SU-E-T-103: Making Plane-Parallel Ionization Chambers Available for Reference Dosimetry of High-Energy Photon Beams
Bibliographic record
Abstract
Purpose: Plane-parallel ionization chambers were not included for reference dosimetry of photon beams in TG-51 because sufficient data was not available. This work aims to experimentally determine absorbed dose beam quality conversion factors, kQ, for several plane-parallel ionization chambers in clinical megavoltage photon beams to potentially enable their use for reference dosimetry of high-energy photon beams and determine if variation in kQ factors for chambers of the same type is considerable. Methods: Measurements traceable to the national standard of absorbed dose were carried out at the National Research Council of Canada with 11 different types of plane-parallel ion chamber. In most cases, two chambers of each type were obtained from the major ion chamber manufacturers. Chamber stabilization, leakage currents, ion recombination and polarity behavior, as well as chamber-to-chamber variations were investigated. Absorbed dose-to-water calibration coefficients were measured for the cobalt-60 irradiator and in 6, 10 and 25 MV photon beams from the Elekta Precise linear accelerator to obtain kQ factors.Results: All chambers investigated gave stable readings within 15 minutes in the cobalt-60 reference field. Leakage currents were negligible (< 0.05% of the chamber reading) for all chambers. Ion recombination corrections were obtained as a function of dose per pulse; the majority of chambers performed as expected. Polarity corrections were less than 0.1% for most chambers. Values of kQ for chambers of the same type differed by less than 0.4% suggesting that chamber-to-chamber variation is not a significant issue Conclusions: Although there are differences between kQ factors determined for chambers of the same type, it is generally not significant. Measurements demonstrate the ability to characterize and use plane-parallel ion chambers for reference dosimetry of MV photon beams using the TG-51 protocol. The uncertainty in calibrating a plane-parallel ion chamber is not significantly greater than for a cylindrical chamber.
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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 | 0.002 | 0.003 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| 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".