Key Clinical Summary: 

• Design/Population: This single-institution series included 19 patients receiving radiopharmaceutical therapy with evaluable post–cycle 1 voxel-level dosimetry, using multi-timepoint SPECT/CT imaging and Monte Carlo–based dose modeling.
• Key Outcomes: Patient-specific dosimetry guided individualized treatment decisions, allowing most patients to safely continue therapy, while identifying others who required dose delays or early discontinuation; absorbed doses to organs at risk were comparable to phase 3 trial benchmarks.
• Clinical Relevance: These data demonstrate the feasibility and clinical utility of voxel-level dosimetry as a decision-support tool to personalize radiopharmaceutical therapy, potentially enabling safe treatment extension beyond conventional fixed-cycle dosing.

Mustafa Basree, DO, University of Wisconsin, Madison, Wisconsin, discusses institutional experience using voxel-level, patient-specific dosimetry to personalize 177Lu-PSMA-617 dosing in patients with metastatic castration-resistant prostate cancer. 

Multi-timepoint SPECT/CT–based dosimetry provided actionable data to guide treatment continuation, delay, or discontinuation while maintaining organ-at-risk safety. These findings highlight the potential to safely extend therapy beyond standard dosing in selected patients.

These results were presented at the 2026 ACRO Radiation Oncology Summit in Orlando, Florida.

Transcript:

My name is Mustafa Basree, I’m a PGY-5 radiation oncology resident at the University of Wisconsin in Madison, Wisconsin. I’m really excited to be here at ACRO to discuss our experience with personalized, multi-timepoint, voxel-level dosimetry for patients with metastatic castration-resistant prostate cancer who were treated with ¹⁷⁷Lu-PSMA-directed therapy.

At the University of Wisconsin, we have been running multi-timepoint dosimetry on our patients routinely as part of standard of care for some patients with high risk of certain toxicities—either baseline kidney dysfunction, baseline risk for bone marrow toxicity, prior external beam radiation therapy, or prior taxane chemotherapy. We also have been getting those for patients who’ve had prior radium therapy like Xofigo. 

We looked at our experience from when we started the program and we were able to identify 19 patients who had evaluable post-cycle 1 dosimetry and received at least 1 cycle of therapy. Those patients were imaged immediately after, 24 hours after, and then 96 hours (day 0, day 1, and day 4) and then we integrate the dose over time to get a sense of what that dosimetry looks like for different organs at risk, and even tumor. Based on those values, we review the patient in conjunction with the rest of their clinical data with our multidisciplinary tumor board, with nuclear medicine and radiology colleagues, and then we make a decision in terms of should we move forward, should we reduce the dose, or should we discontinue treatment early. 

Out of our 19 patients, 11 of them had bone marrow toxicity concerns, about 9 of them had some kidney dysfunction, and there were prior RPT in 2 of them. We initially looked at our OAR dose levels compared with the VISION phase 3 trial data [and] there was really no difference in what we’re seeing compared with the reference trial data, which was really reassuring for us. Currently, we’re monitoring 2 things: we’re monitoring kidney mean dose as well as salivary gland mean dose, and those were essentially within our parameters. Our goal was to maintain a kidney mean dose less than 24 Gy and salivary gland mean dose less than 20 Gy. After we get that 1 post-cycle 1 dosimetry, then we multiply it by 6 and we get a sense of what the patient dosimetry would look like if we deliver all 6 cycles. 

Using this personalized dosimetry in conjunction with the clinical picture for each patient, we were able to safely guide continuation of treatment in the majority of patients, about 13 of them. We recommended discontinuing treatment early, some of them after 3, some of them after 4, depending on some clinical variables, in 5 patients, and then we delayed cycle administration in at least 1 patient.

The other advantage of using personalized dosimetry is that you can get a sense of if there’s room to administer more drug. Currently the guidelines are to administer 6 cycles but if patients are responding and are doing well, and we are well within the kidney tolerance, are we able to administer more drug. Based on the kidney numbers, looking at our data, 15 of our 19 patients could have safely received a 7th cycle and if you look at the salivary gland, 18 of our 19 patients could have received an additional cycle.

We conclude that, yes, the field of voxel-level dosimetry is young, and sometimes we don’t really know what to do with that data. At our institution, we’re using this as part of routine standard of care, and we’re reviewing this data along with nuclear medicine and medical oncology and radiology teams to guide our plan for the patient and tailoring the treatment to every patient, depending on their baseline risk, as well as subsequent risk of therapy.

Source: 

Basree, M. Personalized multi-timepoint voxel-level dosimetry in patients with metastatic castration-resistant prostate cancer treated with 177Lu-PSMA-617 therapy. Presented at the 2026 ACRO Radiation Oncology Summit. February 4 - 7, 2026. Orlando, Florida. Abstract 1608