Evaluation of the dosimetric accuracy in the presence of inhomogeneities of two commercial electron planning systems
Bibliographic record
Abstract
The generally accepted level of dosimetric accuracy for the planning of radiation treatments is + 5 o/o.Presented in this thesis is an evaluation of the quality of the dosimetric predictions generated by the Focus (version 2.5 -ComputerizedMedical Systems) and Helax-TMS (version 4.1 -MDS Nordion) electron planning systems in the presence of inhomogeneities.The dosimetric accuracy in a water equivalent phantom containing cylindrical or slab-shaped inhomogeneities was investigated for nominal beam energies of 9 MeV and 18 MeV, and field sizes of 10 cm x 10 cm and 15 cm x 15 cm.Both air and aluminum inhomogeneities were investigated.A novel PMMA phantom was designed, and used experimentally to verify the accuracy of EGS4 Monte Carlo dose calculations in the presence of these inhomogeneities.The accuracy of treatment planning predictions was then established by comparison with Monte Carlo calculations.Both treatment planning systems exhibited a decrease in calculation accuracy as inhomogeneity thicknesses were increased.Distributions predicted for 15 cm x 15 cm fields were found to exhibit accuracies and trends similar to those predicted for 10 cm x l0 cm fields of the corresponding energy.Overall, neither treatment planning system was found to generate consistently accurate dose predictions beneath the inhomogeneities considered in this study.Dosimetric inaccuracies in excess of I0 %o of the normalization dose were frequently observed for both slab-shaped and cylindrical inhomogeneity geometries.The only dose distributions found to exhibit continual agreement with Monte Carlo results within the therapeutic range were the 18 MeV Focus predictions beneath air slabs (Maximum deviation <3 yo of normalization dose), and the l8 Mev Helax predictions beneath aluminum slabs (Maximum deviation < 4 yo of normalization dose).No straightforward interpretation of the restricting approximations implemented by the Focus and Helax electron dose calculation algorithms could adequately explain the observed discrepancies between prediction and theory.
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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 | 0.014 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".