Cherenkov emission‐based external radiotherapy dosimetry: I. Formalism and feasibility
Bibliographic record
Abstract
Purpose Cherenkov emission (CE)‐based external beam dosimetry is envisioned to involve the detection of CE directly in water with placement of a high‐resolution detector out of the field, avoiding perturbations encountered with traditional dosimeters. In this work, we lay out the groundwork for its implementation in the clinic and motivate CE‐based dosimeter design efforts. To that end, we examine a formalism for broad‐beam in‐water CE‐based dosimetry of external radiotherapy beams, design and test a Monte Carlo (MC) simulation framework for the calculation of CE‐to‐dose conversion factors used by the formalism, and demonstrate the experimental feasibility of this method. Methods The formalism is conceptually analogous to ionization‐based dosimetry and employs CE‐to‐dose conversion factors, , including only and all CE generated within polar angles θ ± δ θ on beam axis. The EGSnrc user code SPRRZnrc is modified to calculate , as well as CE spectral and angular distributions. The modified code is tested with monoenergetic parallel electrons on a thin water slab. Detector configurations are examined for broad 6–22 MeV electron beams from a BEAMnrc TrueBeam model, with a focus on (4π detection), , and ( is the CE angle of relativistic electrons in water). We perform a relative experimental validation at with electron beams, using a simple detector design with spherical optics and geometrical optics approximation of the sensitive volume, which spans the water tank. Due to transient charged particle equilibrium, broad photon beams are generally less sensitive to beam quality, depth, and angle. Results For 0.1–50 MeV electrons on a thin water slab, the code outputs CE photon spectral density per unit mass (calculated from dose and ) and angle in agreement with theory within ±0.03% and , respectively, corresponding to the output precision. The configuration was found impractical due to detection considerations. Detection at for small δ θ exhibited beam quality dependence of the same order as well as strong superficial depth dependence. A 4π configuration ameliorates these effects. A more practical approach may employ a large numerical aperture. In comparing with literature, we find that these effects are less pronounced for broad photon beams in water, as expected. Measured relative at small δ θ were within 1% of simulated factors (relative to their local average) for percent‐depth CE (PDC) >50%. At other depths, deviations were in accordance with signal‐to‐noise, known detector limitations, and approximations. It was found that the CE spectrum is beam quality and depth invariant, while for electron beams the CE angular distribution is strongly dependent on beam quality and depth. However, the uncertainty of CE and PDC measurement at detection for small δ θ due to deviations around δ θ was shown to be ≤1% and <0.1% ( k = 1), respectively. The robustness to expected detector setup variations was found to result in ≤1% ( k = 1) local uncertainty contribution for PDC >50%. Conclusions Based on our MC and experimental studies, we conclude that the CE‐based method is promising for high‐resolution, perturbation‐free, three‐dimensional dosimetry in water, with specific applications contingent on comprehensive detector development and characterization.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 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 teacher head, 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".