Dosimetric comparison of rectal carcinoma radiation therapy using three dimensional conformal radiation therapy and intensity modulated radiation therapy: an analytical observational study

Abstract

Rectal cancer is the second most common cancer in large intestine. Recently, preoperative chemoradiotherapy has been generally used in the management of locally advanced rectal cancer on the basis of several benefits proven by clinical studies, in the aspect of better locoregional tumor control, reduced toxicity of normal organs, and an increased chance of preserving the anal sphincter, when compared with postoperative chemoradiotherapy. In this observational study, conducted between January 2017 and December 2021, pursuant to the recommendations of the radiation therapy oncology group (RTOG), all patients underwent CT simulation, a bladder protocol and target contouring. 10 patients were treated with intensity modulated radiotherapy (IMRT) and 10 with three-dimensional conformal radiation therapy (3DCRT). Planned target volume (PTV) coverage, homogeneity index (HI), conformity index (CI), and doses to organs at risk (OAR) were compared. Our findings showed that 3DCRT and IMRT have statistically significant differences in PTV coverage and dosages to OAR (p<0.001), proving that IMRT achieves improved target dose coverage and superior normal tissue avoidance (bladder and intestine) compared to 3DCRT.