Abstract
The goal of radiation therapy is to deliver a dose as high as possible to the target volume, while limiting radiation damage to the surrounding normal tissues. Advanced radiation therapy techniques, such as static and rotational intensity modulated radiotherapy (IMRT) are proposed to improve the dose conformity of the tumor while sparing the dose to normal tissue. Along with the rising interest in the highly conformal treatments comes the need for appropriate and efficient quality assurance (QA) solutions to ensure the accuracy of plan dose calculation and treatment delivery. This study developed MC-based dose simulation systems for static and rotational IMRT dose verification. For the static IMRT, the measurement based fluence reconstruction approach was proposed. The measurement based Monte Carlo system (MBMC) performs, within one systematic calculation, both pretreatment and on-line transit dose verifications for static intensity-modulated radiotherapy dose verification. An EPID-measured efficiency map was used to reconstruct the IM fluence in MC simulation. For the rotational IMRT, the calculation based fluence reconstruction approach was adopted. The MC-Arc system reconstructs the fluence distribution from the information provided by the DICOM-RT file. The dosimetric features of the MLC, rounded leaf end transmission, intra-leaf transmission, and tongue and groove effect, were included in this system. The reliability and clinical applicability of the built systems were validated via phantom study and patient study. The results showed that the MBMC system was able to preserve multileaf collimator delivery effects such as the tongue-and-groove effect and interleaf leakage. The perfect agreement between measurements and MC simulations supported the reliability of the MBMC system. For the MC-Arc system, the DVH comparison of the phantom study indicated that with all three MLC corrections, the mean doses of the PTV by the MC-Arc and TPS agreed to within 0.4%. The system was combined with an efficient MC code (MCSIM) to dosimetry validation for rotational IMRT treatment plans. The results indicated that MC simulation was necessary especially for the heterogeneous region and complex treatment. With the reasonable CPU time and superior accuracy, we conclude that this system can be clinical used for dose verification, serve as an independent plan check tool and research platform.