Evaluation of Dose Distribution Due to Change in Bowel Position in Patients Treated with SBRT for a Target Lesion Neighboring the Intestine

Abstract

Stereotactic radiotherapy is becoming increasingly important in cancer treatment. Uncertainty due to internal organ movements causes confusion in bowel contouring and dose optimization. In this study, it was aimed to evaluate the dose changes due to bowel movements in patients who applied SBRT to the abdominopelvic area. A fusion was created between the cone beam Computed Tomography (CT) images obtained during the treatment and the planning CT. Thus, the dose to which the bowels were actually exposed during treatment was calculated. Bowel dose (Dmax, D2cc) calculated in the treatment plan was defined as 'Planning dose'. Bowel doses calculated according to the bowel position during treatment was defined as 'Administering dose'. The dosimetric results obtained from the patient's first plan data were compared with the bowels doses obtained by recalculating the dose received in the treatment separately for each fraction. There was no statistically significant difference in terms of bowel total maximum dose (p= 0.615), maximum dose per fraction (p= 0.798), and maximum dose of 2 cc bowel per fraction (p= 0.580). On the other hand, there is a statistically significant difference for the maximum dose of 2 cc in the bowel values between two calculations(p=0.016). According to our study, only bowel 2 cc dose values were found to differ significantly between planning and applied values, depending on bowel movements. Further studies are needed to understand the clinical significance of this difference.