double metrastat consists of two identical symmetrically arranged metrastats, rigidly fixed to each other, thereby forming, after installation, a Y-shaped applicator Rotte. Therefore, the description of the arrangement of active positions (AP) of the source in a double metrastat is reduced to the description of the AP in each metrastat. Moreover, in all dose plans subjected to our analysis, the sequence of arrangement of active positions is the same in each metrastat of double metrastat, i.e. each double metrastat metrastat is symmetrical both in shape and in the arrangement of the AP. Almost two identical metrastats, turned in different directions, form a Y-shaped double metrastat. In the tables, all plans are ranked by decreasing the total number (N, n) of active source positions. In the tables it is difficult to note the periodicity and uniformity of the arrangement of the active positions of the source, therefore this parameter is described in the text. In each DP, active positions in different versions in the endostats were located evenly, their grouping was the main distinguishing feature that defines the name of one or another plan. The numbering of the positions of the source began with the closed end of the metrastat located in the bottom of the uterine cavity. In plan No. 1, all APs are arranged densely one after another without an empty interval in each metrastat of double metrastat. The source pitch is 2.5 mm. In DP No. 2, active positions are grouped in 2 by an empty interval of 2.5 mm from the 10th to the 21st (10-21) position, and from the 1st to the 9th position (1-9) the APs are densely located in DP No. 3 APs are evenly distributed one by one through 2.5 mm (15-20) and tightly 4 each in a group with an interval between groups of 2.5 mm (1-14), in DP No. 4 active positions are located uniformly one after another 2.5 mm (16- 21) and tightly in 3 in a group with an interval between groups of 2.5 mm (1-15), in DP No. 5 APs are located one after 5 mm (11-22) and tightly without an interval (1-10), in DP N6 all active positions are arranged evenly one by one through 2.5 mm, in DP No. 7 AP grouped in pairs after 5 mm (1-14) and one after 2.5 mm (15-21), in DP No. 8 the active positions are arranged uniformly one after 2.5 mm in each metrastat through 2.5 mm (1-11) and then one through 5 mm (12-20).

All 8 Rotte double metrastat dosimetric plans investigated by us solve the task - summarizing the tumorigenic (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 allowed us to solve the technical problem - to minimize the number and severity of early and late radiation complications. In all the presented DPs, we used a single dose of 8 Gy, summed up at 100% isodose with a volume of VI. A general analysis of all DPs of double metrastats shows a direct dependence of the high dose load on critical organs on the volume of the reference isodose, and this correlation is more clearly visible in the dose load in the bladder. Of all DPs, plan No. 5 clearly falls out, and it would seem that, with good dose indicators in critical organs, there is a very poor ratio of dose volumes and uniformity of dose distribution. This is due to the contrast distribution of AP in different parts of the applicator. DP No. 2 and 7 have similar unsuccessful dose characteristics, but in plan No. 7 the active positions are more evenly distributed, which can be seen at the best indicators. The worst in high dose load in critical organs are DP No. 1, 3, 4 with acceptable indicators of the ratio of the dose distribution volumes. The best ratios of almost all indicators are possessed by plans 6 and 8. Primitive by the location of the active positions of the source of PD No. 6 may be the subject of choice in routine clinical practice. But with careful comparison, the latter clearly loses the dose load in critical organs to dosimetric plan No. 8, which is accompanied by a smaller number and severity of radiation complications during brachytherapy of uterine cancer. Therefore, with excellent tumor effect, there were practically no severe radiation complications among patients who underwent intracavitary brachytherapy of uterine cancer using the Rotte Endometrial Applicator Sets dosimetry plan No. 8 with an active length of 50 mm for each metrastat and 6 active positions located uniformly from the end of the endostat one after 2.5 mm and then with 3 APs, one after 5 mm in each metrastat of a walking source of iridium-192 with a step size of 2.5 mm.

We give examples of a specific implementation:

1. Patient V., 75 years old. She was in the hospital of the Radiological Department of the Research Institute of Oncology named after prof. N.N. Petrova of the Ministry of Health of the Russian Federation with a diagnosis of cancer of the uterine body T1a N0 M0. Histology: highly differentiated endometrial adenocarcinoma. Upon admission, it was found: a tumor of 20 mm in the bottom of the uterine cavity. Was subjected to brachytherapy with a double metrastat applicator "Rotte Endometrial Applicator Sets", with an active length of each metrastat 50 mm, apparatus "Microselectron HDR", a single focal dose (ROD) = 8 Gy (P = 10 Gy / hour), administered once a week, total focal dose (SOD) = 40 Gy, dosimetric plan No. 8 in accordance with the above described methodology of the invention. There were no complications.

2. Patient G., 71 years old. Was in the hospital of the Radiological Department of the Oncology Research Institute. prof. N.N. Petrova of the Ministry of Health of the Russian Federation with a diagnosis of cancer of the uterine body T1a N0 M0. Histology: moderately differentiated endometrial adenocarcinoma. Upon admission, a tumor of 30 mm was found on the posterior wall of the uterine cavity. Was subjected to brachytherapy with a double metrastat applicator "Rotte Endometrial Applicator Sets", with an active length of each metrastat 50 mm, apparatus "Microselectron HDR", ROD = 8 Gy (P = 10 Gy / hour), delivered once a week, SOD = 48 Gy, dosimetric plan No. 8 in accordance with the above described methodology of the invention. There were no complications.

Claims (1)

A method for dosimetric planning of intracavitary brachytherapy for uterine body cancer by arranging the active positions of a walking source in a double metrastat applicator "Rotte Endometrial Applicator Sets", characterized in that the active length of each metrastat 50 mm is selected in a double metrastat of the Microselectron HDR apparatus and a dosimetric plan with 6 active positions located from the end of the endostat evenly one after 2.5 mm and then with 3 active positions one after 5 mm in each metrastat of the walking source of iridium-192 with pitch measure 2.5 mm.