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<p>Aim: To develop, validate, and clinically implement a novel forward in-vivo transit dosimetry technique using an electronic portal imaging device (EPID) for intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), and to assess its role in adaptive radiotherapy for head and neck cancers. <i>Methods</i>: The technique was validated in 40 patients (20 IMRT, 20 VMAT) and applied clinically in 100 head and neck patients treated on a Varian Halcyon linear accelerator. Transit fluence measured by EPID during treatment was compared directly with TPS-predicted exit fluence (generated at the EPID plane using simple rectangular or semicircular phantoms for heterogeneity correction) via γ-analysis (primarily 3%DD/3 mm DTA criteria). Head and neck cases were monitored for adaptive replanning based on fluence deviations and body contour changes on CBCT. Results: Mean γ-passing rates (3%/3&#xa0;mm) were 95.1 ± 1.5% (thorax), 96.5 ± 1.0% (brain), 95.3 ± 1.1% (head-and-neck), and 95.9 ± 1.4% (pelvis) for IMRT; and 96.2 ± 0.7%, 97.5 ± 1.1%, 96.7 ± 1.3%, and 97.2 ± 1.4%, respectively, for VMAT. Among 800 analyzed fluences, average γ-passing rates were 91.7 ± 2.0% (2&#xa0;mm/2%), 93.2 ± 1.8% (2&#xa0;mm/3%), 95.1 ± 1.2% (3&#xa0;mm/2%), and 98.6 ± 0.8% (3&#xa0;mm/3%). Adaptation was triggered in 15% (15/100) of patients based on transit fluence deviations and contour changes, with 11 true positives confirmed by clinicians (false-positive rate ≈5%). Conclusion: The proposed forward transit EPID dosimetry method provides a simple, accurate, and clinically feasible in-vivo verification tool for IMRT and VMAT. By integrating TPS-based heterogeneity correction at the EPID plane, it overcomes limitations of back-projection algorithms, maintains high γ-passing rates across anatomical sites, and enables real-time adaptive radiotherapy decisions in routine clinical practice.</p>

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Development of novel forward in-vivo transit dosimetry technique and its implementation on adaptive radiotherapy

  • 期刊论文

  • 发表日期：

    2026年2月19日

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  • Biplab Sarkar,
  • Anirudh Pradhan

摘要

Aim: To develop, validate, and clinically implement a novel forward in-vivo transit dosimetry technique using an electronic portal imaging device (EPID) for intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), and to assess its role in adaptive radiotherapy for head and neck cancers. Methods: The technique was validated in 40 patients (20 IMRT, 20 VMAT) and applied clinically in 100 head and neck patients treated on a Varian Halcyon linear accelerator. Transit fluence measured by EPID during treatment was compared directly with TPS-predicted exit fluence (generated at the EPID plane using simple rectangular or semicircular phantoms for heterogeneity correction) via γ-analysis (primarily 3%DD/3 mm DTA criteria). Head and neck cases were monitored for adaptive replanning based on fluence deviations and body contour changes on CBCT. Results: Mean γ-passing rates (3%/3 mm) were 95.1 ± 1.5% (thorax), 96.5 ± 1.0% (brain), 95.3 ± 1.1% (head-and-neck), and 95.9 ± 1.4% (pelvis) for IMRT; and 96.2 ± 0.7%, 97.5 ± 1.1%, 96.7 ± 1.3%, and 97.2 ± 1.4%, respectively, for VMAT. Among 800 analyzed fluences, average γ-passing rates were 91.7 ± 2.0% (2 mm/2%), 93.2 ± 1.8% (2 mm/3%), 95.1 ± 1.2% (3 mm/2%), and 98.6 ± 0.8% (3 mm/3%). Adaptation was triggered in 15% (15/100) of patients based on transit fluence deviations and contour changes, with 11 true positives confirmed by clinicians (false-positive rate ≈5%). Conclusion: The proposed forward transit EPID dosimetry method provides a simple, accurate, and clinically feasible in-vivo verification tool for IMRT and VMAT. By integrating TPS-based heterogeneity correction at the EPID plane, it overcomes limitations of back-projection algorithms, maintains high γ-passing rates across anatomical sites, and enables real-time adaptive radiotherapy decisions in routine clinical practice.