title: A real-time in vivo dosimetric verification method for high-dose rate intracavitary brachytherapy of nasopharyngeal carcinoma.
abstract: OBJECTIVE
  A real-time in vivo dosimetric verification method using metal-oxide-semiconductor field effect transistor (MOSFET) dosimeters has been developed for patient dosimetry in high-dose rate (HDR) intracavitary brachytherapy of nasopharyngeal carcinoma (NPC).
  
  
  METHODS
  The necessary calibration and correction factors for MOSFET measurements in (192)Iridium source were determined in a water phantom. With the detector placed inside a custom-made nasopharyngeal applicator, the actual dose delivered to the tumor was measured in vivo and compared to the calculated values using a commercial brachytherapy planning system.
  
  
  RESULTS
  Five MOSFETs were independently calibrated with the HDR source, yielding calibration factors of 0.48 ± 0.007 cGy∕mV. The maximum sensitivity variation was no more than 7% in the clinically relevant distance range of 1-5 cm from the source. A total of 70 in vivo measurements in 11 NPC patients demonstrated good agreement with the treatment planning. The mean differences between the planned and the actually delivered dose within a single treatment fraction were -0.1% ± 3.8% and -0.1% ± 3.7%, respectively, for right and left side assessments. The maximum dose deviation was less than 8.5%.
  
  
  CONCLUSIONS
  In vivo measurement using the real-time MOSFET dosimetry system is possible to evaluate the actual dose to the tumor received by the patient during a treatment fraction and thus can offer another line of security to detect and prevent large errors.
authors.affiliation: Sun Yat-sen University Cancer Center, Guangzhou, China.
authors.forename: Zhen-Yu
authors.initials: ZY
authors.lastname: Qi
authors.forename: Xiao-Wu
authors.initials: XW
authors.lastname: Deng
authors.forename: Xin-ping
authors.initials: XP
authors.lastname: Cao
authors.forename: Shao-Min
authors.initials: SM
authors.lastname: Huang
authors.forename: Michael
authors.initials: M
authors.lastname: Lerch
authors.forename: Anatoly
authors.initials: A
authors.lastname: Rosenfeld
mesh_terms: D001918:Brachytherapy / Q000379:methods*; D002138:Calibration; D002277:Carcinoma; D019583:Dose Fractionation, Radiation; D006801:Humans; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*; D015203:Reproducibility of Results; D013997:Time Factors