A new single crystal diamond dosimeter for small beam: comparison with different commercial active detectors

Abstract

Recent developments of new therapy techniques using small photon beams, such as stereotactic radiotherapy, require suitable detectors to determine the delivered dose with a high accuracy. The dosimeter has to be as close as possible to tissue equivalence and to exhibit a small detection volume compared to the size of the irradiation field, because of the lack of lateral electronic equilibrium in small beam. Characteristics of single crystal diamond (tissue equivalent material Z = 6, high density) make it an ideal candidate to fulfil most of small beam dosimetry requirements. A commercially available Element Six electronic grade synthetic diamond was used to develop a single crystal diamond dosimeter (SCDDo) with a small detection volume (0.165 mm(3)). Long term stability was studied by irradiating the SCDDo in a (60)Co beam over 14 h. A good stability (deviation less than ± 0.1%) was observed. Repeatability, dose linearity, dose rate dependence and energy dependence were studied in a 10 × 10 cm(2) beam produced by a Varian Clinac 2100 C linear accelerator. SCDDo lateral dose profile, depth dose curve and output factor (OF) measurements were performed for small photon beams with a micro multileaf collimator m3 (BrainLab) attached to the linac. This study is focused on the comparison of SCDDo measurements to those obtained with different commercially available active detectors: an unshielded silicon diode (PTW 60017), a shielded silicon diode (Sun Nuclear EDGE), a PinPoint ionization chamber (PTW 31014) and two natural diamond detectors (PTW 60003). SCDDo presents an excellent spatial resolution for dose profile measurements, due to its small detection volume. Low energy dependence (variation of 1.2% between 6 and 18 MV photon beam) and low dose rate dependence of the SCDDo (variation of 1% between 0.53 and 2.64 Gy min(-1)) are obtained, explaining the good agreement between the SCDDo and the efficient unshielded diode (PTW 60017) in depth dose curve measurements. For field sizes ranging from 0.6 × 0.6 to 10 × 10 cm(2), OFs obtained with the SCDDo are between the OFs measured with the PinPoint ionization chamber and the Sun Nuclear EDGE diode that are known to respectively underestimate and overestimate OF values in small beam, due to the large detection volume of the chamber and the non-water equivalence of both detectors.

Toward Pulse by Pulse Dosimetry Using an SC CVD Diamond Detector

“…SC CVD diamonds are excellent detectors for radiotherapy: they are very radiation hard, have a fast response time, are near tissue equivalent and, in contrast to natural diamonds, have a uniform response from sensor to sensor. The performance of single crystal diamond dosimeters has been reported widely, see for example [5]- [9]. To achieve pulse by pulse readout a custom frontend was developed.…”

Evaluation of a 3D diamond detector for medical radiation dosimetry

“…The resistivity of the graphitic material made with the fs-laser source was 800 mΩ cm. The resulting structure has arrays of graphitic columns of about 10 m in diameter forming cells of 114 x 70 m with a thickness of 0.5 mm for a single cell sensitive volume of 0.004 mm 3 and a total diamond sensitive volume of about 1.1 mm 3 ( Fig. 3, right).…”

Response of synthetic diamond detectors in proton, carbon, and oxygen ion beams

“…Details of the operational principle of this detector, which is based on a Schottky diode, can be found in papers by Almaviva et al and Di Venanzio et al Characteristics of the PTW‐60019 detector can be found in PTW manuals . In photon, electron and proton beams, this detector is described as suitable for small field dosimetry . Also in protons, most dosimetry studies conclude that the response of the PTW‐60019 microDiamond detector exhibits no LET dependence nor quenching effect (Mandapaka et al, Marinelli et al, Yuichi et al, Rossomme et al, Akino et al).…”