Serenella Russo1, Laura Masi2, Paolo Francescon3, Paolo Dicarolo4, Elena De Martin5, Cristina Frassanito6, Irene Redaelli7, Sabrina Vigorito8, Michele Stasi9, Pietro Mancosu10. 1. Medical Physics Department, Azienda USL Toscana Centro, I-50012 Firenze, Italy. Electronic address: serenella.russo@uslcentro.toscana.it. 2. Department of Medical Physics and Radiation Oncology, IFCA, Radiotherapy, I-50139 Firenze, Italy. 3. Department of Radiation Oncology, Ospedale Di Vicenza, I-36100 Vicenza, Italy. 4. Medical Physics Unit, Meyer Children's University Hospital, I-50139 Firenze, Italy. 5. Medical Physics Unit, Istituto Besta, Radiotherapy, I-20133 Milano, Italy. 6. Radiotherapy Department, Mater Dei Hospital, Città di Bari Hospital spa, I-70125 Bari, Italy. 7. Medical Physics Unit, C.D.I., Radiotherapy, I-20147 Milano, Italy. 8. Unit of Medical Physics, I. E. O., Radiotherapy, I-20141 Milano, Italy. 9. Medical Physics Department, A.O. Ordine Mauriziano, I-10128 Torino, Italy; Medical Physics Department, Candiolo Cancer Institute - FPO, IRCCS, I-10060 Torino, Italy. 10. Medical Physics Unit of Radiation Oncology Dept, Humanitas Clinical and Research Hospital, I-20089 Rozzano-Milano, Italy.
Abstract
PURPOSE: The aims of this study were: (i) to validate in a multi-site context the suitability of the IBA Razor silicon diode detector for CyberKnife relative dosimetry. (ii) to fit the multi-center experimental data into a function relating the field output factors to the effective field size (EFS). METHODS AND MATERIALS: Ratio of detector readings in clinical and reference field (OFdet) and beam profiles were acquired on five CyberKnife units for fixed collimator diameters (range 5-60 mm), using both Razor and PTW 60017 diodes. Measured OFdet were corrected using published MonteCarlo correction factors to get field output factors ΩQclin,Qmsrfclin,fmsr. Profiles were analyzed in terms of penumbra and EFS. ΩQclin,Qmsrfclin,fmsr obtained in four centers were fitted as a function of EFS, while the data of the 5th center were used to validate the fitting curve. RESULTS: Differences between Razor and PTW60017 ΩQclin,Qmsrfclin,fmsr were within 1.5% over all centers down to 7.5 mm aperture and within 3.5% for the 5 mm diameter. The fit showed a coefficient of determination R2 = 0.997. The mean deviation of measured points from the predictive curve was within 0.5%. Data of the 5th center showed a mean deviation of 0.4% from the curve, with maximum differences within 2.5% for the 7.5 mm aperture. CONCLUSIONS: The results confirmed the suitability of Razor detector for CyberKnife dosimetry by comparison to the PTW 60017 diode which has been well characterized and is in widespread use. The proposed mathematical relation between ΩQclin,Qmsrfclin,fmsr and EFS is a robust predictive model applicable to different CyberKnife systems and detectors.
PURPOSE: The aims of this study were: (i) to validate in a multi-site context the suitability of the IBA Razor silicon diode detector for CyberKnife relative dosimetry. (ii) to fit the multi-center experimental data into a function relating the field output factors to the effective field size (EFS). METHODS AND MATERIALS: Ratio of detector readings in clinical and reference field (OFdet) and beam profiles were acquired on five CyberKnife units for fixed collimator diameters (range 5-60 mm), using both Razor and PTW 60017 diodes. Measured OFdet were corrected using published MonteCarlo correction factors to get field output factors ΩQclin,Qmsrfclin,fmsr. Profiles were analyzed in terms of penumbra and EFS. ΩQclin,Qmsrfclin,fmsr obtained in four centers were fitted as a function of EFS, while the data of the 5th center were used to validate the fitting curve. RESULTS: Differences between Razor and PTW60017 ΩQclin,Qmsrfclin,fmsr were within 1.5% over all centers down to 7.5 mm aperture and within 3.5% for the 5 mm diameter. The fit showed a coefficient of determination R2 = 0.997. The mean deviation of measured points from the predictive curve was within 0.5%. Data of the 5th center showed a mean deviation of 0.4% from the curve, with maximum differences within 2.5% for the 7.5 mm aperture. CONCLUSIONS: The results confirmed the suitability of Razor detector for CyberKnife dosimetry by comparison to the PTW 60017 diode which has been well characterized and is in widespread use. The proposed mathematical relation between ΩQclin,Qmsrfclin,fmsr and EFS is a robust predictive model applicable to different CyberKnife systems and detectors.