Deconvolution of detector size effect for output factor measurement for narrow Gamma Knife radiosurgery beams.
This paper presents the results of measurements of output factors (OFs) for a model U Gamma Knife collimator, with special emphasis on the accurate determination of the OF for the 4 mm collimator (OF4). In the past, the OF4 was set to 0.800 relative to the 18 mm collimator. Recently, the manufacturer has recommended a new value of 0.870 for OF4. However, most centres still use the old value of the OF4. In the present study, the Gamma Knife OFs were measured using a commercially available miniature diamond detector and a miniature 0.006 cc ion chamber, which was especially designed for the task. The measured OF4 were corrected for spatial averaging effects by measuring dose profiles for the 4 mm collimator with the same detectors and deconvolving their response from the measured profiles. A Gaussian kernel was used to describe the detector response. The relative OFs measured with the diamond detector/ion chamber were 0.986/0.982, 0.953/0.935 and 0.812/0.765 for the 14,8 and 4 mm collimators, respectively, as compared with the manufacturer's values of 0.984, 0.956 and 0.87. The corrected OF4 was 0.881 +/- 0.012 for the diamond detector and 0.851 +/- 0.012 for the ion chamber, supporting the manufacturer's revised value for this collimator.
Bednarz
G
G
Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, PA 19107, USA. Greg.Bednarz@mail.tju.edu
Saiful Huq
M
M
Rosenow
U F
UF
D002138:Calibration; D019544:Equipment Failure Analysis / Q000295:instrumentation* / Q000379:methods; D011786:Quality Control; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D012680:Sensitivity and Specificity