Radiation therapy is known to deplete the circulating lymphoid cell populations, particularly when the delivery schedule is protracted, as in hyperfractionated radiation therapy, and thus potentially dampening the desired anti-tumor immune response.

To better understand how the radiation treatment delivery parameters affect this depletion, we developed a computational 4D model to estimate the radiation dose to the circulating blood during intracranial irradiation.

The results show that proton therapy (double scattering) reduces the average dose to the circulating blood, compared to photon treatment plan (IMRT), 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, 18.3% and 66.7% for 2 Gy and 10 Gy respectively, compared to 28.4% and 77.5% for the photon treatment.