NCS Report 18: Code of practice for the absorbed dose determination in high energy photon and electron beams
Bibliographic record
Abstract
Absorbed dose to water is the quantity of interest to specify the amount of radiation to be used in radiotherapy and has the advantage that it can be measured more directly than the quantity air kerma.Advances in radiation dosimetry concepts and the development of primary measurement standards based on absorbed dose to water over the last decades offer the possibility to calibrate ionisation chambers directly in terms of absorbed dose to water.Absorbed dose standards have an uncertainty of less than 1% (1 sd) in photon beams up to 25 MV, resulting in improved accuracy in clinical reference dosimetry.Nowadays several international and national Codes of Practice (CoP) for external beam radiotherapy based on absorbed dose standards have been published and adopted in many countries worldwide.In this report a Code of Practice is presented for the dosimetry in high energy photon and electron beams based on absorbed dose to water standards for 60 Co reference beams.The CoP has been written by a Subcommittee of the Netherlands Commission on Radiation Dosimetry (NCS) and corresponds to the current clinical practice in Belgium and The Netherlands.The CoP provides the concepts and methods to determine the absorbed dose in high energy photon and electron beams produced by medical linear accelerators.The CoP covers the reference dosimetry in static, open photon beams with nominal energies between 1 and 25 MV and in static, open electron beams with nominal energies between 4 and 25 MeV produced by conventional linear accelerators.Treatment modalities as intensity modulated therapy (IMRT), stereotactic radiotherapy, robotic radiotherapy, helical tomotherapy, etc. are beyond the scope of this report.Important features are the simple basic concepts to determine absorbed dose to water under reference conditions in a water phantom and the introduction of a single, chamber dependent correction factor taking into account all effects dependent of the radiation beam quality.For photon beams these beam quality correction factors are based on experimental data, partly measured in selected clinical accelerator beams in Belgium and The Netherlands using a portable water calorimeter.The present CoP recommends a limited number of ionisation chambers for reference dosimetry in radiotherapy, but the physical concepts outlined in the Code represent a major simplification compared to the previous Codes based on the concept of air kerma employing Bragg-Gray or Spencer-Attix cavity theory.This CoP uses updated information compared to the codes presented in TRS-398 and AAPM TG-51.
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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 | 0.027 | 0.064 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.002 | 0.002 |
| Bibliometrics | 0.005 | 0.004 |
| Science and technology studies | 0.003 | 0.004 |
| Scholarly communication | 0.004 | 0.002 |
| Open science | 0.005 | 0.003 |
| Research integrity | 0.007 | 0.005 |
| Insufficient payload (model declined to judge) | 0.012 | 0.015 |
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".