Quantification of internal dosimetry in PET patients II: Individualized Monte Carlo‐based dosimetry for [18F]fluorocholine PET

Abstract

Purpose To obtain individualized internal doses with a Monte Carlo (MC) method in patients undergoing diagnostic [18F]FCH‐PET studies and to compare such doses with the MIRD method calculations. Methods A patient cohort of 17 males were imaged after intravenous administration of a mean [18F]FCH activity of 244.3 MBq. The resulting PET/CT images were processed in order to generate individualized input source and geometry files for dose computation with the MC tool GATE. The resulting dose estimates were studied and compared to the MIRD method with two different computational phantoms. Mass correction of the S‐factors was applied when possible. Potential sources of uncertainty were closely examined: the effect of partial body images, urinary bladder emptying, and biokinetic modeling. Results Large differences in doses between our methodology and the MIRD method were found, generally in the range ±25%, and up to ±120% for some cases. The mass scaling showed improvements, especially for non‐walled and high‐uptake tissues. Simulations of the urinary bladder emptying showed negligible effects on doses to other organs, with the exception of the prostate. Dosimetry based on partial PET/CT images (excluding the legs) resulted in an overestimation of mean doses to bone, skin, and remaining tissues, and minor differences in other organs/tissues. Estimated uncertainties associated with the biokinetics of FCH introduce variations of cumulated activities in the range of ±10% in the high‐uptake organs. Conclusions The MC methodology allows for a higher degree of dosimetry individualization than the MIRD methodology, which in some cases leads to important differences in dose values. Dosimetry of FCH‐PET based on a single partial PET study seems viable due to the particular biokinetics of FCH, even though some correction factors may need to be applied to estimate mean skin/bone doses.

Combined Targeted Radiopharmaceutical Therapy and Immune Checkpoint Blockade: From Preclinical Advances to the Clinic

“…Patients with homogeneously high target expression could safely receive increased activity (60) and those with low or variable expression could be evaluated to predict therapeutic effect and the fraction of metastases that could be treated effectively. Individualized Monte Carlobased dosimetry has demonstrated improved accuracy relative to standardized phantom-based methods in small patient cohorts (61). Further, this pretherapy dosimetry could reliably predict tumor or at-risk organ doses for TRT (62).…”

Improved accuracy of the biodistribution and internal radiation dosimetry of 13N‐ammonia using a total‐body PET/CT scanner

“…There is a growing interest in developing methods to compute precise, individualized internal dose distributions in patients. Several Monte-Carlo (MC) methods that can account for heterogeneous activities and medium distributions have been developed for this aim, but to date, they have been barely used in patients 24,25 due to the extensive computational resources and time. Exploring the individual and more accurate internal dose calculation by making use of the CT images (for organ segmentation and dose deposition) and PET images (for organ segmentation and distributions of activities) provided by the TB dynamic PET images, and comparing them with the current work are meaningful and will be left as future work.…”