Remotely pollable Geiger-Müller detector for continuous monitoring of iodine-131 therapy patients

In many countries, patients treated with therapeutic amounts of (131)I are hospitalized because of radiation safety considerations. To determine when they can return home, radiation levels are intermittently monitored at bedside using a handheld Geiger-MIller (GM) counter, although this procedure can be cumbersome and inexact.

We have developed and tested a remotely pollable system for continuous radiation monitoring of (131)I therapy inpatients, using readily available hardware and standard telephone lines. The remote detector system, consisting of a palmtop IBM-compatible personal computer, specialized software, PCMCIA modem and miniature serial port-based GM detector, is placed opposite the patient's bed at a fixed distance, and continuous 1-min acquisitions are started. Initially and at least twice daily, the remote palmtop is contacted by modem, and all interval data are uploaded onto the operator's base computer over the telephone line, including measurements 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 with the patient in standardized position are specially marked to highlight the constant geometry used. The ratio of initial counting rate to administered dose is used to estimate residual (131)I body burden by proportionality. Display of data as a semilogarithmic plot facilitates extrapolation of the activity curves and prediction of the patient's earliest time of discharge.

We have characterized the remote GM detector system to confirm accuracy, counting rate linearity and reliability of data transfer. We describe examples that illustrate the applicability and usefulness of this method for remote monitoring of inpatient (131)I therapy levels.

Monitoring patients with the described remotely pollable GM detector is an accurate and easy-to-implement technique that could conceivably lead to shortened hospital stays for (131)I 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 flexibility of the technique may permit its use in the monitoring of therapy on an outpatient basis, where allowed.