[Target volume delineation for head and neck cancer intensity-modulated radiotherapy]

Abstract

This article describes the determination and the delineation of the target volumes for head-and-neck cancers treated with intensity-modulated radiotherapy (IMRT). The delineation of the clinical target volumes (CTV) on the computerized tomography scanner (CT scan) requires a rigorous methodology due to the complexity of head-and-neck anatomy. The clinical examination with a sketch of pretreatment tumour extension, the surgical and pathological reports and the adequate images (CT scan, magnetic resonance imaging and fluorodeoxyglucose positron emission tomography) are necessary for the delineation. The target volumes depend on the overall strategy: sequential IMRT or simultaneous integrated boost-IMRT (SIB-IMRT). The concept of selectivity of the potential subclinical disease near the primary tumor and the selection of neck nodal targets are described according to the recommendations and the litterature. The planing target volume (PTV), mainly reflecting setup errors (random and systematic), results from a uniform 4-5mm expansion around the CTV. We propose the successive delineation of: (1) the gross volume tumour (GTV); (2) the "high risk" CTV1 around the GTV or including the postoperative tumour bed in case of positive margins or nodal extracapsular spread (65-70 Gy in 30-35 fractions); (3) the CTV2 "intermediate risk" around the CTV1 for SIB-IMRT (59-63 Gy in 30-35 fractions); (4) the "low-risk" CTV3 (54-56 Gy in 30-35 fractions); (5) the PTVs.