Standardization of Lifetime Cumulative Dose Estimation for Re-Irradiated Patients Using Whole-Body Computational Phantoms
Abstract
Purpose
Accurate estimation of lifetime dose accumulation in patients undergoing re-irradiation therapy is essential for assessing long-term toxicity risks and evaluating the effectiveness of multiple radiotherapy (RT) courses. Currently, no standardized practice exists to account for cumulative absorbed dose to organs at risk across multiple RT courses to multiple body sites which may provide vital information for clinical planning and evaluation. Mapping patient dose distributions onto a standardized whole-body reference model may enable proper assessment of cumulative dose and improve the quality of re-irradiation studies.
Methods
ICRP reference adult male and female mesh-based computational phantoms were converted into DICOM image datasets by assigning Hounsfield Unit values to all anatomical structures based on tissue compositions and mass densities reported in ICRP Publication 145. Additional reference images were generated with varied anatomical positioning to reflect realistic treatment geometries. Dose distributions from a large cohort of patients treated with thoracic re-irradiation were mapped onto the reference phantoms using a hybrid intensity- and structure-based deformable image registration algorithm (ANACONDA) implemented in RayStation 2023B. Dose deformation accuracy was assessed using a novel spatial dose evaluation method and comparison of dose-volume histogram (DVH) metrics.
Results
Patient dose distributions were successfully deformed onto the ICRP reference phantoms. DVH analysis demonstrated improved agreement for patients with anatomical features closely matching the reference model compared to those with extensive metastatic disease. In one case, mean dose differences for several critical structures were within 9% between the patient and phantom, while deformation of the same dose distribution onto a secondary scan of the same patient resulted in mean differences of approximately 14%.
Conclusion
This study demonstrates the feasibility of estimating cumulative lifetime dose in re-irradiated patients through dose mapping onto standardized whole-body phantoms. This approach may support more consistent dose tracking and retrospective outcome analysis across multiple RT courses.