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].