title: Technical Note: Nanometric organic photovoltaic thin film detectors for dose monitoring in diagnostic x-ray imaging.
abstract: OBJECTIVE
  To fabricate organic photovoltaic (OPV) cells with nanometric active layers sensitive to ionizing radiation and measure their dosimetric characteristics in clinical x-ray beams in the diagnostic tube potential range of 60-150 kVp.
  
  
  METHODS
  Experiments were designed to optimize the detector's x-ray response and find the best parameter combination by changing the active layer thickness and the area of the electrode. The OPV cell consisted of poly (3-hexylthiophene-2,5-diyl): [6,6]-phenyl C61 butyric acid methyl ester photoactive donor and acceptor semiconducting organic materials sandwiched between an aluminum electrode as an anode and an indium tin oxide electrode as a cathode. The authors measured the radiation-induced electric current at zero bias voltage in all fabricated OPV cells.
  
  
  RESULTS
  The net OPV current as a function of beam potential (kVp) was proportional to kVp(-0.5) when normalized to x-ray tube output, which varies with kVp. Of the tested configurations, the best combination of parameters was 270 nm active layer thicknesses with 0.7 cm(2) electrode area, which provided the highest signal per electrode area. For this cell, the measured current ranged from approximately 0.7 to 2.4 nA/cm(2) for 60-150 kVp, corresponding to about 0.09 nA-0.06 nA/mGy air kerma, respectively. When compared to commercial amorphous silicon thin film photovoltaic cells irradiated under the same conditions, this represents 2.5 times greater sensitivity. An additional 40% signal enhancement was observed when a 1 mm layer of plastic scintillator was attached to the cells' beam-facing side.
  
  
  CONCLUSIONS
  Since both OPVs can be produced as flexible devices and they do not require external bias voltage, they open the possibility for use as thin film in vivo detectors for dose monitoring in diagnostic x-ray imaging.
authors.affiliation: Medical Physics Program, Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854 and Department of Medical Imaging, Royal Jubilee Hospital, Vancouver Island Health Authority, Victoria, British Columbia V8R 1J8, Canada.
authors.forename: Bassem
authors.initials: B
authors.lastname: Elshahat
authors.affiliation: Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854.
authors.forename: Hardeep Singh
authors.initials: HS
authors.lastname: Gill
authors.affiliation: Harvard Medical School, Dana Farber Cancer Institute and Brigham and Women's Hospital, Boston, Massachusetts 02215.
authors.forename: Ilya
authors.initials: I
authors.lastname: Filipyev
authors.affiliation: Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655.
authors.forename: Suman
authors.initials: S
authors.lastname: Shrestha
authors.affiliation: Department of Radiation Oncology, University Medical Center Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, Mannheim 68167, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hesser
authors.affiliation: Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854.
authors.forename: Jayant
authors.initials: J
authors.lastname: Kumar
authors.affiliation: Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655.
authors.forename: Andrew
authors.initials: A
authors.lastname: Karellas
authors.affiliation: Harvard Medical School, Dana Farber Cancer Institute and Brigham and Women's Hospital, Boston, Massachusetts 02215.
authors.forename: Piotr
authors.initials: P
authors.lastname: Zygmanski
authors.affiliation: Medical Physics Program, Department of Physics and Applied Physics, University of Massachusetts Lowell, Lowell, Massachusetts 01854.
authors.forename: Erno
authors.initials: E
authors.lastname: Sajo
mesh_terms: D004566:Electrodes; D004867:Equipment Design; D005373:Film Dosimetry / Q000295:instrumentation* / Q000379:methods; D011829:Radiation Dosage; D011859:Radiography / Q000295:instrumentation* / Q000379:methods; D014965:X-Rays