Clinical Outcomes and Setup Reproducibility in Patients Receiving Synchronous Bilateral Breast Radiation in the Prone Position

Abstract

Standardized radiation therapy (RT) positioning and planning are vital to treat both breasts without excess toxicity in patients with synchronous bilateral breast cancer (SBBC). We studied clinical outcomes and setup reproducibility in patients with SBBC treated in the prone position. This is a retrospective study of patients receiving RT for SBBC from 2012-2022 treated in the prone position. Patient demographics, RT dose and field, toxicity, and outcomes were collected. RT planning used gantry and table shifts to avoid entrance/exit through contralateral breast and organs at risk. RT delivery was standardized, with left breast treated first. After 2014, radiographic films were placed during the first 5 fractions to evaluate field overlap. Consistent overlap required re-simulation or re-planning. Positional shifts during setup were collected for patients receiving bilateral whole breast irradiation (WBI) and bilateral partial breast irradiation (PBI). A total of 45 patients were treated for SBBC. Median age was 67 years. Median follow-up was 28 months. 35 patients were treated with WBI (1 with low axilla on one side) and 5 with PBI. 5 patients were treated with WBI in one breast and PBI in the other. The most common whole breast dose was 40.5Gy, with a simultaneous integrated boost to the lumpectomy cavity to 48Gy. PBI patients were treated with 30Gy (n = 4) or 40.05Gy (n = 1). 8 patients (17.7%) had acute grade 2 and 1 patient (2%) had acute grade 3 dermatitis. This patient was treated WBI bilaterally and was known to have overlap on GaF. Physician and patient accepted higher toxicity for adequate coverage of bilateral upper inner quadrant tumors. Patients with grade > = 2 dermatitis had bilateral WBI (+/- low axilla) except 1. 6 patients had acute dermatitis in the sternal area (5 were WBI and 1 PBI). Only 2 of these patients had overlap on GaF. Of 20 patients with late toxicity follow-up (> 6 months), 5 (25%) had late grade 1-2 dermatitis. 4 (20%) were treated with WBI (+/-low axilla). 1 patient had both a local and distant recurrence. For setup and treatment delivery, couch shifts recorded for patients treated with bilateral WBI (n = 33) and bilateral PBI (n = 5) were minimal. Mean shifts in nearly all dimensions were limited to sub-centimeter or sub-degree changes, with 2D and cone beam CT (CBCT) imaging. Analysis of GaF showed that only 3 patients (10%) had field overlap. A new plan was created for 1 patient to increase the gap between fields, and for the others, patient and physician accepted overlap for adequate coverage. To our knowledge, this is the first study examining clinical outcomes and setup reproducibility in patients treated with SBBC in the prone position. This study indicates the feasibility of prone bilateral breast treatment with minimal shifts and overlap on daily treatments. However, we do see a higher number of acute dermatitis in patients treated with bilateral WBI (vs. PBI) and that overlap was not seen on GaF in all patients who developed sternal dermatitis.