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Modeling the Radiation Dose to Circulating Lymphocytes for Different Radiotherapy Modalities and Delivery Parameters

A Hammi*, C Grassberger , H Shih , J Loeffler , H Paganetti , Massachusetts General Hospital, Boston, MA


(Monday, 7/15/2019) 1:45 PM - 3:45 PM

Room: Stars at Night Ballroom 2-3

Purpose: To better understand how radiotherapy delivery parameters affect the depletion of circulating lymphocytes in the patient, we developed and applied a computational model to estimate the dose to the circulating blood during intracranial irradiation.

Methods: We extracted major brain vasculature from MRI data, and complemented them with an extension network of generic vessels in the frontal and occipital lobes to guarantee even overall blood supply to the entire brain volume. Based on these path lines, an explicit Monte Carlo Blood Flow (BF) model has been developed to track propagation of blood particles through the brain and radiation fields, accumulating dose along their trajectories. We developed an auxiliary BF model for the rest of the body based on known hemodynamics.

Results: The BF model includes 1050 path lines traversing the brain, thus creating a network of paths with a maximum inter-path distance of 4mm (twice the dose calculation voxel size). In equilibrium, the model explicitly simulates 4’456’000 BP, of which 53’763 are being tracked three-dimensionally in the brain at any given time. The time resolution (25ms) was optimized to yield a stepsize below 1mm. Proton therapy reduces the average dose to the circulating blood by a factor 2.3 for a 2Gy fraction, which increases to 2.8 for a 10Gy fraction. The fraction of blood receiving any dose is significantly lower for proton therapy, 18.8% and 66.7% for 2 and 10 Gy respectively, compared to 25.3% and 77.5% for the photon treatment plan.

Conclusion: We developed an accurate technique to calculate the dose received by the circulating blood pool, and demonstrate its application to proton- versus photon-based delivery and various dose rates and fractionation schemes. This model enables us to develop radiation techniques that spare the circulating lymphocyte compartment.


Dose Volume Histograms, Radiobiology, Blood Flow


Not Applicable / None Entered.

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