Quality assurance of modern image guided 3D-conformal radiotherapy treatments

Abstract

Purpose: To describe the Quality Assurance (QA) methods of modern Three-dimensional conformal radiotherapy (3DCRT) treatments such as image guided Intensity-modulated radiation therapy (IMRT), RapidArc, Stereotactic radiosurgery (SRS)/ Stereotactic fractionated radiation (SRT) to ensure quality of treatments delivered to cancer patients. Materials and methods: 3D-RFA and Ionisation chambers were used for the machine specific QA. Imatrixx-2D array with locally fabricated phantom and another locally fabricated spherical phantom with ionization chambers is used for relative and absolute QA respectively. Electronic Portal Imaging Devices and Epiqa software is used for the QA with portal dosimetry. Varians Eclipse and Brainlab’s Iplan treatment planning systems were used for treatment plans and dose calculations. For relative dosimetry the planar dose matrices are analysed using global Gamma Index criteria of 3mm distance to agreement (DTA) and 3% dose difference. The QA of Machines and patient treatments were carried out using national and international protocols. Results: The maximum deviations of percentage of dose points in which γ>1 are 1.98 in relative dosimetric QA and 1.5 for absolute QA in the delivery of IMRT, RapidArc and SRS/SRT treatments. The mean deviations and Standard deviation (SD) values are less in portal dosimetry than that of phantom studies in relative dosimetry and all the absolute dose deviations are less than that of relative dose deviations. Conclusion: The results of machine specific QA as well as relative and absolute dosimetric QA of patient treatments are well within the acceptable limits of values mentioned in the national and international protocols. The study ensures the accuracy and quality of the treatments delivered to the patients at our oncology center.

Keywords

• Quality assurance;
• RapidArc;
• Portal dosimetry;
• Gamma index;
• Image guided radiotherapy