Properties of a commercial PTW-60019 synthetic diamond detector for the dosimetry of small radiotherapy beams

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.

Toward Pulse by Pulse Dosimetry Using an SC CVD Diamond Detector

“…This allowed the Fowler factor for both detectors to be extracted as the slope of a linear fit. The measured Fowler factor for the PTW microDiamond system was (0.9964±0.0004) which agrees well with the value reported in [21] of (0.999±0.07%). The Fowler factor for the DDL SC CVD diamond system was found to be (0.996±0.025) which agrees well with the PTW microDiamond system.…”

Survey of 5 mm small‐field output factor measurements in Australia

“…In all three cases, the microDiamond was used in both the 5 mm and 10 × 10 cm fields. All results were corrected with data from the literature 10, 16. Interestingly, the published correction factors do not agree on whether the microDiamond will under respond or over respond in the 5 mm field.…”

“…The third result used a correction factor from a different publication which was 6.4% larger than the average of the other two correction factors. One publication based their correction factor on Monte Carlo calculations and the other on alanine measurements 10, 16. It is interesting to note that although such a range of correction factors were applied to these three results, the standard deviation was only 0.4%.…”

Spectral distribution of particle fluence in small field detectors and its implication on small field dosimetry

“…The output correction factor takes into account all the small‐field effects that have an impact on the output factor, such as partial volume averaging, atomic number, density and detector shielding. The new formalism was followed by a series of scientific papers providing numerical values of the correction factors for several beam quality, field size and detector combinations . Correction factors for most available radiotherapy and radiosurgery techniques (e.g., linear accelerators, CyberKnifes and Gamma Knifes) and modern radiation detectors (e.g., ionization chambers and solid‐state detectors) can be found in the cited papers.…”