Dosimetric comparison of bone marrow doses with different treatment techniques in long term rectal cancer radiotherapy

Colorectal cancers are among the most common cancers in the world. Recently, preoperative concurrent chemoradiotherapy(CRT) followed by mesorectal excision has been standart treatment for local advanced rectal cancers(LARC). However, the side effect of CRT is myelosuppression which causes hematologic toxicity(HT).HT can interrupt cancer treatments, increase overall treatment time, and cause treatment failure.In order to have a successful surgical operation and to reduce the risk of post hematological complications, reducing of HT is important. Bone marrow, which is the most important hematological structure in the human, is extremely sensitive to radiation.In order to reduce hematological complications, the doses bone marrow(BM) are significant.Recently, IMRT and VMAT have been commonly used to treat patients with rectal cancer.However, BM was generally not used as avoidance organ and not included in reverse planning in IMRT or VMAT. In this study, dose prescription to the target volume (PTV) is 45 Gy (1.8Gy per fraction). Treatments plans of 100 rectal cancer patients will be created with IMRT and VMAT radiotherapy techniques (7-field-IMRT and 2 arc VMAT), and the doses of PTV, Pelvic bone marrow(PBM) and subsections (Sacrum BM, Coxal BM, Pubis Symphysis BM) will be investigated. As a result, the lower PBM(Pelvic BM) doses were obtained with the VMAT techique. Considering the shorter treatment time, it seems that the VMAT technique is preferable in rectal cancer radiotherapy. Whichever techique is chosen in rectal cancer radiotherapy (IMRT or VMAT), the inclusion of the BM structures to treatment plan optimization will reduce hematological risks that may occur later.