Ablative MRI-guided radiation therapy extends survival in inoperable pancreatic cancer
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Ablative MRI-guided radiation therapy prolonged survival compared with standard therapy among patients with inoperable pancreatic cancer, according to results presented during the European Society for Radiotherapy and Oncology Congress.
“When Miami Cancer Institute became the second cancer center in the country to treat patients with the ablative MRI-guided radiation therapy, our intent was to use its unique capabilities to dramatically improve patient outcomes beyond what was achievable using standard CT-guided radiation delivery technology, especially for patients with very difficult-to-treat cancers such as pancreatic cancer,” Michael Chuong, MD, medical director of the Proton Therapy Center, physician director of the MRI-guided radiation therapy program and director of radiation oncology clinical research at Miami Cancer Institute, told Healio.
“MRI scans uniquely offer enhanced soft tissue imaging prior to and continuously throughout treatment compared with CT scans,” Chuong added. “Therefore, the treatment’s ability to more than double the dose to the tumor while sparing critical organs only a few millimeters away allowed us to develop one of the few truly ablative radiation therapy programs for pancreatic cancer in the world.”
The researchers published their initial experience with this treatment last year in Practical Radiation Oncology, demonstrating excellent tumor control and survival after 1 year and with minimal adverse events, Chuong said.
“The intent of the current study was to understand the outcomes of these patients with additional follow-up, and hopefully demonstrate that long-term survival was possible despite patients not being surgical candidates at diagnosis,” he said.
The retrospective analysis included 50 patients (median age, 70 years) with inoperable, nonmetastatic pancreatic adenocarcinoma who underwent MRI-guided stereotactic ablative body radiation therapy on a 0.35T-MR Linac (ViewRay) without fiducial markers between 2018 and 2020. Median prescribed dose was 50 Gy and median biologically effective dose was 100 Gy.
Median follow-up was 18 months after diagnosis.
Results showed median OS of 21 months, with OS rates of 87.9% at 1 year and 50% at 2 years. Expected median OS for patients with unresectable pancreatic cancer after chemotherapy and nonablative radiation therapy is about 12 months, with a 2-year OS rate of approximately 20%, Chuong said.
Median PFS was 16 months, with PFS rates of 67.7% at 1 year and 25.7% at 2 years.
Median, 1-year and 2-year estimated local control rates had not yet been reached, according to the researchers.
Results of a multivariate analysis showed induction chemotherapy for more than 3 months as the only predictor for improvements in PFS (HR = 0.358; 95% CI, 0.141-0.913) and OS (HR = 0.288; 95% CI 0.104-0.799). Researchers reported low incidence of both acute- (2%) and late-grade (10%) toxicities.
“Our study is exciting because it demonstrates a profound improvement in long-term survival achieved with ablative MRI-guided radiation therapy delivered over 5 days compared with historical outcomes from nonablative CT-guided radiation therapy,” Chuong said. “What seems to be a major driver of this difference is that long-term local tumor control was much higher with the ablative dose than would be expected with lower doses — we found that nearly 90% of patients had no evidence of local progression at 2 years.”
These outcomes were achieved with low rates of major adverse events, which were no higher than reported from nonablative radiation therapy, Chuong added.
“Ablative MRI-guided radiation therapy is most ideal for patients who are not surgical candidates at diagnosis because of locally advanced tumors, who then receive several months of chemotherapy without evidence of distant metastasis. Because it is so well-tolerated, it is also an attractive option for patients who are medically inoperable with limited performance status, even if chemotherapy is not able to be given.”
The encouraging results are just the “tip of the iceberg” in achieving long-term survival for patients with a historically grim prognosis, Chuong added.
“As other cancer centers adopt MRI-guided radiation therapy, there will be greater accessibility for patients to this incredible technology,” he said. “Clinical trials are critical to refining how this treatment should be used, and so we are actively enrolling patients in a prospective, multi-institutional, international phase 2 study of ablative MRI-guided radiation therapy for which I am one of the co-principal investigators. We have other trials in development combining ablative MRI-guided radiation therapy with novel systemic agents for pancreatic cancer and other challenging cancers that will soon open at Miami Cancer Institute and other cancer centers worldwide.”
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Chuong M, et al. Abstract OC-0415. Presented at: European Society for Radiotherapy and Oncology Congress; Madrid; Aug. 27-31, 2021.
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