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Purpose <p>To develop a novel methodology for planning target volume (PTV) margin determination by analysing minimum coverage probabilities of virtual clinical target volumes (CTV) with reduced-margins, using accumulated doses in an offline adaptive radiotherapy (ART) framework.</p> Materials and methods <p>Treatment plans from 11 brain tumour patients with varying histologies, geometries, and volumes were analysed. Virtual CTVs (CTV-v0 to CTV-v3) were generated by isotropically contracting the clinical PTV (PTV-c) by 0–3&#xa0;mm in 1&#xa0;mm increments, with corresponding virtual PTVs assigned equal margins. For each treatment fraction, dose distributions were recalculated on setup-corrected daily megavoltage CT (MVCT) images using the clinically approved sinogram. A total of 303 fractions were assessed using two coverage thresholds: V98% ≥ 98% and V95% ≥ 99%.</p> Results <p>A 1&#xa0;mm margin achieved V98% ≥ 98% in 81.8% of patients. Margins of 2&#xa0;mm and 3&#xa0;mm met this criterion in 90.1% and 94.06% of fractions, respectively. Using the V95% ≥ 99% criterion, all patients met the threshold with a 0&#xa0;mm margin, though only 85.48% of fractions achieved this level, indicating reduced consistency. Margins of 1–3&#xa0;mm consistently met this threshold in over 97% of fractions. Maximum differences between planned and accumulated doses were &lt; 3% for V98%, &lt; 0.5% for V95%. Margin reductions of 1–3&#xa0;mm significantly (<i>p</i> &lt; 0.001) decreased the volume of normal brain receiving the prescription dose by 8.27%, 16.19%, and 23.68%, respectively.</p> Conclusion <p>This approach enables patient- and site-specific PTV margin adaptation in ART, improving normal tissue sparing without compromising target coverage.</p>

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Assessing the optimal safety margin using adaptive radiotherapy framework

  • 期刊论文

  • 发表日期：

    2026年3月4日

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  • Aishwarya G.,
  • Dayananda Shamurailatpam Sharma,
  • Arjunan Manikandan,
  • Ganapathy Krishnan,
  • Rajesh S.,
  • Uday Krishna,
  • Rakesh Jalali

摘要

Purpose

To develop a novel methodology for planning target volume (PTV) margin determination by analysing minimum coverage probabilities of virtual clinical target volumes (CTV) with reduced-margins, using accumulated doses in an offline adaptive radiotherapy (ART) framework.

Materials and methods

Treatment plans from 11 brain tumour patients with varying histologies, geometries, and volumes were analysed. Virtual CTVs (CTV-v0 to CTV-v3) were generated by isotropically contracting the clinical PTV (PTV-c) by 0–3 mm in 1 mm increments, with corresponding virtual PTVs assigned equal margins. For each treatment fraction, dose distributions were recalculated on setup-corrected daily megavoltage CT (MVCT) images using the clinically approved sinogram. A total of 303 fractions were assessed using two coverage thresholds: V98% ≥ 98% and V95% ≥ 99%.

Results

A 1 mm margin achieved V98% ≥ 98% in 81.8% of patients. Margins of 2 mm and 3 mm met this criterion in 90.1% and 94.06% of fractions, respectively. Using the V95% ≥ 99% criterion, all patients met the threshold with a 0 mm margin, though only 85.48% of fractions achieved this level, indicating reduced consistency. Margins of 1–3 mm consistently met this threshold in over 97% of fractions. Maximum differences between planned and accumulated doses were < 3% for V98%, < 0.5% for V95%. Margin reductions of 1–3 mm significantly (p < 0.001) decreased the volume of normal brain receiving the prescription dose by 8.27%, 16.19%, and 23.68%, respectively.

Conclusion

This approach enables patient- and site-specific PTV margin adaptation in ART, improving normal tissue sparing without compromising target coverage.