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Intensity modulated radiation therapy (IMRT) is an advanced technique widely applied in developed countries. Credited to the programmable flexibility movement of leaves of the add-on multi-leaf collimators (MLCs), the radiation dose can be closely shaped to fit the tumor. This technique reduces the dose to the critical normal tissues surrounding the target volume. Though the use of MLCs for IMRT is understood by default, some investigators have suggested the so-called Jaws-only IMRT (JO-IMRT) technique; in which the integral jaws of the linear accelerators can be used to deliver non-uniform beam like the one received with the help of MLCs. This technique can be applied as an option for LINAC without MLC, where the technology and financial infrastructure is still limited. In this report we present initial experiences in the implementation of the JO-IMRT technique for head and neck cancer with the Panther Treatment Planning System (TPS) version 4.6 (supplied by Prowess Inc.) at Dong Nai General Hospital, Vietnam. This TPS, including the DAO (Direct Aperture Optimization) algorithm for IMRT inverse planning, is used to generate JO-IMRT plans. The study aims to investigate the implementation of JO-IMRT plans as well as its quality assurance (QA). All treatment plans were verified by using ion chamber (Farmer Type Chamber FC65-P, IBA) and 2D diode array measurements (MapCHECK2, Sun Nuclear Corporation, Melbourne, FL). Average deviation measurements point dose calculations were 2.2 ± 1.5%. For 2D diode array measurements, the gamma passing rate and distance to agreement (DTA) are 98.2 and 96%, respectively. The results show that, in comparison to 3D-CRT, the JO-IMRT technique has generated better dose distribution in the target volume and reduced dose to healthy tissues. |
