Real-time in vivo dosimetry with MOSFET detectors in serial tomotherapy for head and neck cancer patients.
OBJECTIVE
A real-time dose verification method using a recently designed metal oxide semiconductor field effect transistor (MOSFET) dosimetry system was evaluated for quality assurance (QA) of intensity-modulated radiation therapy (IMRT).


METHODS
Following the investigation of key parameters that might affect the accuracy of MOSFET measurements (i.e., source surface distance [SSD], field size, beam incident angles and radiation energy spectrum), the feasibility of this detector in IMRT dose verification was demonstrated by comparison with ion chamber measurements taken in an IMRT QA phantom. Real-time in vivo measurements were also performed with the MOSFET system during serial tomotherapy treatments administered to 8 head and neck cancer patients.


RESULTS
MOSFET sensitivity did not change with SSD. For field sizes smaller than 20 × 20 cm(2), MOFET sensitivity varied within 1.0%. The detector angular response was isotropic within 2% over 360°, and the observed sensitivity variation due to changes in the energy spectrum was negligible in 6-MV photons. MOSFET system measurements and ion chamber measurements agreed at all points in IMRT phantom plan verification, within 5%. The mean difference between 48 IMRT MOSFET-measured doses and calculated values in 8 patients was 3.33% and ranged from -2.20% to 7.89%. More than 90% of the total measurements had deviations of less than 5% from the planned doses.


CONCLUSIONS
The MOSFET dosimetry system has been proven to be an effective tool in evaluating the actual dose within individual patients during IMRT treatment.
Department of Radiation Oncology, Sun Yat-Sen University Cancer Center and State Key Laboratory of Oncology in Southern China, Guangzhou 510060, China
Zhen-Yu
ZY
Qi
Xiao-Wu
XW
Deng
Shao-Min
SM
Huang
Almon
A
Shiu
Michael
M
Lerch
Peter
P
Metcalfe
Anatoly
A
Rosenfeld
Tomas
T
Kron
D004867:Equipment Design; D005240:Feasibility Studies; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D009064:Mouth Protectors; D019047:Phantoms, Imaging; D017785:Photons / Q000627:therapeutic use; D011786:Quality Control; D011874:Radiometry / Q000295:instrumentation; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods / Q000592:standards*; D012666:Semiconductors; D012680:Sensitivity and Specificity; D013997:Time Factors