Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer
Received 1 February 2009; received in revised form 28 July 2009; accepted 2 August 2009. published online 18 September 2009.
Abstract
Introduction
Volumetric modulated arc therapy (VMAT), a complex treatment strategy for intensity-modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares VMAT against established IMRT and 3D-conformal radiation therapy (3D-CRT) delivery techniques.
Methods
Based on CT datasets of 9 patients treated for prostate cancer step-and-shoot IMRT, serial tomotherapy (MIMiC), 3D-CRT and VMAT were compared with regard to plan quality and treatment efficiency. Two VMAT approaches (one rotation (VMAT1x) and one rotation plus a second 200° rotation (VMAT2x)) were calculated for the plan comparison. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D95% (dose encompassing 95% of the target volume). For plan efficiency evaluation, treatment time and number of monitor units (MU) were considered.
Results
For MIMiC/IMRTMLC/VMAT2x/VMAT1x/3D-CRT, mean CI was 1.5/1.23/1.45/1.51/1.46 and HI was 1.19/1.1/1.09/1.11/1.04. For a prescribed dose of 76Gy, mean doses to organs-at-risk (OAR) were 50.69Gy/53.99Gy/60.29Gy/61.59Gy/66.33Gy for the anterior half of the rectum and 31.85Gy/34.89Gy/38.75Gy/38.57Gy/55.43Gy for the posterior rectum. Volumes of non-target normal tissue receiving ⩾70% of prescribed dose (53Gy) were 337ml/284ml/482ml/505ml/414ml, for⩾50% (38Gy) 869ml/933ml/1155ml/1231ml/1993ml and for⩾30% (23Gy) 2819ml/3414ml/3340ml/3438ml /3061ml. D95% was 69.79Gy/70.51Gy/71,7Gy/71.59Gy/73.42Gy. Mean treatment time was 12min/6min/3.7min/1.8min/2.5min.
Conclusion
All approaches yield treatment plans of improved quality when compared to 3D-conformal treatments, with serial tomotherapy providing best OAR sparing and VMAT being the most efficient treatment option in our comparison. Plans which were calculated with 3D-CRT provided good target coverage but resulted in higher dose to the rectum.
ABSTRACT