The MLC tongue-and-groove effect on IMRT dose distributions

We have investigated the tongue-and-groove effect on the IMRT dose distributions using the EGS4/MCDOSE Monte Carlo code. We have compared the dose distributions computed by MCDOSE using the fluence maps with and without tongue-and-groove effect. Our results showed that, for one intensity modulated treatment field, the tongue-and-groove effect could be seen clearly in the dose distributions. For an IMRT treatment with multiple gantry angles, the! difference between the dose distributions with and without the tongue-and-groove effect was reduced significantly. After considering the setup errors, however, no distinguished discrepancies were found, indicating that, for IMRT treatment planning, the tongue-and-groove effect can be neglected due to its negligible Impact on the overall dose distributions.