The first presentation introduces methods for performing organ-level and voxel-level radiopharmaceutical therapy (RPT) dosimetry. The reference model-based MIRD formulism as well as direct Monte Carlo based methods for highly patient specific dose estimation using the patient’s SPECT and CT images as the input are discussed. The main steps of the dosimetry calculation including serial imaging, activity quantification, image registration, segmentation, time-activity fitting, and absorbed dose estimation are introduced together with the main sources of uncertainty. How individualized dosimetry before, during and after therapy can enhance RPT are covered. Methods for simplifying the dosimetry protocol to make it practical for clinical implementation are discussed including recently available AI-based tools.

In the second presentation, basic bio-effect modeling based on the linear-quadratic model is introduced. A large focus is on the biological effective dose (BED), how it is calculated, why it should be more utilized in RPT than in external beam (EBRT), and why it is a better correlate with outcome than absorbed dose. The presentation explores the theoretical comparison of EBRT and RPT doses and the limitations of that translation, especially with regard to normal organ toxicity threshold determination in RPT. Finally, the particularities and challenges of alphaRPTs are explored, including low count rate imaging, radioactive daughters, sub-organ dosimetry, the relative biological effect (RBE), and stochastic energy deposition.  

Topics:

• Dosimetry I: Dosimetry Methods and Individual Dose Planning, Uncertainties ‒ Yuni Dewaraja, PhD
• Dosimetry II/Radiobiology II: Bioeffect Modeling, Toxicities, Alpha Emitters ‒ Robert F. Hobbs, PhD