The replacement correction factors for cylindrical chambers in high-energy photon beams
Bibliographic record
Abstract
The values of the replacement correction factors (P(repl), or in the IAEA's notation p(dis)p(cav)) used for cylindrical chambers in high-energy photon beams represent one of the most significant differences between the AAPM and the IAEA dosimetry protocols. In a previous study (Wang L L W and Rogers D W O 2008 Med. Phys. 35 1747-55), we found that the AAPM protocol adopted incorrect values of P(repl) for cylindrical chambers in photon beams. For a (60)Co beam, the calculated P(repl) value is 0.5% higher than the AAPM value and about 1% higher than the IAEA value. It was still not clear why the IAEA values, which are based on measurements by Johansson et al, are incorrect. In this study, EGSnrc Monte Carlo simulation codes are used to simulate Johansson et al's experimental procedures for determining P(repl) values. The simulation results agree well with the measurements if the chamber responses versus depth are normalized at d(max) as was apparently done in the experiments as it was believed that the chambers of different radii gave the same maximum reading at the respective d(max). However, if the chamber responses are not normalized, then the simulated experimental results lead to a result which agrees well with the P(repl) values calculated by the standard Monte Carlo methods. This demonstrates that the normalization procedure used in the experiments is incorrect as is based on an incorrect assumption, and thus the interpretation of Johansson et al's experimental values as P(repl) (p(dis)) in the IAEA TRS-398 Code of Practice is wrong. The values of P(repl) for cylindrical chambers of different radii in various high-energy photon beams are calculated and an empirical formula is given.
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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 | 0.005 | 0.016 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".