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Background <p>We evaluated whether 16-bit CT reconstruction with explicit CT-to-electron-density (CT-to-ED) calibration improves dose-calculation accuracy versus conventional 12-bit reconstruction in the presence of metallic implants, and whether geometric metrics can identify cases that benefit most.</p> Methods <p>CT-to-ED tables were built for both bit depths. In Solid Water, dose profiles and absolute dose were compared against EBT4 film and TG-51 ion-chamber measurements. Eight clinical IMRT plans were optimized and cross-recalculated between bit-depth domains with segments and monitor units fixed. A beam–metal interaction metric, η<sub>metal</sub> (monitor-unit–weighted beam’s-eye-view overlap), and the volumetric overlap ratio (VOR) between metal and PTV were computed. Gamma passing rate (GPR, 3&#xa0;mm/3%), mean gamma, profile error, and absolute-dose deviation were evaluated.</p> Results <p>In the phantom, 16-bit improved agreement over 12-bit, yielding higher GPR, profile differences ≤ 2%, and absolute-dose errors ≤ 1.0%; 12-bit showed profile errors up to 5.4% (stainless steel) and 3.0% (titanium) and absolute-dose errors of 2.3% and 1.7%. In patients, η<sub>metal</sub> &gt; 35% was associated with GPR &lt; 90% when 12-bit plans were recalculated on 16-bit, whereas low η<sub>metal</sub> maintained ≥ 90%. η<sub>metal</sub> correlated positively with VOR and negatively with GPR, supporting pre-treatment triage via VOR.</p> Conclusions <p>Extended-bit reconstruction mitigates HU saturation, improves RED assignment, and yields better agreement with measurements and calculation. These findings support adopting 16-bit CT with CT-to-ED calibration as the default for planning and verification in patients with metallic implants, with VOR or η<sub>metal</sub> flagging cases where benefit is greatest.</p>

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Dose calculation accuracy with extended CT scales near metal: phantom–patient evaluation using a beam–metal overlap metric

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月17日

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  • Minsoo Chun,
  • Hosik Kim,
  • Jaewon Hong,
  • Jin Hwa Choi,
  • Seungwan Lee,
  • Inbum Lee,
  • Jung-in Kim,
  • Seonghee Kang

摘要

Background

We evaluated whether 16-bit CT reconstruction with explicit CT-to-electron-density (CT-to-ED) calibration improves dose-calculation accuracy versus conventional 12-bit reconstruction in the presence of metallic implants, and whether geometric metrics can identify cases that benefit most.

Methods

CT-to-ED tables were built for both bit depths. In Solid Water, dose profiles and absolute dose were compared against EBT4 film and TG-51 ion-chamber measurements. Eight clinical IMRT plans were optimized and cross-recalculated between bit-depth domains with segments and monitor units fixed. A beam–metal interaction metric, ηmetal (monitor-unit–weighted beam’s-eye-view overlap), and the volumetric overlap ratio (VOR) between metal and PTV were computed. Gamma passing rate (GPR, 3 mm/3%), mean gamma, profile error, and absolute-dose deviation were evaluated.

Results

In the phantom, 16-bit improved agreement over 12-bit, yielding higher GPR, profile differences ≤ 2%, and absolute-dose errors ≤ 1.0%; 12-bit showed profile errors up to 5.4% (stainless steel) and 3.0% (titanium) and absolute-dose errors of 2.3% and 1.7%. In patients, ηmetal > 35% was associated with GPR < 90% when 12-bit plans were recalculated on 16-bit, whereas low ηmetal maintained ≥ 90%. ηmetal correlated positively with VOR and negatively with GPR, supporting pre-treatment triage via VOR.

Conclusions

Extended-bit reconstruction mitigates HU saturation, improves RED assignment, and yields better agreement with measurements and calculation. These findings support adopting 16-bit CT with CT-to-ED calibration as the default for planning and verification in patients with metallic implants, with VOR or ηmetal flagging cases where benefit is greatest.