[Clinical to target volume margins determination in radiotherapy for anal cancers]

There are very few data on the expansion from the clinical target volume (CTV) to the planning target volume (PTV) in the anal cancer treatment. This article aims to collect the different elements needed for the construction of a PTV from scientific data based on a literature analysis. We reviewed the articles published in the medical literature from the last 20years. They concerned setup errors and internal organ mobility of the different volumes of patients treated by conformational radiotherapy and intensity-modulated radiotherapy (anal canal, meso-rectum, common, intern and extern, inguinal and pre-sacral lymph nodes). CTV to PTV margins admitted in the guidelines and atlas of consensus groups (SFRO, RTOG, AGITG) are from 0.7 to 1cm in all directions, based on expert's opinions but not on scientific data. There are no specific studies on the canal anal mobility. Most of the data are from other pelvis cancers (gynecologic, rectum and prostate). Setup errors can be reduced by daily imaging. Patient repositioning and immobilization modalities are mostly local habits rather than scientific consensus. A three-dimensional 1cm margin is generally admitted. Margins reduction must be careful and has to be assessed.

[RapidArc technology: first year of experience at the Montpellier comprehensive cancer centre]

Intensity-modulated radiotherapy (IMRT) has highly impacted on the dose delivery thanks to inverse-planning dosimetry. Conformal isodoses to target volumes and critical organ protection have led to treatment possibilities which were unrealizable with conventional 3D technique. Nevertheless, time delivery using IMRT was in some cases longer than 3D radiotherapy. In order to compensate for this limitation, we have developed since 2007 a volumetric modulated arctherapy (RapidArc) in partnership with Varian. The technique, the results of the dosimetry plans, and quality control of the 142 first patients treated since November 2008 are presented in this review.