Initial clinical results of an in vivo dosimeter during external beam radiation therapy

Purpose: An implantable radiation dosimeter has been developed to monitor dose delivered at depth in patients undergoing external beam therapy. A clinical pilot study was conducted to test the safety, efficacy, and utility of the device. Methods and Materials: Ten patients, all with unresectable malignant disease, were enrolled to assess implantation risk and movement of the device in the body and to compare the in vivo measured dose to the value predicted by the treatment planning system software. Results: Migration of the sensor away from the point of original placement was noted in only 1 patient (due to unconsolidated host tissue) and no adverse events were recorded during the implantation procedure or thereafter. Daily dose measurements were recorded successfully for all sensors in all patients. Variance between measured and predicted dose values was reported as a frequency of error at the ≥5% and ≥8% levels. The error frequency at the ≥8% level was as high as 47%, 29%, and 21% for lung, prostate, and rectal tumors, respectively. Conclusions: The implantable dosimeter was found to be safe and effective in measuring dose at depth. There are many factors that can influence delivered dose, and the implantable dosimeter measures the net effect of these factors. The daily sensor readings provide a new tool for rigorous treatment quality assurance.