Laura Masi1, Serenella Russo2, Paolo Francescon3, Raffaela Doro4, Maria Cristina Frassanito5, Maria Luisa Fumagalli6, Giacomo Reggiori7, Marco Marinelli8, Irene Redaelli9, Maria Pimpinella10, Gianluca Verona Rinati8, Carmelo Siragusa11, Sabrina Vigorito12, Pietro Mancosu7. 1. Department of Medical Physics and Radiation Oncology, IFCA, I-50139 Firenze, Italy. Electronic address: l.masi@giomi.com. 2. Medical Physics Unit of Radiation Oncology Dept, Azienda Sanitaria Firenze, I-50012 Firenze, Italy. 3. Department of Radiation Oncology, Ospedale di Vicenza, I-36100 Vicenza, Italy. 4. Department of Medical Physics and Radiation Oncology, IFCA, I-50139 Firenze, Italy. 5. Radiotherapy Department, Mater Dei Hospital, Città di Bari Hospital spa, I-70124 Bari, Italy. 6. Radiotherapy Department, Istituto Neurologico Besta, I-20133 Milano, Italy. 7. Medical Physics Unit of Radiation Oncology Dept., Humanitas Research Hospital, I-20089 Milano, Italy. 8. INFN-Dipartimento di Ingegneria Industriale, Università di Roma 'Tor Vergata', I-00133 Roma, Italy. 9. Radiotherapy Department, Centro Diagnostico Italiano, I-20147 Milano, Italy. 10. Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti, ENEA-INMRI C R Casaccia, I-00123 Roma, Italy. 11. Medical Physics Unit, A.O.U. Policlinico G. Martino, Messina, Italy. 12. Radiotherapy Department, Istituto Europeo Oncologia, I-20141 Milano, Italy.
Abstract
PURPOSE: New promising detectors are available for measuring small field size output factors (OFs). This study focused on a multicenter evaluation of two new generation detectors for OF measurements on CyberKnife systems. METHODS: PTW-60019 microDiamond and W1 plastic scintillation detector (PSD) were used to measure OFs on eight CyberKnife units of various generations for 5-60mm fixed cones. MicroDiamond and PSD OF were compared to routinely used silicon diodes data corrected applying published Monte Carlo (MC) factors. PSD data were corrected for Čerenkov Light Ratio (CLR). The uncertainties related to CLR determination were estimated. RESULTS: Considering OF values averaged over all centers, the differences between MC corrected diode and the other two detectors were within 1.5%. MicroDiamond exhibited an over-response of 1.3% at 7.5mm and a trend inversion at 5mm with a difference of 0.2%. This behavior was consistent among the different units. OFs measured by PSD slightly under-responded compared to MC corrected diode for the smaller cones and the differences were within 1%. The observed CLR variability was 2.5% and the related variation in OF values was 1.9%. CONCLUSION: This study indicates that CyberKnife microDiamond OF require corrections below 2%. The results are enhanced by the consistency observed among different units. Scintillator shows a good agreement to MC corrected diode but CLR determination remains critical requiring further investigations. The results emphasized the value of a multi-center validation over a single center approach.
PURPOSE: New promising detectors are available for measuring small field size output factors (OFs). This study focused on a multicenter evaluation of two new generation detectors for OF measurements on CyberKnife systems. METHODS: PTW-60019 microDiamond and W1 plastic scintillation detector (PSD) were used to measure OFs on eight CyberKnife units of various generations for 5-60mm fixed cones. MicroDiamond and PSD OF were compared to routinely used silicon diodes data corrected applying published Monte Carlo (MC) factors. PSD data were corrected for Čerenkov Light Ratio (CLR). The uncertainties related to CLR determination were estimated. RESULTS: Considering OF values averaged over all centers, the differences between MC corrected diode and the other two detectors were within 1.5%. MicroDiamond exhibited an over-response of 1.3% at 7.5mm and a trend inversion at 5mm with a difference of 0.2%. This behavior was consistent among the different units. OFs measured by PSD slightly under-responded compared to MC corrected diode for the smaller cones and the differences were within 1%. The observed CLR variability was 2.5% and the related variation in OF values was 1.9%. CONCLUSION: This study indicates that CyberKnife microDiamond OF require corrections below 2%. The results are enhanced by the consistency observed among different units. Scintillator shows a good agreement to MC corrected diode but CLR determination remains critical requiring further investigations. The results emphasized the value of a multi-center validation over a single center approach.
Authors: Giordano Biasi; Marco Petasecca; Susanna Guatelli; Ebert A Martin; Garry Grogan; Benjamin Hug; Jonathan Lane; Vladimir Perevertaylo; Tomas Kron; Anatoly B Rosenfeld Journal: J Appl Clin Med Phys Date: 2018-07-12 Impact factor: 2.102