The utility of SPECT in determining the relationship between radiation dose and salivary gland dysfunction after radiotherapy

Salivary gland scintigraphy (SGS) is used to depict salivary gland dysfunct ion after radiotherapy (RT). The aim of this study was to investigate the u tility of SGS combined with single photon emission computed tomography (SPE CT). Twenty-one patients with a carcinoma of head and neck underwent SGS be fore and 1 month after RT. After injection of 370 MBq Tc-99(m)-pertechnetat e, a biplanar dynamic acquisition (12 x 1 min) was started, followed by a S PECT acquisition during 4 min. Carbachol was then injected and a second dyn amic study (16 x 1 min) was performed, again followed by a SPECT acquisitio n. The salivary excretion fraction (SEF) was calculated both from the geome tric mean planar image for each parotid and from the SPECT data for each tr ansverse plane through the parotids. The RT-induced changes in the SEF (dSE F) were correlated with the mean radiation dose calculated using tomography -based dosimetry. The mean radiation dose to the parotids was 44 Gy (range 4.4-68.1 Gy). The mean range of the variation in radiation dose to the tran sverse slices within the parotids of a patient was 24 Gy (range 6.2-51.9 Gy ). Considering all transverse planes through the parotids in all patients, a linear correlation was found between the dSEF calculated using SGS-SPECT and the radiation dose (r = 0.45, P = 0.0001). Thirteen patients had a vari ation in radiation dose within the parotids of more than 20 Gy. In nine of these a significant intra-individual correlation between radiation dose and the dSEF of the transverse parotid slices was found (r range 0.55-0.97; P value range 0.037-0.0001). In conclusion, SCS-SPECT can be used for monitor ing radiation-induced parotid gland dysfunction. It offers the unique possi bility for the assessment of intra-individual dose-dysfunction curves in pa tients with large variations in the radiation dose within the parotids. ((C ) 2001 Lippincott Williams & Wilkins).