Assessing the Homogeneity of Dose Delivered to Circulating Blood during Sweeping Cobalt-60 Total Body Irradiation
Abstract
Purpose
Total body irradiation (TBI) requires the entirety of the patient's body to be irradiated, and treatment methods vary greatly across treatment centres. For the majority of techniques, excluding intensity modulated TBI, little is known about the heterogeneity of dose delivered to the circulating blood. To assess the dose delivered to the circulating blood volume during Sweeping Cobalt-60 (Co-60) TBI, a full body blood flow simulation was combined with Monte Carlo generated 4D dose distributions.
Methods
A virtual phantom was used to create a Monte Carlo phantom mimicking a Co-60 TBI treatment set-up. Time-resolved Monte Carlo simulations using modified DOSXYZnrc, for both supine and prone patient positions, were completed. The virtual phantom also enabled the creation of a blood flow model which spatio-temporally tracks blood volumes (BVs) through the phantom. The model is composed of 94 vessel segments and 28 compartments. BV trajectories were determined using a combination of one-dimensional blood flow modeling, in-vivo data, and zero-dimensional compartments. The 4D dose distributions were sampled as the BVs moved through the flow model. For a 12 Gy prescription, in 6 fractions with two patient positions (supine and prone) each and 15 sweeps per position per fraction, the dose to the circulating blood was determined for a single fraction and the entire treatment.t
Results
The circulating blood received 1.25 ± 0.98 Gy in one fraction and 10.76 ± 2.36 Gy after all fractions.
Conclusion
A whole-body blood flow model was paired with 4D dose distributions to assess the heterogeneity of the dose to the circulating blood achieved by sweeping beam Co-60 TBI.