Purpose: Current guidelines for high-dose-rate accelerated partial breast irradiation using single-entry implants are based on the National Surgical Adjuvant Breast and Bowel Project B-39/Radiation Therapy Oncology Group 0413 protocol, which assumed a balloon implant geometry. We have developed robust plan evaluation criteria specifically for the strut-adjusted volume implant (SAVI).
Methods and materials: Plan evaluation criteria were established using a "training data set" of 62 SAVI treatment plans and included the percentage volume of target receiving 90%, 95%, and 100% of the prescription dose (V90, V95, and V100), the absolute volume of target receiving 150% and 200% of prescription (V150 and V200), and the maximum doses to skin (Dskin max) and ribs (Drib max). "Ideal" and "expected" (routinely achievable) thresholds were determined for each criterion and compared to B-39 guidelines. A "test data set" collected from the next 25 patients was analyzed using the developed plan evaluation criteria.
Results: Ideal (expected) dosimetric thresholds established from the training data set were V90 ≥ 98% (95%), V95 ≥ 95% (92%), V100 ≥ 91% (88%), Dskin max < 90% (100%), and Drib max < 100%. Thresholds for V150 and V200 were stratified by SAVI size: V150 ≤ 30 cc (50 cc) and V200 ≤ 15 cc (20 cc) for 6-1 and Mini; V150 ≤ 50 cc (50 cc) and V200 ≤ 20 cc (20 cc) for 8-1 and 10-1. There was no significant difference between the training and test data sets in the fractions of patients meeting the criteria. Overall, 58% and 95% of 87 plans met all ideal and all expected criteria, respectively.
Conclusions: The plan evaluation criteria developed specifically for the SAVI device are robust, providing increased target coverage and increased skin sparing compared to B-39 guidelines.
Keywords: APBI; Breast brachytherapy; SAVI; Treatment planning.
Copyright © 2016 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.