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technical-relevance Reirradiation Protons

Structured cumulative-dose review triggered replanning in one-quarter of proton reirradiation cases

Voxel-wise cumulative EQD2 review prompted reoptimization in 25.5% of proton reirradiation courses and exposed frequent registration problems.

RadOncToday · ·1 min read

KEY POINTS

  • Emory implemented a dedicated special medical physics consultation for proton reirradiation using deformable image registration and voxel-wise EQD2 accumulation with organ-specific α/β values. After center-wide rollout, complete cumulative-dose analyses were performed for 192 reirradiation courses.
  • The cohort reflected broad proton reirradiation practice: approximately 21% thoracic, 20% brain/craniospinal, 19% head and neck and 19% pelvic treatments. About 26% used hyper- or hypofractionation, making biological rather than simple physical-dose summation particularly relevant.
  • Median interval from the most recent prior RT course was 33 months, although 20.5% of retreatments occurred within one year. Across evaluated organs, only approximately 75% met institutional cumulative EQD2 goals, highlighting how frequently retreatment operates near or beyond conventional normal-tissue benchmarks.
  • Image registration proved to be a major weak point. Of 249 registration evaluations, only 153 (61.4%) were initially considered acceptable for clinical use; 92 were flagged for problems, commonly major anatomical changes or different treatment positioning. Physics follow-up addressed 66 of 96 identified or presumed issues (68.7%) through correction, mitigation or explicit uncertainty warnings.
  • The consultation changed actual planning: 49/192 cases (25.5%) underwent reoptimization, and 13 (6.8%) required more than one repeat optimization. Reoptimization was particularly frequent for abdominal/liver (45.5%) and thoracic/breast (32.6%) cases and least frequent for brain/CSI at approximately 16%.
  • Certain organs disproportionately triggered replanning. Cases involving the carotid artery were reoptimized in 48% and those involving the duodenum in 43%. Prior irradiation contributed about 51% of maximum cumulative EQD2 overall, increasing to approximately 75% for cauda equina, 65% for spinal cord and 61% for brainstem.
  • The workflow carries substantial operational cost. Prior-treatment documentation typically required 20–40 minutes, preplanning physics review another 20–40 minutes, and post-plan consultation 30–60 minutes; obtaining external DICOM data could take from 30 minutes to a week. Registration uncertainty remained qualitative rather than quantitatively propagated into accumulated dose.

CLINICAL TAKEAWAY

A quarter of proton reirradiation plans changed after systematic cumulative-dose review, supporting voxel-wise EQD2 assessment as more than documentation alone. The study also shows that registration quality may be one of the largest hidden uncertainties in reirradiation, and centers adopting such workflows need both robust DIR review and substantial physics resources.

SOURCE

International Journal of Radiation Oncology, Biology, Physics