In 2022, Vanderbilt University Medical Center became one of the first hospitals in the Southeast to acquire an electron-beam linear accelerator for delivering intraoperative radiation therapy (IORT).
Although IORT technology was developed in the early 20th century, today’s portable, self-shielding machines recently evolved to enable radiation treatment to become an adjunct therapy available during surgery without the need to transfer out of the operating room.
“With IORT, we can expand the universe of surgical candidates.”
Cancer surgeon Kamran Idrees, M.D., chief of the Division of Surgical Oncology and Endocrine Surgery, is confident about IORT’s benefits for patients with pancreatic cancers that have not metastasized, are borderline resectable, or locally advanced.
“This equipment gives us a better chance to kill the cancer cells that have invaded key blood vessels or organs away from the tumor itself,” Idrees explained. “Without eradicating all the cancer cells, these tumors are deemed surgically unresectable, and these patients are put on maintenance chemo. With IORT, we can expand the universe of surgical candidates.”
Being Live with Radiation Targets
Idrees and radiation oncologist Natalie Lockney, M.D., recently led the team using the new IntraOp Mobetron IORT machine in two such pancreatic tumor resection procedures.
“Both patients were considered unresectable, but we were able to remove the tumors and take the margins we wanted where there was the real estate to do so,” Idrees said. “The beauty of IORT is that where, in the past, other structures like nerves, blood vessels or other organs prevented us from getting that margin or resecting these tumors, now we are able to radiate those tissues in areas of concern.”
To help with precision targeting, Vanderbilt purchased several dozen cones capable of aiming the beam at specified targets using varying sizes and angles.
“If some of the key blood vessels, nerves or organs are involved in the cancer site, you remove the majority of the tumor and shave it off of these key structures.”
“When we see the tumor bed directly, we can better determine our margins and select the best beam size, dose and depth,” Idrees said. “If some of the key blood vessels, nerves or organs are involved in the cancer site, you remove the majority of the tumor and shave it off of these key structures.”
According to Lockney, the ability to avoid nearby areas has a particularly high impact in pancreatic cancer and several others that previously had been difficult to target.
“The nearby bowel is often a dose-limiting organ,” she said. “For patients who have already had standard-dose radiation before surgery, IORT allows us to provide a boost dose of additional radiation while they’re in the operating room, with critical organs out of the way.”
Idrees explains that IORT also has distinct advantages to inserting radiation beads during surgery.
“These beads can move, missing their mark, and sometimes emerge from the incision. Surgical clips to mark areas of concern for post-operative radiation can also move. Another benefit of IORT is avoiding unnecessary radiation to organs not involved with cancer.”
Research on Extended Survival
Idrees noted IORT is approved for breast cancer, pancreatic cancer, sarcomas of the extremities, (including retropharyngeal sarcoma), head and neck cancers, and recurrent colorectal cancers. So far, Vanderbilt’s team has used it only on pancreatic tumors but plans to expand its use to all applicable conditions.
Although IORT has not been demonstrated to reduce metastases in pancreatic cancer, studies do demonstrate survival benefits. One study includes resected pancreatic tumors with microscopically positive (R1) margins. Median overall survival was 35 months compared with 24.5 months among patients receiving adjuvant IORT compared with those who received resection alone.
Idrees says IORT may level the playing field for those with unresectable tumors as well, with patients receiving IORT demonstrating similar survival rates as those with resectable tumors and no IORT.
Additional studies of resected patients, most of whom had locally advanced unresectable tumors, also found significantly higher overall and progression-free survival rates among those receiving IORT compared with those who did not.
Organ-Sparing Cancer Eradication
Idrees also heads up Vanderbilt Ingram Cancer Center’s Hyperthermic Intraperitoneal Chemotherapy (HIPEC) program. With a parallel effort in other cancers, including ovarian cancer, HIPEC helps patients avoid systemic treatment wherever possible.
“With HIPEC, we permeate the area of concern with heated chemotherapy drugs and avoid exposing the rest of the body to chemotherapy where it isn’t needed,” Idrees said. “With IORT, we are applying the same principle but using radiation.”
The current goal with pancreatic and ovarian cancer is to lengthen life span, although Idrees is looking ahead.
“With breast cancer, recurrent rectal cancer, or some cancers of the extremities, for example, there is definitely a chance for cure. We believe IORT can be a tool for raising these odds.”