Monte Carlo Simulation Dose Calculation for Intensity Modulated Radiosurgery

Abstract

Aim: Our center commenced intensity-modulated radiosurgery (IMRS) for intracranial patients in 2003. When IMRS was originally commissioned, the dose was checked using thermoluminescence dosimetry (TLD), ion chamber and film dosimetry. Due to the limitations of these methods of dosimetry, the dose is only checked in a homogenous phantom. In a real patient, inhomogeneities such as bones and air cavities are present and so, the dose in this situation should also be tested. A Monte Carlo Simulation (MCS) program was implemented to calculate patient doses and compare them with those calculated using the treatment-planning system (TPS). The oncologist can decide if the discrepancies are crucial for treatment or not. If the discrepancies are not acceptable, a re-plan of the patient may be necessary. Methods: Doses calculated using MCS were compared with the Radionics Xknife RT3 TPS. The radiation doses are delivered using Siemens Primus linear accelerator with Radionics mini multi-leaf collimator. The isodose distributions are compared along with the dose-volume histogram (DVH). Results: It was found that the dose distribution from the TPS matched the MCS to within 3% at 98% volume in the DVH. However, the MCS had a hot spot 6% higher inside the target volume. Conclusion: Investigation is required to find out what caused the difference inside the target volume. Since the hot spot is inside the target volume, it therefore has no clinical importance to the patient.