Analysis of dose perturbation factors of a NACP-02 ionization chamber in clinical electron beams
Bibliographic record
Abstract
For well-guarded plane-parallel ionization chambers, international dosimetry protocols recommend a value of unity for electron perturbation factors in water. However, recent data published by various groups have challenged this. Specifically for the NACP-02 chamber, non-unity electron perturbation factors have already been published by Verhaegen et al (2006 Phys. Med. Biol. 51 1221-35) and Buckley and Rogers (2006 Med. Phys. 33 1788-96). Recently it was found that the mass thickness of the front chamber window can be 35% greater than is listed in the IAEA's TRS-398 absorbed dose protocol (Chin et al 2008 Phys. Med. Biol. 53 N119-26). This study therefore recalculated NACP-02 electron perturbation correction factors for energies 4-18 MeV at depths z(ref) and R(50) to determine the effect of the chamber model change. Results showed that perturbation factors at z(ref) are fairly stable for similar chamber models but become highly sensitive to small changes at deeper depths. The results also showed some dependence on using 1 keV versus 10 keV for the transport cut-off. Additional investigations revealed that the wall perturbation factor, p(wall), is strongly influenced by the chamber back wall at z(ref) and at larger depths small changes in the positioning of the effective point of measurement cause large fluctuations in the final value. Finally, the cavity perturbation factor, p(cav), was found to be primarily influenced by electron backscatter.
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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 | 0.007 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".