Abstract
Purpose:To investigate the variation of TMR for SRS cones obtained by TMR scanning, calculation from PDDs, and point measurements. The obtained TMRs were also compared to the representative data from the vendor.Methods:TMRs for conical cones of 4, 5, 7.5, 10, 12.5, 15, and 17.5 mm diameter (jaws set to 5×5 cm) were obtained for 6X FFF and 10X FFF energies on a Varian Edge linac. TMR scanning was performed with a Sun Nuclear 3D scanner and Edge detector at 100 cm SDD. TMR point measurements were measured with a Wellhofer tank and Edge detector, at multiple depths from 0.5 to 20 cm and 100 cm SDD. PDDs for converting to TMR were scanned with a Wellhofer system and SFD detector. The formalism of converting PDD to TMR, given in Khan's book (4th Edition, p.161) was applied. Sp values at dmax were obtained by measuring Scp and Sc of the cones (jaws set to 5×5 cm) using the Edge detector, and normalized to the 10×10 cm field.Results:Along the central axis beyond dmax, the RMS and maximum percent difference of TMRs obtained with different methods were as follows: (a) 1.3% (max=3.5%) for the calculated TMRs from PDDs versus direct scanning; (b) 1.2% (max=3.3%) for direct scanning versus point measurement; (c) 1.8% (max=5.1%) for the calculated versus point measurements; (d) 1.0% (max=3.6%) for direct scanning versus vendor data; (e) 1.6% (max=7.2%) for the calculated versus vendor data.Conclusion:The overall accuracy of TMRs calculated from PDDs was comparable with that of direct scanning. However, the uncertainty at depths greater than 20 cm, increased up to 5% when compared to point measurements. This issue must be considered when developing a beam model for small field SRS planning using cones.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.