Program Information
Simulation of Bone Tissue Interface to Study Perturbation Effect in Gamma Knife Radiosurgery
Gopishankar Natanasabapathi*, S Vivekanandhan, SS Kale, GK Rath, Raj Kishor Bisht, BS Sharma, All India Institute of Medical Sciences, New Delhi, India
Presentations
SU-E-T-699 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:
To study perturbing effect of bone tissue interface in Gamma Knife dose distribution.
Methods:
PAGAT polymer gel was manufactured in-house and poured into two PET cylinders for 3D measurement. Small vials were used for calibration.For 2D measurement EBT2 film was placed in mid portion of third gel filled PET cylinder. A bone material (+1400HU) of length 7cm and width 1.3cm was placed in the path of radiation beam at a distance of 4.5cm from measurement region to investigate its influence on dose distribution. For treatment planning each gel cylinder was fixed in Leksell frame and imaged in X-Ray CT with scanning parameters: Tube Voltage - 120kVp, Tube Current - 130mAs, Slice Thickness - 1mm. Acquired images were transferred to Leksell Gamma Plan TPS (LGP Version 10.1). A treatment plan consisting of single 16mm collimator with coordinates x=100, y=100, z=100 was generated using convolution algorithm based planning (CABP). Each cylinder was positioned in treatment table and exposed to time calculated by the TPS. Irradiated gel was imaged with MRI (GE Medical Systems) to extract dose information from R2 maps and to determine subtle influence of bone material in the radiation path. Scanning parameter used: TE - 13.6ms, TR - 5000ms, slice thickness - 1.2mm, no of echoes - 8, FOV - 256x256mm2. Similarly exposed EBT2 film was scanned with EPSON scanner (Expression 10000XL) to measure dose.
Results:
3D and 2D measurement showed altered dose distribution in profile measurement, isodose overlay and dose volume histogram (DVH) comparison. For a gamma pass criteria of 1%/1mm voxel pass rate was around 76%.
Conclusion:
Presence of bone material in the radiation path perturbed the dose distribution unnoticeable in TPS calculation. Any HU value above +1024 is truncated by CABP hence need to incorporate higher HU values for accurate dose calculation in Gamma Knife TPS.
Funding Support, Disclosures, and Conflict of Interest: The scientific resources used in this work were from the completed project N-964 provided by AERB, Mumbai.
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