REMOTELY POLLABLE GEIGER-MULLER DETECTOR FOR CONTINUOUS MONITORING OFI-131 THERAPY PATIENTS

In many countries, patients treated with therapeutic amounts of I-131 are hospitalized because of radiation safety considerations. To determ ine when they can return home, radiation levels are intermittently mon itored at bedside using a handheld Geiger-Muller (GM) counter, althoug h this procedure can be cumbersome and inexact. Methods: We have devel oped and tested a remotely pollable system for continuous radiation mo nitoring of I-131 therapy inpatients, using readily available hardware and standard telephone lines. The remote detector system, consisting of a palmtop IBM-compatible personal computer, specialized software, P CMCIA modem and miniature serial port-based GM detector, is placed opp osite the patient's bed at a fixed distance, and continuous 1-min acqu isitions are started. Initially and at least twice daily, the remote p almtop is contacted by modem, and all interval data are uploaded onto the operator's base computer over the telephone line, including measur ements taken with the patient in a predetermined standardized position . Continuous minute-to-minute data may be viewed in native form or can be imported into graphing and spreadsheet programs. Points acquired w ith the patient in standardized position are specially marked to highl ight the constant geometry used. The ratio of initial counting rate to administered dose is used to estimate residual I-131 body burden by p roportionality. Display of data as a semilogarithmic plot facilitates extrapolation of the activity curves and prediction of the patient's e arliest time of discharge. Results: We have characterized the remote G M detector system to confirm accuracy, counting rate linearity and rel iability of data transfer. We describe examples that illustrate the ap plicability and usefulness of this method for remote monitoring of inp atient I-131 therapy levels. Conclusion: Monitoring patients with the described remotely poltable GM detector is an accurate and easy-to-imp lement technique that could conceivably lead to shortened hospital sta ys for I-131 therapy inpatients. Continuous quantitative data obtained are useful for kinetic and dosimetric analyses, which may be applied to study other gamma-emitting radiopharmaceuticals as well. The flexib ility of the technique may permit its use in the monitoring of therapy on an outpatient basis, where allowed.