2278 - Comparison of Single Time Point Radiopharmaceutical Therapy Dosimetry Results from Various Commercial Dosimetry Software Packages
Presenter(s)
E. Yaghoubian1, J. Grudzinski2, A. Rodriguez3, A. Saoudi1, and R. B. Patel4; 1UPMC Hillman Cancer Center, Pittsburgh, PA, 2University of Wisconsin, Madison, WI, 3Voximetry, Madison, WI, United States, 4University Hospitals of Cleveland - Seidman Cancer Center, Cleveland, WI
Purpose/Objective(s): Radiopharmaceutical therapy (RPT) is administered as a uniform activity or by patient body weight and areas of tumor and normal tissue have varying dose deposition. Recently, several commercial software packages have been developed to estimate RPT tissue dose using post-treatment single photon emission computed tomography (SPECT) imaging. While multi-timepoint dosimetry is the gold standard approach, it is difficult for patients to make multiple trips for scans and many centers have older scanners which may limit their ability to perform multi-timepoint post-treatment SPECT scans for RPT dosimetry. In this study we compared two different commercially available dosimetry packages to perform estimates of dose deposition after RPT treatment.
Materials/Methods: Post treatment SPECT scans (cycle 1 of 177Lu-PSMA-617) were collected for three patients for analysis on a retrospective IRB approved protocol. SPECT scans were collected on Day 4 to 5 after RPT administration and single imaging timepoint dosimetry utilizing the Hänscheid approach was performed using parameters optimized for tumor tissue or organ specific time activity curves with two commercially approved RPT dosimetry software packages: MIM’s MRT and Voximetry’s TORCH. Mean total tumor dose and kidney dose were estimated for each patient using vendor specific optimized parameters and adjustment of effective decay rates was investigated for differences in estimates between software packages.
Results: Total tumor dose ranged from 5.25-19.2 (mean 11.84) Gy in MRT vs 6.1-19.3 (mean 12.5) Gy in TORCH with no significant differences (p = 0.15) in tumor dose estimates between MIM and TORCH. However, estimated mean kidney doses were 2.13 times greater in TORCH than MIM (p = 0.04) using vendor optimized effective decay rates. Adjustment of the kidney effective decay rate from 0.01733 to 0.0067387 in TORCH reduced the discrepancy in kidney doses between RPT software.
Conclusion: As RPT dosimetry is incorporated into clinical practice, optimal post treatment imaging schedules which balance patient convenience and imaging resource allocation with improved accuracy of dosimetry must be established. While single time point dosimetry remains a valid option, organ specific time activity curves or first cycle multi-time point post treatment SPECT imaging may improve accuracy and reduce uncertainty of RPT dosimetry calculations.