Image-guided cervix high-dose-rate brachytherapy treatment planning: does custom computed tomography planning for each insertion provide better conformal avoidance of organs at risk?

Purpose: Intracavitary high-dose-rate (HDR) brachytherapy (BT) for cervical cancer involves multiple applicator insertions. Our study addresses whether customized three-dimensional plans generated for the first insertion (using computed tomography [CT] planning) can be applied to subsequent insertions without significant changes in dose distributions if identical applicators are used.

Methods And Materials: Twenty-seven patients were treated with external-beam radiotherapy, platinum-based chemotherapy, and HDR BT. Either tandem and ovoids (TO, n=12) or tandem and ring (TR, n=15) applicators were used, based on clinical indications. Postimplant CT scans were acquired and custom plans generated for each insertion. Dose parameters for organs at risk (OARs) from the second insertion were retrospectively compared to those that would have been delivered using the initial plan.

Results: Overall, we observed a significant increase (p<0.038) in dose to International Commission on Radiation Units and Measurement points and 2cm(3) volumes of bladder and rectum when a single plan was used. The sigmoid and small bowel exhibited a more variable increase in dose. Applicator-specific results revealed a significant increase (p<0.030) to dose points and volumes for the rectum and bladder for TR applicators. Conversely, dose values from the more flexible TO did not show any significant trend, exhibiting large interpatient variations.

Conclusions: A duplication of planned dwell times and positions from one insertion to the next does not duplicate dose distributions in HDR cervix applications. A single plan used for an entire course of BT can result in significant increases to OAR doses for TR and unpredictable OAR doses for TO applicators. Treatment plans should be tailored for each insertion to reflect current applicator and anatomical geometry.