KEY POINTS
- A structured workshop involving radiation oncologists, medical physicists and technologists found striking disagreement when participants applied LQ/LQL dose-equivalence methods to identical clinical scenarios. Mean inter-practitioner agreement was only 25.8% by Jaccard index, with agreement as low as 10% in head-and-neck scenarios.
- Proposed compensatory doses for the same situations ranged from 1.8 to 2.5 Gy per fraction, corresponding to approximately 15–20% differences in biological dose. The workshop was a convenience sample from one congress, with only 17–20 valid responses per item, so it should illustrate variability rather than estimate its population prevalence.
- Treatment interruptions are a particularly clear example. For a head-and-neck course of 70 Gy in 35 fractions, a seven-day prolongation reduced time-corrected EQD2 from 57.97 to 54.60 Gy, a 3.37-Gy loss attributable to the interruption itself when repopulation was explicitly modeled.
- Parameter selection alone can substantially alter the answer. In the same interrupted head-and-neck schedule, changing kick-off time from 14 to 28 days shifted EQD2 by approximately ±3.4 Gy, while varying potential doubling time from 3 to 7 days produced an EQD2 spread of almost 12 Gy.
- Reirradiation magnifies the problem. Published institutional approaches to cumulative spinal-cord dose have produced estimates ranging from 45 to 62 Gy EQD2 for identical prior histories, a 17-Gy spread that can cross from conventional tolerance into higher-risk territory.
- The authors propose minimum operational requirements: document the model and radiobiological parameters, include repopulation correction when appropriate, report LQ/LQL sensitivity for large fraction sizes, use voxel-based BED/EQD2 summation for reirradiation when feasible, and require independent physicist–radiation oncologist review.
- Their graded implementation framework estimates approximately 5 minutes per case for basic documentation, 10 minutes with dual review and 20 minutes for advanced voxel-based assessment. Importantly, the paper documents variation in calculations—not proof that this variation causes differences in tumor control or toxicity.
CLINICAL TAKEAWAY
Radiotherapy has rigorous standards for physical dose delivery, yet biological dose calculations that can influence interruption compensation, hypofractionation and reirradiation remain far less standardized. The paper makes a strong case for transparent parameters, validated tools and dual clinical/physics review, but its proposed workflow is primarily an expert operational framework rather than outcome-validated guidance.