A single-institution retrospective study comparing proton therapy with conventional radiotherapy using tomotherapy or volumetric modulated arc therapy demonstrated low toxicity and significant dosimetric advantage with proton therapy in Chinese breast cancer patients following definitive surgery, according to data presented at PTCOG-AO 2025 conference held in Hong Kong.
“Proton therapy has been shown to be effective for breast cancer, have low toxicity, and to potentially reduce late cardiovascular events,” said Dr Amy Chang of the Comprehensive Oncology Centre at Hong Kong Sanatorium & Hospital (HKSH). “However, there are limited large-scale retrospective data in Asian populations, and we are currently awaiting international randomized trials comparing proton and photon therapy. Therefore, the aim of this study was to benchmark proton therapy outcomes and toxicity in our local population.”
“The primary objective was to compare acute and late radiation side effects between our proton and photon cohorts. Secondary objective was to analyze dose to organs-at-risk for heart, lungs, esophagus, ribcage, and cardiac substructures in both proton and photon patients,” she explained. [Chang ATY, et al, PTCOG-AO 2025, abstract 0129]
A total of 158 patients who received proton therapy to breast or chest wall with or without regional nodal irradiation (RNI) from July 2023 to March 2025 at HKSH were analyzed. Of these, 82 patients were propensity score–matched in a 1:1 ratio with photon cohorts. All patients were Chinese, with a median age of 51 years (range, 24–84). Median follow-up time was 78 days (range, 10–619). Most patients (73 percent) received 40.05 Gy in 15 fractions.
The most common acute side effects were dermatitis (grade 1, 76 percent; grade 2, 19 percent; grade 3, 3 percent), fatigue (grade 1, 19 percent; grade 3, 1 percent), and dysphagia (grade 1, 19 percent; grade 2, 1 percent). Late side effects were dermatitis (grade 1, 56 percent; grade 2–3, 2 percent), subcutaneous fibrosis (grade 1, 23 percent), and chest wall pain (grade 1, 18 percent).
“When we looked at the matched cohorts, the main significance in terms of acute toxicity lied in dermatitis, as well as fatigue and breast oedema, favouring proton therapy,” noted Chang. Compared with the matched photon cohort, proton therapy was associated with a significantly lower rate of acute grade 2–3 dermatitis (30 vs 20 percent; p=0.04), grade 1 fatigue (43 vs 24 percent; p=0.03), and breast oedema (24 vs 2 percent; p<0.01).
Proton therapy achieved a low mean heart dose of 0.17 Gy and V8–20 Gy ipsilateral lung dose of 4.38 percent across patients who did and did not receive RNI. Significant improvements (p<0.01) in all parameters, including mean heart dose (0.14 vs 4.86 Gy), V20 Gy lung (3.52 vs 17.18 percent), esophagus D1cc (8.39 vs 10.11 Gy) and mean contralateral breast dose (0.50 vs 7.07 Gy) were seen in proton vs photon cohorts. “All other dosimetric criteria were also significantly lower for proton therapy, except for skin, which was similar between the two cohorts,” added Chang.
“In conclusion, this study demonstrates low toxicity and significant dosimetric advantage for proton therapy in Chinese breast cancer patients. The main benefits are the improvements in acute radiation dermatitis, breast oedema, and fatigue in the proton cohort compared with the photon cohort,” she summarized. “Longer follow-up is warranted for survival and late toxicity analysis.”