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 D(90) 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.