High dose-rate induced temperature artifacts: thermometry considerations for simultaneous interstitial thermoradiotherapy.
OBJECTIVE
The goal of the present study was to investigate the effect of high dose-rate radiation on a flouroptic thermometry system commonly used during microwave hyperthermia.


METHODS
Measurements were performed by placing the flouroptic thermometry sensors at distances of < or = 1.5, 5, 10, and 15 mm from a remote afterloading high dose-rate 192Ir source in a water bath (at two different temperatures) and in a tissue equivalent radiation bolus medium. A simulated volumetric clinical setup using a radiation bolus medium was performed with thermometry sensors placed at 1.5, 7.5, 8.4, and 10.6 mm from a scanning high dose-rate source.


RESULTS
It was found that high dose-rate radiation caused thermometry artifacts greater than 1.5 degrees C within 2 min for flouroptic thermometers placed 1.5 mm from a 5 Ci activity high dose-rate source. Simple calculations showed that artifacts of this magnitude could not be due to any heating caused by the energy deposited by the high dose-rate source. The artifact decayed, but was still evident 24 h after the exposure. The effect strongly depended on distance with a 0.7 degrees C artifactual increase in temperature seen for the probe 5 mm from the high dose-rate source. Moreover, experiments performed under conditions that represented a clinical setup with a 7 Ci high dose-rate source showed that for exposure times of 10 s, at distances of 1.5 mm, significant artifacts (> 0.5 degrees C) are produced.


CONCLUSIONS
These findings indicate that high dose-rate-induced temperature artifacts should be taken into account in the quality assurance procedures for the treatment of patients with simultaneous interstitial thermoradiotherapy.
Straube
W L
WL
Radiation Oncology Center, Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO 63110.
Meigooni
A S
AS
Moros
E G
EG
Williamson
J F
JF
Myerson
R J
RJ
D016477:Artifacts; D006801:Humans; D006979:Hyperthermia, Induced; D011878:Radiotherapy; D011879:Radiotherapy Dosage; D013696:Temperature