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Salivary gland dosimetry using 124I-PET/CT imaging and MIRD method

Pettinato, C., Celli, M., Cima, S., Monari, F., Civollani, S., Nanni, C., Allegri, V., Zagni, P., Mazzarotto, R., Spezi, Emiliano and Fanti, S. 2013. Salivary gland dosimetry using 124I-PET/CT imaging and MIRD method. European Journal of Nuclear Medicine and Molecular Imaging 40 , S125-S126.

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Abstract

Salivary gland toxicity is often of concern on radioiodine therapy of thyroid cancer. The major problem is that toxicity could occur even if the absorbed doses are below the expected limits (26 Gy for EBRT). In the past this was associated to the fact that the poor accuracy of standard dosimetric Methods, based on planar I131 images, assuming that calculated absorbed doses were underestimated. The Aim of this work was the evaluation of the feasibility of using serial 124I-PET/CT scans for the measurement of absorbed doses to salivary glands. Material and Methods: Twenty-five patients affected by metastatic thyroid cancer (MTC) were enrolled in a study approved by the ethical Committee of our Institution, with the Aim to evaluate the usefulness of 124I PET/CT sequential scans to predict absorbed doses to metastatic thyroid cancer patients undergoing 131I therapy. Fifteen patients had salivary glands included in the PET FOV and were used for absorbed dose measurements to submandibular salivary glands and parotids. For each of the four PET/CT scans the mean activity concentration in the glands were obtained, corrected for partial volume effect and scaled to 131I decay time. Absorbed doses were calculated using the sphere model of the MIRD formalism, with volumes segmented on CT images. Results: The 131I administered activity was 3700 MBq for patients presenting negative PET/CT finding and 7400-11100 MBq for patients with iodine avid metastases. Mean dose per administered 131I activity was respectively 0.67 ± 0.35 mGy/MBq and 0.56 ± 0.37 mGy/MBq for parotids and submandibular glands. The corresponding mean absorbed doses were 4.11 ± 2.55 Gy (range: 0.19 - 11 Gy) and 3.38 ± 2.62Gy (range: 0.26 - 10.3 Gy). Two patients complained for mild salivary complications and none of the patient had severe impairment. Discussion and Conclusion: 124I-PET/CT imaging can usefully be used for salivary gland dosimetry following the MIRD formalism. Although the values found in this work are slightly lower than similar data published in literature, they are quite below the toxicity thresholds. Considering the mean doses per unit of 131I administered activity, the toxicity limit would not be exceeded even following high dose protocols. However the clinical toxicity occurs and probably the reason should be related with a possible higher radiosensitivity of the glands and the influence of cumulative dose due to multiple treatments.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Engineering
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Publisher: Springer
ISSN: 1619-7070
Related URLs:
Last Modified: 04 Jun 2017 08:05
URI: http://orca.cf.ac.uk/id/eprint/72532

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