Evaluation of the applicability of pinpoint ion chambers for SRS dosimetric quality assurance

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• 作者：Jong Geun Baek ; Hyun Soo Jang ; Eng Chan Kim…
• 关键词：Pinpoint ionization chamber ; Diamond detector ; Stereotactic radiosurgery ; Dosimetric quality
• 刊名：Journal of the Korean Physical Society
• 出版年：2015
• 出版时间：June 2015
• 年：2015
• 卷：66
• 期：11
• 页码：1771-1776
• 全文大小：2,261 KB
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• 作者单位：Jong Geun Baek (1) (2)
  Hyun Soo Jang (2)
  Eng Chan Kim (1)
  Yong Hee Lee (1)
  Young Kee Oh (3)
  Sung Kyu Kim (1)
  
  1. Department of Physics, Yeungnam University, Gyeongsan, 712-749, Korea
  2. Department of Radiation Oncology, Dongguk University Gyeongju Hospital, Gyeongju, 780-350, Korea
  3. Department of Radiation Oncology, Keimyung University Dongsan Medical Center, Daegu, 700-712, Korea
  
• 刊物主题：Physics, general; Theoretical, Mathematical and Computational Physics; Particle and Nuclear Physics;
• 出版者：Springer Netherlands
• ISSN：1976-8524

文摘

The aim of the present study was to evaluate the applicability of a Pinpoint ion chamber for the measurement of the absolute dose for dosimetric quality assurance (QA) under the same conditions as are used for actual stereotactic radiosurgery (SRS). A PTW 31014 Pinpoint chamber with a active volume of 0.015 cm3 was used to measure the absolute doses of small beams. The PTW 60003 natural diamond detector was used as a reference dosimeter. A custom-made cylindrical acrylic phantom (15 cm diameter, 15 cm long) was produced to obtain measurements, and a noncoplanar arc plan was devised to deliver a prescription dose (15?5 Gy) to 80% of the maximum dose to the target in a single fraction by using the BrainLAB planning system. All irradiations were performed by using a Varian Clinac IX 6 MV equipped with a micro-multileaf-collimators (m3) designed by BrainLAB. The acceptability criterion used was a dose difference of less than 3%. The diameter of the target volume was considered the standard parameter in the present study and was used to divide the cases into two groups, that is, a ?10 mm target diameter group (10 cases) and a > 10 mm target diameter group (13 cases). For the Pinpoint chamber and target diameters of ?10 mm, dosimetric uncertainties of > 3% were seen in 4 of the 10 cases, and differences ranged widely from 0.7% to 4.85%. On the other hand, for the Pinpoint chamber and target diameters of > 10 mm all dose differences were less than 1.6%, and the mean discrepancy was 0.81%. A highly significant, but moderate, correlation between dosimetric uncertainties and all target diameters was observed for the Pinpoint chamber (R2 = 0.483, p 0.001). This result indicates that Pinpoint chambers exhibit a field-size dependency when used for SRS dosimetric QA. Based on the results of the present study, we conclude that the use of a Pinpoint chamber for verification of SRS dosimetric QA is unsuitable for all field sizes, but that it can be used to verify the delivered dose of clinical SRS photon beams given a target diameter of >10 mm. In addition, the use of Pinpoint chambers should be limited to a field size of 12 mm for SRS dosimetric QA, and cross checking with another type of dosimeter should be performed when Pinpoint chambers are used for SRS dosimetric QA.