Development of new chemical dosimeter for low dose range

Accurate measurement of low dose radiation in complex systems is of utmost importance in radiation biology and related areas. Ferrous Benzoic acid Xylenol orange (FBX) system is being widely used for measurement of low dose gamma radiation because of its reproducibility and precision. However, an additional step, i.e., dissolution of benzoic acid in water at higher temperature followed by cooling at room temperature is involved for the preparation of this dosimeter. This makes it inconvenient as a ready to use dosimeter. In the present work, the organic molecule, sorbitol has been used for measurement of low doses of radiation. The advantages of using sorbitol are its ready availability and instantaneous water solubility. Owing to its dissolution at room temperature, possible errors those are involved in calculation of dose due to thermal oxidation of ferrous ions during preparation of the FBX dosimetric solution could be made insignificant in the proposed dosimeter. In the present system, sorbitol acts as radiolytic sensitizer for the oxidation of ferrous ion, and xylenol orange forms a 1:1 complex specifically with ferric ions. Thus, the analytical detection limit of ferric ions is enhanced compared to other systems. Final composition of the dosimetric solution is; 0.5 mol/m³ xylenol orange, 10 mol/m³ sorbitol and 0.2 mol/m³ ferrous ion in 50 mol/m³ sulfuric acid. Radiolytic sensitization in combination with analytical enhancement of the ferrous based system, allows us to measure radiation dose in the range of 0.05 Gy–12 Gy with ease and high reproducibility.     

Testing of a scintillator and fibre optic based radiation sensor

We describe the optimisation of RadLine^®; a small, real time, remotely operated radiation detector, which consists of an inorganic scintillation crystal coupled to a fibre optic cable transporting produced photons to a CCD camera some distance away. RadLine^® is tested in a beta and gamma narrow radiation field of 2.4 GBq, from a Caesium-137 (662 KeV) source, at doses rates between 0.125 mSvhr⁻¹ and 10 mSvhr⁻¹. Our results establish that the lower limit of the device corresponds to a dose rate of 0.2 mSvhr⁻¹, constrained by the signal to noise ratio of the instrument. We also demonstrate the process of characterising the RadLine^® for utilisation underwater due to its partial electrical inactiveness; and to consider how the instrument might perform in aquatic environments and ultimately in a First Generation Magnox Storage Ponds (FGMSP). The RadLine^® brings a marked difference to actual underwater radiation monitoring devices such as; HPGe, CZT and GM detectors, which not only incorporate the whole electronics within and are more bulky, only perform over a short range. The RadLine^®’s design offers signification value for intermediate (>100 m) and long range detection.     

Characterisation of 32P beta source for external radiation protection

Custom-made design of ³²P patch sources are used in brachytherapy applications. Use of this source requires external radiation protection. This implies measurement of absorbed dose rate to tissue at a depth of 0.07 mm. Towards this goal, 2.75 mCi ³²P patch source was locally developed. Characterization of this source has been carried out by measuring source parameters such as uniformity in the activity distribution and beam uniformity. The characterization also includes output measurements in terms of absorbed dose rate to air using an extrapolation chamber at 11, 20 and 30 cm from the source. Various correction factors which are dependent on the cavity length as well as independent of the cavity length were also determined in this study. The backscatter correction and Bragg–Grapy stopping power ratio were calculated using the Monte Carlo techniques. Using these correction factors and the measured absorbed dose rate to air, absorbed dose rate to tissue at a depth of 0.07 mm was determined. The study also includes measurements of H_p(0.07) and H_p(10) at different source-to-detector distances using an electronic pocket dosimeter.     

Measurement-based Monte Carlo simulation of high definition dose evaluation for nasopharyngeal cancer patients treated by using intensity modulated radiation therapy

Measurement-based Monte Carlo (MBMC) simulation using a high definition (HD) phantom was used to evaluate the dose distribution in nasopharyngeal cancer (NPC) patients treated with intensity modulated radiation therapy (IMRT). Around nasopharyngeal cavity, there exists many small volume organs-at-risk (OARs) such as the optic nerves, auditory nerves, cochlea, and semicircular canal which necessitate the use of a high definition phantom for accurate and correct dose evaluation. The aim of this research was to study the advantages of using an HD phantom for MBMC simulation in NPC patients treated with IMRT. The MBMC simulation in this study was based on the IMRT treatment plan of three NPC patients generated by the anisotropic analytical algorithm (AAA) of the Eclipse treatment planning system (Varian Medical Systems, Palo Alto, CA, USA) using a calculation grid of 2 mm². The NPC tumor was treated to a cumulative dose of 7000 cGy in 35 fractions using the shrinking-field sequential IMRT (SIMRT) method. The BEAMnrc MC Code was used to simulate a Varian EX21 linear accelerator treatment head. The HD phantom contained 0.5 × 0.5 × 1 mm³ voxels for the nasopharyngeal area and 0.5 × 0.5 × 3 mm³ for the rest of the head area. An efficiency map was obtained for the amorphous silicon aS1000 electronic portal imaging device (EPID) to adjust the weighting of each particle in the phase-space file for each IMRT beam. Our analysis revealed that small volume organs such as the eighth cranial nerve, semicircular canal, cochlea and external auditory canal showed an absolute dose difference of ≥200 cGy, while the dose difference for larger organs such as the parotid glands and tumor was negligible for the MBMC simulation using the HD phantom. The HD phantom was found to be suitable for Monte Carlo dose volume analysis of small volume organs.     

Medical dosimetry using a RL/OSL prototype

A portable and robust instrument has been developed for the routine assessment of patient exposure to ionizing radiation during radiotherapy treatments. The design principles of hardware and software are described, along with preliminary measurements that illustrate the operation of the system and its capabilities. In this study the authors used radioluminescence (RL) and Optically Stimulated Luminescence (OSL) from Al₂O₃:C detectors coupled to a PMMA optical fibre to acquire dose in medical dosimetry. The RL/OSL prototype can provide two independent dose estimates from the same in vivo treatment: one integrated dose estimate (OSL) and one real-time dose estimate (RL), which can be compared to one another. The authors first characterized the dose–response to a calibration source (¹³⁷Cs), analysing the OSL and the RL signal to doses from 0.5 to 3 Gy. Later the percentage dose depth from RL is presented for two gamma (6 and 15 MV) and two electron (6 and 12 MeV) medical beams.     

双极线性稳压器电离辐射剂量率效应及其损伤分析

为了对双极线性稳压器在电离辐射环境下损伤变化特征及其剂量率效应进行研究,选择一组器件进行⁶⁰Co γ高低剂量率的辐照和退火试验. 结果表明线性稳压器的输出电压、最大负载电流、线性调整率、压降电压等多个关键参数都有不同程度的蜕变. 且各器件在高低剂量率下的辐照响应略有不同,表现出不同的剂量率效应. 文中通过多种形式的测试结果分析,系统地讨论了各参数变化的原因及其内部各模块对稳压器功能的影响. 结合电离损伤退火特性,探讨了各剂量率效应形成的原因. 这不但对工程应用考核提供了参考,而且为设 关键词： 双极线性稳压器 总剂量效应 剂量率效应 辐射损伤     

Electrical and dosimetric characterization of a CVD diamond detector with high sensitivity

A prototype detector has been built using commercial high quality single crystal epitaxial diamond and novel electrical contacts resulting in two asymmetric Schottky junctions able to operate the detector at zero bias like a photodiode. Aiming at evaluating the detector suitability for radiotherapy applications we report on results related to signal dynamics, linearity with the dose and dose rate, signal stability and measurement repeatability determined in a Co-60 reference beam. In addition, we measured the detector sensitivity and its dependence on the applied bias voltage. The detector has a wide active volume leading to high current signal values. The signal dynamics is wide, with a dark current of 3.2 × 10⁻¹⁴ A at zero bias and a current of 6.8 × 10⁻¹⁰ A under irradiation with a dose rate of 0.95 Gy min⁻¹. The sensitivity to ionizing radiation increases with the bias voltage and values up to 10⁴ nC Gy⁻¹ mm⁻³ have been evaluated at −300 V. When operated at −5 V, the detector shows a linear response on a wide range of Co-60 dose rates from 1.3 × 10⁻³ Gy min⁻¹ to 1.2 Gy min⁻¹ following the Fowler's power law with a coefficient Δ = 0.99 ± 0.01. The device also shows rise and fall times of less than 1.0 s with a stability of the signal under irradiation better than 0.3%. The characteristics of the detector, as determined in the Co-60 beam, appear suitable for radiotherapy dosimetry, when fast response on the transient, wide signal dynamics, linearity and high sensitivity are required.     

Area radiation monitoring on ISS Increments 17 to 22 using PADLES in the Japanese Experiment Module Kibo

The measurement of radiation environmental parameters in space is essential to support radiation risk assessments for astronauts and establish a benchmark for space radiation models for present and future human space activities. The Japan Aerospace Exploration Agency (JAXA) is performing a continuous area radiation monitoring experiment using the “PAssive Dosimeters for Lifescience Experiments in Space” (PADLES) system inside the Japanese Experiment Module Kibo on board the International Space Station (ISS). The PADLES dosimeter consists of thermoluminescent dosimeters (TLDs) and CR-39 plastic nuclear track detectors (PNTDs). JAXA has run the Area PADLES experiment since the Kibo module was attached to the ISS in June 2008, using 17 dosimeters in fixed locations on the Pressurized Module (PM) and the Experiment Logistics Module-Pressurized Section (ELM-PS) of Kibo, which are replaced every 6 months or every Increment, respectively. For three monitoring periods, known as Area PADLES experiment series #1 to #3, of 301, 180, and 232 days in June 2008 to April 2010 over ISS Increments 17 to 22, the average absorbed dose (dose equivalent) rates of 12 positions in the PM of Kibo were 319 ± 30 μGy/day (618 ± 102 μSv/day), 276 ± 30 μGy/day (608 ± 94 μSv/day), and 293 ± 33 μGy/day (588 ± 84 μSv/day), respectively. The radiation measurement in the ELM-PS was conducted in only Area PADLES experiment series #3 from August 2009 to April 2010 (232 days) over ISS Increments 21 to 22, the average absorbed dose (dose equivalent) rates of 5 positions was 297 ± 28 μGy/day (661 ± 65 μSv/day). The directional dependence of the radiation field was also investigated by installing PADLES dosimeters located in the zenith of ELM-PS of Kibo.     

Study of the luminescent behavior of Spectrolite + Teflon pellets in 90Sr + 90Y beams

The Spectrolite, from the silicate family, a variety of Labradorite, was already studied in relation to its thermoluminescence (TL) and optically stimulated luminescence (OSL) responses, in high-dose gamma radiation fields; the results indicated their good application as gamma radiation detectors. In the present work, the analyses performed to investigate powdered Spectrolite are presented, by means of the XRD, SEM and EDX techniques. The luminescent behavior of Spectrolite + Teflon samples, in the concentration of 1:1, was studied in beta radiation beams (⁹⁰Sr + ⁹⁰Y), using the luminescent phenomena of TL and OSL. The results showed adequate TL and OSL reproducibility of the samples; the dose–response curves for both techniques presented a linear behavior in a range from 0.5 Gy to 1 kGy, and the fading showed that after 150 h there were 46.7% and 31.6% of the remaining signal of samples for TL and OSL responses, respectively. Therefore, the Spectrolite + Teflon pellets may be used in beta radiation dosimetry.     

Determination of Very Slow Diffusion of Paramagnetic Ions by NMR Spectroscopy

In this paper, we propose a new method of measuring the very slow paramagnetic ion diffusion coefficient using a commercial high-resolution spectrometer. If there are distinct paramagnetic ions influencing the hydrogen nuclear magnetic relaxation time differently, their diffusion coefficients can be measured separately. A cylindrical phantom filled with Fricke xylenol gel solution and irradiated with gamma rays was used to validate the method. The Fricke xylenol gel solution was prepared with 270 Bloom porcine gelatin, the phantom was irradiated with gamma rays originated from a ⁶⁰Co source and a high-resolution 200 MHz nuclear magnetic resonance (NMR) spectrometer was used to obtain the phantom ¹H profile in the presence of a linear magnetic field gradient. By observing the temporal evolution of the phantom NMR profile, an apparent ferric ion diffusion coefficient of 0.50 μm²/ms due to ferric ions diffusion was obtained. In any medical process where the ionizing radiation is used, the dose planning and the dose delivery are the key elements for the patient safety and success of treatment. These points become even more important in modern conformal radio therapy techniques, such as stereotactic radiosurgery, where the delivered dose in a single session of treatment can be an order of magnitude higher than the regular doses of radiotherapy. Several methods have been proposed to obtain the three-dimensional (3-D) dose distribution. Recently, we proposed an alternative method for the 3-D radiation dose mapping, where the ionizing radiation modifies the local relative concentration of Fe²⁺/Fe³⁺ in a phantom containing Fricke gel and this variation is associated to the MR image intensity. The smearing of the intensity gradient is proportional to the diffusion coefficient of the Fe³⁺ and Fe²⁺ in the phantom. There are several methods for measurement of the ionic diffusion using NMR, however, they are applicable when the diffusion is not very slow.     

The influence of field size and off-axis distance on photoneutron spectra of the 18 MV Siemens Oncor linear accelerator beam

At present, high energy electron linear accelerators (LINACs) producing photons with energies higher than 10 MeV have a wide use in radiotherapy (RT). However, in these beams fast neutrons could be generated, which results in undesired contamination of the therapeutic beams. These neutrons affect the shielding requirements in RT rooms and also increase the out-of-field radiation dose to patients. The neutron flux becomes even more important when high numbers of monitor units are used, as in the intensity modulated radiotherapy. Herein, to evaluate the exposure of patients and medical personnel, it is important to determine the full radiation field correctly. A model of the dual photon beam medical LINAC, Siemens ONCOR, used at the University Hospital Centre of Osijek was built using the MCNP611 code. We tuned the model according to measured photon percentage depth dose curves and profiles. Only 18 MV photon beams were modeled. The dependence of neutron dose equivalent and energy spectrum on field size and off-axis distance in the patient plane was analyzed. The neutron source strength (Q) defined as a number of neutrons coming from the head of the treatment unit per x-ray dose (Gy) delivered at the isocenter was calculated and found to be 1.12 × 10¹² neutrons per photon Gy at isocenter. The simulation showed that the neutron flux increases with increasing field size but field size has almost no effect on the shape of neutron dose profiles. The calculated neutron dose equivalent of different field sizes was between 1 and 3 mSv per photon Gy at isocenter. The mean energy changed from 0.21 MeV to 0.63 MeV with collimator opening from 0 × 0 cm² to 40 × 40 cm². At the 50 cm off-axis the change was less pronounced. According to the results, it is reasonable to conclude that the neutron dose equivalent to the patient is proportional to the photon beam-on time as suggested before. Since the beam-on time is much higher when advanced radiotherapy techniques are used to fulfill high conformity demands, this makes the neutron flux determination even more important. We also showed that the neutron energy in the patient plane significantly changes with field size. This can introduce significant uncertainty in dosimetry of neutrons due to strong dependence of the neutron detector response on the neutron energy in the interval 0.1–5 MeV.     

Polyamide woven fabrics with 2,3,5-triphenyltetrazolium chloride or nitro blue tetrazolium chloride as 2D ionizing radiation dosimeters

The development of flat woven fabric-based ionizing radiation 2D dosimeters is reported in this work. Polyamide fabric was surface modified with radiation-sensitive 2,3,5-triphenyltetrazolium chloride (TTC) or nitro blue tetrazolium chloride (NBT). These samples responded to gamma radiation of ⁶⁰Co through a colour change: red and blue for TTC and NBT, respectively. The tinge intensity was observed to depend on the absorbed dose, which allowed for the reflectance of light (R) measurements and calculation of the calibration parameters: dose range, quasi-linear range, threshold dose and sensitivity. Oxygen was shown to be an important factor determining the dose response of the samples. For this reason, a range of additional modifications to the TTC- and NBT-polyamide fabric was proposed which lead to a decrease in the threshold dose and increase in the sensitivity to irradiation of the samples. For instance, a dosimeter made of polyamide fabric modified with 10 g/dm³ TTC, 0.5 mol/dm³ tert-butyl alcohol, 7.5% gelatine hydrogel at pH 10 (vacuum packed) showed the lowest dose threshold (50 Gy), dose range up to 2.8 kGy and the highest sensitivity to irradiation (?0.0396%/Gy) among the compositions studied. In consequence, this dosimeter was examined in terms of response to inhomogeneous irradiation from a ¹⁹²Ir brachytherapy radiation source. The relative dose distribution profiles across the source's longitudinal axis were calculated. This showed potential of the textile dosimeters for 2D dose distribution measurements; however, further modifications towards improvement of the dosimeter's low dose response can be considered.     

Development and application of chip calorimeter as an X-ray detector

Radiotherapy for cancer patients requires accurate measurement of the absorbed dose of radiation in a treatment planning step. Various types of radiation detectors are currently utilized for dose measurement. Among them, calorimeters are known to be the most precise detector for measuring absorbed dose, but their on-site application is limited by the large size of the equipment. We developed a miniaturized chip calorimeter for application as a radiation detector. The calorimetric radiation detector was built using micro/nano fabrication techniques, and consists of an SU-8 photoresist absorber and high-sensitivity vanadium oxide (VO_x) thermistors. The thermistors had a temperature resolution of 135 μK, and the calorimeter showed a thermal conductance of 11 μW/K. The detector was irradiated with various X-ray dose rates from a linear accelerator, and the absorbed dose to SU-8 was measured. The detector responses showed high linearity with dose rates, demonstrating the feasibility of the radiation detector for practical uses.     

Construction and calibration of a multipurpose instrument to simultaneously measure dose,voltage and half-value layer in X-ray emission equipment

This work reports on the development of a multipurpose instrument that simultaneously measures delivered dose (air kerma), peak voltage (kVp) and half value layer (HVL) in X-ray machines. The device will help control quality of X-ray equipment routinely used in diagnostic and interventional radiological procedures. The measuring device is equipped with several attenuating filters of different materials and thicknesses, and Gafchromic^® XR-QA2 radiochromic films are used as sensitive elements. The films are scanned after being irradiated and the resulting color intensities indicate a relationship between the degree of film darkening under each individual filter and the quantities of interest, i.e. air kerma, kVp and HVL. Comparing HVL values measured using the proposed multipurpose instrument with those of a reference standard ionization chamber, discrepancy reached 8.4%. As for the kVp evaluation, anomalous results were observed for low atomic number materials and small thicknesses, especially for peak voltages higher than 70 kVp. However, for materials with higher Z and reasonable thickness, the calibration curve R × kVp was quite satisfactory, being R the ratio between the color intensities obtained with two distinct filters. We have also observed a decrease in the influence of Tungsten characteristic radiation on the calibration curve. These results suggest that the proposed instrument may be satisfactorily used to routinely control quality of X-ray equipment, estimating the radiation dose resulting from the direct beam, the applied voltage across the electrodes and the half value layer.     

High-temperature measurement techniques for the application in photometry,radiometry and thermometry

Well characterised sources of thermal radiation are essential for photometry, radiometry, and thermometry. They serve as reference radiators for the calibration of detectors and radiance sources. Thermal radiation sources are advantageous for this purpose compared to other radiance sources such as lamps or LEDs because they possess a continuous spectrum of the emitted spectral radiance, which, for blackbody sources, can be calculated analytically using Planck’s law of radiation.For application in thermometry, blackbody sources starting from temperatures near absolute zero to temperatures up to 3000 ^°C are needed for the calibration of radiation thermometers. For application in photometry and radiometry high intensity sources of radiation in the visible and UV region of the optical spectrum were required. This latter requirement is met by blackbody sources at temperatures well above 2000 ^°C. An ideal reference source should always emit the same amount of radiation at any time of use. This is realised by fixed-point radiators. Such radiators are based on a phase transition of a substance, at high temperatures the melting and freezing points of metals. However, current metal fixed-points are limited to relatively low temperatures. In the present work innovative techniques necessary for research into high-temperature thermal radiation sources are developed and thoroughly described. Starting with variable temperature blackbody sources the techniques required are: Precise apertures determination and detailed characterisation of the applied optical detectors.The described techniques are then used to undertake research into the development of high-temperature fixed-points above the copper fixed-point for application in photometry, radiometry, and thermometry. Applying these sophisticated techniques it was shown that these new high-temperature fixed-points are reproducible and repeatable to better than 100 mK at temperatures up to nearly 3200 K. Finally, a forward look is given that shows the potential of such fixed-points for improving traceability and accuracy in photometry, radiometry, and thermometry. This work forms the foundation for accurate and practical applications of high-temperature fixed-point sources and sets the international benchmark for measurement techniques in photometry, radiometry, and thermometry. This work will open the use of the novel high-temperature fixed-points in an improved International Temperature Scale and will significantly improve and ease the realisation and dissemination of the SI base unit candela, significantly reducing the uncertainty for industrial measurements in these fields.     

Development of human hand phantom containing radiophotoluminescence material

A radiophotoluminescence (RPL) material with high radiation sensitivity was made of polyurethane resin, silver-activated metaphosphate glass particles, and hollow glass microspheres. The density was adjusted to be 1.1 g/cm³ by controlling the amount of hollow glass microspheres. The response to high-energy photons over 100 keV was similar to that of the tissue-equivalent material (polymethylmethacrylate) because the two electron densities were similar. The RPL response had satisfactory linearity in the dose range from 10 to 6 × 10⁴ mGy.An RPL scanner for three-dimensional (3-D) dose measurement was composed of an XYZθ motorized stage, a UV pulse laser, a gated photomultiplier tube (PMT), a red-laser displacement sensor, and an integrating ammeter. The surface profile was measured by the red-laser-displacement sensor. The UV laser was used as an excitation source, and the RPL responses were effectively detected with the gated PMT.An RPL material hand phantom was fabricated to understand the extremity dosimetry of a radiation worker's hand. The hand phantom was exposed to X-rays, and its surface dose profile was obtained by the RPL scanner. Subsequently, the hand phantom was sliced into dozens of square plates using a diamond wire saw. Each inner dose profile was obtained with the RPL scanner. The inner dose profiles were roughly consistent with the computational simulation results. These results indicated that RPL imaging of the hand phantom was useful to understand extremity dosimetry.     

OSL and TL retrospective dosimetry with a fluorapatite glass-ceramic used for dental restorations

Optically Stimulated Luminescence (OSL) and Thermoluminescence (TL) properties of a fluorapatite glass-ceramic have been investigated, with a view to developing a dose assessment technique for medical triage following unplanned exposures of individuals to ionizing radiation. The ceramic is an innovative material used in dental prostheses and restorations. It is strongly sensitive to radiation and the intensity of both the OSL and TL signals are proportional to the absorbed radiation dose. We focused on the optimization of the measuring procedure and investigated characteristics such as reproducibility, fading, minimum detectable dose (MDD), dose response and photon energy response of TL and OSL signals. The dental ceramic exhibited very good reproducibility (<5% at 2σ level) when measured and a linear dose response for a wide range of doses (50 mGy–20 Gy). The MDD values for the samples investigated were ∼5 mGy. The material is not tissue equivalent and the OSL and TL signals are strongly dependent on incident photon energy. Both the luminescence signals exhibited significant fading during the first few hours after irradiation. Its rate was dependent on the parameters of measurement. The results indicate that the material can be used for the purposes of accident dosimetry, however, the fading and photon energy response have to be properly corrected for a reliable dose assessment.     

A radiochromic film based on leucomalachite green for high-dose dosimetry applications

A colorless polyvinyl butyral film (PVB) based on radiation-sensitive dye of leucomalachite green (LMG) was investigated as a high-dose dosimeter for gamma radiation processing applications in the dose range of 3–150 kGy. The useful applications for such dose range are food irradiation treatment, medical devices sterilization and polymer modification. Gamma irradiation of the film induces a significant intensity of green color, which can be characterized by a main absorption band at 627 nm and a small band at 425 nm. The variation in response of irradiated film stored in the dark and under laboratory light illumination was less than 3% during the first 6 days of storage. The response of film during irradiation was slightly influenced by relative humidity in the range of 12–76%; however, it was significantly affected by temperature in the range of 5–40 °C. The radiation chemical yield was reported to be 6.76 × 10⁻⁶ mol/J at the absorbed dose of 30 kGy for the film containing 6.5% of LMG dye. The overall uncertainty associated with routine dose monitoring would be less than 6% at a 95% confidence level if the dosimeter was being corrected for irradiation conditions and being calibrated with reference standard dosimeter in the production facility.     

Development of a micro-size dosimeter using an optical fiber probe based on photostimulable phosphorescence

We have developed a novel micro-size dosimeter using an optical fiber probe coupled with a photostimulable storage phosphor, such as BaFBr:Eu²⁺. Our micro-size dosimeter is based on the concept in which the radiation dose response is temporally compressed by using integrating-type dosimeter elements, such as a photostimulable storage phosphor, and the signal-to-noise ratio is improved to downsize the dosimeter probe. We fabricate the prototype dosimeter probe which has the detectable volume of 100 μm thick and 400 μm diameter and the outer diameter of 900 μm. The lower limit of detectable dose, which is defined as three times the noise level, is evaluated to be 0.9 mGy. This value is much smaller than the typical irradiation dose (a few Gy per treatment) in the radiotherapy. We, therefore, conclude that the proposed micro-size dosimeter can be a promising candidate of in-vivo and on-line dose monitor in the radiotherapy.