In vivo dosimetry using a linear Mosfet-array dosimeter to determine the urethra dose in 125I permanent prostate implants.
OBJECTIVE
In vivo dosimetry during brachytherapy of the prostate with (125)I seeds is challenging because of the high dose gradients and low photon energies involved. We present the results of a study using metal-oxide-semiconductor field-effect transistor (MOSFET) dosimeters to evaluate the dose in the urethra after a permanent prostate implantation procedure.


METHODS
Phantom measurements were made to validate the measurement technique, determine the measurement accuracy, and define action levels for clinical measurements. Patient measurements were performed with a MOSFET array in the urinary catheter immediately after the implantation procedure. A CT scan was performed, and dose values, calculated by the treatment planning system, were compared to in vivo dose values measured with MOSFET dosimeters.


RESULTS
Corrections for temperature dependence of the MOSFET array response and photon attenuation in the catheter on the in vivo dose values are necessary. The overall uncertainty in the measurement procedure, determined in a simulation experiment, is 8.0% (1 SD). In vivo dose values were obtained for 17 patients. In the high-dose region (> 100 Gy), calculated and measured dose values agreed within 1.7% +/- 10.7% (1 SD). In the low-dose region outside the prostate (< 100 Gy), larger deviations occurred.


CONCLUSIONS
MOSFET detectors are suitable for in vivo dosimetry during (125)I brachytherapy of prostate cancer. An action level of +/- 16% (2 SD) for detection of errors in the implantation procedure is achievable after validation of the detector system and measurement conditions.
Bloemen-van Gurp
Esther J
EJ
Department of Radiation Oncology, Maastro Clinic, Research Institute Growth and Development (GROW), University Hospital Maastricht, Maastricht, The Netherlands.
Murrer
Lars H P
LH
Haanstra
Björk K C
BK
van Gils
Francis C J M
FC
Dekker
Andre L A J
AL
Mijnheer
Ben J
BJ
Lambin
Philippe
P
D001918:Brachytherapy / Q000379:methods*; D006801:Humans; D007457:Iodine Radioisotopes / Q000032:analysis* / Q000627:therapeutic use*; D008297:Male; D009928:Organ Specificity; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods*; D011879:Radiotherapy Dosage; D012062:Relative Biological Effectiveness; D012542:Scattering, Radiation; D012666:Semiconductors; D014521:Urethra
D007457:Iodine Radioisotopes