Single Magnetic Resonance Imaging vs Magnetic Resonance Imaging/Computed Tomography Planning in Cervical Cancer Brachytherapy

Abstract Aims To compare differences in dose to the target volume and organs at risk (OARs) for ring and tandem brachytherapy using individualised magnetic resonance imaging (MRI)/computed tomography-based three-dimensional treatment plans for each application vs plans based on a single scan for all fractions. Materials and methods The study was carried out in 10 patients with carcinoma of the uterine cervix, treated with external beam radiotherapy and five fractions of high dose rate brachytherapy. Planning was carried out using MRI for the first fraction and computed tomography for each of the four subsequent fractions. The MRI-based plan was taken as the reference and the single-plan procedure was calculated by using the weights from the reference plan to calculate the dose distribution for each subsequent computed tomography-based plan. The high-risk clinical target volume (HRCTV) and OARs were delineated as per GEC-ESTRO guidelines. Total doses from external beam radiotherapy and brachytherapy were summated and normalised to a 2Gy fraction size. Results The mean D 90 for the HRCTV was 81.9Gy when using one plan and 84Gy when using individual treatment plans. Similarly, the mean D 2cc was 75.68Gy vs 74.99Gy for the bladder, 55.84Gy vs 56.56Gy for the rectum and 64.8Gy vs 65.5Gy for the sigmoid. Ring rotation was identified in three patients, resulting in a change in dwell positions, which otherwise could have led to either a high bladder dose or suboptimal coverage of the HRCTV. Conclusions Our study has shown that a single-plan procedure achieved acceptable dosimetry in most patients. However, the individualised plan improved dosimetry by accounting for variations in applicator geometry and the position of critical organs.