An energy‐conserving dose summation method for dose accumulation in radiotherapy

Abstract Background Radiation therapy often requires the accumulation of doses from multiple treatment fractions or courses for plan evaluation and treatment response assessment. However, due to underlying mass changes, the accumulated dose may not accurately reflect the total deposited energy, leading to potential inaccuracies in characterizing the treatment input. Purpose This study introduces an energy‐conserving dose summation method to calculate the total dose in scenarios where patients experience changes in body mass during treatment. Methods and materials The proposed method transfers dose and mass data from dosimetry images, where the delivered doses were calculated, to a reference image using an energy and mass‐conserving dose reconstruction technique. The reconstructed dose assumes the same resolution and dimension as the reference image. The transferred masses are averaged at each image voxel in the reference image to generate an average mass. The transferred doses are then adjusted by multiplying by the ratio of their transferred mass to the average mass, and subsequently summed to calculate a mass‐weighted (MW) total dose at each voxel. This method is demonstrated with a case of lung cancer retreatment. Results The MW total dose was shown to be equivalent to the total deposited energy divided by the average mass. In the lung cancer retreatment case, the energy derived from the MW total dose was consistent with the sum of energy transferred from two treatments across all evaluated organs. Conclusion The MW dose summation method can produce a total dose that accurately reflects the total energy deposited in each organ. The consistency may provide a robust foundation for verifying dose accumulations in adaptive radiotherapy.