Reirradiation Special Medical Physics Consultations: Lessons Learned From Nearly 3000 Courses of Treatment

Reirradiation (reRT) has become increasingly prevalent due to an aging population and advancements in cancer detection and treatment. However, the field is still lacking standardized dosimetric evaluation methods and reRT workflows, which leads to difficulty in correlating clinical outcomes with delivered dose. This study reports on the implementation and evolution of a standardized reRT workflow in the Department of Radiation Oncology at University of Michigan, describing insights gained from nearly 3000 external beam reirradiation courses delivered since 2017.

A systematic workflow for reRT special medical physics consultations (SMPCs) was established in 2017. Patient SMPC records from the past 7 years were reviewed, with an additional more in-depth review of the past 1 year, to report on course characteristics including treatment sites, where prior treatment was delivered (in-house vs an outside institution), whether institutional dose limits were met and the associate reasoning, time intervals between RT, the type of dose summation method used (rigid image registration-based vs point dose-based), as well as the evolution of this workflow.

Of the 2929 SMPCs conducted from 2017 to mid-2024, the most common treatment sites for reRT were the pelvis, brain, and thorax. About a third of patients had prior treatments at outside institutions. Of the 427 courses treated in the past year, institutional reirradiation dose limits were met in 82.2%. Rigid image registration was most successful for calculating composite dose in the brain (93.8% of cases) and least successful in the abdomen and pelvis (53.1% and 51.2%, respectively), and most reRT cases (80.3%) had a single prior course of treatment. Several updates were made to our institutional reRT dosimetric evaluation template, including increasing some time-dependent tissue recovery factors, adding and removing some OARs, and adding new point-based and volumetric dose objectives.

On the basis of our 7 years of experience with nearly 3,000 courses of reRT, we highlight the critical need for standardized reirradiation workflows, improved tools for cumulative dose assessment, and standardized reporting. These efforts will facilitate cross-institutional data sharing to enhance data-driven clinical decision-making and improve patient outcomes in reRT. As the prevalence of reRT rises, these efforts are vital for advancing safe and effective cancer care.