Technical note: a fast laser-based optical-CT scanner for three-dimensional radiation dosimetry.

PURPOSE To introduce a novel laser-based optical-CT scanner for the readout of three-dimensional (3D) radiation dosimeters. METHODS The scanner employs a diode laser, a cylindrical lens, a motorized linear rail, a rotation stage, and a charge-coupled device camera. The scanner operates in a translate-rotate fashion and may be set up in two configurations depending on the orientation of the cylindrical lens. The attenuation coefficient versus dose response was determined for a normoxic N-vinylpyrrolidone based polymer gel dosimeter. Cylindrical dosimeters, 2 cm diameter, were homogenously irradiated to known doses up to 60 Gy using a 6 MV linear accelerator. For a test irradiation, a 5 cm diameter dosimeter was irradiated along its cylindrical axis using a rectangular 1 cm x 1 cm irradiation beam. The dose readout of this scanner was compared to the corresponding readout of a common wide illumination and area detector optical-CT scanner. RESULTS The attenuation coefficient versus dose response of the laser-based system was found to be linear up to 60 Gy (r2 = 0.997) compared to the wide field illumination based optical-CT scanner, which exhibits linearity up to 32 Gy (r2 = 0.996). The noise in the reconstructed attenuation coefficient maps was +/- 7.2 x 10(-2) mm(-1) versus +/- 9.5 x 10(-3) mm(-1) for the laser-based system and the wide field illumination system, respectively. CONCLUSIONS We have developed a novel laser-based optical-CT scanner, which is capable of generating fast 3D dosimetric data using a scattering polymer gel dosimeter. Our data demonstrate that the dose readout of this scanner preserves the advantage of existing laser-based optical-CT scanners in providing measurements, which are minimally affected by scattered light. For accurate reconstruction of the attenuation coefficients, noise reduction techniques need to be applied.

[1]  N. Krstajić,et al.  Focusing optics of a parallel beam CCD optical tomography apparatus for 3D radiation gel dosimetry , 2006, Physics in medicine and biology.

[2]  Andrea McNiven,et al.  Three-dimensional dosimetry of small megavoltage radiation fields using radiochromic gels and optical CT scanning , 2009, Physics in medicine and biology.

[3]  Simon J. Doran,et al.  Characterization of a parallel-beam CCD optical-CT apparatus for 3D radiation dosimetry , 2006, Physics in medicine and biology.

[4]  J. Gore,et al.  Radiation dose distributions in three dimensions from tomographic optical density scanning of polymer gels: I. Development of an optical scanner. , 1996, Physics in medicine and biology.

[5]  M Oldham,et al.  Fast, large field-of-view, telecentric optical-CT scanning system for 3D radiochromic dosimetry , 2010, Journal of physics. Conference series.

[6]  Nikola Krstajić,et al.  Fast laser scanning optical-CT apparatus for 3D radiation dosimetry , 2007, Physics in medicine and biology.

[7]  Tian Liu,et al.  Dosimetry study of Re-188 liquid balloon for intravascular brachytherapy using polymer gel dosimeters and laser-beam optical CT scanner. , 2003, Medical physics.

[8]  M Oldham,et al.  Fast, high-resolution 3D dosimetry utilizing a novel optical-CT scanner incorporating tertiary telecentric collimation. , 2007, Medical physics.

[9]  E Pappas,et al.  An evaluation of the dosimetric performance characteristics of N-vinylpyrrolidone-based polymer gels , 2007, Physics in medicine and biology.

[10]  T. Olding,et al.  Cone beam optical computed tomography for gel dosimetry I: scanner characterization , 2010, Physics in medicine and biology.

[11]  Jorge Ripoll,et al.  A New Optical-CT Apparatus for 3-D Radiotherapy Dosimetry: Is Free Space Scanning Feasible? , 2010, IEEE Transactions on Medical Imaging.

[12]  M. Oldham,et al.  A comprehensive evaluation of the PRESAGE/optical-CT 3D dosimetry system. , 2008, Medical physics.

[13]  T. Tschudi,et al.  Speckle reduction in laser projection systems by diffractive optical elements. , 1998, Applied optics.

[14]  M. Oldham,et al.  Optical-CT gel-dosimetry. II: Optical artifacts and geometrical distortion. , 2004, Medical physics.

[15]  J G Wolodzko,et al.  CCD imaging for optical tomography of gel radiation dosimeters. , 1999, Medical physics.

[16]  S L Meeks,et al.  Performance evaluation of an improved optical computed tomography polymer gel dosimeter system for 3D dose verification of static and dynamic phantom deliveries. , 2008, Medical physics.

[17]  Mark Oldham,et al.  A practical three-dimensional dosimetry system for radiation therapy. , 2006, Medical physics.

[18]  Mark Oldham,et al.  An investigation of the accuracy of an IMRT dose distribution using two- and three-dimensional dosimetry techniques. , 2008, Medical physics.

[19]  S. Doran,et al.  A CCD-based optical CT scanner for high-resolution 3D imaging of radiation dose distributions: equipment specifications, optical simulations and preliminary results , 2001 .

[20]  E Pappas,et al.  Small SRS photon field profile dosimetry performed using a PinPoint air ion chamber, a diamond detector, a novel silicon-diode array (DOSI), and polymer gel dosimetry. Analysis and intercomparison. , 2008, Medical physics.