(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: The updated executive summary of ASTRO evidence-based consensus on APBI published in 2017 (Practical Radiation Oncology; vol.7, p73-79) does not recommend in favor or against the use of EBRT-based APBI. This study evaluates the dosimetric quality of 3DCRT, electron, IMRT, and VMAT treatment plans for APBI to guide clinical decisions.
Methods: Data from five patients treated with electron APBI were used for this study. Contours created were GTV, CTV, PTV, markers, spinal cord, heart, ipsilateral and contralateral lung and breast, and skin (4mm from body). The 3DCRT plans were made to simulate a whole breast plan or AP/PA depending on the PTV’s location. Electron plans used suitable energy to cover the PTV and were normalized to 100% of prescription dose located at dmax. IMRT plans used 5 beams, and were normalized to ensure 95% of the PTV received 100% of the prescription dose, while VMAT plans were made with half arcs and similarly normalized. The prescription dose was 3000cGy in 5 fractions. Plans were calculated with AAA15603 for photons and EMC11031 for electrons (Eclipse, Varian). Plan quality parameters for all structures used Livi et al.
Results: The PTV maximum dose was highest in electron plans (range 5.3–11.8%) compared to the photon techniques. The skin maximum dose was higher in the electron plans in four patients (range 4.5-10.3%), one patient had lower skin dose when compared to the 3DCRT and VMAT plans (~1.3%). The 3DCRT plans resulted in higher ipsilateral lung and contralateral breast doses in three and all five patients, respectively, than IMRT or VMAT. All IMRT/VMAT plans had similar dosimetric qualities.
Conclusion: Solely based on the quality of these plans, the use of IMRT or VMAT is recommended for the treatment of APBI patients. Normal tissue toxicities related to these techniques would have to be further researched.
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