QDI~THERAPY & ONCOLOGY Radiotherapy and Oncology 43 (1997) 81-86 ELSEVIER Treatment portals for elective radiotherapy of the neck: an inventory in The Netherlands Peter Nowak*, Erik van Dieren, John van Siirnsen de Koste, Henry van der Est, Ben Heijmen, Peter Levendag Department of Radiation Oncology, Dr. Daniel den Hoed Cancer Center/University Hospital Rotterdam-Dijkzigt, Greene Hilledijk 301, 3075 EA, Rotterdam, The Netherlands Received 26 April 1996; revised version received 15 October 1996; accepted6 December 1996 Abstract Purpose: To assess the variation in and the three-dimensional dosimetric consequences of treatment portals for elective neck irradiation. Materials and methods: Radiation oncologists (n = 16) from all major Head and Neck Co-operative Groups in The Netherlands (n = 11) were askedto delineate treatmentportals on a lateral and an anterior simulation film in caseof elective neck irradiation for a T3NO tumour of the supraglottic larynx and a T2NO tumour of the mobile tongue. In addition, they had to define their target, i.e. which parts of the neck nodal regions they would choose to irradiate electively for these particular tumour sites. Subsequently,treatment portals were comparedand evaluated using CT-data and a 3-dimensional (3D) treatment planning system. Results: Significant variations were found in the shapesand sizes of the applied treatment techniques and portals. Also, among radiation oncologists who elected to irradiate the samelymph node regions, a significant variation in the delineated treatment portals was observed.As a consequence, substantial variations in treated volumes and in calculated normal tissue complication probabilities (NTCPs) for the parotid- and submandibularglands were observed. Conclusion: For the tumour sites studied there appearsto be a lack of standardisation in the areas of the neck to be irradiated electively. The observed differences may have consequences for the ultimate failure rate and particularly with regard to the side effects, e.g. the degreeof xerostomia. It is argued that in the near future a more precise three-dimensionaldefinition on CT of the lymph node regions in the neck might allow for a better standardisation of the treatment portals and, in addition, for the development and application of conformal radiotherapy techniques for optimal sparing of the critical normal tissues (e.g. parotid- and submandibularglands) with maximum tumour control probability. 0 1997 Elsevier Science B.V. All rights reserved Keywords: Head and neck; Radiotherapy; Treatment portals; Elective radiation 1. Introduction Elective irradiation of the NO neck has shown to be effective in eliminating subclinical disease [ 1,6-91. Unfor- tunately, this treatment is not without morbidity, that is, xerostomia is usually experienced because of (partial) inclusion of the (major) salivary glands in the treatment portals [lo]. * Correspondingauthor. The purpose of the present study was to assessthe var- iation in the routinely applied treatment portals in case of elective neck irradiation. This was done through a nation- wide inventory. To study the 3D consequences of the observed variation in treatment portals, the portals were compared and evaluated using CT-scans and a 3D treat- ment planning system. In a recent study, Leslie and Dische [5] showed that the radiation-induced reduction in pre-treatment parotid sali- vary flow is dependent on the percentage of the parotid gland volume irradiated. For this reason, in this study spe- cial attention is also given to the potential consequences of 0167.8140/97/$17.00 0 1997 Elsevier ScienceB.V. All rights reserved PII SO167-8140(96)01894-4