title: An in-house developed resettable MOSFET dosimeter for radiotherapy.
abstract: The purpose of this note is to report the feasibility and clinical validation of an in-house developed MOSFET dosimetry system and describe an integrated non-destructive reset procedure. Off-the-shelf MOSFETs are connected to a common PC using an 18 bit/analogue-input and 16 bit/output data acquisition card. A reading algorithm was developed defining the zero-temperature-coefficient point (ZTC) to determine the threshold voltage. A wireless interface was established for ease of use. The reset procedure consists of an internal circuit generating a local heating induced by an electrical current. Sensitivity has been investigated as a function of bias voltage (0-9 V) to the gate. Dosimetric properties have been evaluated for 6 MV and 15 MV clinical photon beams and in vivo benchmarking was performed against thermoluminescence dosimeters (TLD) for conventional treatments (two groups of ten patients for each energy) and total body irradiation (TBI). MOSFETS were pre-irradiated with 20 Gy. Sensitivity of 0.08 mV cGy(-1) can be obtained for 200 cGy irradiations at 5 V bias voltage. Ten consecutive measurements at 200 cGy yield a SD of 2.08 cGy (1.05%). Increasing the dose in steps from 5 cGy to 1000 cGy yields a 1.00 Pearson correlation coefficient and agreement within 2.0%. Dose rate dependence (160-800 cGy min(-1)) was within 2.5%, temperature dependence within 2.0% (25-37 degrees C). A strong angular dependence has been observed for gantry incidences exceeding +/-30 degrees C. Dose response is stable up to 50 Gy (saturation occurs at approximately 90 Gy), which is used as threshold dose before resetting the MOSFET. An average measured-over-calculated dose ratio within 1.05 (SD: 0.04) has been obtained in vivo. TBI midplane-dose assessed by entrance and exit dose measurements agreed within 1.9% with ionization chamber in phantom, and within 1.0% with TLD in vivo. An in-house developed resettable MOSFET-based dosimetry system is proposed. The system has been validated and is currently used for in vivo entrance dose measurement in clinical routine for simple (open field) treatment configurations.
authors.affiliation: UZ Brussel, Oncologisch Centrum, Radiotherapie, Brussels, Belgium. dirk.verellen@uzbrussel.be
authors.forename: Dirk
authors.initials: D
authors.lastname: Verellen
authors.forename: Sven
authors.initials: S
authors.lastname: Van Vaerenbergh
authors.forename: Koen
authors.initials: K
authors.lastname: Tournel
authors.forename: Karina
authors.initials: K
authors.lastname: Heuninckx
authors.forename: Laurent
authors.initials: L
authors.lastname: Joris
authors.forename: Michael
authors.initials: M
authors.lastname: Duchateau
authors.forename: Nadine
authors.initials: N
authors.lastname: Linthout
authors.forename: Thierry
authors.initials: T
authors.lastname: Gevaert
authors.forename: Truus
authors.initials: T
authors.lastname: Reynders
authors.forename: Iwein
authors.initials: I
authors.lastname: Van de Vondel
authors.forename: Luc
authors.initials: L
authors.lastname: Coppens
authors.forename: Tom
authors.initials: T
authors.lastname: Depuydt
authors.forename: Mark
authors.initials: M
authors.lastname: De Ridder
authors.forename: Guy
authors.initials: G
authors.lastname: Storme
mesh_terms: D000465:Algorithms; D002138:Calibration; D005240:Feasibility Studies; D006801:Humans; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use; D010865:Pilot Projects; D011839:Radiation, Ionizing; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011878:Radiotherapy / Q000295:instrumentation* / Q000379:methods*; D011879:Radiotherapy Dosage; D013696:Temperature; D013819:Thermoluminescent Dosimetry; D013997:Time Factors; D014867:Water
chemical_list: D014867:Water