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Background <p>Dose variation due to changes in bowel air poses significant challenges for carbon radiotherapy in pancreatic cancer. This retrospective study evaluated a&#xa0;density-override optimization technique to mitigate dosimetric uncertainties caused by bowel air changes.</p> Materials and methods <p>Planning CT and cone-beam CT data from 8&#xa0;patients with locally advanced pancreatic cancer undergoing stereotactic ablative radiotherapy were analyzed. Treatment simulations used a&#xa0;dose of 55.2&#xa0;GyE in 12&#xa0;fractions with a&#xa0;four-field setup (anterior, lateral, posterior, posterior oblique). Four density-override patterns were compared: pattern&#xa0;0 (no override), pattern&#xa0;1 (replacing bowel gas with water), pattern&#xa0;2 (replacing the entire bowel with mean bowel HU), and pattern&#xa0;3 (replacing bowel gas with mean bowel HU). Dose evaluations included fraction-wise and accumulated dose analyses, focusing on target coverage, homogeneity index, and organs at risk doses.</p> Results <p>Pattern&#xa0;2 achieved the largest clinical tumor volume coverage and the fewest fractions with &gt; 5% coverage loss for the anterior beam, followed by pattern&#xa0;3. However, pattern&#xa0;2 demonstrated poorer homogeneity for the lateral beam compared to patterns&#xa0;1 and&#xa0;3 and a&#xa0;higher gastrointestinal (GI) dose for the anterior beam.</p> Conclusion <p>This study evaluated the importance of density overrides to address bowel air variations. For patients where a&#xa0;more uniform dose is desirable or whose tumor is adjacent to the GI tract, a&#xa0;pattern&#xa0;3 density-override should be considered.</p>

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Carbon ion radiotherapy optimization techniques for pancreatic cancer: accounting for the effect of bowel gas variation

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年8月21日

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  • Chaebeom Sheen,
  • Sunghyun Lee,
  • Bitbyeol Kim,
  • Jaeman Son,
  • Kyungsu Kim,
  • Hyeongmin Jin

摘要

Background

Dose variation due to changes in bowel air poses significant challenges for carbon radiotherapy in pancreatic cancer. This retrospective study evaluated a density-override optimization technique to mitigate dosimetric uncertainties caused by bowel air changes.

Materials and methods

Planning CT and cone-beam CT data from 8 patients with locally advanced pancreatic cancer undergoing stereotactic ablative radiotherapy were analyzed. Treatment simulations used a dose of 55.2 GyE in 12 fractions with a four-field setup (anterior, lateral, posterior, posterior oblique). Four density-override patterns were compared: pattern 0 (no override), pattern 1 (replacing bowel gas with water), pattern 2 (replacing the entire bowel with mean bowel HU), and pattern 3 (replacing bowel gas with mean bowel HU). Dose evaluations included fraction-wise and accumulated dose analyses, focusing on target coverage, homogeneity index, and organs at risk doses.

Results

Pattern 2 achieved the largest clinical tumor volume coverage and the fewest fractions with > 5% coverage loss for the anterior beam, followed by pattern 3. However, pattern 2 demonstrated poorer homogeneity for the lateral beam compared to patterns 1 and 3 and a higher gastrointestinal (GI) dose for the anterior beam.

Conclusion

This study evaluated the importance of density overrides to address bowel air variations. For patients where a more uniform dose is desirable or whose tumor is adjacent to the GI tract, a pattern 3 density-override should be considered.