A refined method for assessing 99mTc-MDP whole body retention in prostate cancer patients

Abstract

Whole body retention (WBR) of 99mTc labeled methylene diphosphonate (MDP) has been shown to significantly differentiate various clinical stages of prostate cancer. Whole body measurements, when performed at 5 min and 24 h after i.v. administration of 99mTc-MDP, allows for the calculations of percentage whole body retention (% WBR) after one day. The latter can be expressed relative to either the anterior or posterior projection, or in combination as the geometric mean value. In an attempt to better describe the clinical course of prostate cancer patients with bone metastases we have refined the % WBR calculations to include a normalization factor. The latter consists of the mean 24-h value of WBR's as obtained from 10 prostate cancer patients without bony métastases as determined by bone scintigram. These values were determined for each projection to be: anterior = 26.5 ± 4.7%, posterior = 37.5 ± 7.4%, and geometric mean = 31.5 ± 5.7%. The % WBR is then divided by the normalization factor of choice and expressed as (% WBR) N. These data are used to better express 99mTc MDP 24-h whole body retentions when following the clinical course of patients with metastatic carcinoma of the prostate. Caution should be exercised when interpreting these data when metabolic bone pathology is present. A false negative (% WBR) N value will result if an infiltration of the 99mTc-MDP occurs during administration.