Standard whole-breast radiation treatment in the U.S. ranges between a conventional five-to six-week course of 60 Gray in 30 fractions or a three- to four-week hypofractionated course of 40 Gray in 15 fractions.
FAST-Forward, a United Kingdom (U.K.) multicenter phase three randomized trial published in April 2020, identified that a 26 Gray five-fraction schedule of radiation therapy to the whole breast delivered over just one week is as safe as the standard 40 Gray 15-fraction regimen over three weeks after primary surgery for early-stage breast cancer. The trial’s findings allow for the opportunity to further reduce toxicity and enhance the patient’s experience.
UT Southwestern Medical Center’s Department of Radiation Oncology has found that using a linear accelerator for the FAST-Forward trial can add a significant amount of swelling within the breast, potentially adding higher doses that weren’t accounted for in the original plan.
Led by Asal Rahimi, M.D., M.S., Professor of Radiation Oncology, Associate Vice Chair for Program Development, Chief of Breast Radiation Oncology Service, and Medical Director of the SCCC Clinical Research Office, the Department’s breast disease-oriented team has further hypothesized that by using an adaptive IMRT technique with the FAST-Forward dose fractionation of 26 Gray in five fractions, acute toxicity can be reduced by treating on the Ethos adaptive platform.
“With Ethos, we are able to capture the swelling that occurs in the breast, which can modify the radiation dose to nearby organs, such as the heart and lungs, as well as hot spots that occur inside of the breast,” Dr. Rahimi says. “Then we can re-plan daily based off the new anatomy that occurs with the swelling. This is a major benefit of an adaptive FAST-Forward plan.”
Leading the adaptive FAST-Forward study alongside Dr. Rahimi are David Parsons, Ph.D., Assistant Professor of Radiation Oncology and Associate Program Director, Medical Physics Residency, and Mu-Han Lin, Ph.D., Associate Professor of Radiation Oncology and Director of Adaptive Therapy in Medical Physics. The study aims to have 64 early-stage node negative breast cancer patients that require whole-breast radiation on a single-arm phase two trial comparing historical data from the U.K. trial.
On the U.K. FAST-Forward regimen, ultrahypofractionated breast cancer treatments used a one-centimeter margin, which limited normal tissue sparing. Using online adaptive therapy, the Department’s study can significantly reduce margins and improve plan quality.
“While the conventional FAST-Forward is implemented with a simple 3D plan, we feel there is an opportunity for further improvement with our adaptive technology,” Dr. Lin says. “Through our team’s efforts, we found we can shrink the margin to three millimeters.”
In addition to margins, reduction of the patient’s time on the table to under 30 minutes is a key goal in the study. To do so, the team envisions the adaptive workflow as radiation therapist-centric.
The plan is for radiation therapists assigned on Ethos to drive the adaptive treatments, including contouring the organs at risk, the human body, and the clinical target volume. Once these steps are complete and the patient is brought to the treatment vault, the physician will then review the plan prior to treatment. This workflow both optimizes the physician’s time at the console and minimizes the patient’s time on the treatment couch.
To get to the under-30-minute patient-time-on-table mark, the goal is to reduce all steps in the adaptive session to under 15 minutes, with most of these reductions coming from patient setup and contouring. The belief is that patient setup can be reduced to under five minutes with the use of markerless surface guidance, a tool that was implemented for the Department’s breast patients in May 2023.
Four of the five fractions in the study are delivered with standard cone beam computed tomography. The other fraction is delivered with HyperSight, an imaging software that not only specifically amplifies the FAST-Forward implementation but also significantly enhances Ethos treatments to all treatment sites in the Department. HyperSight use will be further evaluated, with the hope that contouring can be reduced from over 10 minutes to under five minutes.
Over 40 patients have been treated for the study so far. According to Dr. Parsons, while the first several patients were routinely treated in around an hour, the treatment time has already been reduced to 45 minutes with radiation therapist training and utilization of the Ethos’ existing tools. It is expected that the overall time will continue to decrease as the team becomes more familiarized with the workflow.
Once data analysis is completed, there are plans to submit the study as a manuscript to a radiation oncology audience, further aiding in the improvement of whole-breast adaptive radiotherapy on the Ethos platform.
Asal Rahimi, M.D., M.S., Professor, Associate Vice Chair for Program Development, Medical Director of the SCCC Clinical Research Office, Chief of Breast Radiation Oncology Service
Mu-Han Lin, Ph.D., Associate Professor and Director of Adaptive Therapy in Medical Physics
David Parsons, Ph.D., Assistant Professor and Associate Program Director of the Medical Physics Residency