SU‐E‐T‐314: Challenges in Radiochromic Film Dosimetry Applied to Microbeam Radiation Therapy (MRT)
Bibliographic record
Abstract
Purpose: Uncertainties in radiochromic film dosimetry applied to microbeam radiation therapy (MRT) dosimetry at the Canadian Light Source (CLS) are investigated. A dose‐dependent change in film response as a function of microbeam width is characterized and its impact on peak‐to‐valley dose ratios (PVDRs) evaluated. Variation across the MRT collimator and inhomogeneity in film construction are also studied. Methods: Gafchromic® EBT2 film was used to measure doses from a filtered synchrotron source on the surface of solid water for microbeams ranging from 10 micrometers to 1 mm and doses between 0.4 – 74 Gy. The microbeams were generated using a variable slit or a MRT collimator (50 micrometer slits, 400 micrometer spacing). The film was scanned with an Epson Perfection V700 Photo digital scanner (4800 dpi). Corresponding Monte Carlo (PENELOPE) simulations were performed.Results: A dose‐dependent reduction in film response with decreasing microbeam width was observed. The measured ratio of dose for a 50 micrometer slit beam relative to a 1 mm beam ranged from 0.15 and 0.56, decreasing as the dose is increased. A corresponding simulation predicts a ratio of 0.91. Depending on dose, measured PVDRs ranged from 7 to 64. Variability in measured doses between different slits of the MRT collimator is also problematic, with deviations from the average of up to 26% in the microbeam path, and over 70% between two microbeams. Inherent inhomogeneity in optical density of the unexposed EBT2 film may also result in uncertainties of approximately 0.15 Gy. Conclusions: Although the high resolution of radiochromic film makes it a potentially attractive two‐dimensional dosimeter for MRT, large uncertainties arise from variations in dose‐response as a function of microbeam size, and spatial inhomogeneity of the response. These problems must be addressed before film can be considered for accurate measurement of absolute doses, and even relative metrics.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.010 | 0.010 |
| Meta-epidemiology (narrow) | 0.000 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".