(P117) Anatomical Variations and Radiation Technique for Breast Cancer

P117: Figure A

P117: Figure B

Julie A. Bradley, MD, Meng Wei Ho, MSc, Roi Dagan, MD, Nancy P. Mendenhall, MD; University of Florida Proton Therapy Institute

Purpose: To compare conventional radiotherapy (RT) with proton-based RT in a series of patients with right- or left-sided breast cancer and anatomical variations resulting in technically challenging radiation plans.

Methods: Eight women had conventional (photon and/or electron) and proton-based (proton only or combined photon-proton) radiation plans developed. Four were treated with the conventional plan, and four were treated with the proton-based plan. Cardiac V5, V20, and V50; mean heart dose; and ipsilateral lung V5 and V20 were documented for each plan, along with D95 to the breast or chest wall and regional lymphatics (supraclavicular, level I–III axilla, and internal mammary chain [IMC]). All plans were optimized to achieve adequate target coverage.

Results: Dose-volume constraints were difficult to meet with conventional radiation in three patients with right-sided breast cancer because of significant breast ptosis (n = 2) or bilateral implants (n = 1). For two of the three patients, IMC irradiation was omitted in order to meet the lung V20 constraint. In these three patients, ipsilateral lung V20 with a conventional plan treating the IMC ranged from 44.7% to 47.5%. The lung V20 was decreased by adding a proton component to the plan, with lung V20 ranging from 14.4% to 26.1%. The mean heart dose ranged from 1.7–4.3 Gy for the conventional plans compared with 0.6–0.8 Gy for the proton-based plans. In the five patients with left-sided disease, constraints were difficult to meet in the two postmastectomy patients with a chest wall too thick or too variable in depth for electrons only, in one patient with large breasts and significant ptosis, in one patient with a heart-shaped thorax, and in one patient with severe arthritis limiting upper-extremity extension. In these five patients, the mean heart dose ranged from 6–19 Gy for the conventional plans compared with 0.8–2.9 Gy for the proton-based plans. In the conventional plans, ipsilateral lung V20 ranged from 40% to 46% compared with 9.8% to 31.6% with the proton-based plans. Cardiac V5 and lung V5 were reduced for both right- and left-sided disease treated with proton-based RT (mean cardiac V5 right: 15% vs 1.3%; mean lung V5 right: 75% vs 40%; mean cardiac V5 left: 29% vs 5%; mean lung V5 left: 58% vs 32% for conventional vs proton radiotherapy, respectively). In addition, for left-sided breast cancers, a decrease in cardiac V20 and V50 was seen with the proton-based plans (mean cardiac V20: 18% vs 2% and mean cardiac V50: 5.5% vs 1.5% for conventional vs proton radiotherapy, respectively).

Conclusion: Proton-based RT decreases the heart and lung doses for both left- and right-sided breast cancer patients with unfavorable anatomy, such as implants, large breasts, a heart-shaped thorax, and limited upper-extremity range of motion. In these cases, proton-based RT allows adequate target coverage and goal organ-at-risk constraints to be achieved simultaneously.