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KMID : 1164220070190010027
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Journal of Korean Society for Radiotherapeutic Technology
2007 Volume.19 No. 1 p.27 ~ p.33
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Feasibility Study of Dose Evaluation of Stereotactic Radiosurgery using GafChromic RBT[R] Film
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Jang Eun-Sung
Lee Chul-Soo
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Abstract
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Purpose: We have performed SRS (stereotactic radiosurgery) for avm (arterry vein malformation) and brain cancer. In order to verify dose and localization of SRS, dose distributions from TPS X-Knife[R] ( 3.0, Radionics, USA) and GafChromic RBT[R] film in a head phantom were compared.
Materials and Methods: In this study, head and neck region of conventional humanoid phantom was modified by substituting one of 2.5 cm slap with five 0.5 cm acrylic plates to stack the GafChromic RBT[R] film slice by slice with 5 mm intervals. Four films and five acrylic plates were cut along the contour of head phantom in axial plane. The head phantom was fixed with SRS head ring and adapted SRS localizer as same as real SRS procedure. CT images of the head phantom were acquired in 5 mm slice intervals as film interval. Five arc 6 MV photon beams using the SRS cone with 2 cm diameter were delivered 300 cGy to the target in the phantom. Ten small pieces of the film were exposed to 0, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900 cGy, respectively to calibrate the GafChromic RBT[R] film. The films in the phantom were digitized after 24 hours and its linearity was calibrated. The pixel values of the film were converted to the dose and compared with the dose distribution from the TPS calculation.
Results: Calibration curve for the GafChromic RBT[R] film was linear up to 900 cGy. The R2 value was better than 0.992. Discrepancy between calculated from X-Knife[R] 3.0 and measured dose distributions with the film was less than 5% through all slices.
Conclusion: It was possible to evaluate every slice of humanoid phantom by stacking the GafChromic EBT film which is suitable for 2 dimensional dosimetry, It was found that film dosimetry using the GafChromic RBT[R] film is feasible for routine dosimetric QA of stereotactic radiosurgery.
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KEYWORD
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Gafchromic RBT[R] film, sterotactic radiosurgery, QA
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