Dosimetric comparison of organs at risk in 5 different radiotherapy plans in patients with preoperatively irradiated rectal cancer

BACKGROUND: Intensity-modulated radiotherapy (IMRT) is a widely used irradiation technique in rectal cancer patients. We aimed to compare 4 different IMRT plans with 3-dimensional conformal radiotherapy (3D-CRT) considering organs at risk (OARs) in patients with rectal carcinoma. METHODS: This retrospective study included 27 rectal cancer patients who were irradiated preoperatively between January 2016 and December 2018. Five different plans (4-field 3D-CRT in 2 phases, 7-field IMRT in 2 phases, 9-field IMRT in 2 phases, 7-field simultaneous integrated boost [SIB] IMRT, and 9-field SIB IMRT) were generated for each patient. Comparison of 5 different plans according to bladder and bilateral femoral head mean doses, bladder V40, bilateral femoral head V40, and small bowel V35 values were evaluated. RESULTS: Most of the OAR parameters significantly favored IMRT plans compared to the 3D-CRT plan. The largest difference was observed in bladder V40 values (reduction of V40 value up to 51.2% reduction) in favor of IMRT. In addition, SIB plans showed significantly better reduction in OARs than phase plans except for small bowel V35 values. CONCLUSIONS: IMRT plans reduced almost all the OARs doses compared with the 3D-CRT plan in rectal cancer patients. Furthermore, SIB plans demonstrated lower OAR doses than the phase plans. IMRT techniques, especially SIB plans, reduce OAR doses and provide safer doses for the treatment of rectal carcinoma.