Elsevier

Radiotherapy and Oncology

Volume 73, Issue 3, December 2004, Pages 289-296
Radiotherapy and Oncology

11C-methionine PET, a novel method for measuring regional salivary gland function after radiotherapy of head and neck cancer

https://doi.org/10.1016/j.radonc.2004.09.009Get rights and content

Abstract

Background and purpose

Loss of salivary gland function is a distressing side-effect of radiotherapy (RT) for head and neck cancer. The aim of this study was to develop a positron emission tomography (PET) method for measuring regional salivary gland function in the major salivary glands irradiated during RT.

Patients and methods

Eight head and neck cancer patients were included; two were examined before RT and six after parotid sparing RT. Patients were examined by dynamic 11C-methionine PET of the major salivary glands and parotid gland salivary flow measurements. PET data were analysed using a kinetic model of salivary gland 11C-methionine metabolism, in which salivary gland function was quantified by the net metabolic clearance of 11C-methionine, K. Functional voxel-wise images of K were calculated and matched with the CT-dose-plan for comparing regional salivary gland function with the regional radiation dose.

Results

Parotid gland K correlated positively with parotid gland salivary flow, indicating that K can be used as an index of salivary gland function. K of parotid and submandibular glands was reduced dependent on the median radiation dose. In one patient, receiving a heterogeneous radiation dose to the parotid glands, regional salivary gland function was inversely correlated to the regional radiation dose.

Conclusions

Salivary gland function can be measured by dynamic 11C-methionine PET. The net metabolic clearance of 11C-methionine of salivary glands was reduced dependent on the radiation dose. Dynamic 11C-methionine PET offers a method for studying the individual response of the major salivary glands to irradiation.

Introduction

Loss of salivary gland function is a distressing side-effect after radiotherapy (RT) for head and neck cancer [12], caused by incidental irradiation of the major salivary glands. Much recent research has examined whether new techniques of RT spare salivary gland function [6], [18], assessed by stimulated parotid salivary flow measurements. This method, however, is not applicable to the submandibular glands, and it cannot assess function in smaller regions of the salivary glands. 99mTc-pertechnetate SPECT has been proposed for investigating regional parotid gland function after RT [22]. PET is a comparable imaging technique, which enables in vivo studies of human metabolism in 3D, but provides superior spatial resolution than SPECT imaging [17].

The aim of this study was to develop a PET method for measuring regional salivary gland function in the major salivary glands irradiated during RT. For this purpose, we decided to use dynamic PET with the tracer l-[methyl-11C] methionine (11C-methionine). 11C-methionine is a commonly used PET tracer that has been tested for defining tumour volume in head and neck cancer [8], measuring liver protein synthesis [10], [11], and assessing excretory pancreas function [20], [21]. Furthermore, 11C-methionine has been tested for imaging response of head and neck cancer to RT [13], wherein it was noted that salivary gland uptake of 11C-methionine decreased after RT. We hypothesised that regional salivary gland function can be measured by dynamic 11C-methionine PET, and that the PET measure of salivary gland function are reduced dependent on the radiation dose.

To test this hypothesis, dynamic 11C-methionine PET and parotid gland salivary flow measurements were performed in patients with head and neck cancer after RT.

Section snippets

Patients

Eight head and neck cancer patients were included in the study. Two patients were studied before RT, and six patients were studied after minimum 6 months following RT. RT was delivered using either an ipsilateral conformal technique or IMRT for sparing the contralateral parotid gland. Radiation dose to the gross tumour volume was 66–68 Gy in 33–34 fractions over 6 weeks. Elective lymph node areas received 46–50 Gy. All patients except from Patient 5 were treated with the hypoxic radiosensitizer

Results

The sublingual, submandibular, and parotid glands were identified in the summed 11C-methionine PET images. The 11C-radioactivity concentration was consistently higher in salivary glands irradiated with a low radiation dose than in glands irradiated with a high dose (Fig. 1). There was a moderate 11C-radioactivity concentration in the brain and high 11C-radioactivity concentration of the oral and pharyngeal cavity. In specimens of parotid saliva, the 11C-radioactivity concentration was about 300 

Discussion

New techniques of RT have enabled sparing of the salivary glands during treatment for head and neck cancer, calling attention to the dose-response relationship of the major salivary glands. For this purpose, we developed a new 3D PET method for measuring regional salivary gland function after RT. Dynamic 11C-methionine PET provides the net metabolic clearance of 11C-methionine as a quantitative measure of regional salivary gland function in the major salivary glands. We found that the net

Acknowledgements

This study was supported by grants from the Danish Medical Research Council (22-02-0337) and the Danish Cancer Society (KFE–Å-235-02). The authors thank Anne Marie Nehen, Department of Neuroradiology P, Aarhus University Hospital for interpreting MR images, and Paul Cumming for critical reading of the manuscript.

References (22)

  • A.J. Fischman et al.

    Muscle protein synthesis by positron-emission tomography with L-[methyl-11C]methionine in adult humans

    Proc Natl Acad Sci U S A

    (1998)
  • Cited by (0)

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