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Application of IMRT Class Solution for Improved Prone Accelerated Partial Breast Irradiation Dosimetry

S Quirk*(1,2), K Thind (1,2) , J Cao (1) , A Frederick (2) , P Grendarova (1) , P Craighead(1) , IA Olivotto (1) , M Roumeliotis (1,2) , (1) Department of Oncology, University of Calgary, Calgary, AB, (2)Department of Physics and Astronomy, University of Calgary, Calgary, AB


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To apply the IMRT class solution used in the ACCEL accelerated partial breast irradiation (APBI) supine trial ( to show feasibility of an APBI prone planning implementation to meet the RTOG 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.


Breast, Treatment Planning, Dosimetry


TH- External beam- photons: treatment planning/virtual clinical studies

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