Technical evaluation of radiation dose delivered in prostate cancer patients as measured by an implantable MOSFET dosimeter.

PURPOSE: To perform a comparison of the daily measured dose at depth in tissue with the predicted dose values from treatment plans for 29 prostate cancer patients involved in a clinical trial. METHODS AND MATERIALS: Patients from three clinical sites were implanted with one or two dosimeters in or near the prostatic capsule. The implantable device, known as the DVS, is based on a metal-oxide-semiconductor field effect transistor (MOSFET) detector. A portable telemetric readout system couples to the dosimeter antenna (visible on kilovoltage, computed tomography, and ultrasonography) for data transfer. The predicted dose values were determined by the location of the MOSFET on the treatment planning computed tomography scan. Serial computed tomography images were taken every 2 weeks to evaluate any migration of the device. The clinical protocol did not permit alteration of the treatment parameters using the dosimeter readings. For some patients, one of several image-guided radiotherapy (RT) modalities was used for target localization. RESULTS: The evaluation of dose discrepancy showed that in many patients the standard deviation exceeded the previous values obtained for the dosimeter in a phantom. In some patients, the cumulative dose disagreed with the planned dose by > or =5%. The data presented suggest that an implantable dosimeter can help identify dose discrepancies (random or systematic) for patients treated with external beam RT and could be used as a daily treatment verification tool for image-guided RT and adaptive RT. CONCLUSION: The results of our study have shown that knowledge of the dose delivered per fraction can potentially prevent over- or under-dosage to the treatment area and increase the accuracy of RT. The implantable dosimeter could also be used as a localizer for image-guided RT.

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 > or =5% and > or =8% levels. The error frequency at the > or =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.