Three-dimensional dose verification for intensity-modulated radiation therapy in the radiological physics centre head-and-neck phantom using optical computed tomography scans of ferrous xylenol-orange gel dosimeters.
OBJECTIVE
To extend the Radiological Physics Centre (RPC) intensity-modulated radiation therapy dose verification protocol to three dimensions using optical computed tomography (CT) scans of ferrous xylenol-orange (FX) gels.


METHODS
The dosimetry insert in the RPC head-and-neck phantom was replaced with an FX cylindrical gel dosimeter. Two gels were calibrated, independently irradiated with 6-MV X-ray beams and scanned using laser and cone-beam (Vista) optical CT, respectively. For matching dose slices, measured dose distributions were compared with Pinnacle3 computed distributions.


RESULTS
Within high-dose regions and low gradients, doses measured using laser CT were 2% to 3% less than the computed dose, whereas with cone-beam CT they were 4% to 5% less. Inside the central 90% of the gel cylinder diameter, the fraction of voxels satisfying the two-dimensional gamma analysis (5% dose difference, 3-mm distance to agreement) with laser-beam- and cone-beam-measured dose distributions were 98.4% and 99.0%, respectively. A three-dimensional gamma analysis with cone-beam data revealed that 96.7% of voxels within the central 90% gel volume satisfied the above criteria. Within the axial and sagittal planes through the primary planning target volume (PTV), computed and measured doses using GAFChromicEBT film (RPC measured) and cone-beam scanned FX gel generally agreed. At equivalent points in the planning target volumes, computed, thermoluminescent dosimeter (RPC-measured), and gel point doses agreed to within 5.1% in absolute dose.


CONCLUSIONS
Laser and cone-beam CT yield comparable dose distributions in high-dose regions. The RPC head phantom and optical CT-scanned FX gels can be used for accurate intensity-modulated radiation therapy dose verification in three dimensions.
Babic
Steven
S
Department of Physics and Engineering, London Regional Cancer Program at London Health Sciences Centre, London, ON, Canada. steven.babic@lhsc.on.ca
Battista
Jerry
J
Jordan
Kevin
K
D002138:Calibration; D054893:Cone-Beam Computed Tomography / Q000379:methods; D005296:Ferrous Compounds; D005456:Fluorescent Dyes; D005782:Gels; D006257:Head; D019047:Phantoms, Imaging; D010636:Phenols; D011874:Radiometry / Q000295:instrumentation / Q000379:methods; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated; D013454:Sulfoxides; D041622:Tomography, Optical / Q000379:methods*; D014992:Xylenes
D005296:Ferrous Compounds; D005456:Fluorescent Dyes; D005782:Gels; D010636:Phenols; D013454:Sulfoxides; D014992:Xylenes; C016833:xylenol orange