Formulation and initial experience on patient specific quality assurance for clinical implementation of dynamic IMRT

Intensity modulated radiotherapy (IMRT) is an advanced form of 3D conformal radiotherapy combining several intensity modulated beams to deliver the prescribed dose to the target with precision, sparing the adjacent normal tissue structures. The complex nature of IMRT delivery needs a precise patient specific quality assurance (QA), proper verification of dosimetry and treatment. QA procedures are important measures to ensure that the treatment can be delivered according to the treatment plan. In this report, we are presenting a formulation of a proposed protocol and results of patient specific QA carried on two IMRT plans. The QA consists of an absolute dosimetry, film dosimetry and dynalog files verification of treatment plans. The absolute doses, planar and fluence doses calculated by the TPS are compared with the measured values. The dynalog files recorded during the treatment delivery of two plans were analysed. The measured error in absolute dose is <3% in both the plans. An average of >98% of counts are having <0.1 cm errors in dMLC positions. The average RMS value of leaf motions is <0.05 cm in both the cases. The errors in film dosimetry are <3%. All the results obtained are comparable to the standard values and well within the acceptable limits. The paper outlines the minimum procedures required for the patient specific QA measurements for the clinical implementation of IMRT. The measurements help to understand and confirm the accuracy of IMRT delivery system.