Shoulder Muscle Dosimetry and Post-Treatment Rehabilitation Utilization for Early-Stage Breast Cancer Patients

Abstract

Rehabilitation services for recovery of impaired physical function following breast cancer treatments are largely underutilized. We previously found that breast cancer survivors treated with radiation who received higher radiation doses to the pectoralis major are more likely to self-report shoulder pain and disability. This study aims to address whether radiation dose delivered to the pectoralis major (Pmaj) and pectoralis minor (Pmin) are correlated with referrals for rehabilitation services post-treatment. A retrospective 1:1 matched case-control study was conducted for breast cancer patients who were and were not referred for breast or shoulder rehabilitation services between 2014-2019 at a single academic institution. Patients were included if they had a lumpectomy and adjuvant radiation without regional nodal irradiation. Cohorts were matched based on age, axillary surgery (none vs. sentinel lymph node biopsy (SLNB)), and use of radiation boost. We used non-parametric Mann-Whitney U tests to determine whether Pmaj or Pmin doses (mean, V50Gy, V45Gy, V40Gy, V35Gy, V30Gy, V20Gy) were different between the two groups. Muscle doses were converted to EQD2 assuming an α/β ratio of 2.5. In our study of 30 patients of a median age 57 years (IQR 12.75), 20 (66.67%) patients underwent SLNB in addition to lumpectomy. Median tumor size was 1.1cm (range 0.16 - 7.30cm). Stage was 0 for 11 patients (36.67%), I for 14 patients (46.67%), and II for 5 patients (16.67%). 3D conformal radiation was delivered to the whole breast with a moderately hypofractionated (n = 17) or conventionally fractionated regimen (n = 13). The most common rehabilitation diagnoses were lymphedema (n = 8), scar management (n = 7) and shoulder pain (n = 5). Mean dose to both the Pmaj (20.8Gy vs. 18.6Gy; p = 0.02) and Pmin (30.6Gy vs. 24.6Gy; p = 0.01) were significantly higher in patients who received post-treatment rehabilitation compared to those without. The V40Gy, V35Gy, V30Gy and V20Gy (all p<0.02) for the Pmin and V35Gy, V30Gy and V20Gy for the Pmaj (all p<0.04) were also significantly higher in those who underwent rehabilitation. In this cohort of patients with early-stage breast cancer, increased mean doses to the pectoralis muscles were correlated with increased use of rehabilitation services after radiation. Physicians might consider using these dosimetric data to complement clinical symptoms in the decision-making process for referrals for rehabilitation services. This may help facilitate earlier referral to rehabilitation interventions, which is important since early intervention is correlated with improved shoulder morbidity.