K McConnell*, C Cardenas, J Belliveau, H Boggs, D Stanley, The University of Alabama at Birmingham, Birmingham, AL

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  K McConnell

PO-GePV-T-428 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

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Purpose: Accelerated partial breast irradiation (APBI) in early stage breast cancer necessitates a reduction in non-target breast tissue to decrease long term toxicity and adverse cosmetic outcome. Since lumpectomy cavity seromas may decrease in size and deform in shape during treatment, we utilized the ETHOS platform for daily online adaption of short course APBI and dosimetrically compared the results to the standard of care.

Methods: Two patients receiving a regimen of 600 cGy x 5 fractions for breast SBRT were treated using online adaptive plans on the ETHOS platform. The CTV consisted of the seroma cavity+ 5-10mm with a PTV margin of 3mm. Both were planned in the Ethos Treatment Management system with 10 IMRT fields with a laterally localized hemi-spherical field distribution. Plans were optimized using the Ethos Intelligent Optimization Engine with primary planning objectives for the V3000cGy_CTV and V3000cGy_PTV of >= 99% and 95% respectively. Two planning scenarios were compared to elucidate how dosimetric parameters change between the scenarios: (1) deformed dose of five-fraction adaptive on original planning CT and (2) five-fraction non-adaptive on original planning CT. The GTV_Dmean(cGy) and PTVsb_Eval_V3000cGy(%) were evaluated. For the OARs, heart_Dmean(cGy), ipsilateral-lung_V900cGy(%), contralateral-lung_V150cGy(%), ipsilateral-breast_V1500cGy(%), and the contralateral-breast_V500cGy(%) were evaluated.

Results: For the first patient, the volume of PTVsb_Eval at planning CT was 72.2cc and over the five fraction course was 69.01cc, 59.87cc, 60.18cc, 62.5cc, and 51.54cc. The second patient had volumes of 82.75cc at planning CT and 68.71cc, 64.89cc, 59.89cc, 62.05cc, 63.05cc over the course of treatment. Adapted plans showed lower OAR dose, particularly the heart Dmean, which was reduced from 49cGy to 25cGy on a right-sided case.

Conclusion: Adaptive breast SBRT for short course APBI shows potential for reduced PTV margins, online adaption to changing seroma values, and reduced OAR doses as compared to the standard of care, non-adaptive.

Keywords

Breast

Taxonomy

TH- External Beam- Photons: adaptive therapy

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