Yannick Poirier1,2, Christopher Daniel Johnstone1,3, Charles Kirkby4,5,6. 1. 1 Department of Radiation Oncology, Division of Translational Radiation Sciences, University of Maryland School of Medicine , Baltimore, MD , USA. 2. 2 Department of Radiation Oncology, Division of Medical Physics, University of Maryland School of Medicine , Baltimore, MD , USA. 3. 3 Department of Physics and Astronomy, University of Victoria , Victoria, BC , Canada. 4. 4 Department of Medical Physics, Jack Ady Cancer Center , Lethbridge, AB , Canada. 5. 5 Department of Physics and Astronomy, University of Calgary , Calgary, AB , Canada. 6. 6 Department of Oncology, University of Calgary , Calgary, AB , Canada.
Abstract
OBJECTIVE: : Modern image-guided small animal irradiators like the Xstrahl Small Animal Radiation Research Platform (SARRP) are designed with ultrathin 0.15 mm Cu filters, which compared with more heavily filtrated traditional cabinet-style biological irradiators, produce X-ray spectra weighted toward lower energies, impacting the dosimetric properties and the relative biological effectiveness (RBE). This study quantifies the effect of ultrathin filter design on relative depth dose profiles, absolute dose output, and RBE using Monte Carlo techniques. METHODS: : The percent depth-dose and absolute dose output are calculated using kVDoseCalc and EGSnrc, respectively, while a tally based on the induction of double-strand breaks as a function of electron spectra invoked in PENELOPE is used to estimate the RBE. RESULTS: : The RBE increases by >2.4% in the ultrathin filter design compared to a traditional irradiator. Furthermore, minute variations in filter thickness have notable effects on the dosimetric properties of the X-ray beam, increasing the percent depth dose (at 2 cm in water) by + 0.4%/0.01 mm Cu and decreasing absolute dose (at 2 cm depth in water) by -1.8%/0.01 mm Cu for the SARRP. CONCLUSIONS: : These results show that modern image-guided irradiators are quite sensitive to small manufacturing variations in filter thickness, and show a small change in RBE compared to traditional X-ray irradiators. ADVANCES IN KNOWLEDGE:: We quantify the consequences of ultrathin filter design in modern image-guided biological irradiators on relative and absolute dose, and RBE. Our results show these to be small, but not insignificant, suggesting laboratories transitioning between irradiators should carefully design their radiobiological experiments.
OBJECTIVE: : Modern image-guided small animal irradiators like the Xstrahl Small Animal Radiation Research Platform (SARRP) are designed with ultrathin 0.15 mm Cu filters, which compared with more heavily filtrated traditional cabinet-style biological irradiators, produce X-ray spectra weighted toward lower energies, impacting the dosimetric properties and the relative biological effectiveness (RBE). This study quantifies the effect of ultrathin filter design on relative depth dose profiles, absolute dose output, and RBE using Monte Carlo techniques. METHODS: : The percent depth-dose and absolute dose output are calculated using kVDoseCalc and EGSnrc, respectively, while a tally based on the induction of double-strand breaks as a function of electron spectra invoked in PENELOPE is used to estimate the RBE. RESULTS: : The RBE increases by >2.4% in the ultrathin filter design compared to a traditional irradiator. Furthermore, minute variations in filter thickness have notable effects on the dosimetric properties of the X-ray beam, increasing the percent depth dose (at 2 cm in water) by + 0.4%/0.01 mm Cu and decreasing absolute dose (at 2 cm depth in water) by -1.8%/0.01 mm Cu for the SARRP. CONCLUSIONS: : These results show that modern image-guided irradiators are quite sensitive to small manufacturing variations in filter thickness, and show a small change in RBE compared to traditional X-ray irradiators. ADVANCES IN KNOWLEDGE:: We quantify the consequences of ultrathin filter design in modern image-guided biological irradiators on relative and absolute dose, and RBE. Our results show these to be small, but not insignificant, suggesting laboratories transitioning between irradiators should carefully design their radiobiological experiments.
Authors: Hua Deng; Christopher W Kennedy; Elwood Armour; Erik Tryggestad; Eric Ford; Todd McNutt; Licai Jiang; John Wong Journal: Phys Med Biol Date: 2007-04-26 Impact factor: 3.609
Authors: John Wong; Elwood Armour; Peter Kazanzides; Iulian Iordachita; Erik Tryggestad; Hua Deng; Mohammad Matinfar; Christopher Kennedy; Zejian Liu; Timothy Chan; Owen Gray; Frank Verhaegen; Todd McNutt; Eric Ford; Theodore L DeWeese Journal: Int J Radiat Oncol Biol Phys Date: 2008-08-01 Impact factor: 7.038