TREATMENT PORTALS FOR ELECTIVE RADIOTHERAPY OF THE NECK - AN INVENTORY IN THE NETHERLANDS

Purpose: To assess the variation in and the three-dimensional dosimetr ic consequences of treatment portals for elective neck irradiation. Ma terials and methods: Radiation oncologists (n = 16) from all major Hea d and Neck Go-operative Groups in The Netherlands (n = 11) were asked to delineate treatment portals on a lateral and an anterior simulation film in case of elective neck irradiation for a T3NO tumour of the su praglottic larynx and a T2NO tumour of the mobile tongue. Ln addition, they had to define their target, i.e. which parts of the neck nodal r egions they would choose to irradiate electively for these particular tumour sites. Subsequently, treatment portals were compared and evalua ted using CT-data and a 3-dimensional (3D) treatment planning system. Results: Significant variations were found in the shapes and sizes of the applied treatment techniques and portals. Also, among radiation on cologists who elected to irradiate the same lymph node regions, a sign ificant variation in the delineated treatment portals was observed. As a consequence, substantial variations in treated volumes and in calcu lated normal tissue complication probabilities (NTCPs) for the parotid - and submandibular glands were observed. Conclusion: For the tumour s ites studied there appears to be a lack of standardisation in the area s of the neck to be irradiated electively. The observed differences ma y have consequences for the ultimate failure rate and particularly wit h regard to the side effects, e.g. the degree of xerostomia. It is arg ued that in the near future a more precise three-dimensional definitio n 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 de velopment and application of conformal radiotherapy techniques for opt imal sparing of the critical normal tissues (e.g. parotid- and submand ibular glands) with maximum tumour control probability. (C) 1997 Elsev ier Science B.V.