Top Line: Dose hypofractionated postmastectomy proton therapy reduce complications compared to conventionally fractionated proton therapy?
The Study: While hypofractionation is considered the standard technique for whole breast radiation, many of us use conventional fractionation for PMRT while we await the results of randomized trials like RT CHARM. More extensive target volumes and the common integration of reconstruction make this more than a simple extrapolation from whole breast RT. The same questions also exist for proton-based PMRT. In this randomized, phase 2 trial from the Mayo system, 82 breast cancer patients with plans to receive proton PMRT were randomized to either conventional fractionation (CF, 50 Gy in 25 fractions) or hypofractionation (HF, 40 Gy in 15 fractions). The target volume included the chest wall, levels 1-3 of the axilla, the supraclavicular fossa, and the internal mammary nodes, and 95% of the target received at least 95% of the prescribed dose with a maximum dose (D0.01cc) of 110%. The primary endpoint was the rate of complications at 24 months. Importantly, the trial was stratified according to type of reconstruction to balance the increased risk of complications seen with immediate reconstruction. Most patients (66% in the CF group and 73% in the HF group) had immediate reconstruction most commonly (84%) with staged reconstruction using a tissue expander. At 24 months, the rate of complications was 15% with CF and 20% with HF. All complications occurred in patients who had immediate reconstruction. Failed reconstruction was observed in 4% of those who had CF compared to 17% who had HF. These differences were relatively small and likely driven by differences in reconstruction between arms, but statistically, the study wasn’t able to show the non-inferiority of HF proton PMRT. There were no significant differences in recurrence or treatment outcomes. Toxicity was also similar, although there was less skin toxicity with HF.
TBL: In this small, randomized phase 2 trial, the risk of complications was similar after conventional and hypofractionation and mainly seen in patients who had immediate reconstruction. | Mutter, Lancet Oncol 2023
The Study: While hypofractionation is considered the standard technique for whole breast radiation, many of us use conventional fractionation for PMRT while we await the results of randomized trials like RT CHARM. More extensive target volumes and the common integration of reconstruction make this more than a simple extrapolation from whole breast RT. The same questions also exist for proton-based PMRT. In this randomized, phase 2 trial from the Mayo system, 82 breast cancer patients with plans to receive proton PMRT were randomized to either conventional fractionation (CF, 50 Gy in 25 fractions) or hypofractionation (HF, 40 Gy in 15 fractions). The target volume included the chest wall, levels 1-3 of the axilla, the supraclavicular fossa, and the internal mammary nodes, and 95% of the target received at least 95% of the prescribed dose with a maximum dose (D0.01cc) of 110%. The primary endpoint was the rate of complications at 24 months. Importantly, the trial was stratified according to type of reconstruction to balance the increased risk of complications seen with immediate reconstruction. Most patients (66% in the CF group and 73% in the HF group) had immediate reconstruction most commonly (84%) with staged reconstruction using a tissue expander. At 24 months, the rate of complications was 15% with CF and 20% with HF. All complications occurred in patients who had immediate reconstruction. Failed reconstruction was observed in 4% of those who had CF compared to 17% who had HF. These differences were relatively small and likely driven by differences in reconstruction between arms, but statistically, the study wasn’t able to show the non-inferiority of HF proton PMRT. There were no significant differences in recurrence or treatment outcomes. Toxicity was also similar, although there was less skin toxicity with HF.
TBL: In this small, randomized phase 2 trial, the risk of complications was similar after conventional and hypofractionation and mainly seen in patients who had immediate reconstruction. | Mutter, Lancet Oncol 2023