A Dosimetric Comparison of VMAT and IMRT for Head & Neck and Pelvis Cancers

Cancer, which is the uncontrolled division of cells, is a leading fatal disease in the world with high mortality rates. It can be treated using several methods, including radiotherapy, which involves ionizing radiation. Radiotherapy on the basis of source placement has two types, i.e. brachytherapy and external beam radiotherapy. External beam radiotherapy has evolved from 2-D conventional therapy to 3-D Conformal radiotherapy (3D-CRT) and then intensity-modulated radiotherapy (IMRT). Modern radiation therapy techniques such as IMRT improve dose conformity and sparing of organs at risk. Volumetric modulated arc therapy (VMAT) is a newly developed technique that uses treatment in arcs. In this report, a dosimetry comparison was performed between IMRT and VMAT. This study was conducted in the Radiotherapy Department of the Institute of Nuclear Medicine and Oncology Lahore (INMOL). Two types of cancer patients were selected for this comparison, i.e., five patients with Nasopharyngeal Carcinoma and ten patients with Prostate Carcinoma. Simulation of these patients was done with the help of a CT Simulator. The oncologists delineated all target volumes and organs. Then suitable fields/arcs were applied, which cover volumes effectively. This was followed by the optimization of plans for both techniques for every patient. Finally, evaluating parameters were compared, including volume coverage, conformity index, homogeneity index, organ doses, and monitor units. We obtained better results of target conformity indices from VMAT (1.16 and 1.25) than IMRT (1.24 and 1.30). VMAT was better in organ sparing too. Also, VMAT shows very few monitor units (468 and 733) as compared to IMRT (2325 and 2149). On the basis of the results obtained, it was concluded that VMAT is better than IMRT. This technique will enhance treatment efficiency as it takes less time to obtain the required results. Also, a very less scatter dose will be delivered to the patient.