Purpose: To compare the dose distribution between customized planning (CP) and adopting a single plan (SP) in multifractionated high-dose-rate brachytherapy and to establish predictors for the necessity of CP in a given patient.
Methods and materials: A total of 50 computed tomography-based plans for 10 patients were evaluated. Each patient had received 6 Gy for five fractions. The clinical target volume and organs at risk (i.e., rectum, bladder, sigmoid, and small bowel) were delineated on each computed tomography scan. For the SP approach, the same dwell position and time was used for all fractions. For the CP approach, the dwell position and time were reoptimized for each fraction. Applicator position variation was determined by measuring the distance between the posterior bladder wall and the tandem at the level of the vaginal fornices.
Results: The organs at risk D(2cc) (dose to 2 cc volume) was increased with the SP approach. The dose variation was statistically similar between the tandem and ring and tandem and ovoid groups. The bladder D(2cc) dose was 81.95-105.42 Gy(2) for CP and 82.11-122.49 Gy(2) for SP. In 5 of the 10 patients, the bladder would have been significantly overdosed with the SP approach. The variation of the posterior bladder wall distance from that in the first fraction was correlated with the increase in the bladder D(2cc) (SP/CP), with a correlation coefficient of -0.59.
Conclusion: Our results support the use of CP instead of the SP approach to help avoid a significant overdose to the bladder. This is especially true for a decrease in the posterior wall distance of >/=0.5 cm compared with that in the first fraction.