Radiotherapy to the breast in the prone position is less toxic compared to the supine position in women with large breast size, according to a randomized phase III trial.
Among the 357 patients, those treated in the supine position had significantly higher rates of wet desquamation anywhere in the breast compared with those treated in the prone position (39.6% vs 26.9%; OR 1.78, 95% CI 1.24-2.56, s= 0.002), reported by Danny Vesprini, MD, MA, of the Sunnybrook Health Sciences Center in Toronto, and colleagues in gamma tumors.
This association was confirmed in a multivariate analysis (OR 1.99, 95% CI 1.48–2.66, s<0.001), along with other independent factors, including use of reinforcement (OR 2.71, 95% CI 1.95–3.77, s<0.001), extended segmentation (OR 2.85, 95% CI 1.41-5.79, s= 0.004), bra size (OR 2.56, 95% CI 1.50-4.37, s<0.001).
“Treatment in the prone position has several dosimetric advantages for these patients,” said Fesprini and his team. “It allows for a more homogeneous distribution of the dose due to the smaller separation when compared to the supine position, which reduces deposition of higher doses in the sub-breast and axillary fold.”
Among all the women, they added, the toxic effects to the skin were lower when patients were treated with underfractionated radiotherapy compared to extended fractionation.
“Exposure radiotherapy appears to be an excellent option for patients with large breast cancer and right-sided cancer, and may benefit many women with left-sided breast cancer with large breast size if acceptable heart avoidance is possible,” notes Dean Shamway, MD. , of the Mayo Clinic in Rochester, Minn., and Kathleen Atkins, MD, of Cedars-Sinai Medical Center in Los Angeles, in an accompanying editorial. In short, the prone position for whole breast radiotherapy represents a valuable addition to the suite of treatment techniques to reduce the adverse effects associated with whole breast radiotherapy.
Vesprini and colleagues also found that the supine position was associated with more grade III desquamation compared to the prone position (15.4% vs. 8.0%; OR 2.09, 95% CI 1.62-2.69, s<0.001).
Additionally, when segmenting by processing with either the extended hash or under-fragmentation, the extended hash was associated with more than:
- Toxic effects (43.3% vs. 23.2%; OR 2.56, 95% CI 1.50-4.37, s<0.001)
- Grade 3 desquamation (17.2% vs 6.3%; OR 3.14, 95% CI 1.62-6.11, s= 0.001)
- Pain (9.4% vs 3.4%, or 2.97, 95% CI 1.06-8.31, s= 0.04)
The authors noted that “these differences were primarily driven by rates of toxicological effects in patients treated in the supine position.”
Specifically, in patients treated in the supine position, extended segmentation was associated with increased desquamation compared to decreased segmentation (51.1% vs 27.8%; OR 2.72, 95% CI 1.18-6.24, s= 0.02), and grade 3 exfoliation (23.9% vs 6.7%; OR 4.40, 95% CI 1.83-10.57, s<0.001).
Extended segmentation was also associated with increased toxicity in patients treated in the prone position, although the association was less clear. Exfoliation occurred in 35.2% of patients treated with extended fragmentation versus 18.4% of patients treated with extended fragmentation (OR 2.41, 95% CI 1.65–3.52, s<0.001), while grade 3 desquamation occurred in 10.2% versus 5.7% of patients (OR 1.87, 95% CI 1.05–3.32, s= 0.03).
This trial was conducted at five centers across Canada from April 2013 to March 2018. Eligible patients included those with large breast size and invasive or ductal carcinoma in situ who were treated with breast-conserving surgery and referred to adjuvant radiotherapy alone. . Of the 357 women (median age 61 years), 182 were treated in the supine position and 175 were treated in the prone position.
From April 2013 through June 2016, 167 patients received 50 Gy in 25 segments (extended segmentation) with or without a boost (range 10-16 Gy). After trial adjustment in June 2016, the majority of patients (93.2%) received the hash-deficiency regimen of 42.5 Gy in 16 portions.
Vesperini and colleagues note that there are no differences in quality of life as measured by global health status, breast symptoms, or pain measures between vulnerable and exposed groups.
The study was supported by the Canadian Cancer Society.
Vesprini had no disclosures. Co-authors have reported relationships with Genomic Health, AstraZeneca, and Accuray outside of the presented work.
Shamway reported grants from the Agency for Healthcare Research and Quality outside the scope of the work submitted. Atkins reported fees from OncLive outside of submitted work.