Room: Exhibit Hall
Purpose: Although intensity-modulated radiotherapy (IMRT) is a common radiation dose delivery technique in developed countries, some cancer centres in developing countries are still using linac without multileaf collimator (MLC). Jaws-only IMRT (JO-IMRT) is a technique using the integrated jaws in a linac to deliver IMRT plan. The objectives of this study were to evaluate and validate the accuracy of JO-IMRT dose distributions calculated by the Prowess Panther treatment planning system (TPS) using the Octavius 4D QA phantom and Monte Carlo (MC) simulation.
Methods: Photon beams from a Siemens Primus linac were simulated using the EGSnrc-based BEAMnrc code with experimental validations on the percentage depth dose (PDD) and off-center ratio (OCR) using a water phantom. The dose in the Octavius 4D phantom treated by a fixed-field IMRT was then computed using the DOSCTP MC interface. The simulated dose distributions were compared to results calculated by the Prowess Panther TPS using the Collapsed Cone Convolution algorithm, and measurements. Dose comparison was carried out based on the 3D gamma index using global methods implemented in the PTW-VeriSoft with 3%/3 mm, 2%/2 mm and 1%/1 mm criteria.
Results: There is very good agreement among results from MC, TPS, and measurements. The average gamma index was 95.1 Â± 1.3%, 94.6 Â± 1.2 and 94.2 Â± 1.1 based on 3%/3 mm; 2%/2 mm and 1%/1 mm criteria, respectively. The gamma index (3%/3 mm, 2%/2 mm and 1%/1 mm) is 96.4%, 95.8% and 95.4% for comparison between the TPS and MC. In addition, the gamma index (3%/3 mm, 2%/2 mm and 1%/1 mm) is 93.8%, 93.4% and 93.1% when MC and measurement were compared.
Conclusion: Our results show that dose distributions planned using the JO-IMRT TPS for the Octavius 4D phantom are accurate and suitable for clinical studies.
Monte Carlo, Intensity Modulation, Quality Assurance