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On the Dosimetric Quality of Current External Beam Radiation Technologies for Partial Breast Irradiation

Z Richards*, T Nguyen^, C Henson*, S Ahmad*, T Herman*, T De La Fuente Herman* *University of Oklahoma HSC, Oklahoma City, OK ^Advanced Medical Physics Inc., Houston, TX


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To evaluate dosimetric quality of IMRT, VMAT, and IMPT plans for Accelerated Partial Breast Irradiation (APBI) to guide clinical decisions. APBI has shown to yield excellent local control rate and good-to-excellent cosmetic outcomes. The updated ASTRO evidence-based consensus on APBI (PRO; 7, 73-79) does not recommend in favor or against the use of EBRT-based APBI.

Methods: Data from twelve patients treated with photon APBI were utilized. Segmentations of interests were CTV, PTV, markers, spinal cord, heart, ipsilateral and contralateral lung, breast, and skin (5mm and 10mm from body). Original treatment plans were generated using IMRT of five to seven 6 MV beams and VMAT with 2 half-arcs, both normalized to 100% of dose to cover 95% of PTV. IMPT plans were generated using two to three MFO beams with an added 3.5% plus 5mm robustness, and were normalized so that 100% of dose covered 98% of CTV. The prescription was 30 Gy over 5 fractions. The AAA15603 was used to calculate photon plans (Eclipse, Varian), and RayStation Clinical Monte Carlo v4.4 for proton plans (Raystation, Raysearch). Plan quality parameters for targets and organs at risk from Livi et al. were used. Conformity, heterogeneity, and uniformity indices were calculated to asses PTV coverage, and Student’s t-tests were performed.

Results: PTV coverage in IMRT, VMAT, and IMPT plans was similar. The IMPT plans had better homogeneity and uniformity index than IMRT and VMAT, but worse conformity index due to the 5 mm robustness. Dose constraints for skin, heart, ipsilateral lung, and ipsilateral breast had statistically significant improvement in IMPT compared to IMRT and VMAT.

Conclusion: Comparing dosimetry of external beam techniques for APBI, this study demonstrated advantages of IMPT. Further study warrants a greater number of patient data and careful post-treatment follow up to create a clinically based consensus.


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