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Proton Uniform Scanning Treatment of Breast Cancer Patients with Tissue Expanders

D Mah

G Del Rosario1 , C Chen1 , O Cahlon2 , J Fox3 , C Zeng1, D Mah1*, (1) ProCure NJ, Somerset, New Jersey, (2) Memorial Sloan Kettering Cancer Center, New York, New York, (3) Montefiore Medical Center, Bronx, New York


SU-I-GPD-T-172 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Breast cancer patients treated with protons may have lower lung and heart doses than photon treatments. Proton treatments of breast cancer patients with tissue expanders have only been reported using pencil beam scanning (PBS). Two approaches have been developed. The high Z magnet in the expander is either avoided by junctioning fields around it or treated directly through. We investigated treating through the magnet using uniform scanning (US).

Methods: Three postmastectomy breast cancer patients with expanders were evaluated. A template of the expander was generated based upon the manufacturer’s specifications. The transmission of the uniform scanning beam through the implant was verified by measurement. Two sets of plans were generated to a dose of 50.4 Gy (RBE). Clinical plans using PBS to junction two fields around the magnet were compared to en face US plans treating through the magnet. For the latter, compensators were generated with a conservative smear of 1 cm to account for possible displacements of the magnet relative to bony anatomy.

Results: Both sets of plans were found to be clinically acceptable. PTV-skin V95 was >95% for both sets of plans. Dosimetric parameters were comparable for a given patient. For the three patients, dose to ipsilateral lung V20Gy(RBE) = [19.5; 18.5; 17.2]% for PBS and V20Gy(RBE) = [20.1; 19.3; 16.3]% for US. Mean heart doses (MHD) were very well correlated. MDH was [1.0, 0.4, 2.6] Gy (RBE) for PBS and [1.0, 0.4, 2.3] Gy (RBE). The skin dose for was higher with US.

Conclusion: Treatment of breast cancer patients through the magnet of tissue expanders with US is feasible. The US distributions and DVHs are comparable to PBS. This study suggests that breast expander patients could be treated in proton facilities where PBS is unavailable.

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