An investigation of the operating characteristics of two PTW diamond detectors in photon and electron beams

University of Florence, Florens, Tuscany, Italy
Medical Physics (Impact Factor: 2.64). 03/2002; 29(2):248-54. DOI: 10.1118/1.1446101
Source: PubMed


The dosimetric properties of two PTW Riga diamond detectors type 60003 were studied in high-energy photon and electron therapy beam. Properties under study were current-voltage characteristic, polarization effect, time stability of response, dose response, dose-rate dependence, temperature stability, and beam quality dependence of the sensitivity factor. Differences were shown between the two detectors for most of the previous properties. Also, the observed behavior was, to some extent, different from what was reported in the PTW technical specifications. The necessity to characterize each diamond detector individually was addressed.

1 Follower
33 Reads
    • "On the other hand, diamond detectors possess certain disadvantages such as the need of preirradiation (2–15 Gy) to stabilize detector response and dose rate dependence. Traditionally, these detectors are manufactured with natural diamonds, which may cause discrepancies of the detector response from equally manufactured dosimeters (De Angelis et al 2002). The sensitive volume radius varies from 1.0 to 2.2 mm and thickness varies from 0.2 to 0.4 mm (Mobit and Sandison 1999). "
    [Show abstract] [Hide abstract]
    ABSTRACT: A CVD based radiation detector has recently become commercially available from the manufacturer PTW-Freiburg (Germany). This detector has a sensitive volume of 0.004 mm 3 , a nominal sensitivity of 1 nC Gy −1 and operates at 0 V. Unlike natural diamond based detectors, the CVD diamond detector reports a low dose rate dependence. The dosimetric properties investigated in this work were dose rate, angular dependence and detector sensitivity and linearity. Also, percentage depth dose, off-axis dose profiles and total scatter ratios were measured and compared against equivalent measurements performed with a stereotactic diode. A Monte Carlo simulation was carried out to estimate the CVD small beam correction factors for a 6 MV photon beam. The small beam correction factors were compared with those obtained from stereotactic diode and ionization chambers in the same irradiation conditions The experimental measurements were performed in 6 and 15 MV photon beams with the following square field sizes: 10 × 10, 5 × 5, 4 × 4, 3 × 3, 2 × 2, 1.5 × 1.5, 1 × 1 and 0.5 × 0.5 cm. The CVD detector showed an excellent signal stability (<0.2%) and linearity, negligible dose rate dependence (<0.2%) and lower response angular dependence. The percentage depth dose and off-axis dose profiles measurements were comparable (within 1%) to the measurements performed with ionization chamber and diode in both conventional and small radiotherapy beams. For the 0.5 × 0.5 cm, the measurements performed with the CVD detector showed a partial volume effect for all the dosimetric quantities measured. The Monte Carlo simulation showed that the small beam correction factors were close to unity (within 1.0%) for field sizes ≥1 cm. The synthetic diamond detector had high linearity, low angular and negligible dose rate dependence, and its response was energy independent within 1% for field sizes from 1.0 to 5.0 cm. This work provides new data showing the performance of the CVD detector compared against a high spatial resolution diode. It also presents a comparison of the CVD small beam correction factors with those of diode and ionization chamber for a 6 MV photon beam.
    Physics in Medicine and Biology 01/2015; 60(1):905. DOI:10.1088/0031-9155/60/2/905 · 2.76 Impact Factor
  • Source
    • "Moreover, its good resistance to radiation damage makes diamond attractive for radiation detector application (Planskoy 1980). Many authors have studied natural diamond dosimeter commercialized by PTW (Hoban et al 1994, Laub et al 1997, 1999, Fidanzio et al 2000, De Angelis et al 2002). The non-reproducibility between devices, the high cost, the long delivery times and particularly their large detection volume are the main drawbacks for these detectors. "
    [Show abstract] [Hide abstract]
    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.
    Physics in Medicine and Biology 10/2013; 58(21):7647-7660. DOI:10.1088/0031-9155/58/21/7647 · 2.76 Impact Factor
  • Source
    • "There are suggested dosimetric probes. Some are based on radioelectric effects employing either semiconductor devices such as diodes [1] and MOSFETs [2] [3], or diamond [4], and others utilize scintillation materials such as Al 2 O 3 with optical or thermal stimulation schemes for luminescence output [5]. Unfortunately, semiconductor devices have directional dependence, and many organic and inorganic scintillators even with activators do not produce sufficient light output to allow design of special-revolved miniature probes. "
    [Show abstract] [Hide abstract]
    ABSTRACT: This paper presents an implantable real-time dosimetric probe using near-tissue-equivalent GaN as a scintillator and an optical fiber for radioluminescence (RL) collection and transmission. Heavily-doped GaN was preferred because of enhanced light output with dominant near-band-edge UV emission and minimized yellow luminescence (YL) contribution. For encapsulating the small-volume GaN bulk at the end of the coupled fiber, a polymer cladding fiber was chosen and a core cavity was formed by a chemical-etching and tip-cleavage process. For testing the realized dosimetric probe, a probe-readout system was designed with UV-narrow-band selection and photodetection. Real-time measurements showed detected radiation pulses with fluctuations, but integrating the detected pulses exhibited a dose response curve steadily increasing, with less than 2% reproducibility errors between runs for a dose of more than 50 cGy. The GaN and fiber contributions to the averaged output signal were evaluated by different field size measurements. The fiber contribution was significant because of its much larger irradiated volume compared to that of GaN in the probe. On the other hand, the GaN contribution per volume was much larger than the fiber: 186 times for 6 MV photons and 89 times for 18 MV photons. The probe was also irradiated by receiving a 18 MeV 300 Gy electron beam dose. The GaN contribution was unchanged, while the fiber contribution was increased by 20%. This further demonstrates the need to subtract the fiber contribution for accurate measurements.
    Sensors and Actuators A Physical 04/2009; 151(1-151):29-34. DOI:10.1016/j.sna.2009.02.018 · 1.90 Impact Factor
Show more