4D blood flow model for dose calculation to circulating blood and lymphocytes

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Biology

Background:

• Radiotherapy for intracranial tumors can lead to lymphopenia, a decrease in lymphocytes.
• Understanding radiation dose to circulating blood is crucial for predicting and mitigating this side effect.

Purpose of the Study:

• To develop and validate a 4D computational human blood flow model (BFM) for estimating radiation dose to circulating blood during fractionated radiotherapy for intracranial tumors.
• To investigate the impact of different radiotherapy techniques (proton vs. photon), dose rates, and patient characteristics on the radiation dose delivered to the blood pool.

Main Methods:

• Developed a hemodynamic cardiovascular system and a detailed cerebral vasculature model from MRI data.
• Implemented a Monte Carlo simulation to track individual blood particles (BP) and accumulate radiation dose along their trajectories.
• Simulated a whole-body BFM with over 22 million BPs and a cerebral model with over 266,000 BPs.

Main Results:

• Proton therapy resulted in a mean blood pool dose of 0.06 Gy versus 0.13 Gy for photon therapy after 30 fractions.
• Proton therapy irradiated a significantly lower fraction of blood volume (10.1%) compared to photon therapy (18.4%) after the first fraction.
• Higher dose rates reduced the fraction of blood receiving low doses but increased high-dose exposure; patient characteristics had minor effects.

Conclusions:

• The developed 4D BFM accurately estimates radiation dose to circulating blood during intracranial radiotherapy.
• Findings demonstrate the dosimetric advantages of proton therapy over photon therapy in reducing blood pool irradiation.
• This model provides valuable insights into the mechanisms of radiation-induced lymphopenia and can inform treatment planning.