Commissioning and cross-comparison of four scanning water tanks
Purpose: Water scanning systems are commonly used for data collection to characterize dosimetric properties of photon and electron beams, and the commissioning of such systems has been previously described. The aim in this study, however, was to investigate tank-specific dependencies as well as conduct a dosimetric comparison between four distinct water scanning systems.
Methods: Four water scanning systems were studied including the PTW MP3-M Phantom Tank, the Standard Imaging DoseView 3D, the IBA Blue Phantom, and the Sun Nuclear 3D Scanner. Mechanical accuracy and reproducibility was investigated by driving the chamber holder to nominal positions relative to a zero point and using a leveled caliper with 30 cm range to measure the actual position. Dosimetric measurements were also performed not only to compare percent-depth-dose (PDD) curves and profiles between tanks but also to assess dependencies such as directionality, scanning speed, and reproducibility for each tank individually. A PTW Semiflex 31010 ionization chamber with a sensitive volume of 0.125 cc was used at a Varian Clinac 2300 linear accelerator.
Results: Mechanical precision was ensured to within 0.1 mm with the standard deviation (SD) of reproducibility <0.1 mm for measurements made with calipers. Dependencies on scanning direction and speed are presented. 6 MV PDDs between tanks agreed to within 0.6% relative to an averaged PDD beyond dmax and within 2.5% in the build-up region. Specifically, the maximum difference was 1.0% between MP3-M and Blue Phantom at 6.1 cm depth. Lateral profiles agreed between tanks within 0.5% in the central 80% of the field. 6 MeV PDD maximum difference was 1.3% occurring at the steepest portion, where the R50 was nevertheless within 0.6 mm across tanks. Setup uncertainties estimated at ≤1 mm are presumed to have contributed some of the difference between water tank data.
Conclusion: Modern water scanning systems have achieved high accuracy across vendors, but commissioning tests nevertheless reveal tank-specific dependencies. This study not only ensures confidence in the individual systems but also provides the medical physicist with an understanding of variation in water tank properties between vendors.
Mellenberg DE, Dahl RA, Blackwell CR. Acceptance testing of an automated scanning water phantom. Med Phys. 1990;17:311-4.
Purdy JA, American Association of Physicists in Medicine. Advances in Radiation Oncology Physics Dosimetry, Treatment Planning, and Brachtherapy: Medical Physics Monograph, No. 19, American Institute of Physics; New York, NY: 1992: 111-47.
Das IJ, Cheng CW, Watts RJ, et al. Accelerator beam data commissioning equipment and procedures: report of the TG-106 of the Therapy Physics Committee of the AAPM. Med Phys. 2008;35:4186-215.
Peng JL, Ashenafi MS, McDonald DG, Vanek KN. Assessment of a three-dimensional (3D) water scanning system for beam commissioning and measurements on a helical tomotherapy unit. J Appl Clin Med Phys. 2015;16:4980.
García-Vicente F, Béjar MJ, Pérez L, Torres JJ. Clinical impact of the detector size effect in 3D-CRT. Radiother Oncol. 2005;74:315-22.
Cranmer-Sargison G, Weston S, Sidhu NP, Thwaites DI. Experimental small field 6 MV output ratio analysis for various diode detector and accelerator combinations. Radioth Oncol. 2011;100:429-435.
Sharma SC, Ott JT, Williams JB, Dickow D. Commissioning and acceptance testing of a CyberKnife linear accelerator. J Appl Clin Med Phys. 2007;8:2473.
Patel B, Syh J, Durci M, et al. Comparison of TomoScanner™ 2D Water Phantom versus IBA Helix for Tomotherapy Profile Measurements. Med Phys. 2012;39:3734.
Akino Y, Gibbons JP, Neck DW, et al. Intra- and intervariability in beam data commissioning among water phantom scanning systems. J Appl Clin Med Phys. 2014;15:4850.
Bakhtiari M. Effect of surface waves on radiotherapy dosimetric measurements in water tanks. J Med Phys. 2011;36:230-3.
Dieterich S, Ford E, Pavord D, Zeng J. Practical Radiation Oncology Physics: A Companion to Gunderson Tepper’s Clinical Radiation Oncology. Philadelphia, PA: Elsevier; 2015.
Mayles P, Nahum A, Rosenwald JC. Handbook of Radiotherapy Physics: Theory and Practice. Boca Raton, FL: Taylor & Francis Group; 2007.
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