| Abstract [eng] |
Prostate cancer is one of the most common forms of cancer among men. Radiation therapy is often used to treat prostate cancer. The prostate is a moving organ, but its locations can also be affected by the nearby bladder and rectum, whose volumes are always changing. For this reason, in order to estimate the changing organ volumes in radiotherapy before each therapeutic fraction could be used one of the image-guided radiotherapy techniques, for example, cone-beam computed tomography (CBCT). CBCT is an important part of radiotherapy. This helps to assess the localisation of the targets of the prescribed treatment, allows for the adjustment of treatment plans, if necessary, reduces errors and improves the detection of moving organs. CBCT has two energy types – megavoltage and kilovoltage. It consists of a megavoltage and kilovoltage “source” and detector. In the final degree project, were used a linear accelerator Halcyon system with an integrated kVCBCT imaging technique, for patient scanning was selected protocol called Pelvis. Images of the patient were transferred to the treatment planning system (TPS) Eclipse, where the bladder and rectum re-contouring and treatment planning on daily kV-iCBCT images were performed, analysing irradiation doses and volume changes of these organs, and additionally to the irradiated target volume. Results of the research were evaluated regarding the daily kV-iCBCT volume values (mean, minimum, and maximum) of bladder and rectum changes for the patients. Two patients were analysed in total. Bladder and rectum volume varied from 64.5 cc to 319.0 cc (Patient 1/ bladder), and from 49.5 cc to 148.3 cc (Patient 1/ rectum), respectively, while for the Patient 2 - 55.4 cc ÷ 298.8 cc (bladder), and 38.2 cc ÷ 107.9 cc (rectum). Dose-volume histograms showed that the changing volumes of organs affect the dose of ionizing radiation. Also, volumes were compared between treatment planning results planned on computed tomography and kV-iCBCT. The final results showed a good agreement for PTV target volumes coverage from 0.00 % to 0.02 % (Patient 1) and from -0.03 to -0.05 % (Patient 2), Boost coverage differed from -0.03 % to -0.07 % (Patient 1) and from -0.01 % to -0.02 % (Patient 2), which means that treatment planning could be successfully performed on daily kV-iCBCT images. |
