{
  "abstract": "Applicator-specific phase space (PHSP) files recorded at the aperture exit reduce Monte Carlo dose calculation time by 30-50% for electron FLASH radiotherapy. However, positioning PHSP scoring planes coincident with the applicator-air interface introduces boundary sampling artifacts. This study characterizes these artifacts in Geant4-based simulations and demonstrates their mitigation. PHSP files were generated using GAMOS 6.2.0 for a 9 MeV Mobetron UHDR model across twelve clinical aperture configurations (2.5-10 cm diameter). Three scoring plane positions were evaluated relative to the physical aperture exit: coincident with the interface, 0.1 mm downstream, and 1 mm downstream. Scoring at the exact interface produced proximal R50 shifts of up to 2.2 mm and Distance-to-Agreement (DTA) values of 4-6 mm, exceeding clinical acceptance criteria. Artifact severity scaled inversely with aperture diameter, with the smallest configurations most severely affected. A 0.1 mm offset partially restored the primary electron energy spectrum but failed to recover the bremsstrahlung tail. A 1 mm offset fully resolved all artifacts, achieving mean DTA values within 2.0 mm, equivalent to or better than linac-exit references. These artifacts arise from the degenerate behavior of the fUseSafety step-limitation algorithm when safety equals zero at exact material boundaries, producing incomplete secondary electron equilibration and suppressed bremsstrahlung production. Angular distribution analysis revealed a near-forward particle pileup in the 0 mm PHSP and a deficit of large-angle secondaries recovered by the 1 mm offset. A 1 mm downstream offset fully mitigates these artifacts while introducing negligible perturbation to primary beam characteristics. This requirement applies to any Geant4-based framework (including TOPAS and GATE) scoring PHSP files at material exit surfaces.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2605.02605",
  "author_total": 5,
  "authors": [
    {
      "name": "Rafael Carballeira"
    },
    {
      "name": "Rongxiao Zhang"
    },
    {
      "name": "Kevin J. Willy"
    },
    {
      "name": "Hayley Cash"
    },
    {
      "name": "David J. Gladstone"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/31ttxg1zhae1g.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2605.02605",
  "fulltext_url": null,
  "id": "31ttxg1zhae1g",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2605.02605",
  "language": null,
  "licence": "CC-BY-NC-ND-4.0",
  "licence_label": "CC BY-NC-ND 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.med-ph"
    ],
    [
      "openalex",
      "3108|Advanced Radiotherapy Techniques"
    ]
  ],
  "openalex": "W7160272505",
  "pdf_url": "https://arxiv.org/pdf/2605.02605",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-24",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/31ttxg1zhae1g.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:24:11Z",
      "native_id": "2605.02605",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2605.02605"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:physics.med-ph",
      "subfield": "biological-medical"
    }
  ],
  "title": "Characterization and Mitigation of Boundary Sampling Artifacts in Electron Phase Space Generation for Clinical FLASH-RT Deployment",
  "title_text": "Characterization and Mitigation of Boundary Sampling Artifacts in Electron Phase Space Generation for Clinical FLASH-RT Deployment",
  "type": "preprint",
  "updated_at": "2026-10-30T12:24:11Z",
  "url": "https://research.draconitic.com/paper/31ttxg1zhae1g",
  "venue": "arXiv",
  "versions": []
}