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

• Published in: Physics in medicine & biology Vol. 60; no. 2; pp. 905 - 924
• Main Authors: Lárraga-Gutiérrez, José Manuel, Ballesteros-Zebadúa, Paola, Rodríguez-Ponce, Miguel, García-Garduño, Olivia Amanda, de la Cruz, Olga Olinca Galván
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 21.01.2015
• Subjects: Diamond - analysis; Diamond - chemistry; Humans; Monte Carlo Method; Monte Carlo simulation; non-reference dosimetry; Particle Accelerators; Photons - therapeutic use; Radiometry - instrumentation; Radiometry - methods; Radiotherapy - instrumentation; Radiotherapy - methods; small beam correction factors; small beam dosimetry; synthetic diamond detector
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/0031-9155/60/2/905

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 mm3, 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.