A University of California San Diego (UCSD) research team showed that voxel-based dosimetry could accurately predict tumor pathology response in patients with hepatocellular carcinoma (HCC) undergoing yttrium-90 radioembolization.
The Medical Internal Radiation Dose (MIRD) formula is the current standard of care to estimate the dose for patients undergoing transarterial radioembolization (TARE) for HCC. But MIRD assumes that the dose is distributed uniformly throughout the perfused volume.
Voxel-based dosimetry would provide a more personalized approach, taking into consideration patient-specific radiation distribution and an individual’s unique organ anatomy.
The team’s findings will be presented as a Featured Abstract, “Correlating Voxel-based Tumor Dose to Tumor Explant Pathology after Y-90 Transarterial Radioembolization for Hepatocellular Carcinoma (HCC),” during Monday’s Scientific Session 15, Liver Locoregional 1, from 3 to 4:30 p.m. MT. The abstract will be presented by Kurt Pianka, a medical student on the UCSD research team.
In a retrospective study, the researchers analyzed pathology reports from patients with HCC who were treated with Y-90 radioembolization at a single institution between 2015 and 2023 who subsequently underwent liver transplant.
Forty-one patients were included, representing 54 HCC lesions. Thirty-two lesions, or about 59%, met the criteria for complete response. Of the other 22 lesions, six underwent further locoregional therapy before transplant due to residual viability.
The study showed that doses administered to 50% (D50), 70% (D70) and 95% (D95) of the tumor volume were all independently predictive of complete response. For lesions with complete response, the median D95 was 755 Gy vs. 188 Gy. Based on a 70% probability of complete response, the researchers propose a D95 cutoff of >668 Gy, which had 59% sensitivity and 91% specificity (72% accuracy).
“It was very exciting,” Pianka said. “We were able to find different dose thresholds that were predictive of pathologic response. There were a few different tumor-specific dose metrics that we found that were significantly predictive. One that we’re really excited about is the D95.”
While the study helps build the evidence base for using personalized dosimetry, there are still plenty of questions, Pianka said. The initial implication for patient care would be to use multicompartment voxel dosimetry after TARE to see whether the tumor received a high enough treatment dose. The goal would eventually be to determine the dose amount specific to each individual before TARE.
“What we’re doing here is after-treatment dosimetry,” Pianka explained. “It isn’t necessarily directly feeding into treatment planning. We’re basically able to say, after the treatment has been delivered, ‘This was the dose for 90% of the tumor, for 50% of the tumor, etc.’ But by doing that, we haven’t necessarily solved for the problem of how to plan better clinically.”
Pianka, who has spent the past year dedicated to research, is planning to graduate from medical school in 2025 and hopes to land an IR residency spot. He earned a bachelor’s degree in biomedical engineering before he started medical school, where he was initially interested in medical oncology.
“Then, through sampling various different fields, I found my way to IR,” he said. “I realized this was a really incredible space where still I got to be a really important part of the oncology care team for patients, but I also got to do a lot of different types of procedures.”
