TU‐E‐224A‐05: Intermediate Energy X‐Ray Photons (0.2 – 1.0 MeV) for Radiosurgery: Producing a Beam and Measurement of Radiological Penumbra
Bibliographic record
Abstract
Purpose: The main advantage of stereotactic radiosurgery is the steep dose gradient associated with the intracranial dose distribution. We are examining the effects of x‐ray energy on penumbra and dose gradient. Specifically, we are exploring the reduction in radiological penumbra for intermediate energy x‐ray photons (0.2–1.0 MeV) or so called IEP's. The purpose of this work is two‐fold: 1.) to produce an IEP beam using a medical linear accelerator and 2.) to examine the radiological penumbra associated with this beam. Method and Materials: A Siemens medical linear accelerator was adapted to produce IEP's. PDD measurements versus depth (SSD=100cm,FS=2×2cm2) were done in solid water using a Markus parallel plate ionization chamber (PTW Freiburg). These were compared with Monte Carlo computer simulations (MCNP‐4C). Monte Carlo involved generating x‐ray spectra that impinged upon a SW phantom. A penumbra measurement device (consisting of a half‐beam block) was constructed to examine radiation beam edge profiles using film (Gafchromic EBT) at SSD=100cm,FS=1.1cm2 and depth=2cm. In a separate experiment, film irradiations were done collimating a 3×3mm2 beam using a 10cm thick brass block flush with the SW surface. In all cases, the geometric penumbra (due to the finite source size) was made negligible by having the collimation very close to the phantom. A high‐resolution digital microscope (Axiomat) was used to acquire film profiles. Results: Measured PDD values were 55.4%(surface), 62.6%(5cm), and 34.7%(10cm). Monte Carlo PDD's compared with measurement suggest a nominal 800kV x‐ray beam. For the half‐beam block, the 80%–20% film edge profiles were 0.345mm (IEP) and 2.10mm (6MV). For the 3×3mm2 field, there was a 5‐fold reduction in radiological penumbra (IEP vs. 6MV). Conclusions: A novel intermediate energy photon beam (of nominal energy 800kV) has been produced using a conventional linear accelerator. There is a substantial reduction in radiological penumbra when using IEP's with small fields.
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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 | 0.001 | 0.001 |
| 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 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.007 | 0.001 |
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".