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Dosimetric Equivalence of FB and DIBH Plans for Post-Lumpectomy Electron Boosts

R Thapa*, J Siebers, K Forbes, D Lain, K Ward, A Murray, K Wijesooriya, University of Virginia, Charlottesville, VA

Presentations

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

Room: AAPM ePoster Library

Purpose: purpose of this study is to ascertain if deep inspiration breath-hold (DIBH) during electron boost treatments reduces mean, maximum heart dose, left anterior descending (LAD) artery, and left lung dose compared with free breathing (FB) for post lumpectomy electron boost treatments.


Methods: boost treatment plans were created on FB and DIBH CTs for 30 left breast radiation therapy (RT) patient treatments. Electron energies of 6-18 MeV were utilized, depending on the tumor depth, with the beam perpendicular to the tumor/chest wall without bolus. The 10 Gy prescription ensured 95% dose to 95% of the lumpectomy volume. Significance in the dosimetric differences between DIBH and FB in mean and maximum heart, LAD and left lung doses were assessed via Student’s t-test. The left lung volume covered by 3, 5, and 9 Gy (V3Gy,V5Gy and V9Gy) was also assessed.


Results: statistically significant difference between mean, and maximum heart, LAD, and left lung dose was found. Maximum heart dose and LAD in DIBH were 2.0-100.3% (average 29.7%), 3.0-105.6% (average 36%) of the prescription dose, while for FB values were 1.9-95% (average 20.6%), and 1.2-93.4% (average 22.8%). The range of mean heart and LAD doses were 0.1-10.5% (average 3.6%), 0.2-9.6% (average 2.9%) for DIBH and 0.04-40.8% (average 8.9%), 0.07-31.6% (average 8.6%) for FB. Left lung V3Gy, V5Gy and V9Gy showed no significant difference between DIBH and FB. In the worst case scenario, DIBH and FB V3Gy,V5Gy and V9Gy differed by 0.12, 0.07, and 0.03% respectively.


Conclusion: LAD, and left lung doses from post lumpectomy electron boost RT do not differ significantly between DIBH and FB. Bypassing DIBH for post lumpectomy electron boosts may be warranted.

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