Dosimetric study on gated and non gated volumetric modulated arc therapy

Abstract

In the modern radiotherapy era the use of intensity modulated treatment techniques have become a daily routine due to the advancement of science and technology. Though the intensity modulated techniques like Intensity Modulated Radiotherapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) is promising in many situations by reducing the OAR doses dramatically, the use of the same for locally advanced diseases may not be commendable as the target volumes were large and might include part of the surrounding OARs. The ability to deposit differential dose, simultaneous integrated boost (SIB) was feasible only with intensity modulated techniques with ease. Since hypofractionation and reduction in overall treatment time were found to be beneficial to the patients in terms of shorter treatment duration compared to conventional treatment regimen, SIB technique has become the choice of treatment wherever possible. For patients with locally advanced disease of carcinoma of cervix, as an alternative to IMRT or VMAT technique without any compromise, a dosimetrically equivalent SIB plan using conformal field in field technique was attempted. Our results were encouraging with no statistical superiority of IMRT and VMAT techniques over the conformal FiF plans on comparing dosimetric parameters. As radiotherapy evolves, more emphasize is given to the precision and accuracy of the treatment. One of the common and inevitable uncertainty in radiotherapy is the uncertainty in dose deposition due to the internal organ motion. This organ motion is mostly respiration induced and also involuntary. Many organ motion managements have been introduced over the decades. The most commonly used, without much difficulty is the Gating methods. Varian Real-time position management (RPMTM) system is devised to enable beam gating in image acquisition as well as during treatment. Gating is classified into prospective and retrospective. Prospective gating is again sub divided into amplitude gating and phase gating. We wanted to find the patient population which actually gets benefit out of these different gating techniques and also to find the effective treatment delivery technique (IMRT or VMAT) to pair with to reap the best dosimetrical and clinical outcomes. We tried to dosimetrically compare three different gating techniques in tumors of three anatomical sites (known for respiratory induced organ motions) paired with two intensity modulated treatment delivery techniques. Our observations were suggesting that treatment technique wise VMAT is superior to IMRT but gating techniques were very much patient specific and the tumor geometric location specific as for the same site (e.g. lungs) our results were not favoring single gating technique newline