MO‐G‐BRA‐06: A Primary Standard for HDR Brachytherapy Calibrations
Bibliographic record
Abstract
Purpose: A new Canadian primary standard for high dose rate (HDR) brachytherapy calibrations has been developed, offering improved accuracy through the use of a Pb wedge to determine the scatter component ksc at each measurement position. Methods: The new HDR standard calibrates, 192,Ir brachytherapy sources in terms of air‐kerma strength (SK). An HDR brachytherapy calibration rig was manufactured and commissioned. This rig utilizes a low (0.5 m) aluminum table to which is mounted a motorized single‐axis linear stage. An afterloader feeds an, 192,Ir source vertically up through a fixed 1 m tall PMMA tube column attached to the table. A second 1 m PMMA tube column is attached to a movable carriage on the linear stage and supports a spherical graphite ionization chamber. A series of 10 measurements are made with the source‐to‐detector distance varying from 10 cm to 55 cm in 5 cm increments. The largest correction factor, ksc (scatter from the stage, walls, floor and ceiling) is determined using a Pb‐wedge technique to block the direct beam and allow a direct measurement of scatter at each distance. The small distance correction is then a simple matter to determine, allowing a more accurate determination of the source strength based on distance squared. Results: : Measurements with a Pb‐wedge technique for determining ksc demonstrated that the scatter component for each position varied, in contradiction to the constant‐scatter supposition of the alternative 7‐distance measurement calculation. These measurements were supported by EGSnrc Monte Carlo simulations. The disagreement between these two techniques for determining ksc represent an (SK) difference of approximately 0.4%. Conclusions: The new HDR brachytherapy calibration capability demonstrates higher accuracy through a more accurate scatter correction. This standard will participate in a formal international comparison for HDR brachytherapy, tentatively scheduled for 2011.
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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 | 0.006 | 0.007 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.003 | 0.003 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.004 | 0.002 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.009 | 0.006 |
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".