Fewer, Higher Doses of Radiation Therapy Safe for Early Breast Cancer
For people with early breast cancer, delivering radiation therapy in fewer, larger doses does not increase the risk of long-term side effects from treatment, a new study demonstrates.
The study, “Ten-Year Results of FAST: A Randomized Controlled Trial of 5-Fraction Whole-Breast Radiotherapy for Early Breast Cancer,” was published in the Journal of Clinical Oncology.
Radiation therapy, or radiotherapy, involves using X-rays — high doses of radiation — to kill cancer cells. In breast cancer, it is most commonly used following surgery, since radiotherapy can kill tumor cells that remain after such procedures. The therapy limits the possibility that the tumor will grow back. However, radiotherapy can also cause substantial injury to healthy tissue, resulting in side effects.
The clinical trial FAST (ISRCTN62488883), which was initiated in 2004, tested whether changing the schedule in which radiotherapy is administered could reduce its side effects. The new follow-up study reports the results from this trial up to 10 years after the radiation therapy was given (median follow-up time 9.9 years).
“The aim of the FAST trial was to figure out if using fewer fractions overall, with careful consideration of the total dose, would reduce the side effects observed,” Judith Bliss, a professor of clinical trials at the Institute of Cancer Research (ICR) in the U.K. and co-author of the study, said in a press release.
FAST enrolled 915 women from 18 centers in the U.K. The average age at enrollment was 62.9 years.
The participants were divided into three groups. One group received 50 Gray (Gy) of radiation, divided into 25 daily doses of 2 Gy delivered every day over five weeks. This was the international standard at the time the trial was initiated. The other groups received 30 Gy, delivered as five once-weekly fractions of 6 Gy, or 28.5 Gy, delivered as five once-weekly fractions of 5.7 Gy.
“After undergoing surgery, I received one of the shorter radiotherapy courses and went into hospital once a week for five weeks,” said Joyce Charlton, a study participant.
“I felt tired, but didn’t experience any notable discomfort immediately after treatment,” Charlton said. “A few months later, my scans came back clear and I have remained cancer-free ever since.”
The main goal of the trial was to determine the relative risk of changes in breast appearance — rated as “none,” “mild,” or “marked” by blinded evaluators viewing photographs — and of damage to normal tissue. Tissue damage was assessed by clinicians at annual exams. Notably, because the trial only enrolled people with comparatively low-risk cancer, it was not designed to assess the efficacy of the treatments for tumor control.
Compared with those given the 50 Gy radiation therapy dosage, the risk of mild or marked breast appearance changes after two or five years was significantly higher (64%) in the group given the 30 Gy dosage. However, there was no difference in risk between the 50 Gy and the 28.5 Gy groups.
Five years after radiation therapy, the risk of any normal tissue effects (NTEs) was 10% higher in the 30 Gy group compared with the 50 Gy group. Meanwhile, there was no significant difference between the 28.5 and 50 Gy groups. There also were no significant differences between the 28.5 and 50 Gy groups in terms of NTEs after 10 years.
The most commonly reported normal tissue effect was breast shrinkage.
“The FAST trial confirms the safety of a radiotherapy course consisting of a lower total dose of radiotherapy delivered in five fractions of radiation,” said John Yarnold, a professor of clinical oncology at ICR and co-author of the study.
The researchers said their findings support treatment options for patients who cannot tolerate long daily courses of radiation.
“The FAST trial identifies a five-fraction once-a-week regimen that is equivalent to daily treatment over the same time period,” added study co-author Murray Brunt, a professor of clinical oncology at the University Hospitals of North Midlands.
“The follow-up to 10 years is important in establishing the principle of a five-treatment option,” Brunt said. “For patients unable to attend daily this offers an alternative much more convenient once-a-week treatment option that is attractive to both patients and their carers.”
Other dosing regimens also may help reduce long-term radiotherapy side effects, the researchers said. FAST has helped to inform the design of the FAST-Forward trial (ISRCTN19906132), which is comparing other schedules.
“FAST has also laid the groundwork for the FAST-Forward trial, testing an even shorter treatment course of five fractions of breast radiotherapy delivered in a single week, which is likely to become a UK standard for patients with early breast cancer,” Yarnold said.
Although the study was not designed to evaluate the effects of treatment on tumor control, the results indicated a generally low risk of recurrence: the 10-year cumulative incidence estimate was 1.3%.
“Although not powered for tumor control, the FAST trial suggests that for patients at low risk of relapse and for whom daily visits over 3 or 5 weeks are not possible because of frailty or comorbidities, 28 Gy in 5 fractions as a once-weekly schedule might be an appropriate alternative to no treatment,” the researchers concluded.
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