A Diamond-Based Dose-per-Pulse X-ray Detector for Radiation Therapy

Abstract

One of the goals of modern dynamic radiotherapy treatments is to deliver high-dose values in the shortest irradiation time possible. In such a context, fast X-ray detectors and reliable front-end readout electronics for beam diagnostics are crucial to meet the necessary quality assurance requirements of care plans. This work describes a diamond-based detection system able to acquire and process the dose delivered by every single pulse sourced by a linear accelerator (LINAC) generating 6-MV X-ray beams. The proposed system is able to measure the intensity of X-ray pulses in a limited integration period around each pulse, thus reducing the inaccuracy induced by unnecessarily long acquisition times. Detector sensitivity under 6-MV X-photons in the 0.1–10 Gy dose range was measured to be 302.2 nC/Gy at a bias voltage of 10 V. Pulse-by-pulse measurements returned a charge-per-pulse value of 84.68 pC, in excellent agreement with the value estimated (but not directly measured) with a commercial electrometer operating in a continuous integration mode. Significantly, by intrinsically holding the acquired signal, the proposed system enables signal processing even in the millisecond period between two consecutive pulses, thus allowing for effective real-time dose-per-pulse monitoring.

Accurate Signal Conditioning for Pulsed-Current Synchronous Measurements

“…To emulate the typical signal produced by a diamond detector irradiated by 6 MV pulsed X-rays [ 20 ], the 6221 was set to PRF = 360 Hz, I peak = 25 µA, and D.C. = 0.14% (Δt ≈ 3.889 µs). In this case, the injected charge-per-pulse is about 97.22 pC.…”

“…The front-end/readout electronics used in this work was designed for the pulse-by-pulse monitoring of X-ray beams generated by a medical LINAC. For the on-field tests described in Section 3.2 , a diamond dosimeter was connected to the GI input and biased at 10 V. Detector sensitivity was measured to be S d = 302.2 nC/Gy with a standard calibration procedure [ 20 ]. X-ray characterizations were performed by means of a Clinac iX (Varian Medical Systems, Inc., Palo Alto, CA, USA) installed at the Radiation Therapy Department of “San Giovanni–Addolorata” hospital, in Rome (Italy).…”

“…The inset shows the percentage of the reading error (lower than ±1%) in the investigated dynamics, which reduced to ±0.1% in the 10-300 pC range. To emulate the typical signal produced by a diamond detector irradiated by 6 MV pulsed X-rays [20], the 6221 was set to PRF = 360 Hz, I peak = 25 µA, and D.C. = 0.14% (∆t ≈ 3.889 µs). In this case, the injected charge-per-pulse is about 97.22 pC.…”

X-ray Detectors Based on Halide Perovskite Materials

“…Various semiconductor materials have been utilized in X-ray detectors, such as silicon (Si), amorphous selenium (α-Se), germanium (Ge), and cadmium zinc telluride (CdZnTe). In addition, diamond is considered the elective material for X-ray detection and has a wide range of applications in the radiotherapy field mainly due to its "tissue equivalence" characteristic [10][11][12][13]. However, traditional materials such as α-Se, Ge, and CdZnTe suffer from many issues, including relatively small atomic numbers, the low attenuation coefficient of X-rays, and complex and costly fabrication processes [14][15][16].…”

A Highly Versatile X-ray and Electron Beam Diamond Dosimeter for Radiation Therapy and Protection

“…High-quality “electronic-grade” diamond samples with an impurity concentration three orders of magnitude lower than natural diamond are now available at a relatively low cost, thanks to the optimization of the chemical vapor deposition (CVD) technique. Dosimeters based on CVD diamond are, indeed, widely used for EBRT [ 14 , 15 , 16 , 17 , 18 ] and IORT [ 19 , 20 , 21 ], as well as for soft X-rays [ 22 , 23 , 24 ], UV light [ 25 , 26 ], charged particles [ 27 , 28 , 29 ], and neutrons [ 30 , 31 , 32 ].…”