pith. sign in

arxiv: 2509.17370 · v3 · submitted 2025-09-22 · ⚛️ physics.med-ph

Non-invasive Reversible Software-based Electron FLASH Irradiation Configuration of a Linear Accelerator in Clinical Use

Stavros Melemenidis , Dixin Chen , Cody Jensen , Joseph B. Schulz , Murat Surucu , Amy S. Yu , Edward E. Graves , Mengying Shi
show 5 more authors
Peter G. Maxim Andrew Currell Billy W. Loo Jr Lawrie Skinner M. Ramish Ashraf
This is my paper

Pith reviewed 2026-05-18 15:22 UTC · model grok-4.3

classification ⚛️ physics.med-ph
keywords ultra-high dose rateFLASH radiotherapylinear acceleratorelectron beampreclinical irradiationreversible configurationTrueBeamnon-invasive modification
0
0 comments X

The pith

A standard clinical linear accelerator can be configured for ultra-high dose rate electron irradiation using only reversible software settings.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper demonstrates a method to convert a clinical TrueBeam linac into an ultra-high dose rate electron beam source for FLASH research without any permanent hardware changes. By entering service mode, retracting the photon target, and inserting a specific scattering foil along with external monitoring, they achieve dose rates suitable for preclinical experiments. The configuration is fully reversible, allowing the machine to return to normal clinical use. This matters because it makes FLASH radiotherapy research accessible on widely available equipment, reducing the need for specialized machines.

Core claim

The authors show that setting the linac to service mode with photon-beam RF and beam current parameters, retracting the target and monitor chamber, and inserting a low-energy scattering foil produces electron beams with energies around 12 MeV and dose per pulse up to 1.5 Gy for in vivo setups. Beam profiles remain flat and symmetric, calibration across film, ACCT, and ion chamber is linear, and day-to-day output varies by less than 4%. This setup supports organ-specific irradiations and tissue culture experiments while maintaining safety and reproducibility.

What carries the argument

Non-invasive service-mode configuration with retracted photon target, inserted scattering foil, and external AC current transformer for UHDR electron delivery.

Load-bearing premise

The service mode settings with retracted target and inserted foil will reliably produce stable ultra-high dose rates and consistent beam quality without introducing unforeseen risks or instabilities.

What would settle it

Repeated measurements over multiple days showing output variation exceeding 4% or dose per pulse falling below 0.5 Gy at the intended source-to-surface distances would indicate the configuration does not meet the requirements for reliable preclinical use.

read the original abstract

Configuring clinical linear accelerators (linacs) for ultra-high dose rate (UHDR) electron experiments typically requires invasive hardware manipulation and/or irreversible manufacturer modifications, limiting broader implementation. We present an independently developed UHDR electron configuration of a clinical TrueBeam linac that allows reversible switching between preclinical UHDR and conventional (CONV) modes using only non-invasive software settings. UHDR mode was achieved via service mode software with RF and beam current settings typical of a photon beam, the photon target and monitor chamber retracted, and a clinically unused low-energy scattering foil inserted. An external AC current transformer (ACCT) for beam monitoring, anatomy-specific collimator, and sample holder were mounted on the accessory tray, with external ion chamber in solid water for exit dose monitoring. Percent depth dose (PDD) was measured for UHDR and CONV beams. Dose-per-pulse (DPP) was varied by adjusting gun voltage and quantified with radiochromic film at different source-to-surface distances (SSD). Beam profiles assessed dose uniformity and usable field size. Dose calibration was established between film, ACCT, and ion chamber, and day-to-day reproducibility was tested. PDD confirmed similar energies for UHDR (12.8MeV) and CONV (11.9MeV) beams with matching profiles through mouse thickness. Maximum DPP exceeded 0.5Gy, reaching ~1.5Gy for collimated in vivo setups and ~0.7Gy at extended SSD for tissue culture. Field flatness and symmetry were maintained, supporting organ-specific irradiations and up to 5cm fields for culture. Calibration showed strong linearity across detectors, and output variation was <4%. We demonstrated accurate, reproducible UHDR delivery on a widely available clinical linac with no invasive hardware manipulation, enabling preclinical FLASH research on a clinical treatment machine.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript describes a non-invasive, reversible software-based configuration for delivering ultra-high dose rate (UHDR) electron beams on a clinical Varian TrueBeam linear accelerator. Using service-mode RF and beam-current settings with the photon target and monitor chamber retracted and a low-energy scattering foil inserted, the authors achieve DPP values exceeding 0.5 Gy (up to ~1.5 Gy in collimated setups), report PDD curves indicating comparable beam energies to conventional mode (~12.8 MeV vs 11.9 MeV), demonstrate acceptable flatness/symmetry for preclinical fields, and show linear calibration across film, ACCT, and ion chamber with <4% day-to-day output variation. The central claim is that this enables accurate, reproducible preclinical FLASH research on a standard clinical machine without hardware modifications.

Significance. If the reported beam quality and short-term reproducibility hold under repeated use, the work would meaningfully lower barriers to preclinical FLASH studies by allowing reversible UHDR access on widely available clinical linacs. The experimental approach relies on direct measurements (PDD, profiles, multi-detector calibration) rather than simulations, which strengthens the practical utility claim.

major comments (2)
  1. [Results (day-to-day reproducibility and calibration subsections)] The central claim of 'accurate, reproducible' UHDR delivery for preclinical use rests on single-session PDD, profile, and calibration data plus <4% day-to-day output variation. No measurements of pulse-to-pulse stability, interlock behavior during repeated service-mode cycling, or beam drift after prolonged target retraction are presented; these are load-bearing for the reproducibility assertion.
  2. [Methods (beam monitoring and safety considerations)] The configuration bypasses the primary monitor chamber and relies on an external ACCT for monitoring. While exit-dose ion-chamber checks are mentioned, the manuscript does not quantify how this affects safety interlock integrity or real-time dose verification during extended preclinical sessions.
minor comments (2)
  1. [Abstract and Results] The abstract states 'matching profiles through mouse thickness' but the corresponding figure or table should explicitly overlay UHDR and CONV PDD curves with error bars for direct visual comparison.
  2. [Results] Notation for DPP values (e.g., 'exceeded 0.5 Gy' vs specific measured maxima at each SSD) should be standardized across text, tables, and figures to avoid ambiguity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their positive assessment of the significance of our work and for the detailed comments on reproducibility and safety. We address each major comment below and have made revisions to the manuscript accordingly where appropriate.

read point-by-point responses

  1. Referee: [Results (day-to-day reproducibility and calibration subsections)] The central claim of 'accurate, reproducible' UHDR delivery for preclinical use rests on single-session PDD, profile, and calibration data plus <4% day-to-day output variation. No measurements of pulse-to-pulse stability, interlock behavior during repeated service-mode cycling, or beam drift after prolonged target retraction are presented; these are load-bearing for the reproducibility assertion.

    Authors: We appreciate this observation. The reported <4% day-to-day variation was obtained from measurements performed on separate days, providing evidence of short-term reproducibility suitable for typical preclinical sessions. Although pulse-to-pulse stability, interlock behavior under cycling, and long-term drift were not specifically quantified, the strong correlation in multi-detector calibration and consistent beam characteristics across measurements support the reliability of the configuration. We will include a discussion of these limitations in the revised manuscript to provide a more balanced view. revision: partial

  2. Referee: [Methods (beam monitoring and safety considerations)] The configuration bypasses the primary monitor chamber and relies on an external ACCT for monitoring. While exit-dose ion-chamber checks are mentioned, the manuscript does not quantify how this affects safety interlock integrity or real-time dose verification during extended preclinical sessions.

    Authors: In our setup, the monitor chamber retraction is a standard procedure for high-energy electron beams in service mode, and the linac's built-in safety interlocks are not bypassed or disabled. The ACCT serves as the primary real-time beam monitor, calibrated against film and ion chamber, while the external ion chamber provides independent verification of exit dose. We acknowledge that specific quantification of interlock performance during extended sessions was not included. In the revised version, we will expand the methods section to detail the monitoring approach and safety rationale more explicitly. revision: yes

Circularity Check

0 steps flagged

No circularity: purely experimental measurements with no derivations or self-referential fittings

full rationale

The manuscript reports an experimental hardware/software configuration for UHDR electron delivery on a clinical TrueBeam linac, followed by direct measurements of PDD, DPP, beam profiles, uniformity, and day-to-day output variation using external detectors (radiochromic film, ACCT, ion chamber). No equations, fitted parameters, predictions, or uniqueness theorems appear; all claims are grounded in empirical calibration and reproducibility data against independent instruments. No self-citations form load-bearing steps, and the work is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

This is an applied engineering paper focused on practical implementation and validation through dosimetry measurements rather than introducing new theoretical constructs.

axioms (1)
  • standard math Linear accelerator beam physics principles for electron and photon modes
    The configuration relies on known behavior of linac components when target is retracted and scattering foil inserted.

pith-pipeline@v0.9.0 · 5921 in / 1213 out tokens · 65477 ms · 2026-05-18T15:22:13.596613+00:00 · methodology

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

What do these tags mean?
matches
The paper's claim is directly supported by a theorem in the formal canon.
supports
The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends
The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses
The paper appears to rely on the theorem as machinery.
contradicts
The paper's claim conflicts with a theorem or certificate in the canon.
unclear
Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

2 extracted references · 2 canonical work pages

  1. [1]

    Rapid switching of a C-series linear accelerator between conventional and ultrahigh-dose-rate research mode with beamline modifications and output stabilization

    Sloop A, Ashraf MR, Rahman M, Sunnerberg J, Dexter CA, Thompson L, et al. Rapid switching of a C-series linear accelerator between conventional and ultrahigh-dose-rate research mode with beamline modifications and output stabilization. International Journal of Radiation Oncology* Biology* Physics. 2024;119(4):1317-25

    work page 2024

  2. [2]

    Individual pulse monitoring and dose control system for pre-clinical implementation of FLASH-RT

    Ashraf MR, Rahman M, Cao X, Duval K, Williams BB, Hoopes PJ, et al. Individual pulse monitoring and dose control system for pre-clinical implementation of FLASH-RT. Physics in Medicine & Biology. 2022;67(9):095003. 12

    work page 2022