Author(s)

Guerda Massillon-JL¹, Nestor Aragón-Martínez¹, Arnulfo Gómez-Muñoz²

¹Instituto de Física, Universidad Nacional Autónoma de México, Ciudad de México, México.
²Hospital de Oncología, Centro Médico Nacional Siglo XXI, Ciudad de México, México.

This work investigated the absorbed dose to water rate under reference conditions in a Cyberknife VSI system using radiochromic films EBT3 and MD-V3 and three ionization chambers: an Exradin A12 and two FC65P Welhöfer Scanditronix with different serial numbers. The correction factor,, was studied using a Varian iX linac and the Cyberknife system. The measurements in the Varian iX were performed in a 10 × 10 cm² field, 10 cm depth in liquid water at 90 cm and 70 cm SSD and in a 5.4 × 5.4 cm² field, 10 cm depth at 70 cm SSD to simulate the Cyberknife conditions. In the Cyberknife system, measurements were performed using ionization chambers and both film types at 70 cm SSD and 10 cm depth in its 6 cm diameter reference field. The results indicate that  is independent of the dosimeters and the evaluation methods. Maximum differences of 0.22% - 0.55% (combined uncertainties of 1.22% - 1.98%, k = 1) are obtained on  using Varian iX, whereas discrepancies of 2.08% - 2.09% (combined uncertainties of 1.87% - 2.13%, k = 1) are observed using the Cyberknife system. Given the agreement between detectors and the combined standard uncertainties, the data from Varian iX could be considered the most accurate and consequently a weighted average factor of 0.902 ± 0.006 could be used for the Cyberknife VSI system reference field. Within measurement uncertainties, the absorbed dose rate measured in the Cyberknife VSI system reference field was found to be independent of the dosimeters used. These results suggest that the absorbed dose measured at a point within a given field size should be the same, regardless the dosimeter used, if their dosimetric characteristics are well known. This highlighted the importance of performing dosimetry by controlling all parameters that could affect the dosimeter response. One can conclude that radiochromic film dosimetry can be considered as an appropriate alternative for measuring absorbed dose to water rate.

Small Field Dosimetry, Reference Field, Cyberknife, Gafchromic Films, Ionization Chambers, Dose Rate, EBT3, MD-V3, 6 MV X-Rays

Massillon-JL, G. , Aragón-Martínez, N. and Gómez-Muñoz, A. (2017) Absorbed Dose to Water Rate in a Cyberknife VSI System Reference Field Using Ionization Chambers and Gafchromic Films. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 6, 80-92. doi: 10.4236/ijmpcero.2017.61008.