{"title":"The LET enhancement of energy-specific collimation in pencil beam scanning proton therapy.","authors":"Blake R Smith, Daniel E Hyer","doi":"10.1002/acm2.14477","DOIUrl":null,"url":null,"abstract":"<p><strong>Purpose: </strong>To computationally characterize the LET distribution during dynamic collimation in PBS and quantify its impact on the resultant dose distribution.</p><p><strong>Methods: </strong>Monte Carlo simulations using Geant4 were used to model the production of low-energy proton scatter produced in the collimating components of a novel PBS collimator. Custom spectral tallies were created to quantify the energy, track- and dose-averaged LET resulting from individual beamlet and composite fields simulated from a model of the IBA dedicated nozzle system. The composite dose distributions were optimized to achieve a uniform physical dose coverage of a cubical and pyramidal target, and the resulting dose-average LET distributions were calculated for uncollimated and collimated PBS deliveries and used to generate RBE-weighted dose distributions.</p><p><strong>Results: </strong>For collimated beamlets, the scattered proton energy fluence is strongly dependent on collimator position relative to the central axis of the beamlet. When delivering a uniform profile, the distribution of dose-average LET was nearly identical within the target and increased between 1 and <math> <semantics><mrow><mn>2</mn> <mspace></mspace> <mi>keV</mi> <mo>/</mo> <mi>μ</mi> <mi>m</mi></mrow> <annotation>$2 \\,{\\rm keV}/\\mathrm{\\umu }\\mathrm{m}$</annotation></semantics> </math> within 10 mm surrounding the target. Dynamic collimation resulted in larger dose-average LET changes: increasing the dose-average LET between 1 and <math> <semantics><mrow><mn>3</mn> <mspace></mspace> <mi>keV</mi> <mo>/</mo> <mi>μ</mi> <mi>m</mi></mrow> <annotation>$3 \\,{\\rm keV}/\\mathrm{\\umu }\\mathrm{m}$</annotation></semantics> </math> within 10 mm of a pyramidal target while reducing the dose-average LET outside this margin by as much as <math> <semantics><mrow><mn>10</mn> <mspace></mspace> <mi>keV</mi> <mo>/</mo> <mi>μ</mi> <mi>m</mi></mrow> <annotation>$10 \\,{\\rm keV}/\\mathrm{\\umu }\\mathrm{m}$</annotation></semantics> </math> . Biological dose distributions are improved with energy-specific collimation in reducing the lateral penumbra.</p><p><strong>Conclusion: </strong>The presence of energy-specific collimation in PBS can lead to dose-average LET changes relative to an uncollimated delivery. In some clinical situations, the placement and application of energy-specific collimation may require additional planning considerations based on its reduction to the lateral penumbra and increase in high-dose conformity. Future applications may embody these unique dosimetric characteristics to redirect high-LET portions of a collimated proton beamlet from healthy tissues while enhancing the dose-average LET distribution within target.</p>","PeriodicalId":14989,"journal":{"name":"Journal of Applied Clinical Medical Physics","volume":" ","pages":"e14477"},"PeriodicalIF":2.0000,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of Applied Clinical Medical Physics","FirstCategoryId":"3","ListUrlMain":"https://doi.org/10.1002/acm2.14477","RegionNum":4,"RegionCategory":"医学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING","Score":null,"Total":0}
引用次数: 0
Abstract
Purpose: To computationally characterize the LET distribution during dynamic collimation in PBS and quantify its impact on the resultant dose distribution.
Methods: Monte Carlo simulations using Geant4 were used to model the production of low-energy proton scatter produced in the collimating components of a novel PBS collimator. Custom spectral tallies were created to quantify the energy, track- and dose-averaged LET resulting from individual beamlet and composite fields simulated from a model of the IBA dedicated nozzle system. The composite dose distributions were optimized to achieve a uniform physical dose coverage of a cubical and pyramidal target, and the resulting dose-average LET distributions were calculated for uncollimated and collimated PBS deliveries and used to generate RBE-weighted dose distributions.
Results: For collimated beamlets, the scattered proton energy fluence is strongly dependent on collimator position relative to the central axis of the beamlet. When delivering a uniform profile, the distribution of dose-average LET was nearly identical within the target and increased between 1 and within 10 mm surrounding the target. Dynamic collimation resulted in larger dose-average LET changes: increasing the dose-average LET between 1 and within 10 mm of a pyramidal target while reducing the dose-average LET outside this margin by as much as . Biological dose distributions are improved with energy-specific collimation in reducing the lateral penumbra.
Conclusion: The presence of energy-specific collimation in PBS can lead to dose-average LET changes relative to an uncollimated delivery. In some clinical situations, the placement and application of energy-specific collimation may require additional planning considerations based on its reduction to the lateral penumbra and increase in high-dose conformity. Future applications may embody these unique dosimetric characteristics to redirect high-LET portions of a collimated proton beamlet from healthy tissues while enhancing the dose-average LET distribution within target.
期刊介绍:
Journal of Applied Clinical Medical Physics is an international Open Access publication dedicated to clinical medical physics. JACMP welcomes original contributions dealing with all aspects of medical physics from scientists working in the clinical medical physics around the world. JACMP accepts only online submission.
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