Abstract

Laura Hoeng¹, Olga Unterkirhere¹, Alexander Kaever¹, Sarah Abbeel¹, Christoph Glanzmann¹, Gabriela Studer¹

¹Cantonal Hospital Lucerne, Department of Radiation Oncology, Lucerne, Switzerland

The purpose of this study was to evaluate early/intermediate treatment tolerance in patients undergoing postoperative moderate hypofractionated whole breast radiotherapy with simultaneous integrated boost (SIB-mhWBRT) following breast-conserving surgery (BCS).

SIB-mhWBRT for breast cancer patients was introduced in our department in July 2017. This prospective study includes 391 patients treated with SIB-mhWBRT for invasive breast cancer (n=361; pT1(198), pT2 (156), pT3 (4), pT4a (2)/,Tx (2), N0-3, M0) and/or ductal carcinoma in situ (DCIS, n=30) after BCS until April 2020. Mean age was 60 years (range 27–88). Mean/median follow-up was 18/16 months (range 1–38). SIB-mhWBRT was applied with 40 Gy in 15 daily fractions over 3 weeks with a SIB dose to the tumor bed of 48 Gy, delivered either as 3D conformal radiotherapy (3D-CRT, n=369), intensity-modulated radiotherapy (IMRT, n=4) or volumetric-modulated arc therapy (VMAT, n=18). Since 05/2018 also patients indicating for lymphatic pathway irradiation were included (n=62). Follow-up data including objective assessment of baseline parameters and treatment-related outcomes as well as subjective patient reported outcome measures (PROMs) was recorded and reported. Ethical approval is available.

Skin toxicity (including erythema, desquamation, necrosis/ ulceration, breast edema and bleeding) for grades 0/1/2/3 was distributed as 24.3/61.8/13.6/0.3% at the completion of treatment. The most common acute toxicities at completion of treatment were erythema and breast edema. The only patient with a documented grade 3 bleeding presented this already before start of radiotherapy. 6-months follow-up data was available for 225 patients: with fibrosis grade 0/1/2 in 75.6/20.0/4.4%, skin telangiectasia grade 0/1/2 in 95.6/4.0/0.4%, pigmentation changes grade 0/1/2 in 71.0/27.7/1.3% cases. Patient-reported cosmetic results 6 months post treatment were evaluated in 55.0/41.7/2.3/0.9% cases as excellent/good/fair/poor. Results of 1-year follow-up (available from 137 patients) were comparable: fibrosis grade 0/1/2 in 78.1/20.4/1.5%, no skin telangiectasia (only grade 0), pigmentation changes grade 0/1/2 in 78.7/20.6/0.7% cases. 1-year patient-reported cosmetic results were evaluated in 62.2/34.1/3.7% as excellent/good/fair. 31 patients examined on the 2-year follow-up visit presented with fibrosis grade 0/1 in 93.5/6.5%, pigmentation changes grade 0/1/2 in 80.6/16.1/3.2%. PROM of cosmetic results were evaluated in 59.4/34.4/3.1/3.1% as excellent/good/fair/poor.

Ipsilateral breast tumor recurrence developed in 2/391 patients (0.5%) (one in-boost, one marginal to the 40 Gy volume, both triple negative), distant metastatic disease developed in 6 patients (1.5%) at the time of this analysis. No cancer related mortality was observed so far.

We found a high subjective and objective early/intermediate treatment tolerance of SIB-mhWBRT. This short term regimen offers substantial patient comfort and improves institutional efficacy.