Synthetic Diamond Devices for Radiotherapy Applications: Passive and Active Dosimetry
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0956-J09-13
Synthetic Diamond Devices for Radiotherapy Applications: Passive and Active Dosimetry Caroline Descamps, Dominique Tromson, Christine Mer, Milos Nesladek, and Philippe Bergonzo LIST - DETECS/SSTM/LTD, CEA Saclay, Gif sur yvette, 91191, France ABSTRACT For all its remarkable properties, diamond is well known as an interesting material for radiation detection and more particularly for medical uses. Natural diamond use for detection application is limited because of its high cost and the severe gem selection needed to fabricate reproducible and reliable devices. The recent progress of the chemical vapour deposition (CVD) technique offers new possibilities in the fabrication of ionisation chambers as well as thermoluminescent dosimeters for the particular field of radiotherapy. This paper presents the use of CVD diamond for both applications. For the use of diamond for TL applications, the purpose of this study was to control the trapping levels in the material with deliberate incorporation of impurities in CVD diamond film during the growth. For ionisation chamber fabrication, the aim was to purposely incorporate defects (with nitrogen incorporation) in the material in order to better understand the modification of the charge transport during irradiation. The first results obtained when the device is used to monitor the beam fluency of a medical accelerator facility are presented here. For both applications, several preliminary dosimetric parameters were probed and namely the reproducibility of the response, the linearity of the signal with the dose, and for TL dosimeters, both the optical and thermal fadings were carefully studied. Results are extremely encouraging and lead to interesting prospects for the use of diamond for dosimetry.
INTRODUCTION Diamond exhibits several interesting characteristics that make it a good candidate for radiation detection [1]. Indeed, it is soft-tissue equivalent (Z=6 compared to Z=7.42 for human tissue), mechanically robust and relatively insensitive to radiation damage. Moreover, it is chemically stable and non toxic, properties that make it of great interest for medical uses. However, natural diamond devices remain very expensive and a long delivery times are common. This is the reason why the recent progress of synthetic samples grown using the chemical vapour deposition (CVD) technique for example offer novel and attractive perspectives. The work described in this paper was performed in the framework of the European Integrated Project entitled MAESTRO, Methods and Advanced Equipment for Simulation and Treatment in Radio-Oncology, (6th FP) within which approaches that concern the development of dosimeters for radiotherapy applications are conducted. The major usage of dosimeters in radiotherapy field is in the measurement of the dose received by the patient during radiotherapy (in-vivo measurements) and in beam calibration and uniformity checks. Diamond can be used for both applications: passive dosimetry such as thermoluminescent (TL) dosimeters or for on-line active
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