{
  "abstract": "Background: Very small photon fields are sensitive to both measurement conditions and radiation-source modelling, but the connection between effective primary-electron source width, downstream photon angular phase space, and field-size-dependent dosimetric response remains incompletely characterized.\n\nMethods: The study was restricted to 6 MV. Empirical measurement variability was evaluated using five ionization-chamber datasets acquired on a clinical Elekta Versa HD for fields from 20×20 to 3 × 3 cm ² . A generalized Versa HD/Agility EGSnrc/BEAMnrc model was evaluated with two prescribed stationary Gaussian source endpoints, M1 (FWHM x = FWHM y = 0.15 cm) and M2 (FWHM x = 0.35 cm, FWHM y = 0.60 cm). DOSXYZnrc dose responses and final pre-phantom photon phase-space data were analysed for 3×3, 2×2, 1×1, and 0.5×0.5 cm ² . The 3×3 cm ² field provided the experimental–Monte Carlo overlap; the smaller fields were controlled Monte Carlo endpoint-sensitivity analyses. M1 was additionally benchmarked against a 10×10 cm ² CC13 commissioning PDD.\n\nResults: Mean experimental coefficient of variation increased from 2.46% at 20×20 cm ² to 15.45% at 3×3 cm ² . The M2 central-axis reductions were 8.48%, 8.27%, 29.59%, and 56.34% for 3×3, 2×2, 1×1, and 0.5×0.5 cm ² , respectively. The corresponding M2/M1 ratios of the 95% angular-containment solid angle were 1.275, 1.498, 2.415, and 3.835. The four-field comparison demonstrates clear field-size progression in angular containment, while showing that amplification is observable-dependent rather than universally monotonic. The M1 PDD benchmark supported reference depth-dose behaviour, whereas lateral-profile findings were restricted to controlled numerical sensitivity because absolute lateral agreement was not independently established in this study alone.\n\nConclusion: The demonstrated result is a stationary endpoint-sensitivity chain linking effective primary-electron source representation, linac-head transport, photon angular phase space, and small-field dose/profile response. A reduced covariance formulation is retained only as a prospective framework for testing whether a stationary effective source can represent unresolved accelerator-source states; no time-resolved source dynamics were measured or simulated.",
  "abstract_shown": true,
  "affiliations": [
    "Department of Radiation Physics, Maadi Armed Forces Medical Compound"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 1,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Mina M. Habib"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/5v5f6fx40k6e3.bib",
  "cited_by": 0,
  "doi": "10.3389/fonc.2026.1968378",
  "fulltext_url": null,
  "id": "5v5f6fx40k6e3",
  "issns": [
    "2234-943X"
  ],
  "landing_url": "https://www.frontiersin.org/articles/10.3389/fonc.2026.1968378/full",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "3108|Advanced Radiotherapy Techniques"
    ]
  ],
  "openalex": "W7224104741",
  "pdf_url": "https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2026.1968378/pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-28",
  "publisher": "Frontiers Media SA",
  "ris": "https://research.draconitic.com/paper/5v5f6fx40k6e3.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:14Z",
      "native_id": "10.3389/fonc.2026.1968378",
      "source": "crossref",
      "url": "https://www.frontiersin.org/articles/10.3389/fonc.2026.1968378/full"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "openalex:3108|Advanced Radiotherapy Techniques",
      "subfield": "applied-instrumentation"
    }
  ],
  "title": "Toward dynamic Monte Carlo source modeling: measurement variability and primary electron source-width sensitivity in very small photon fields",
  "title_text": "Toward dynamic Monte Carlo source modeling: measurement variability and primary electron source-width sensitivity in very small photon fields",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:20:14Z",
  "url": "https://research.draconitic.com/paper/5v5f6fx40k6e3",
  "venue": "Frontiers in Oncology",
  "versions": []
}