IGRT couch study with AcurosXB using cylindrical diode phantom.

• Main Author: Chew, Melvin Ming Long.
• Other Authors: Jacek Maciej Zurada
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Science
• Online Access: http://hdl.handle.net/10356/53670
• Institution: Nanyang Technological University

As arc therapy treatment like RapidArc requires the beam to pass through the treatment couch at various angles, it is important to determine the effect of the couch in the treatment plans and hence apply to determine a correction to it. The image guided radiotherapy (IGRT) couch contains three different sections with three different thicknesses in the couch. The IGRT couch cross section has two structures, the interior and the surface structures. In a previous study the Hounsfield Unit (HU) characterization for a Monte Carlo model was found to have -700 HU for the surface structure and -960HU for the interior structure of the IGRT couch. The objectives of this study are to verify that the HU characterization used by the Monte Carlo model is also suitable for use in a AcurosXB algorithm model, also to provide a couch correction on quality assurance (QA) results for AcurosXB dose calculation for RapidArc Treatments. A cylindrical diode array phantom (ArcCheck, Sun Nuclear Corp., USA) was used in this study. The Arc Check was placed in the thick part of the couch. Static beams at different gantry angles and field sizes were measures and also used in the treatment planning system to verify if the HU characterization for AcurosXB. Comparison was done by using different sets of HU values for the surface and interior of the IGRT couch. To determine the couch correction, static beams were measured at sufficiently small gantry angle intervals to determine the threshold angle where the gamma passing rates start to decrease. Results have shown that the set of HU values of -400HU and polystyrene material, assigned for the couch surface is accurate for use in Acuros. Results showed that when using the optimal couch setting, at couch directional angles a higher gamma pass rate and lower dose difference were achieved. In general the results from the criterions gamma passing rates and dose differences were in good agreement.