Volumetric modulated arc therapy: a review of current literature and clinical use in practice

Abstract

Volumetric modulated arc therapy (VMAT) is a novel radiation technique, which can achieve highly conformal dose distributions with improved target volume coverage and sparing of normal tissues compared with conventional radiotherapy techniques. VMAT also has the potential to offer additional advantages, such as reduced treatment delivery time compared with conventional static field intensity modulated radiotherapy (IMRT). The clinical worldwide use of VMAT is increasing significantly. Currently the majority of published data on VMAT are limited to planning and feasibility studies, although there is emerging clinical outcome data in several tumour sites. This article aims to discuss the current use of VMAT techniques in practice and review the available data from planning and clinical outcome studies in various tumour sites including prostate, pelvis (lower gastrointestinal, gynaecological), head and neck, thoracic, central nervous system, breast and other tumour sites.

Figure 1

Example of dose distributions in (a,b) IMRT and (c,d) VMAT plans for radiotherapy to prostate (primary planning target volume (PTV)) and pelvic lymph nodes (elective PTV). The dose prescribed to the primary PTV and elective PTV is 74 Gy and 55 Gy in 37 fractions, respectively. The primary PTV (red contour) is encompassed by the 95% isodose (orange line and colour wash) and the elective PTV (pink contour) is encompassed by the 70.6% isodose (dark blue line and light green colour wash). Some sparing of the rectum (brown contour) and bladder (yellow contour) is achieved. Figures courtesy of Department of Medical Physics, Royal Surrey County Hospital, UK.

Figure 2

Example of dose distributions in (a,b) IMRT and (c,d) VMAT plans for oropharyngeal cancer. The dose prescribed to the primary planning target volume (PTV) (encompasses the tumour and involved lymph nodes) and elective PTV (regional lymph nodes at risk of microscopic spread) is 65 Gy and 54 Gy in 30 fractions, respectively. The primary PTV (red contour) is encompassed by the 95% isodose (orange line and colour wash) and the elective PTV (pink contour) is encompassed by the 78.9% isodose (dark blue line and light green colour wash). Some sparing of the parotid gland (light blue contour) is achieved. Figures courtesy of Department of Medical Physics, Royal Surrey County Hospital, UK.

Figure 3

Example of dose distributions in (a) IMRT and (b) VMAT plans for malignant glioma. The dose prescribed to the planning target volume (PTV) (red contour) is 60 Gy in 30 fractions. The 95% isodose (green line) is encompassing most of the PTV. There is compromise of PTV coverage to allow sparing of the optic nerves (dark blue contour) and brain stem (pink contour). Figures courtesy of Dr R Shaffer. Reprinted from Int J Radiat Oncology Biol Phys, Vol. 76, No.4, Shaffer R, Nichol AM, Vollans E, Fong M, Nakano S, Moiseenko V et al. A comparison of volumetric modulated arc therapy and conventional intensity-modulated radiotherapy for frontal and temporal high-grade gliomas, pp. 1177-1184, Copyright 2010, with permission from Elsevier [133].

Figure 4

Example of dose distributions in (a) IMRT and (b) VMAT plans for radiotherapy to a retroperitoneal tumour in a paediatric patient. The planning target volume (PTV) (red contour) is encompassed by the 95% isodose (green line). The organs at risk include liver (blue contour), kidneys (dark orange and light blue), vertebral body (pink contour) and spinal cord (lilac contour). Figures courtesy of Dr R Shaffer. This material is reproduced with permission of John Wiley & Sons, Inc from Pediatr Blood Cancer, 2011, Vol 56, Shaffer R, Vollans E, Vellani R, Welsh M, Moiseenko V, Goddard K. A radiotherapy planning study of RapidArc, Intensity Modulated Radiotherapy, Three-Dimensional Conformal Radiotherapy, and Parallel Opposed Beams in the Treatment of Pediatric Retroperitoneal Tumors, pp.16-23, Copyright 2011Wiley-Liss, Inc [157].