A new method to estimate doses to the normal tissues after past extended and involved field radiotherapy for Hodgkin lymphoma.

Introduction: Reconstruction of radiotherapy (RT) performed decades ago is challenging, but is necessary to address dose-response questions from epidemiological data and may be relevant in re-irradiation scenarios. Here, a novel method to reconstruct extended and involved field RT for patients with Hodgkin lymphoma was used.
Materials and Methods: For 46 model patients, 29 organs at risk (OARs) were contoured and seven treatment fields reconstructed (mantle, mediastinal, right/left neck, right/left axillary, and spleen field). Extended and involved field RT were simulated by generating RT plans by superpositions of the seven individual fields. The mean (standard deviation) of the 46 individual mean organ doses were extracted as percent of prescribed dose for each field superposition.
Results: The estimated mean doses to the OARs from 17 field combinations were presented. The inter-patient variability was found to be a larger contributor to the uncertainty than the field simulation process. The inter-patient variability depended on the OAR and primarily affected the estimates for OARs located at the edge of the RT field.
Conclusions: Dose estimates for 29 OARs were reported from extended and involved field RT. These estimates could be employed when individual reconstruction is not feasible and estimated doses from past treatments are needed.
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