Proton beam therapy shortens breast cancer treatment, creating access for more patients
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Key takeaways:
- Hypofractionated postmastectomy proton radiotherapy shortened treatment duration.
- Both treatment groups experienced similar recurrence and complication rates.
Hypofractionated postmastectomy proton radiotherapy shortened the duration of breast cancer treatment, according to results published in The Lancet Oncology.
The findings also suggest that a shortened course of proton radiotherapy is safe and feasible immediately after breast reconstruction surgery.
“Pencil-beam scanning proton [postmastectomy radiotherapy (PMRT)] provided excellent locoregional control and normal tissue sparing,” Robert W. Mutter, MD, radiation oncologist and physician-scientist at Mayo Clinic Comprehensive Cancer Center, told Healio. “As there are a limited number of proton therapy facilities in the United States and throughout the world, our findings demonstrating safety and feasibility of shorter course treatment could result in greater access to proton beam technology for difficult-to-treat breast cancer cases.”
Background and methodology
Studies investigating proton PMRT have traditionally used fractionation over a 25- to 28-day timespan; however, little data exist regarding the safety and feasibility of hypofractionated PMRT that could reduce the treatment timeframe to as few as 15 days over 3 weeks.
Researchers conducted a randomized phase 2 study comparing the safety and effectiveness of conventional fractionated with hypofractionated proton PMRT with pencil-beam scanning.
Patient eligibility criteria included adults having an ECOG performance status of 0 to 2 and breast cancer resected by mastectomy with or without immediate reconstruction with indications for PMRT.
Researchers randomly assigned 88 adults in a 1:1 ratio to receive either conventional fractionated (50 Gy in 25 fractions of 2 Gy) or hypofractionated (40.05 Gy in 15 fractions of 2·67 Gy) proton PMRT.
The 24-month complication rate from the date of first radiotherapy — defined as grade 3 or worse adverse events occurring from 90 days after last radiotherapy or unplanned surgical interventions in patients with immediate reconstruction — served as the study’s primary outcome.
Results
Median follow-up was 39.3 months (interquartile range, 37.5–61.2), with a data cutoff date of Jan. 30, 2023.
Overall, the results could not establish noninferiority of the hypofractionation group.
Eighty-two of 88 study participants received the protocol treatment (41 from each group; median age, 52 years; 96% white).
Meanwhile, researchers observed 14 protocol-defined complications in six patients (15%) in the conventional fractionation group and eight patients (20%) in the hypofractionation group (absolute difference, 4.9%; one-sided 95% CI, 18.5).
Complications in the conventionally fractionated group included contracture in five patients and fat necrosis in one patient who required surgical intervention. Eight patients experienced infection-related complications in the hypofractionation group (three acute infections and five late infections), seven of whom required surgical intervention.
All 14 complications occurred in patients with immediate expander or implant-based reconstruction.
Next steps
“There were no significant differences in recurrence or complication rates between the 25 fraction and 15 fraction groups,” Mutter told Healio. “Therefore, 15 fraction proton PMRT appears to be an appropriate option for the delivery of proton PMRT.”
Researchers believe the data warrant additional research into the utilization of hypofractionation for these patients, with additional studies possibly researching the effectiveness and safety of treatment quicker than the 15 days evaluated in this study.
“Our team at Mayo Clinic Arizona, Mayo Clinic Florida and Mayo Clinic Rochester is currently investigating the delivery of PMRT in as few as 5 days,” Mutter said. “Ultimately, our goal is to personalize radiotherapy based on tumor biology and identify the best possible radiotherapy schedules or drug-radiotherapy combinations to optimize the therapeutic ratio and improve outcomes for patients.”
For more information:
Robert W. Mutter, MD, can be reached at Mayo Clinic, Department of Radiation Oncology, Rochester, MN 55905; email: mutter.robert@mayo.edu.
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