Development of novel MLC delivery fields of IMRT and VMAT plans

Abstract

Multileaf collimator (MLC) segmentation is an important step in intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) treatment delivery. IMRT treatment planning process concretely involves three steps: gantry angles selection, fluence optimisation and MLC aperture segmentation. MLC segmentation is a key parameter which determines the total MU and total number of segments of a treatment plan which eventually affects the efficiency of a treatment plan. The optimal fluence is used as input to leaf motion calculator (LMC) to extract aperture shapes in Eclipse treatment planning system (TPS) for IMRT planning. The MLC segmentation in Eclipse allows unidirectional movement of leaves in both dynamic and segmental IMRT. However, bidirectional movement of leaves offer various advantages pertaining to efficiency of treatment plan and reduction in motion related uncertainties. In this research work, the fluence is reconstructed from treatment log files, which is used as input for MLC aperture shaping algorithm. The MLC shapes are developed to deliver the optimal fluence for bidirectional movement of leaves so as to improve efficiency of the treatment. VMAT treatment delivery involves change in gantry speed, dose rate and leaf speed to achieve desired dose distribution. Nowadays SBRT treatments are gaining success and fame where hotspots are deemed to be acceptable. VMAT is primary choice for treatment planning owing to its better TCP and OAR sparing. However, more complex MLC shapes results in increased modulation of the treatment plan. As the increased modulation might affect the treatment accuracy, quality assurance of treatment plans is necessary to ensure qualitative treatment. As the quality assurance process using array detector is time consuming process, a predictive model is derived to quantify the gamma pass rates at the planning stage for VMAT plans of SBRT treatments. newline