Direct detection of 6 MV x-rays from a medical linear accelerator using a semiconducting polymer diode

Abstract

Abstract:Recently, a new family of low-cost X-radiation detectors have been developed, based on semiconducting polymer diodes, which are easy to process, mechanically flexible, relatively inexpensive, and able to cover large areas. To test their potential for radiotherapy applications such as beam monitors or dosimeters, as an alternative to the use of solid-state inorganic detectors, we present the direct detection of 6 MV X-rays from a medical linear accelerator using a thick film, semiconducting polymer detector. The diode was subjected to 4 ms pulses of 6 MV X-rays at a rate of 60 Hz, and produces a linear increase in photocurrent with increasing dose rate (from 16.7 to 66.7 mGy.s -1). The sensitivity of the diode was found to range from 13 to 20 nC.mGy -1 .cm -3 , for operating voltages from -50 to -150 V, respectively. The diode response was found to be stable after exposure to doses up to 15 Gy. Testing beyond this dose range was not carried out. Theoretical calculations show that the addition of heavy metallic nanoparticles to polymer films, even at low volume fractions, increases the X-ray sensitivity of the polymer film/nanoparticle composite so that it exceeds that for Published in: Physics in Medicine and Biology, 58 (2013) 2 silicon over a wide range of X-ray energies. The possibility of detecting X-rays with energies relevant to medical oncology applications opens up the potential for these polymer detectors to be used in detection and imaging applications using medical X-ray beams. IntroductionOver the past 60 years, radiation oncology apparatus has been developed, based on Linear Particle a lower activation energy is required to produce an ionisation pair (approx. 10 times lower), and the higher material density leads to a higher efficiency (up to 10 3 times greater), making them ideal produced from a medical LINAC. In this case, the attenuation coefficient of the polymer for the high energy X-rays is approx. 30 times less than that for the lower energy X-rays. Methods MaterialsPoly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene) (F8T2, number-average molecular weight (Mn) = 45,000 g.mol -1 , weight-average molecular weight (Mw) = 120,000 g.mol -1 ) was prepared as previously reported. [Theim et. al. 2005 accelerated at 100 rpm/s to 500 rpm and held for 60 s, 3) accelerated at 100 rpm/s to 2000 rpm and held for 30 s, 4) decelerated at 100 rpm/s. This procedure produced a relatively smooth polymer film with a thickness of approx. 10 μm. After this, the films were typically dry to the touch; a short period of drying under atmospheric conditions was however required for some films, before annealing under vacuum at 110°C for 24 h. The thickness of the polymer layers was subsequently measured using a surface profilometer (Dektak 8, Veeco Instruments). To complete the diode, gold (Au) or Al electrodes (100 nm thick, 0.5 x 0.5 cm 2 ), depending on the substrate used, were thermally evaporated onto the F8T2, through a shadow mask, at a pressure of 10 -6 mbar. The diodes were connected to the measurem...

High sensitivity organic inorganic hybrid X-ray detectors with direct transduction and broadband response

“…a Device schematic structure. b Performance comparison of current solid state X-ray detectors—(1) 13 , (2) 10 , (3) 36 , (4) 37 , (5) 38 , (7) 8 , (9) 11 , (11) 3 , (14) 39 , (15) 40 , (16) 7 , (17) 41 , (18) 42 , (19) 43 , (20) 44 , and (24) 20 are direct detectors, (6) 45 , (8) 46 , (21) 7 , 47 and (22) 48 are inorganic detectors, and (10) 12 , (12) 9 , (13) 25 and (23) 49 are indirect detectors—with the technology developed in this work—(25) Bi 2 O 3 -40, (26) Bi 2 O 3 -80, (27) Bi 2 O 3 -40 and (28) Bi 2 O 3 -40. The operating voltage is given adjacent to each data point.…”

“…For example, direct conversion detectors based on materials such as amorphous selenium 2 are currently used in mammography, but are limited by their low X-ray attenuation for energies higher than 50 keV. Detectors based on p-type silicon with its high radiation-damage resistance are used in radiotherapy for dose measurement or beam imaging 3 . However, their propensity to damage from accumulated dose and drift due to environmental effects makes these less useful for beam calibration 4 .…”

Optical properties of conjugated polymer: review of its change mechanism for ionizing radiation sensor

“…[20][21][22][23][24][25] The latest development was in the use of CPs for radiation sensing, which entails the hybridization of the material with another inorganic or organic component. [26][27][28][29][30][31] In basic sensing application, CP acts in two ways-first, it reacts upon stimulant (recognition), and second, it produces signal (transduction). Unlike inorganic semiconductor, both recognition and transduction process in CPs can be achieved within the same chemical moiety, [32] thus, lead to faster response, and less material is required in sensor production.…”

“…In year 2000, studies on the use of CP for radiation detection and measurement began to expand . The latest development was in the use of CPs for radiation sensing, which entails the hybridization of the material with another inorganic or organic component …”

Hybrid Multipixel Array X-Ray Detectors for Real-Time Direct Detection of Hard X-Rays

“…However, limited work has been reported on the performance of the organic semiconductors under X-ray energies of 1-15 MV range; which will be termed as 'hard Xrays' in this study. [5], [15] Here we demonstrate the use of an organic-inorganic hybrid material as a hybrid X-ray detector (HXD) for the direct detection of hard X-rays produced from a medical LINAC. The performance of this system under soft X-rays (~50 kV) has been previously reported.…”