Evaluation of linear array MOSFET detectors for in vivo dosimetry to measure rectal dose in HDR brachytherapy

  • Aisling HaugheyEmail author
  • George Coalter
  • Koki Mugabe
Scientific Paper


The study aimed to assess the suitability of linear array metal oxide semiconductor field effect transistor detectors (MOSFETs) as in vivo dosimeters to measure rectal dose in high dose rate brachytherapy treatments. The MOSFET arrays were calibrated with an Ir192 source and phantom measurements were performed to check agreement with the treatment planning system. The angular dependence, linearity and constancy of the detectors were evaluated. For in vivo measurements two sites were investigated, transperineal needle implants for prostate cancer and Fletcher suites for cervical cancer. The MOSFETs were inserted into the patients’ rectum in theatre inside a modified flatus tube. The patients were then CT scanned for treatment planning. Measured rectal doses during treatment were compared with point dose measurements predicted by the TPS. The MOSFETs were found to require individual calibration factors. The calibration was found to drift by approximately 1% ±0.8 per 500 mV accumulated and varies with distance from source due to energy dependence. In vivo results for prostate patients found only 33% of measured doses agreed with the TPS within ±10%. For cervix cases 42% of measured doses agreed with the TPS within ±10%, however of those not agreeing variations of up to 70% were observed. One of the most limiting factors in this study was found to be the inability to prevent the MOSFET moving internally between the time of CT and treatment. Due to the many uncertainties associated with MOSFETs including calibration drift, angular dependence and the inability to know their exact position at the time of treatment, we consider them to be unsuitable for in vivo dosimetry in rectum for HDR brachytherapy.


MOSFETs In vivo dosimetry Brachytherapy 


  1. 1.
    Nath R, Anderson LL, Meli JA, Olch A, Stitt J, Williamson J (1997) Code of practice for brachytherapy physics: report of the AAPM radiation therapy committee task group 56. Med Phys 24:1557–1598Google Scholar
  2. 2.
    ICRU (1976) Determination of absorbed dose in a patient irradiated by beams of x or gamma rays in radiotherapy procedures. ICRU Report 24, Bethesda, MEGoogle Scholar
  3. 3.
    Tolli H, Johansson KA (1998) Absorbed dose determination at short distance from 60Co and 192Ir brachytherapy sources. Phys Med Biol 43:3183–3194PubMedCrossRefGoogle Scholar
  4. 4.
    Waldhausl C, Wambersie A, Potter R, Georg D (2005) In vivo dosimetry for gynaecological brachytherapy: physical and clinical considerations. Radiother Oncol 77:310–317PubMedCrossRefGoogle Scholar
  5. 5.
    Anagnostopoulos G, Baltas D, Geretschlaeger A, Martin T, Papagiannis P, Tselis N, Zamboglou N (2003) In vivo thermoluminescence dosimetry dose verification of transperineal 192Ir high dose rate brachytherapy using CT-based planning for the treatment of prostate cancer. Int J Radiat Oncol Biol Phys 57:1183–1191PubMedCrossRefGoogle Scholar
  6. 6.
    Ramasheshan R, Russell S, O’Brien P (1997) Clinical dosimetry using MOSFETs. Int J Radiat Oncol Biol Phys 37:959–964CrossRefGoogle Scholar
  7. 7.
    Zhen-Yu Q, Deng XW, Huang SM Lu J, Lerch M, Cutajar D, Rosenfeld A (2007) Verification of the plan dosimetry for high dose rate brachytherapy using metal-oxide-semiconductor field effect transistor detectors. Med Phys 34(6): 224–232Google Scholar
  8. 8.
    Scalchi P, Francescon P (1998) Calibration of a MOSFET detection system for 6-MV in vivo dosimetry. Int J Radiat Oncol Biol Phys 40:987–993PubMedCrossRefGoogle Scholar
  9. 9.
    Soubra M, Cygler J, Mackay G (1994) Evaluation of a dual bias dual metal oxide-silicon semiconductor field effect transistor detector as radiation dosimeter. Med Phys 21:567–572PubMedCrossRefGoogle Scholar
  10. 10.
    Butson M, Rozenfeld A, Mathur N, Carolan M, Wong T, Metcalfe P (1996) A new radiotherapy surface dose detector: The MOSFET. Med Phys 23:655–658PubMedCrossRefGoogle Scholar
  11. 11.
    Lambert J, Nakano T, Law S, Elsey J, McKenzie D, Suchowerska N (2007) In vivo dosimeters for HDR brachytherapy: A comparison of a diamond detector, MOSFET, TLD, and scintillation detector. Med Phys 34:1759–1765PubMedCrossRefGoogle Scholar

Copyright information

© Australasian College of Physical Scientists and Engineers in Medicine 2011

Authors and Affiliations

  1. 1.Department of Medical PhysicsWaikato District Health BoardHamiltonNew Zealand

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