Evaluation of patient DVH-based QA metrics for prostate VMAT: Correlation between accuracy of estimated 3D patient dose and magnitude of MLC misalignment

Noriyuki Kadoya, Masahide Saito, Makoto Ogasawara, Yukio Fujita, Kengo Ito, Kiyokazu Sato, Kazuma Kishi, Suguru Dobashi, Ken Takeda, Keiichi Jingu

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

The purpose of this study was to evaluate the accuracy of commercially available software, using patient DVH-based QA metrics, by investigating the correlation between estimated 3D patient dose and magnitude of MLC misalignments. We tested 3DVH software with an ArcCHECK. Two different calculating modes of ArcCHECK Planned Dose Perturbation (ACPDP) were used: "Normal Sensitivity" and "High Sensitivity". Ten prostate cancer patients treated with hypofractionated VMAT (67.6 Gy/26 Fr) in our hospital were studied. For the baseline plan, we induced MLC errors (-0.75, -0.5, -0.25, 0.25, 0.5, and 0.75 mm for each single bank). We calculated the dose differences between the ACPDP dose with error and TPS dose with error using gamma passing rates and using DVH-based QA metrics. The correlations between dose estimation error and MLC position error varied with each structure and metric. A comparison using 1%/1 mm gamma index showed that the larger was the MLC error-induced, the worse were the gamma passing rates. Slopes of linear fit to dose estimation error versus MLC position error for mean dose and D95 to the PTV were 1.76 and 1.40% mm-1, respectively, for "Normal Sensitivity", and -0.53 and -0.88% mm-1, respectively, for "High Sensitivity", showing better accuracy for "High Sensitivity" than "Normal Sensitivity". On the other hand, the slopes for mean dose to the rectum and bladder, V35 to the rectum and bladder and V55 to the rectum and bladder, were -1.00, -0.55, -2.56, -1.25, -3.53, and -1.85% mm-1, respectively, for "Normal Sensitivity", and -2.89, -2.39, -4.54, -3.12, -6.24, and -4.11% mm-1, respectively, for "High Sensitivity", showing significant better accuracy for "Normal Sensitivity" than "High Sensitivity". Our results showed that 3DVH had some residual error for both sensitivities. Furthermore, we found that "Normal Sensitivity" might have better accuracy for the DVH metric for the PTV and that "High Sensitivity" might have better accuracy for DVH metrics for the rectum and bladder. We must be willing to tolerate this residual error in clinical care.

Original languageEnglish
Pages (from-to)179-189
Number of pages11
JournalJournal of applied clinical medical physics
Volume16
Issue number3
DOIs
Publication statusPublished - 2015

Keywords

  • 3D patient dose
  • Diode array
  • Dose distribution comparison
  • Patient QA
  • Radiotherapy

ASJC Scopus subject areas

  • Radiation
  • Instrumentation
  • Radiology Nuclear Medicine and imaging

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