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Purpose <p>Small fields are frequently used in modern radiotherapy, yet the optimal approach to enhancing small field dosimetry remains unresolved.</p> Materials and methods <p>A 30 × 30 × 30&#xa0;cm³ homogeneous density solid phantom was utilized as the treatment target for treatment planning system (TPS) calculations. Picket Fence Test deviations from expected positions were recorded to check the MLC positional accuracy. Dosimetry in field sizes of 1 × 1, 2 × 2, 3 × 3, and 4 × 4&#xa0;cm² using 6MV, 10MV, 6MV FFF, and 10MV FFF beams were measured by electronic portal image device (EPID) with the portal dose imaging prediction (PDIP) algorithm and compared to the predicted dose from modeling profiles.</p> Results <p>The largest picket fence test deviations within a 30 × 30&#xa0;cm² testing field were 2.3% for 6MV and 2.1% for 10MV. A total of 636 data calibrated by EPID with PDIP algorithm were collected. The largest difference compared to golden beam profile in PDIP measurement was 7% at 1 × 1&#xa0;cm² with 10MVFFF. Other energies showed maximum differences of 4.4%, 4.3%, and 4.8% for 6MV, 6MVFFF, and 10MV, respectively. If a 2% threshold is used, corrections are needed for fields smaller than 4 × 4&#xa0;cm², especially for 10MV 1 × 1&#xa0;cm² (mean difference 2.65%, one-sample t-test <i>p</i> = 0.012) and 3 × 3&#xa0;cm² (mean difference 3.05%, one-sample t-test <i>p</i> = 0.002) fields beyond 10&#xa0;cm off-axis from the beam center. Mean differences for fields larger than 4 × 4&#xa0;cm² were within 2%.</p> Conclusion <p>PDIP is a quick and effective quality assurance tool to check small field dosimetry. For fields smaller than 4 × 4&#xa0;cm², the mean dosimetry differences can reach up to 3.05%, necessitating cautious correction.</p>

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Improving small field beam accuracy using EPID-based portal dosimetry: a potential novel approach for quality assurance

  • 期刊论文

  • 发表日期：

    2025年1月10日

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  • Pei-Hsuan Lee,
  • Jian-Kuen Wu,
  • Yu-Jen Wang

摘要

Purpose

Small fields are frequently used in modern radiotherapy, yet the optimal approach to enhancing small field dosimetry remains unresolved.

Materials and methods

A 30 × 30 × 30 cm³ homogeneous density solid phantom was utilized as the treatment target for treatment planning system (TPS) calculations. Picket Fence Test deviations from expected positions were recorded to check the MLC positional accuracy. Dosimetry in field sizes of 1 × 1, 2 × 2, 3 × 3, and 4 × 4 cm² using 6MV, 10MV, 6MV FFF, and 10MV FFF beams were measured by electronic portal image device (EPID) with the portal dose imaging prediction (PDIP) algorithm and compared to the predicted dose from modeling profiles.

Results

The largest picket fence test deviations within a 30 × 30 cm² testing field were 2.3% for 6MV and 2.1% for 10MV. A total of 636 data calibrated by EPID with PDIP algorithm were collected. The largest difference compared to golden beam profile in PDIP measurement was 7% at 1 × 1 cm² with 10MVFFF. Other energies showed maximum differences of 4.4%, 4.3%, and 4.8% for 6MV, 6MVFFF, and 10MV, respectively. If a 2% threshold is used, corrections are needed for fields smaller than 4 × 4 cm², especially for 10MV 1 × 1 cm² (mean difference 2.65%, one-sample t-test p = 0.012) and 3 × 3 cm² (mean difference 3.05%, one-sample t-test p = 0.002) fields beyond 10 cm off-axis from the beam center. Mean differences for fields larger than 4 × 4 cm² were within 2%.

Conclusion

PDIP is a quick and effective quality assurance tool to check small field dosimetry. For fields smaller than 4 × 4 cm², the mean dosimetry differences can reach up to 3.05%, necessitating cautious correction.