Analysis of translational and rotational correction values of hexapod table and its effect on target volume margin in breast cancer patients using image guided radiotherapy

Objective: This thesis investigated the impact of translational and translastional-rotational correction values obtained from 3D imaging of breast cancer patients treated with RT with a HexaPOD table equipped lineer accelarator on the target volume margin at Akdeniz University Department of Radiation Oncology. Method: This retrospective research involved planning referance CT images and pre-treatment 3D CBCT images for 10 female breast cancer patients. The images were automatically matched using bone and gray value methods. Systematic and random errors were found. The PTV margin was calculated using Amsterdam and Rotterdam protocols. Results: According the bone matching method, translational and transrotational systematic errors ranged from 0,22-0,32 cm and 0,21-0,35 cm respectively. The ranges were 0,18-0,33 cm and 0,17-0,31 cm regarding gray-value matching. During bone matching, random error values were found in range of 0,23-0,34 cm and 0,27-0,40 cm respectively. Meanwhile, for gray-value matching, the error ranges were 0,24-0,34 cm and 0,23-0,34 cm, respectively. Translational and transrotational PTV margin values calculated by the bone matching method according to the Amsterdam protocol were calculated as 1,0-1,2 cm, respectively, while in the Rotterdam protocol they were calculated as 0,8-1,0 cm. Regarding translational and transrotational correction in gray-value matching, this margin value was 1,0 cm in the Amsterdam protocol and 0,8 cm in the Rotterdam protocol. Conclusion: This study observed low-level differences at the negative and positive directions of PTV margins. The difference in PTV margins calculated using translational correction data between bone and gray-value matching methods was found to be 0,3 cm according to the Amsterdam protocol, while it was 0,2 cm in the Rotterdam protocol. Upon comparing transrotational correction values across both matching methods for each protocols, the discrepancy in PTV margin was determined to be 0,2 cm. Key words: breast radiotherapy, IGRT, set-up errors