SU-E-T-96: Toward Absolute Dose Measuments Using Radiochromic Film
Bibliographic record
Abstract
Purpose: To identify and quantify factors that can influence radiochromic film dose response and to determine whether they are suitable for absolute dose measurements. Methods: The effect of the film storage temperature was investigated by comparing the performance of three lots of Gafchromic EBT2 films (ISP Corp. inc.) stored either at 4°C or at room temperature. The effect of ambient humidity was determined by placing the films in a sealed container in the presence of either a bath of water or drierite desiccant. The resulting ambient humidity was above 80% or below 20% respectively. The effect of the scanning temperature was determined by mounting a custom made temperature controlled reflecting slab on top of the scanner bed. For absolute dose comparisons, the output of a Varian linac was measured using an Exradin A12 ionization chamber. Results: Storing the film at 4°C improves stability of the film over time but does not eliminate film autodevelopment. Relative humidity variations from 80% to 20% have a strong impact on the optical density (4% difference for an optical density of 0.5) and could introduce dose errors of 15%. During the scanning procedure, the film temperature influences the optical density measured (0.1% per °C for an optical density of 0.5). When controlling these parameters, the absolute dose difference between EBT2 and the A12 chamber is 3% or less over a dose range of 20–350 cGy. Conclusions: Humidity is the dominant factor that influences film dose response and must be controlled. The scanning temperature influences the optical density of the film to a lesser degree. Storing EBT2 at low temperature reduces the autodevelopment of the film, but cannot fully prevent it. When controlling for these parameters, absolute dose measurements can be performed to an uncertainty of 3%. This work has been supported by the Ministère de la Santé et des Services Sociaux and Natural Sciences and Engineering Research Council Discovery Grant No. 357402.
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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 | 0.004 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".