Purpose: To understand how radiation modality and dose distribution impacts the dosedelivered to the circulating lymphocytes, a dynamic computational model was developed toestimate the dose to the circulating blood for a variety of radiation treatment modalities.
Methods: To describe the 4D propagation of blood particles through organs and radiationfields, an explicit Monte Carlo blood flow model was developed based on the whole-bodyhemodynamics. For head-and-neck patients, the large-scale architecture of cerebralarteries is extracted from MRA images. The propagation of the blood was described aslaminar along the vasculatures and through radiation fields. A dynamic delivery modelwas implemented to simulate different radiation modalities such as proton pencil beamscanning (PBS) and passive scattering (PS) as well as photon therapy. The modelincluded dynamic details of clinical delivery system, such up-/down-ramping of the currentas well as the dead time during steering between spot positions and switching betweenenergy layers were all taken into account.
Results: For a 2 Gy fraction, PBS reduced the average dose to the circulating blood by1.9% compared to PS and by 30% compared to photon therapy. The fraction of bloodreceiving any dose was only 1.1% for PBS, compared to 7.3% and 18.1% for PS andphoton therapy, respectively. The blood volume receiving at least 0.07 Gy, which is knownto deplete the lymphocyte count by 2 percentage points, increased from 0.65% for PBSto 1.4% for PS and 2.1% for photon therapy.
Conclusion: A computational model able to estimate the dose accumulated by thecirculating blood for different radiation modalities and various dose rates and fractionationschemes was developed. Said model enables us to analyze a radiation modality’spotential impact on the circulating lymphocyte count, which may be especially importantgiven the growing interest in immunotherapy.
Not Applicable / None Entered.