Evaluation of Volumetric Doses of Organs at Risk in Carcinoma Cervix Patients with HDR Intracavitary Brachytherapy and Comparison of CT-based and Conventional Plans

Background: Brachytherapy treatment planning in cervix carcinoma patients using two dimensional (۲D) orthogonal images provides only point dose estimates while CT-based planning provides volumetric dose assessment helping in understanding the correlation between morbidity and the dose to organs at risk (OARs) and treatment volume. Objective: Aim of present study is to compare International Commission on Radiation Units and Measurements Report ۳۸ (ICRU ۳۸) reference point doses to OARs with volumetric doses using ۲D images and CT images in patients with cervical cancer. Material and Methods: In this prospective study, ۲۰ patients with cervical cancer stages (IIB-IIIB) were planned for a brachytherapy dose of ۷Gy per fraction for three fractions using ۲D image-based treatment plan and CT-based plan. ICRU ۳۸ points for bladder and rectum were identified on both ۲D image-based plan and CT-based plan and doses (DICRU) at these points were compared to the minimum dose to ۲cc volume (D۲cc) of bladder and rectum receiving the highest dose. Results: D۲cc bladder dose was ۱.۶۰ (±۰.۶۷) times more than DICRUb bladder dose whereas D۲cc rectum dose was ۱.۱۳±۰.۴۰ times DICRUr. Significant difference was found between DICRUb and D۲cc dose for bladder (p=.۰.۰۱۶) while no significant difference was seen between DICRUr and D۲cc dose for rectum (p=۰.۹۶۴). Conclusion: The study suggests that ICRU ۳۸ point doses are not the true representation of maximum doses to OARs. CT-based treatment planning is more a reliable tool for OAR dose assessment than the conventional ۲D radiograph-based plan.