Optimization of radiotherapy combined course for rectal cancer

Due to the new rapidly developed technological equipment for radiotherapy available in cancer clinics, the study of the optimal combination of topometric preparation of a patient with planning and the delivery of treatment in order to achieve the main goal of radiation therapy - maximum exposure of the foci with minimal damage to healthy tissue. The reduction of dose to critical organs and healthy tissues in general is an important and urgent task. The purpose of the paper is to explore the possibility of optimization of the combined radiation therapy in patients with rectal cancer, with account of advanced approaches to topometric preparation of a patient and dosimetry planning. Six patients 47-59 years of age, with the stage III of the lower ampullary rectal cancer, received two-phase pre-operative combined radiotherapy at the Tomsk Cancer Research Institute NMRC. The Phase 1 - distant radiation therapy delivery in standard mode with a single focal dose (ROD) of 2 Gy, 5 times a week, totally 20 fractions, to focal dose (SOD) of 40 Gy. The Phase 2 - intracavitary radiation therapy, ROD - 3 Gy, SOD - 15 Gy, locally in the tumor area, 2 times a week, total number - 5 fractions. The conventional radiation therapy planning was carried out with the use of the XiO 3-D dosimetry planning system for the "Theratron Equinox 80" (radiation of the isotope 60Co, Eg=1.25 MeV), gamma-therapeutic apparatus, and for the SL75-5-MT (Electron braking radiation, E=6 MeV) linear accelerator. For conformal radial therapy the planning system for linear accelerator «Elekta Synergy» (electron brake radiation, E=6 MeV) is used. For intracavitary radiotherapy the dosimetry planning system HDRPlus for the apparatus "MultiSource" (radiation of isotope 60Co, Eg=1.25 MeV) is used. Radiation doses to critical organs of patients with lower ampullary rectal cancer exposed to combined course of radiotherapy was calculated. It has been shown that the use of advanced techniques for pre-treatment topometric preparation of a patient and dosimetry planning makes possible optimization of combined radiotherapy with account of radiation doses to critical organs.