In vivo dosimetry with semiconducting diodes for dose verification in total-body irradiation. A 10-year experience.
OBJECTIVE
For total-body irradiation (TBI) using the translation method, dose distribution cannot be computed with computer-assisted three-dimensional planning systems. Therefore, dose distribution has to be primarily estimated based on CT scans (beam-zone method) which is followed by in vivo measurements to ascertain a homogeneous dose delivery. The aim of this study was to clinically establish semiconductor probes as a simple and fast method to obtain an online verification of the dose at relevant points.


METHODS
In 110 consecutively irradiated TBI patients (12.6 Gy, 2 x 1.8 Gy/day), six semiconductor probes were attached to the body surface at dose-relevant points (eye/head, neck, lung, navel). The mid-body point of the abdomen was defined as dose reference point. The speed of translation was optimized to definitively reach the prescribed dose in this point. Based on the entrance and exit doses, the mid-body doses at the other points were computed. The dose homogeneity in the entire target volume was determined comparing all measured data with the dose at the reference point.


RESULTS
After calibration of the semiconductor probes under treatment conditions the dose in selected points and the dose homogeneity in the target volume could be quantitatively specified. In the TBI patients, conformity of calculated and measured doses in the given points was achieved with small deviations of adequate accuracy. The data of 80% of the patients are within an uncertainty of +/- 5%.


CONCLUSIONS
During TBI using the translation method, dose distribution and dose homogeneity can be easily controlled in selected points by means of semiconductor probes. Semiconductor probes are recommended for further use in the physical evaluation of TBI.
Ramm
Ulla
U
Department of Radiotherapy and Oncology, Center of Radiology, University Hospital, Johann Wolfgang Goethe University, Frankfurt/Main, Germany. Ulla.Ramm@kgu.de
Licher
Jörg
J
Moog
Jussi
J
Scherf
Christian
C
Kara
Eugen
E
Böttcher
Heinz-Dietrich
HD
Rödel
Claus
C
Mose
Stephan
S
D019583:Dose Fractionation, Radiation; D004867:Equipment Design; D006801:Humans; D008168:Lung / Q000528:radiation effects; D011835:Radiation Protection / Q000295:instrumentation; D011874:Radiometry / Q000295:instrumentation*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D011882:Radiotherapy, High-Energy / Q000295:instrumentation*; D012666:Semiconductors / Q000295:instrumentation*; D014916:Whole-Body Irradiation / Q000295:instrumentation*