
Correlation Between Incidental Glenohumeral Joint Dose and Shoulder Dysfunction in Patients Undergoing Adjuvant Radiotherapy for Breast Cancer: A Comparative Cross-Sectional Study
Seyed Alireza Javadnia 1 ©, Zahra Sebyani 2, Pezhman Porouhan 1, Mostafa Robatjazi 3, Paria Saffarzadeh 2, Seyed Hojjat Hashemi Alizadeh 2 ℗, Elham Khakshour 4
Abstract
Introduction: Adjuvant radiotherapy is a cornerstone of breast cancer management, yet it is often associated with persistent shoulder morbidity that impairs survivors' quality of life. The association between incidental radiation dose to the glenohumeral (GH) joint and specific functional impairments remains poorly defined. This study aimed to quantify the association between incidental GH joint radiation dose and objective measures of shoulder dysfunction. Methods and Materials: This cross-sectional study was conducted on 60 women who had completed adjuvant radiotherapy for unilateral breast cancer. The study protocol was approved by the Research Ethics Committee of Sabzevar University of Medical Sciences (IR.MEDSAB.REC.1402.027) and adhered to STROBE reporting guidelines. Shoulder function was assessed bilaterally, with each patient's non-irradiated contralateral limb serving as an internal control. The evaluation included goniometric measurement of active range of motion (ROM) and a battery of standardized physical examinations for rotator cuff integrity and impingement signs. Dosimetric parameters for the GH joint, including mean dose (Dmean), maximum dose (Dmax), and dose-volume parameters (V5–V40), were retrospectively extracted from treatment planning CT scans. Paired statistical tests were used to compare functional outcomes between sides. Results: Significant functional decline was documented on the irradiated side. For instance, limited abduction was observed in 71.6% of treated shoulders compared to 15.0% of contralateral shoulders (P 0.001). This was accompanied by a higher prevalence of positive impingement signs and specific rotator cuff weaknesses. The mean incidental radiation dose to the GH joint was 16.27 ± 4.82 Gy. However, correlation analysis revealed no significant association between most clinical deficits and key dosimetric variables, including Dmean and Dmax. A single, paradoxical association was observed: a positive Patte test (indicating infraspinatus weakness) was linked to a lower V40 (volume receiving ≥40 Gy) (P = 0.029), suggesting the dose-toxicity relationship is not linear. Conclusion and Discussion: The substantial shoulder morbidity observed in breast cancer survivors does not appear to be primarily driven by the incidental radiation dose delivered to the glenohumeral joint. Our findings suggest that other factors, such as the type of surgery and subsequent soft tissue fibrosis, are likely more dominant etiological contributors. Therefore, clinical focus should expand from solely dose-sparing strategies to a holistic approach incorporating optimized surgical techniques and early, targeted rehabilitation. The specific, albeit complex, association between high-dose volumes and rotator cuff integrity merits further investigation to clarify potential mechanisms of radiation-induced injury
Keywords: Breast Cancer, Radiotherapy, Adjuvant, Shoulder Morbidity, Shoulder Dysfunction, Survivorship