Home About us Editorial board Ahead of print Current issue Search Archives Submit article Instructions Subscribe Contacts Login 
Year : 2009  |  Volume : 5  |  Issue : 4  |  Page : 284-289

Characterization of metal oxide field-effect transistors for first helical tomotherapy Hi-Art II unit in India

Department of Medical Physics, Tata Memorial Centre, Parel, Mumbai, India

Correspondence Address:
Rajesh A Kinhikar
Department of Medical Physics, Tata Memorial Hospital, Parel, Mumbai - 400 012
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0973-1482.59911

Rights and Permissions

Purpose : To characterize metal oxide semiconductor field-effect transistors (MOSFETs) for a 6-MV photon beam with a first helical tomotherapy Hi-Art II unit in India. Materials and Methods : Standard sensitivity MOSFETs were first calibrated and then characterized for reproducibility, field size dependence, angular dependence, fade effects, and temperature dependence. The detector sensitivity was estimated for static as well as rotational modes for three jaw settings (1.0 cm × 40 cm, 2.5 cm × 40 cm, and 5 cm × 40 cm) at 1.5-cm depth with a source-to-axis distance (SAD) of 85 cm in virtual water slabs. The A1SL ion chamber and thermoluminescence dosimeters (TLDs) were used to compare the results. Results : No significant difference was found in the detector sensitivity for static and rotational procedures. The average detector sensitivity for static procedures was 1.10 mV/cGy (SD 0.02) while it was 1.12 mV/cGy (SD 0.02) for rotational procedures. The average detector sensitivity found was the same within the experimental uncertainty for static and rotational dose deliveries. The MOSFET reading was consistent and its reproducibility was excellent (+0.5%) while there was no significant dependence of field size. The angular dependence of less than 1.0% was observed. There was negligible fading effect of the MOSFET. The MOSFET response was found independent of temperature in the range 18°-30°. The ion chamber readings were assumed to be a reference for the estimation of the MOSFET calibration factor. The ion chamber and the TLD were in good agreement (+2%) with each other. Conclusion : This study deals only with the measurements and calibration performed on the surface of the phantom. MOSFET was calibrated and validated for phantom surface measurements for a 6-MV photon beam generated by a tomotherapy machine. The sensitivity of the detector was the same for both modes of treatment delivery with tomotherapy. The performance of the MOSFET was validated for and satisfactory for the helical tomotherapy Hi-Art II unit. However, MOSFET may be used for in vivo surface dosimetry only after it is calibrated under the conditions replicating as much as possible the manner in which the dosimeter will be used clinically.

Print this article     Email this article
 Next article
 Previous article
 Table of Contents

 Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
 Citation Manager
 Access Statistics
 Reader Comments
 Email Alert *
 Add to My List *
 * Requires registration (Free)

 Article Access Statistics
    PDF Downloaded199    
    Comments [Add]    
    Cited by others 2    

Recommend this journal