Routine IMRT verification by means of an automated Monte Carlo simulation system

A tool to simulate complete intensity-modulated radiation therapy (IMRT) treatments with the Monte Carlo (MC) method has been developed. This application is based on a distribution model to employ as short processing times as possible for an operative verification.

The Clinical Primus-Siemens Linac beam was simulated with MC, using the EGS4 OMEGA-BEAM code package. An additional home-made program prepares the appropriate parameters for the code, using as input the file sent from the planning system to the linac. These parameters are adapted to the simulation code, making physical and clinical subdivisions of the global simulation of the treatment. Each resultant partition is ordered to a client personal computer in a cluster with 47 machines under a Linux environment. The verification procedure starts delivering the treatment on a plastic phantom containing an ionization chamber. If differences are less than 2%, films are inserted at selected planes in the phantom and the treatment is delivered again to evaluate the relative doses. When matching between treatment planning system (TPS), film, and MC is acceptable, a new evaluation of the patient is then performed between TPS and MC. Three different cases are shown to prove the applicability of the verification model.

Acceptable agreement between the three methods used was obtained. The results are presented using different analysis tools. The actual time employed to simulate the total treatment in each case was no more than 5 h, depending on the number of segments.

The MC model presented is fully automated, and results can be achieved within the operative time limits. The procedure is a reliable tool to verify any IMRT treatment.