Evaluation of jaws-only intensity modulated radiation therapy treatment plans using Octavius 4D system

Introduction: Jaws-Only Intensity modulated radiation therapy (JO-IMRT) is a technique uses the collimator jaws of the linear accelerator (LINAC) to delivery of complex intensity patterns. In previous studies, pretreatment patient specific quality assurance for those JO-IMRT were also performed using ionization chamber, MapCHECK2, and Octavius 4D and good agreements were shown. The aim of this study is to further verify JO-IMRT plans in 2 different cases: one with the gantry angle set equal to beam angle as in the plans and the other with gantry angle set to zero degree. Materials and Methods: Twenty-five JO-IMRT, previously verified, were executed twice for each plan. The first one used a real gantry angle, and the second one used a 0 degrees gantry angle. Measurements were performed using Octavius 4D 1500. Results: The results were analyzed using Verisoft software. The results show that the Gamma average was 97.32 +/- 2.21% for IMRT with a 0 degrees gantry angle and 94.72 +/- 2.67% for IMRT with a true gantry angle. Conclusion: In both cases, gamma index of more than 90% were found for all of our 25 JO-IMRT treatment plans.