Electron radiotherapy: a study on dosimetric uncertainty using small cutouts
Bibliographic record
Abstract
This note investigated the dosimetric uncertainties due to the positional error when centring a small cutout to the machine central beam axis (CAX) in electron radiotherapy. A group of six circular cutouts with 4 cm diameter were made with their centres shifting 0, 2, 4, 6, 8 and 10 mm from the machine CAX for the 6 x 6 cm(2) applicator. The per cent depth doses, beam profiles and output factors were measured using the 4, 9 and 16 MeV clinical electron beams produced by a Varian 21 EX linear accelerator. The 2D isodose distributions in the z-x (or cross-line) and z-y (or in-line) plane were calculated by Monte Carlo simulation using the EGSnrc system. When the cutout centre was shifted away from the machine CAX for the 4 MeV beam, the d(m), R(80) and R(90) at the machine CAX had no significant change (<0.1 mm). For higher energies of 9 and 16 MeV beams, the d(m) was reduced by 0.45 and 1.63 mm per mm, between the cutout centre and the machine CAX with off-axis shift <6 mm respectively. R(80) and R(90) were reduced by more than 0.3 mm per mm off-axis shift for both energies. The isodose coverage of the in-line axis beam profile was reduced when the cutout centre was shifted away from machine CAX. It is important for oncology staff to note such dosimetric changes in the clinical electron radiotherapy, particularly when a high energy electron beam is used for small cutout. Such positional uncertainty is unavoidable in fabricating an electron cutout in the mould room.
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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 | 0.003 | 0.010 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 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".