Boston IRs collaborated with medical physicists to show that yttrium-90 (Y-90) radioembolization could be delivered via the bronchial artery for patients with inoperable primary lung cancer or cancer that has spread into the lungs.
Their findings will be presented as a featured abstract, “Bronchial Artery Tc99m-MAA Injection in Patients with Pulmonary Malignancies Demonstrates Future Treatment Potential of Bronchial Y-90 Radioembolization,” during Sunday’s Scientific Session 2, New Frontiers in IR, from 3–4:30 p.m. MT. The abstract will be presented by Eric Wehrenberg-Klee, MD, assistant radiologist at Massachusetts General Hospital and an assistant professor at Harvard Medical School.
To evaluate the safety and efficacy of Y-90 radioembolization via the bronchial artery without actually administering Y-90 into patients, the researchers recruited eight patients with pulmonary malignancy undergoing bronchial artery embolization (BAE) for secondary prevention of hemoptysis. The patients were injected with the diagnostic radiotracer Tc99m-MAA as a surrogate for Y-90 via the bronchial artery before undergoing BAE. Afterward, the patients had a single-photon emission computed tomography (SPECT/CT) scan), which allowed the researchers to assess the anticipated dose to tumors as well as which organs might be at risk.
“Using the SPECT/CT scans we worked with Alejandro Bertolet, PhD, and his team of medical physicists in the radiation oncology department who have a computational methodology that is used for radiation planning in external beam radiation and is the best way to do radiation dosimetry,” Dr. Wehrenberg-Klee explained.
Determining the proper dosage is particularly challenging when treating the lungs because air tissue interfaces can cause a lot of different radiation interactions, he said.
“For every sort of particle of MAA that we identify, we say instead if this was a Y-90 microsphere we can then calculate what the dose would be to tumors and other structures in the lung and mediastinum,” he said. “In the chest, there’s all sorts of structures that you don’t want to get radiation into in significant numbers, and in the external beam radiation therapy world they call those organs at risk.”
The study showed that a therapeutic dose of Y-90 could have been delivered safely in all eight patients. Furthermore, patients could receive at least 175Gy of a biologically effective dose and up to 2,928Gy without putting organs at risk. The mean dose was 813Gy.
While this study is preliminary and used a surrogate for Y-90, Dr. Wehrenberg-Klee finds the results promising. “It’s very encouraging. Our takeaway is that this provides a pretty solid foundation for arguing for a Phase 1 clinical trial of Y-90 via the bronchial artery.”
He sees a couple of different patient populations that could benefit from injecting Y-90 through the bronchial artery. Patients with non-small cell lung cancer with only one tumor who are not good surgical candidates might currently undergo stereotactic body radiation therapy (SBRT). However, patients with an ultra-central tumor—one that abuts the proximal bronchial tree or heart—cannot receive a full therapeutic dose of radiation without a high incidence of radiation toxicity. The bronchial artery path might provide a better alternative.
The procedure could also benefit patients with widespread metastatic disease, Dr. Wehrenberg-Klee said. These patients may currently receive SBRT, but there is a limit to how many lung lesions can be safely treated before causing radiation-induced lung disease.
Collaborating with medical physicists can help IRs improve radiation therapies, Dr. Wehrenberg-Klee said. “Medical physicists can give a lot of perspective and nuance into what we’re doing and what the effects are, particularly through the dosimetry simulations,” he said. “They’re really adding a lot of value in terms of us understanding how much radiation is going to place X, Y or Z, which improves our understanding of what we’re doing to patients, both in our ability to treat but also the risks of toxicity.”
