To compare the dosimetric and geometric properties of a commercial x-ray based image-guided small animal irradiation system, installed at three institutions and to establish a complete and broadly accessible commissioning procedure.
The system consists of a 225 kVp x-ray tube with fixed field size collimators ranging from 1 to 44 mm equivalent diameter. The x-ray tube is mounted opposite a flat-panel imaging detector, on a C-arm gantry with 360° coplanar rotation. Each institution performed a full commissioning of their system, including half-value layer, absolute dosimetry, relative dosimetry (profiles, percent depth dose, and relative output factors), and characterization of the system geometry and mechanical flex of the x-ray tube and detector. Dosimetric measurements were made using Farmer-type ionization chambers, small volume air and liquid ionization chambers, and radiochromic film. The results between the three institutions were compared.
At 225 kVp, with 0.3 mm Cu added filtration, the first half value layer ranged from 0.9 to 1.0 mm Cu. The dose-rate in-air for a 40 × 40 mm2 field size, at a source-to-axis distance of 30 cm, ranged from 3.5 to 3.9 Gy/min between the three institutions. For field sizes between 2.5 mm diameter and 40 × 40 mm2, the differences between percent depth dose curves up to depths of 3.5 cm were between 1% and 4% on average, with the maximum difference being 7%. The profiles agreed very well for fields >5 mm diameter. The relative output factors differed by up to 6% for fields larger than 10 mm diameter, but differed by up to 49% for fields ≤5 mm diameter. The mechanical characteristics of the system (source-to-axis and source-to-detector distances) were consistent between all three institutions. There were substantial differences in the flex of each system.
With the exception of the half-value layer, and mechanical properties, there were significant differences between the dosimetric and geometric properties of the three systems. This underscores the need for careful commissioning of each individual system for use in radiobiological experiments.
As this was a joint effort between three institutions, the authors would like to recognize that equal contribution was made to this manuscript by P. Lindsay, P. Granton and A. Gasparini. The authors would furthermore like to recognize that equal contribution to the senior authorship of this manuscript was made by J.-J. Sonke, F. Verhaegen and D. Jaffray. The authors would like to acknowledge the assistance of Precision X-Ray Inc. (Robert Hase and Peter Rowland) in providing details of the system as well as useful discussions. The Princess Margaret Cancer Centre would like to acknowledge the technical and scientific contributions of Steve Ansell, Graham Wilson, and Richard Hill. The Netherlands Cancer Institute would like to acknowledge Thijs Perik for his support with the dosimetry. Financial support at Princess Margaret Cancer Centre was received from the Canadian Foundation for Innovation. The senior author (D.A.J.) would like to acknowledge the support of the Fidani Family Chair in Radiation Physics. Financial support for the purchase and operation of the micro-IR at Maastro Clinic was provided by a Marie Curie grant (Grant No. PIRG03-GA-2008-230911), a ZonMW grant (Grant No. 40-00506-98-9019), and by the GROW research institute. P.V.G. is supported by a PGSD3 scholarship from the Natural Sciences and Engineering Research Council of Canada (NSERC). Some of the authors (P.E.L., D.A.J.) of this work are listed as inventors of the system described herein. This system has been licensed to Precision X-Ray Inc. for commercial development. The NKI receives license fees from Precision X-Ray Inc. and Xstrahl Ltd.
I. INTRODUCTION II. MATERIALS AND METHODS II.A. System description II.A.1. Hardware and software II.A.2. Radiation safety II.B. Absolute dosimetry II.C. Relative dosimetry II.C.1. Measurement conditions II.C.2. X-ray tube linearity with current and time II.C.3. Percent depth dose (PDD) II.C.4. Relative output factors (ROFs) II.C.5. Dose profiles II.C.6. Inverse square law II.C.7. Out-of-field dose II.D. Mechanical operation and performance II.D.1. Magnification II.D.2. Gantry flex during imaging and radiation delivery III. RESULTS III.A. Absolute dosimetry III.B. Relative dosimetry III.B.1. Measurement conditions III.B.2. Linearity III.B.3. PDD III.B.4. ROF III.B.5. Dose profiles III.B.6. Inverse square law III.B.7. Out-of-field dose III.C. Mechanical operation III.C.1. Magnification III.C.2. System flex during imaging and radiation delivery IV. DISCUSSION IV.A. Absolute dosimetric quantities IV.B. Relative dosimetric quantities IV.C. Mechanical quantities V. CONCLUSIONS
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