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Can Fiducial Marker-Based Setup Using ExacTrac Be An Alternative to Soft Tissue-Based Setup Using Cone-Beam CT for Prostate IMRT?

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S Tanabe

S Tanabe1*, S Utsunomiya2 , E Abe2 , H Satou3 , H Sakai4 , T Yamada4 , H Aoyama2 , (1) Department of Radiation Oncology, Niigata University Medical and Dental Hospital (2) Department of Radiology, Niigata University Graduate School of Medical and Dental Sciences (3) Department of Radiation Oncology, Niigata Cancer Center Hospital (4) Section of Radiology, Department of Clinical Support, Niigata University Medical and Dental Hospital


SU-E-J-24 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

To assess an accuracy of fiducial maker-based setup using ExacTrac (ExT-based setup) as compared with soft tissue-based setup using Cone-beam CT (CBCT-based setup) for patients with prostate cancer receiving intensity-modulated radiation therapy (IMRT) for the purpose of investigating whether ExT-based setup can be an alternative to CBCT-based setup.

The setup accuracy was analyzed prospectively for 7 prostate cancer patients with implanted three fiducial markers received IMRT. All patients were treated after CBCT-based setup was performed and corresponding shifts were recorded. ExacTrac images were obtained before and after CBCT-based setup. The fiducial marker-based shifts were calculated based on those two images and recorded on the assumption that the setup correction was carried out by fiducial marker-based auto correction. Mean and standard deviation of absolute differences and the correlation between CBCT and ExT shifts were estimated.

A total of 178 image dataset were analyzed. On the differences between CBCT and ExT shifts, 133 (75%) of 178 image dataset resulted in smaller differences than 3 mm in all dimensions. Mean differences in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) dimensions were 1.8 ± 1.9 mm, 0.7 ± 1.9 mm, and 0.6 ± 0.8 mm, respectively. The percentages of shift agreements within ±3 mm were 76% for AP, 90% for SI, and 100% for LR. The Pearson coefficient of correlation for CBCT and ExT shifts were 0.80 for AP, 0.80 for SI, and 0.65 for LR.

This work showed that the accuracy of ExT-based setup was correlated with that of CBCT-based setup, implying that ExT-based setup has a potential ability to be an alternative to CBCT-based setup. The further work is to specify the conditions that ExT -based setup can provide the accuracy comparable to CBCT-based setup.

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