TAT-10: Optimization of the patient dosimetry in alphatherapy

Kanazawa, Japan (UroToday.com) Accurate dosimetry is essential in order to deliver maximum dosage to the tumor site while minimizing the dose to other organs at risk. This study develops tools for measuring the dose from Ra223. The range of alphas is to too short to image directly in humans but the decay of Ra223 also emits gamma rays as the daughter nuclei de-excite to their ground state. These gammas can be detected. SPECT imaging of the gammas was investigated for the first time.

Phantoms containing known amounts and shapes of Ra223 in containers were used to optimize the adjustable parameters (angular and energy range) of the SPECT instrument. A 5.6ml sphere containing 20 kBq/ml showed quantitative accuracy of about 4%.

Ra223 is usually used to treat bone metastases and bone has a highly complex structure. Moreover, bone marrow is an organ at risk so the details of dosimetry are very important. A comparison was made between the alpha absorbed fractions given in ICRP Publication 30 and a Monte Carlo (MCNP6) calculation using a realistic volexized model of an adult male skeleton developed by the University of Florida. Differences of up to 50% were observed

Presented By: Nadia Benabdallah from IRSN, Institute for Radiological Protection and Safety, Paris, France

Written By: William Carithers, Lawrence Berkeley National Laboratory

at the 10th International Symposium on Targeted Alpha Therapy (TAT-10)  May 31 - June 1, 2017 - Kanazawa, Japan.