The impact of inter-unit variations on small field dosimetry correction factors, with application to the CyberKnife system.

The impact of inter-unit variations on small field dosimetry correction factors, with application to the CyberKnife system.
Phys Med Biol. 2018 Dec 18;:
Authors: Francescon P, Kilby W, Satariano N, Orlandi C, Elshamndy SK
Abstract
Small field dosimetry correction factors are usually determined from calculations or measurements using one specific example of a treatment system. The sensitivity of the corrections to inter-unit variation is therefore not evaluated. We propose two methods for this evaluation that could be applied to any system. We use them to assess the variability in k_(Q_msr,Q_0)^(f_msr,f_ref ) for the CyberKnife System caused by design changes between pre-M6 and M6 versions, and to the variability in k_(Q_msr,Q_0)^(f_msr,f_ref )and k_(Q_clin,Q_msr)^(f_clin,f_msr ) resulting from measured beam-data variations across 139 units. We also perform measurements to investigate the differences in k_(Q_clin,Q_msr)^(f_clin,f_msr ) reported for microchambers in a CyberKnife-specific study vs. TRS-483. The results show that k_(Q_msr,Q_0)^(f_msr,f_ref )is smaller for the M6 version than pre-M6 versions by 0.4% for a Farmer chamber, and 0.1% for shorter chambers. The presence or absence of a lead filter within the treatment head had no significant impact on k_(Q_msr,Q_0)^(f_msr,f_ref ). The beam-data analysis showed inter-unit variations in k_(Q_msr,Q_0)^(f_msr,f_ref ) of ±0.8% (2 s.d.) for Farmer chambers and ≤±0.5% for shorter ...

Source: Physics in Medicine and Biology - December 18, 2018 Category: Physics Authors: Francescon P, Kilby W, Satariano N, Orlandi C, Elshamndy SK Tags: Phys Med Biol Source Type: research