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SAN ANTONIO -- Use of ablative stereotactic MR-guided on-table adaptive radiation therapy (SMART) is feasible and safe in patients with borderline resectable or locally advanced unresectable pancreatic cancer, according to a prospective phase II study.

None of the 136 patients included in the study experienced grade ≥3 toxicity "definitely" related to SMART at 90 days, thus meeting the study's primary endpoint of a reduction in grade ≥3 adverse events from a historical comparison of 15.8% to 8%, reported Parag Jitendra Parikh, MD, of Henry Ford Health in Detroit.

Three patients experienced grade 3 abdominal pain considered "probably" related to SMART, and there were nine cases of grade ≥3 toxicities "possibly" related to SMART, he noted during a late-breaking abstract session at the American Society for Radiation Oncology annual meeting.

"If we look at all grade 3 [or higher] toxicities, it is still only 9%, when including even those possibly related," Parikh said.

Furthermore, "early survival data is promising," he noted. "But we are going to need further follow-up to look at long-term toxicity, as well as 2-year overall survival."

The initial survival analysis demonstrated favorable overall survival (OS) rates compared with previously reported studies that included radiation therapy.

OS from the time of diagnosis for the entire study cohort was a median 22.5 months, with 1-year and 18-month OS rates of 93.9% and 75.3%, respectively. One-year and 18-month OS rates were 92.7% and 83.7% for borderline resectable patients, and 94.7% and 68.5% for patients with locally advanced unresectable cancer.

Parikh pointed out that the most recent data on standard-dose radiation in pancreatic cancer -- whether in borderline or locally advanced disease -- showed no improvement in OS with the addition of radiation. However, research on the use of ablative doses of radiation suggested that "it just might improve overall survival in this deadly disease."

For example, a from 2019 showed a signal for OS without an increase in toxicity.

Parikh also noted that the randomized will compare induction chemotherapy followed by ablative SMART versus chemotherapy alone in locally advanced pancreatic cancer patients, with 2-year OS rate as the primary outcome.

Why Does SMART Work?

With SMART, "we have excellent soft tissue visualization and we can localize what we're treating," Parikh said. "Most importantly, we can read just the organs at risk for every treatment. We know that these organs move and we know that toxicity to the stomach and duodenum is the most common problem with radiation to the abdomen."

"We can create a new plan while the patient is on the table, we can evaluate that plan, and then deliver it," he added. "And not just deliver it blindly, but with continual MR guidance so that we can see the tumor while we're treating it and so that the beam will not go on if the patients move."

While this process was initially laborious -- lasting at least 90 minutes, Parikh said that the last patient he treated was only on the table for 45 minutes.

Study Details

The 136 patients in this study (mean age 65.7 years) were enrolled across 13 sites from 2019 to 2021. Among this group, Eastern Cooperative Oncology Group (ECOG) performance status was 0-1, there were no contraindications to MRI, and all had received a minimum of 3 months of lead-in chemotherapy.

More than half (56.6%) had locally advanced unresectable pancreatic cancer, while the remainder had borderline resectable cancer. Most patients had pancreatic head tumors (66.9%).

SMART was delivered over consecutive days for 56.6%, and every other day for 43.4%; 93.1% of patients needed to have their plans adapted. Median follow-up was 16.4 months from diagnosis and 8.8 months from the end of radiation therapy with SMART.

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