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The aim of this study was to assess shoulder’s exposure in hypofractionated 3D conformal breast cancer radiotherapy with regional lymph nodes irradiation (RNI), and to analyse the correlation between dosimetric parameters and late patient-reported outcomes involving shoulder/arm morbidity.

A total of 276 breast cancer patients treated with regional lymph nodes radiotherapy between 2018 and 2020, were included in this study.  All patients underwent 3D conformal hypofractionated radiotherapy with a prescription dose of 40.05 Gy delivered in 15 daily fractions +/- an additional boost of 13.35 Gy. For each patient, the shoulder was contoured including all bone structures (humeral head, acromion, coracoid process and scapula), muscles and soft tissues in the shoulder region, extending 2cm caudally to the inferior slice of the supraclavicular CTV. Dose volume histograms were analysed and the following dosimetric parameters to the shoulder were calculated: V5Gy, V10Gy, V30Gy, Dmean, Dmax. Late shoulder morbidity (> 6 months) was assessed using the quick disabilities of the arm, shoulder, and hand (q-DASH) questionnaire. Statistical associations between the q-DASH scores and dosimetric parameters to the shoulder were analysed.

The mean Dmean/Dmax to the shoulder was 8.82 Gy/21.69 Gy. The mean V5 Gy, V10 Gy, and V30 Gy were respectively 639 cc, 521 cc and 408 cc. Chest wall radiotherapy yielded higher doses to the shoulder when compared to radiotherapy to the remaining breast (p<0.01). Shoulder exposure was substantially higher when berg levels 1 and 2 were irradiated. After a median follow-up of 34 months, 117 (42%) patients completed the q-DASH questionnaire. The mean q-DASH score was 20.8 ranging between 8.9 and 27.6. The mean q-DASH score tended to be lower in patients treated with lumpectomy when compared to patients treated with mastectomy at 17.3 vs 19.6, p=0.08. The V30 Gy to the shoulder was statistically related to higher q-DASH scores, thus to higher shoulder morbidity, with Pearson coefficient of 0.37, p=0.042. No other statistical association was found between dosimetric parameters to the shoulder and patient reported late toxicity.

We found that 3D conformal breast cancer radiotherapy with RNI results in long-term shoulder morbidity, which was statistically related to the volume of the shoulder receiving 30 Gy. These results need to be prospectively confirmed with consistent baseline and post treatment assessment (pre and post-surgery/radiotherapy) to better understand the real impact of radiotherapy on shoulder morbidity.