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In radiotherapy, point doses via surface dose measurement are confirmed using a dosimeter attached to the patient's skin. This results in an error margin of about 11.8% or higher because the attachment site is visually confirmed. Thus, a digital flexible array dosimeter that can analyse body surface area is needed. Here, a lead (II) iodide (PbI2)-based unit cell flexible dosimeter was developed, and its electrical properties were evaluated based on its mechanical flexibility by assessing its reproducibility and linearity for bending. The relative standard deviation (RSD) for measurement by the sensor over 10,000 cycles was 1.74% and 2.21% at 6 MV and 15 MV, respectively, which is higher than RSD's evaluation criterion ( 0.9990, the sensitivity at 15 MV was lower than that at 6 MV. The results of this study confirm the applicability and usefulness of the PbI2-based flexible dosimeter in radiation measurements.

To improve the image quality in cone-beam computerized tomography, a detector containing an insulator layer made of parylene-C was utilized in this study. In HgI2 sensors with photoconducting materials, we analyzed the signal based on the thickness of the parylene-C layer and leakage current. In addition, we tried to evaluate the reproducibility of Hgl2 that decreases gradually based on the continuous X-ray study. For the signal-to-noise ratio, we evaluated the photocurrent/darkcurrent (P/D) ratio according to the reduction in the leakage current. Our results indicated a detector reproducibility of 0.82% for a parylene-layer thickness of 18 μm, which represents an improvement of 0.43% over that of a "parylene-free" detector. Compared with the parylene-free sensors, the ones with a parylene layer displayed an approximately linear increase of the P/D ratio with increasing parylene layer thickness. For layers 18 or 20 μm thick this ratio, indicative of image quality, exhibited an improvement of ~ 70 times or more in comparison to a parylene-free sensor.

In the application of radiotherapy to the skin, the need for ensuring the accuracy of surface dose measurements has attracted increasing attention because dose accumulation and inaccurate skin registration during irradiation can compromise patient safety. Here, we develop a dosimeter with mechanical stability against bending by mixing a photoconductive material, HgI2, and silicon rubber binder. We fabricate a film-type unit cell dosimeter and evaluate the device performance in terms of reproducibility and linearity. We also fabricate a flexible array dosimeter to demonstrate the feasibility of accurate surface dose measurements. To evaluate the robustness of the proposed device to bending, an acrylic filter is applied to form a beam, and the signals measured on flat and curved substrates are compared. The reproducibility values of the film-type unit cell dosimeter are 0.6% (SE) at 6 MV and 1.4% (SE) at 15 MV. The linearity values are 0.9999 (R2) at 6 MV and 0.9981 (R2) at 15 MV. The surface dose measurement error rates are 11.073% at 6 MV and 3.318% at 15 MV, demonstrating the feasibility of the flexible array dosimeter.

With the recent market entries of new types of linear accelerators (LINACs) with a multi leaf collimator (MLC) mounted on them, high-precision radiosurgery applying a LINAC to measure high-dose radiation on the target region has been gaining popularity. Systematic and accurate quality assurance (QA) is of vital important for high-precision radiosurgery because of its increased risk of side effects including life-threatening ones such as overexposure of healthy tissues to high-dose radiation beams concentrated on small areas. Therefore, accurate dose and dose-distribution measurements are crucial in the treatment procedure. The accurate measurement of the properties of beams concentrated on small areas requires high-precision dosimeters capable of high-resolution output and dose mapping as well as accurate dosimetry in penumbra regions. In general, the properties of beams concentrated on small areas are measured using thermos luminescent dosimeters (TLD), diode detectors, ion chambers, diamond detectors, or films, and many papers have presented the advantages and disadvantages of each of these detectors for dosimetry. In this study, a solid-state photoconductor dosimeter was developed, and its clinical usability was tested by comparing its relative dosimetric performance with that of a conventional ion chamber. As materials best-suited for radiation dosimeters, four candidates namely lead (II) iodide (PbI2), lead (II) oxide (PbO), mercury (II) iodide (HgI2), and HgI2/ titanium dioxide (TiO2) composite, the performances of which were proved in previous studies, were used. The electrical properties of each candidate material were examined using the sedimentation method, one of the particle-in-binder (PIB) methods, and unit-cell-type prototypes were fabricated. The unit-cell samples thus prepared were cut into specimens of area 1 × 1 cm2 with 400-μ m thickness. The electrical properties of each sample, such as sensitivity, dark current, output current, rising time, falling time, and response delay, were then measured, in addition to the consistency, reproducibility and linearity of each unit-cell. According to the measurement results, HgI2/TiO2 composite outperformed the other candidate materials. A radiation dosimeter with a chamber-type structure was fabricated in this study using a LINAC under accelerating voltages of 6, and 15 MV and compared with a commercial ion chamber. Percent depth dose (PDD) and beam profile were measured on a water phantom at a fixed area of 10 × 10 cm2 by using the fabricated chamber-type dosimeter, and the values were compared with those measured by a commercial ion chamber. Additionally, a homogeneous phantom was fabricated, and the exposure doses of the center points were measured according to a real treatment plan, followed by a comparison of the measured values as relative values. In this paper, we report that the manufactured dosimeter shows similar characteristics in terms of PDD and beam profile and results for the conventional ion chamber. Based on these results, it is demonstrated that the HgI2/TiO2-based dosimeter complies with radiotherapy QA requirements, namely Superior detection characteristics, consistency, dose linearity, reproducibility. Thus, we expect the HgI2/TiO2-based dosimeter to be used commercially in the future.

The most widely used form of radiotherapy to treat tumors uses a linear accelerator, and the apparatus requires regular quality assurance (QA). QA for a linear accelerator demands accuracy throughout, from mock treatment and treatment planning, up to treatment itself. Therefore, verifying a radiation dose is essential to ensure that the radiation is being applied as planned. In current clinical practice, ionization chambers and diodes are used for QA. However, using conventional gaseous ionization chambers presents drawbacks such as complex analytical procedures, difficult measurement procedures, and slow response time. In this study, we discuss the potential of a lead(II) iodide (PbI2)-based radiation dosimeter for radiotherapy QA. PbI2 is a semiconductor material suited to measurements of X-rays and gamma rays, because of its excellent response properties to radiation signals. Our results show that the PbI2-based dosimeter offers outstanding linearity and reproducibility, as well as dose-independent characteristics. In addition, percentage depth dose (PDD) measurements indicate that the error at a fixed reference depth Dmax was 0.3%, very similar to the measurement results obtained using ionization chambers. Based on these results, we confirm that the PbI2-based dosimeter has all the properties required for radiotherapy: stable dose detection, dose linearity, and rapid response time. Based on the evidence of this experimental verification, we believe that the PbI2-based dosimeter could be used commercially in various fields for precise measurements of radiation doses in the human body and for measuring the dose required for stereotactic radiosurgery or localized radiosurgery.

The Gd3Al2Ga3O12 (Ce:GAGG) is a new inorganic scintillator known for its attractive properties such as high light yield, stopping power and relatively fast decay time. In this study, we fabricated a ceramic Ce:GAGG scintillator as a cost-effective alternative to single crystal Ce:GAGG and, for the first time, investigated their performances when coupled to the digital silicon photomultiplier (dSiPM)—a new type of photosensor designed for applications in medical imaging, high energy and astrophysics. Compared to 3 × 3 × 2 mm3 sized single crystal Ce:GAGG, the translucent ceramic Ce:GAGG, which has a much lower transmittance than the single crystal, was determined to give an output signal amplitude that is approximately 61% of single crystal Ce:GAGG. The energy resolution of the 511 keV annihilation peak of a 22Na source was measured to be 9.9 ± 0.2% and 13.0 ± 0.3% for the single and ceramic scintillators respectively. On the other hand, the coincidence resolving time (CRT) of ceramic Ce:GAGG was 307 ± 23 ps, better than the 465 ± 37 ps acquired with single crystals—probably attributed to its slightly faster decay time and higher proportion of the fast decay component. The ceramic Ce:GAGG may be a promising cost-effective candidate for applications that do not require thick scintillators such as x-ray detectors and charged particle detectors, and those that require time-of-flight capabilities.

Lately, cancer has been treated using high-energy radiation, and this requires highly reliable treatment plans. Therefore, a dosimeter with excellent performance, which is capable of precise dose measurement, is critical. In current clinical practices, an ionization chamber and diode utilizing the ionization reaction mechanism are widely used. Several studies have been carried out to determine optimal materials for the detector in a dosimeter to enable diagnostic imaging. Recently, studies with lead monoxide, which was shown to have low drift current and high resolving power at a high bias, were reported with the dosimeter exhibiting a fast response time against incident photons. This research aims to investigate the feasibility of a lead monoxide-based dosimeter for QA (quality assurance) in radiotherapy. In this paper, we report that the manufactured dosimeter shows similar linearity to a silicon diode and demonstrates similar characteristics in terms of PDD (percent depth dose) results for the thimble ionization chamber. Based on these results, it is demonstrated that the lead monoxide-based dosimeter complies with radiotherapy QA requirements, namely rapid response time, dose linearity, dose rate independence. Thus, we expect the lead monoxide-based dosimeter to be used commercially in the future.