Dosimetric evaluation of Point A and volume-based high-dose-rate plans: a single institution study on adaptive brachytherapy planning for cervical cancer

Purpose
External beam radiation therapy (EBRT) and brachytherapy (BT) with concurrent cisplatin is the standard of care for locally advanced cervical cancer. The applicability of image-guided adaptive volume-based high-dose-rate (HDR) intracavitary brachytherapy planning is an active area of investigation. In this study, we examined whether volume-based HDR-BT (HDR_VOL) plans leads to more conformal plans compared to Point A (HDR_PointA)-based plans.

Material and methods
Two hundred and forty HDR_PointA plans from 48 cervical cancer patients treated with chemoradiotherapy were retrospectively collected. Point A plans were renormalized with respect to the high-risk clinical target volume (HR-CTV) for the HDR_VOL plans. The doses to organs at risk (OAR; rectum, sigmoid, and bladder), and HR-CTV and the conformal index were compared between HDR_PointA and HDR_VOL plans.

Results
HDR_VOL plans resulted in a 6-12% reduction in the total dose (EBRT + HDR-BT) to 0.1 cc, 1.0 cc, and 2.0 cc of the OAR as well as an 8-37% reduction in the dose to 2 cc of OAR per HDR-BT fraction compared to HDR_PointA plans. Differences in the conformal indexes between the two groups of plans showed an 18-31% relative increase per HDR-BT fraction for HDR_VOL plans. The D90 of the HR-CTV was reduced by 11% by HDR_VOL planning and had a median dose of 86 Gy.

Conclusions
Our study reports the relative improvement in OAR doses per HDR-BT fraction by HDR_VOL planning compared to HDR_PointA planning and demonstrates the dosimetric advantages of volume-based HDR-BT planning in creating more conformal plans.