199: Cone Beam Computer Tomography (CBCT) Verification of Stereotactic Body Radiotherapy (SBRT): A Prospective Analysis on the Concordance Between Radiation Therapists and Radiation Oncologists
Bibliographic record
Abstract
Purpose: Image-guidance to ensure correct patient set-up prior to treatment delivery is of utmost importance in SBRT.Many studies have demonstrated high levels of concordance between radiation therapists (RTs) and radiation oncologists (ROs) on daily verification based on electronic portal imaging and simulator films.There is limited data, however, on the concordance between RTs and ROs using CBCT pre-treatment images prior to SBRT.The primary objective of this study is to evaluate the level of concordance between RTs and ROs on CBCT pre-treatment verification images for SBRT.Methods and Materials: Twenty-one consecutively treated SBRT patients at a provincial institution were included in the study.CBCT was performed by both RO and RTs prior to delivery of each fraction for abdominal and bone SBRT treatments, and prior to first fraction for lung SBRT.RTs performed subsequent daily matches for lung SBRT.Initial CBCT match was performed by RTs as per centre guidelines or by previously specified instructions.ROs performed second match prior to SBRT delivery.Directional differences between RT and RO match were recorded and analyzed.Intraclass correlation coefficients were calculated to determine variability between RT and RO match, with values approaching 1 suggesting high concordance.Results: Thirty-six CBCT images were analyzed.Thirteen were lung, 20 abdominal (five liver, 15 pancreas) and three were bone SBRT cases.RO made adjustments to initial RT match in 12 (33%) of CBCT matches, with six matches having a direction shift of 0.1 to < 0.2 cm in any direction, and two matches with a directional shift of ≥ 0.2 cm.Mean maximum match difference was 0.12 cm (range: 0.02, 0.31 cm).Treatments requiring adjustment to the initial RT match did not differ by treatment site.Review of the two plans with match difference of ≥ 0.2 cm revealed no appreciable change in GTV coverage and with dose to organs at risk still within accepted constraints.Intraclass correlation coefficients for all CBCT matches were 0.998 (95% CI: 0.996-0.999),0.997 (95% CI: 0.995-0.999),0.996 (95% CI: 0.992-0.998) in the x, y, and z directions respectively.Intraclass correlation coefficients for CBCT matches that required adjustment by RO were similar at 0.995 (95%CI: 0.982-0.9980.982-0.998),0.995 (95% CI: 0.984-0.9990.984-0.999),0.989 (95% CI: 0.962-0.997) in the x, y, and z directions respectively.Conclusions: CBCT match for SBRT at our center shows high concordance between RTs and ROs.These findings support potential expansion of RT scope of practice at our institution to include independent CBCT matches for SBRT.
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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 | 0.011 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
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".