Measured and Monte Carlo calculated <i>k</i><sub><i>Q</i></sub> factors: Accuracy and comparison
Bibliographic record
Abstract
PURPOSE: The journal Medical Physics recently published two papers that determine beam quality conversion factors, k(Q), for large sets of ion chambers. In the first paper [McEwen Med. Phys. 37, 2179-2193 (2010)], k(Q) was determined experimentally, while the second paper [Muir and Rogers Med. Phys. 37, 5939-5950 (2010)] provides k(Q) factors calculated using Monte Carlo simulations. This work investigates a variety of additional consistency checks to verify the accuracy of the k(Q) factors determined in each publication and a comparison of the two data sets. Uncertainty introduced in calculated k(Q) factors by possible variation of W/e with beam energy is investigated further. METHODS: The validity of the experimental set of k(Q) factors relies on the accuracy of the NE2571 reference chamber measurements to which k(Q) factors for all other ion chambers are correlated. The stability of NE2571 absorbed dose to water calibration coefficients is determined and comparison to other experimental k(Q) factors is analyzed. Reliability of Monte Carlo calculated k(Q) factors is assessed through comparison to other publications that provide Monte Carlo calculations of k(Q) as well as an analysis of the sleeve effect, the effect of cavity length and self-consistencies between graphite-walled Farmer-chambers. Comparison between the two data sets is given in terms of the percent difference between the k(Q) factors presented in both publications. RESULTS: Monitoring of the absorbed dose calibration coefficients for the NE2571 chambers over a period of more than 15 yrs exhibit consistency at a level better than 0.1%. Agreement of the NE2571 k(Q) factors with a quadratic fit to all other experimental data from standards labs for the same chamber is observed within 0.3%. Monte Carlo calculated k(Q) factors are in good agreement with most other Monte Carlo calculated k(Q) factors. Expected results are observed for the sleeve effect and the effect of cavity length on k(Q). The mean percent differences between experimental and Monte Carlo calculated k(Q) factors are -0.08, -0.07, and -0.23% for the Elekta 6, 10, and 25 MV nominal beam energies, respectively. An upper limit on the variation of W/e in photon beams from cobalt-60 to 25 MV is determined as 0.4% with 95% confidence. The combined uncertainty on Monte Carlo calculated k(Q) factors is reassessed and amounts to between 0.40 and 0.49% depending on the wall material of the chamber. CONCLUSIONS: Excellent agreement (mean percent difference of only 0.13% for the entire data set) between experimental and calculated k(Q) factors is observed. For some chambers, k(Q) is measured for only one chamber of each type--the level of agreement observed in this study would suggest that for those chambers the measured k(Q) values are generally representative of the chamber type.
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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 | 0.040 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| 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".