Comparisons of 3-Dimensional Conformal and Intensity-Modulated Neutron Therapy for Head and Neck Cancers

Comparisons of 3-Dimensional Conformal and Intensity-Modulated Neutron Therapy for Head and Neck Cancers

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Purpose: Neutron therapy is a high linear energy transfer modality that is useful for the treatment of radioresistant head and neck (H&N) cancers.It has been limited to 3-dimensioanal conformal-based fast-neutron therapy (3DCNT), but recent technical advances have enabled the clinical implementation of intensity-modulated neutron therapy (IMNT).This study evaluated the comparative dosimetry Vehicle Covers of IMNT and 3DCNT plans for the treatment of H&N cancers.Materials and Methods: Seven H&N IMNT plans were retrospectively created for patients previously treated with 3DCNT at the University of Washington (Seattle).A custom RayStation model with neutron-specific scattering kernels was used for inverse planning.

Organ-at-risk (OAR) objectives from the original 3DCNT plan were initially used and were then systematically reduced to investigate the feasibility of improving a therapeutic ratio, defined as the ratio of the mean tumor to OAR dose.The IMNT and 3DCNT plan quality was evaluated using the therapeutic ratio, isodose contours, and dose volume histograms.Results: When compared with the 3DCNT plans, IMNT reduces the OAR dose for the equivalent tumor coverage.Moreover, IMNT is most advantageous for OARs in close spatial proximity to the target.For the 7 patients with H&N cancers examined, the therapeutic ratio for IMNT increased by an average of 56% when compared with the 3DCNT.

The maximum OAR Girls 4th of July Dress dose was reduced by an average of 20.5% and 20.7% for the spinal cord and temporal lobe, respectively.The mean dose to the larynx decreased by an average of 80%.Conclusion: The IMNT significantly decreases the OAR doses compared with 3DCNT and provides comparable tumor coverage.

Improvements in the therapeutic ratio with IMNT are especially significant for dose-limiting OARs near tumor targets.Moreover, IMNT provides superior sparing of healthy tissues and creates significant new opportunities to improve the care of patients with H&N cancers treated with neutron therapy.