Preliminary treatment planning strategy for blood dose reduction in head and neck radiotherapy

Radiation dose to circulating blood, a surrogate for circulating lymphocyte damage by radiotherapy (RT), has emerged as a factor predicting treatment outcomes, including overall survival, tumor recurrence, and lymphopenia occurrence. This study aimed to investigate strategies for reducing circulating blood dose in head and neck cancer (HNC) patients by comparing treatment plans, the implementation of which varied by modality and blood vessel-sparing (BVS) approach.

Using a publicly available dataset, 20 HNC patients were randomly selected and a total of 120 treatment plans were generated using RayStation. For each of the two modalities, including intensity-modulated radiation therapy (IMRT) and intensity-modulated proton therapy (IMPT), three planning strategies were evaluated: a conventional plan (Conv) and two blood vessel-sparing plans with mean dose constraints targeting 90% and 80% of the conventional vessel dose (BVS-90% and BVS-80%, respectively). Blood dose was estimated using the HEDOS simulation framework.

IMPT reduced circulating blood dose compared to IMRT, lowering the mean blood dose by 21.5% and D_90% by 31.8%. The BVS-80% constraint further decreased the mean blood dose by 12.5% for IMPT and 12.6% for IMRT, while the intermediate BVS-90% constraint yielded reductions of 8%. These reductions were achieved without clinically meaningful compromise in target coverage or increase in dose to other organs-at-risk (OARs). Monitor unit analysis revealed no significant increase in delivery complexity with BVS planning.

In this preliminary planning study, incorporating blood-rich structures as OARs and adopting IMPT effectively reduced blood dose. Integrating blood dose considerations into RT planning is readily implementable within existing clinical workflows to minimize lymphocyte damage.