A systematic study of techniques for elective cervical nodal irradiation with anterior or opposed anterior and posterior beams

Abstract

Purpose: To assess target coverage and dose homogeneity using conventional radiotherapy (RT) and intensity-modulated RT (IMRT) with anterior and posterior beams for elective irradiation of the cervical lymph nodes in patients with head and neck cancer.Materials and methods: A planning study was performed in six patients who had undergone radical RT for head and neck cancer. RT plans to irradiate the cervical lymph nodes using a single anterior field, or opposed anterior and posterior fields, with 6 or 10 MV photons were compared. Plans using IMRT for missing-tissue compensation were also studied. An algorithm was developed to guide clinicians to the most appropriate treatment technique depending on the nodal groups to be irradiated.Results: With 6 MV single field (SF) irradiation significant under-dose (minimum dose <70% of prescription dose) was seen in nodal groups II and V, due to their posterior position. With SF 10 MV the mean dose to level II was higher (p<0.001) and dose homogeneity to levels Ib and II was improved. Using opposed fields (OF), minimum doses to the nodes in levels II and V were improved. OF using 10 MV showed significant advantage over 6 MV with reduction of maximum doses to levels II, III and V. SF 10 MV IMRT improved maximum doses to levels Ib and II compared to SF 6 MV IMRT. OF IMRT gave the best dose distributions with optimal mean dose and dose homogeneity. Beam energy made no difference with OF IMRT.Conclusions: The optimal technique for elective cervical node irradiation depends on the lymph node levels within the PTV. If irradiation of the level II or V nodes is required, then the OF IMRT technique with either 6 or 10 MV gives the best dose distributions. In the absence of IMRT, then OF conventional techniques are best. If the aim is to irradiate levels III and IV or level IV only, then 6 MV SF non-IMRT is the simplest technique.