Room: Exhibit Hall
Purpose: To apply the IMRT class solution used in the ACCEL accelerated partial breast irradiation (APBI) supine trial (clinicaltrials.gov/NCT02681107) to show feasibility of an APBI prone planning implementation to meet the RTOG 0413 (www.rtog.org/ClinicalTrials/0413) clinical trial constraints.
Methods: The ACCEL trial utilizes comprehensive gantry-patient clearance tables to indicate the available beam arrangements for IMRT planning. A conservative subset of these supine class solutions was applied to a prone patient cohort where body habitus frequently limits the gantry clearance. IMRT APBI plans were retrospectively created for 10 breast cancer patients (five right- and five left-sided) that were setup in a prone treatment position. The CTVs were expanded by 7 mm to create PTVs. The prescription dose was 27 Gy in 5 fractions with target coverage normalized to 98% of the target receiving 95% of prescription dose. The cohort average dosimetry was evaluated for target conformity, ipsilateral breast, contralateral breast, ipsilateral lung, and heart. Target conformity index is defined as the ratio of the 95% prescription dose volume and target volume.
Results: All 10 patients met the organ-at-risk constraints for both RTOG 0413 and ACCEL clinical trials. The target conformity specified by the ACCEL trial was met by 4 of 10 patients. Compared to the supine ACCEL cohort, the breast V30% and V50% of the prone cohort was reduced by an average of 19.6% and 10.7%, respectively. The improvement observed in ipsilateral breast dose is due to favourable patient setup, allowing a smaller portion of the total breast volume to be irradiated.
Conclusion: Although the cause of cosmetic deterioration is not well-correlated to a specific dose metric, reducing the volume of breast irradiated to a high dose per fraction may be beneficial. This study demonstrates potential for improved treatment quality using that APBI class solution planning approach for the prone cohort.