Background: Currently the significance of the sentinel node (SN) biopsy also for head and neck cancer is discussed intensively. Based on the complex anatomic structures of this region with a low distance between primary and sentinel node as well as approximately 300 lymph nodes an intensive discussion of the methodical basis of sentinel node detection seems to be essential. Thus it was the aim of the present study to examine the detection spectrum of a gamma probe for identification of cervical lymph nodes using an in vitro model to describe and objectify the particularities of measurement existing in the head and neck region.
Material/methods: In an in vitro model the detection spectrum of a gamma probe is examined in 29 different series of measurements (variation of the specimen filled with 99m pertechnetat regarding activity, position, collimator distance, tissue sheath).
Results: The presented in vitro model reflects the clinical problem of narrow intranodal activity of neighbouring lymph nodes and reveals a direct relation between the number of radiation sources and their isolated evidence. Using muscle tissue with a thickness of 0.4 cm, two two-rowed radiation sources, the more powerful is placed 1.5 cm behind the other specimen, with a lateral difference of 3 cm, can be resolved only with a maximal detector distance of 1 cm. Not the difference of the tissue but the thickness of the tissue is decisive for detection.
Conclusion: Especially for pharyngeal and laryngeal lymph nodes a transcutaneous measurement reflecting the exact localisation of hot nodes in the area of the deep jugular lymph nodes is not possible with increasing tissue thickness. The described results require a critical discussion of the different detection techniques varying among the different working groups of this field.