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Technical Treatment Accuracy in a Clinic of Fractionated Stereotactic Radiosurgery

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R Bisht

R Bisht*, S Kale , G Natanasabapathi , M Singh , D Agarwal , G Rath , P Julka , P Kumar , S Thulkar , A Garg , B Sharma , All India Institute of Medical Sciences, Delhi, Delhi


SU-F-T-593 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose:The purpose of this study is to estimate technical treatment accuracy in fractionated stereotactic radiosurgery (fSRS) using extend system (ES) of Gamma Knife (GK).

Methods:The fSRS with GK relies on a patient specific re-locatable immobilization system. The reference treatment position is estimated using a digital probe and a repositioning check tool (RCT). The “calibration values” of RCT apertures were compared with measured values on RCT-QA tool to evaluate the standard error (SE) associated with RCT measurements. A treatment plan with single “4 mm collimator shot” was created to deliver a radiation dose of 5 Gy at the predefined plane of a newly designed in-house head-neck phantom. The plan was investigated using radiochromic EBT3 films. The stereotactic CT imaging of a designed mini CT phantom and distortion study of MR imaging, were combined to calculate imaging SE. The focal precision check for GK machine tolerance was performed using a central diode test tool.

Results:Twenty observations of RCT and digital probe, shown the SE of +/-0.0186mm and +/-0.0002mm respectively. A mean positional shift of 0.2752mm (σ=0.0696mm) was observed for twenty similar treatment settings of head-neck phantom. The difference between radiological and predefined exposure point was 0.4650mm and 0.4270mm; for two independent experiments. The imaging studies showed a combined SE of +/- 0.1055mm. Twenty frequent runs of a diode test tool showed the tolerance SE of +/-0.0096mm. If, the measurements are considered to be at 95% of confidence level, an expanded uncertainty was evaluated as +/- 0.2371mm with our system. The positional shift, when combined with an expanded uncertainty, a trivial variation of 0.07mm (max) was observed in comparing resultant radiological precision through film investigations.

Conclusion:The study proposes an expression of “technical treatment accuracy” within “known uncertainties” is rational in the estimation of routine fSRS quality.

Funding Support, Disclosures, and Conflict of Interest: The research work is supported by the research section of "All India Institute of Medical Sciences" - New Delhi, India under project no A-247.

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