Commissioning the First Mobile Dedicated Accelerator for Intraoperative Electron Radiotherapy in Iran

Introduction: Intraoperative radiotherapy is a radiotherapy technique in which a high single fraction of radiation dose is delivered to the patient after surgery and Concurrent with anesthesia time. The most frequent method for IORT implementation is Intraoperative electron radiotherapy (IOERT), in which, some dedicated and high dose per pulse electron accelerators are employed for radiotherapy. Recently, Iran is also equipped to these dedicated machines for IOERT. Commissioning procedure of this dedicated IOERT machine and dosimetric characteristics of intraoperative electron beam have been evaluated in current study. Materials and Methods: LIAC accelerator, a mobile dedicated IOERT machine with the maximum energy of 12 MeV, was commissioned in this study. Commissioning procedure was performed inside a MP3-XS automatic water phantom which is introduced for small field dosimetry. 10 cm diameter reference applicator was considered and applicator edge was in contact to the phantom surface. All of measurements including percentage depth dose (PDD) along clinical axis, transverse dose profiles (TDP) at the depth of maximum dose and output factors (OF) were performed using ionometric dosimetry. During the measurements, Advanced Markus and Semiflex ion chambers were employed as field and reference detector, respectively. All of the obtained data were processed and analyzed using Mephysto Navigator software. Results: Measured PDDs showed that the intraoperative electron beam has a steep dose fall-off gradient which increases with decrement of electron energy. This fact can effectively spare the underlying healthy tissues. The symmetry and flatness of obtained TDPs at all studied energies were less than 2% which can improve the dose uniformity inside the tumor bed. As expected, the OFs were increased with increment of electron energy, but In contrast to the conventional accelerator, OF values reduce at greater radiation field sizes.   Conclusion: According to the obtained results, it can be concluded that dosimetric characteristics of intraoperative electron beam are quite favorable regarding to the mandatory issues which should be satisfied in intraoperative radiotherapy.