Search

The Oak Ridge National Laboratory (ORNL) phantoms based on data of Caucasians have been widely used for fetal dosimetry. However, there are differences in body size during pregnancy among Taiwanese and Caucasians. In this study, the uterine dose conversion coefficients (DCCs) of Taiwanese pregnant women were evaluated to facilitate the use of it to estimate the possible uterine dose (usually regarded as fetal dose) of pregnant Taiwanese women during radiation practice or medical exposures. The uterine DCCs in this study were calculated based on the established Taiwanese pregnancy voxel phantoms, and were compared with the uterine DCCs of the International Commission on Radiological Protection. The applicability of evaluating uterine DCCs with different phantoms was also discussed. Results showed that if the ORNL phantoms are used to evaluate the uterine dose of Taiwanese pregnant women, the uterine dose may be underestimated. This study provides the uterine DCCs assessed with the Taiwanese pregnancy phantoms for future dose assessment of Taiwanese.

For some special radiation practices, such as working with radioisotopes in the nuclear medicine department, hand exposure is inevitable and usually results in high radiation doses. Therefore, ring dosimeters are frequently worn on the finger to monitor the does to the hand (extremity). Most current commercial ring dosimeters are thermoluminescence type and consist of a single dosimetry chip; they do not have the ability to discern the energy of radiation. This study developed a new optically stimulated luminescence (OSL) ring dosimeter. Each OSL ring dosimeter consists of two OSL chips, one cast, one ring holder, and one ring clip. A dose algorithm was also designed to calculate the dose with correction for energy dependence. The new OSL ring dosimeter and algorithm were validated using blind tests under irradiation from X-ray, gamma ray, and beta in the National Radiation Standard Laboratory at the Institute of Nuclear Energy Research in Taiwan. The newly designed OSL ring dosimeter and algorithm could pass the blind test following American National Standards Institute/Health Physics Society standard N13.32–2008 from category I to III. For category IV, the feasibility was confirmed under assumptions specific to this study. The reproducibility and lower limit of detection of this system were also represented in this study.

The International Commission on Radiological Protection (ICRP) recommended that the equivalent dose limit for the lens of the eye be decreased from 150 mSv/y ( ICRP, 2007 ) to 20 mSv/y averaged over five years ( ICRP, 2011 ). How to accurately measure the eye-lens dose has, therefore, been an issue of interest recently. Interventional radiologists are at a higher risk of radiation-induced eye injury, such as cataracts, than all other occupational radiation workers. The main objective of this study is to investigate the relationship between the doses to the eye lenses of interventional radiologists measured by different commercial eye-lens dosimeters. This study measured a reference eye-lens dose, which involved placing thermoluminescent dosimeter (TLD) chips at the surface of the eye of the Rando Phantom, and the TLD chips were covered by a 3-mm-thick tissue-equivalent bolus. Commercial eye-lens dosimeters, such as a headband dosimeter and standard personnel dose badges, were placed at the positions recommended by the manufacturers. The results show that the personnel dose badge is not an appropriate dosimeter for evaluating eye-lens dose. Dose deviations for different dosimeters are discussed and presented in this study.

Urolithiasis is a common disease; patients suspected of suffering from urolithiasis will be examined by abdomen x-ray, Sono, Intraudio Videonous Urography (IVU) and Computed Tomography (CT). The detection rates for calculus in above examinations are respectively: 50–70% (x-ray), 50–60% (Sono), 70–90% (IVU) and 97% (CT). In addition, the effective doses are respectively: 0.63 mSv (x-ray), no radiation dose (Sono), 2.6 mSv (IVU) and 8–16 mSv (CT). Although CT has the highest detection rate for calculus, it also has the highest radiation dose. This research sought to lower the radiation dose by using CT scans with different dose conditions of standard dose (SD), 50% SD, 25% SD, and 15% SD to diagnose patients who suffer from urolithiasis and thus explore the feasibility of examining urolithiasis via CT with lower dose conditions. This research simulated the examination of patients with RANDO phantom, collocating PMMA slice phantom and pig's kidney. Fake calculuses made of five different materials of different sizes were put into the phantom and scanned individually. The results of the scanned images were given to two physicians who had many years of diagnostic experience to interpret the urolithiasis images. This study explored the different image qualities of CT with different dose conditions. In addition, this research used thermoluminescent dosimeters (TLD) to measure the radiation doses and compared the results with the dose values shown on the screen of the CT scanner to estimate the dose conversion factor (k). The research results showed that a low-dose CT was able to provide good image quality and thus have a lower radiation dose. Therefore, a low-dose CT is suggested the main examination method to diagnose patients with urolithiasis.

Released thyroid cancer patients treated with 131I may cause a radiation risk to their family members. However, no current regulations exist in Taiwan to limit the radiation dose among patients released post-treatment. This study assessed radiation exposure to caregivers of thyroid cancer patients treated with 131I to verify whether their doses exceed the 5-mSv limit per treatment session. The study population comprised 63 patients from four hospitals and their caregivers. Dose rates at a 1-m distance from patients were quantified before their release. Dosimetry data of caregivers were obtained using personalized thermoluminescent dosimetry badges. Upon the release of patients treated with 131I, Dose rates at a 1-m distance from the patients were 3.9–55 μSv/h. The radiation doses to caregivers ranged from 0.21 to 1.7 mSv after the patients released. When the 1-m dose rate of patients upon hospital release was 50 μSv/h, the highest possible radiation dose was assessed of 4.76 mSv for caregivers. In conclusion, as the dose rates at a 1-m distance from patients upon release were

Modern dental X-ray examination that consists of traditional form, panorama, and cone-beamed 3D technologies is one of the most frequent diagnostic applications nowadays. This study used the Rando Phantom and thermoluminescence dosimeters (TLD) to measure the absorbed doses of radiosensitive organs recommended by International Commission on Radiological Protection (ICRP), and whole body effective doses which were delivered due to dental X-ray examination performed with different types of X-ray instrument. Besides, enamel samples which performed reading with Electronic Paramagnetic Resonance (EPR) procedure were also used to estimate the tooth doses. EPR is a dose reconstruction method of measuring free radicals induced by radiation exposure to the calcified tissue (mainly in the tooth enamel or bone) to evaluate the accepted high dose. The tooth doses estimated by TLD and EPR methods were compared. Relationships between the tooth doses and effective doses by dental X-ray examinations with different types of X-ray equipment were investigated in this work.

Unlike conventional photon radiotherapy, sophisticated patient positioning tools are not available for boron neutron capture therapy (BNCT). Thus, BNCT remains vulnerable to setup errors and intra-fractional patient motion. The aim of this study was to estimate the impact of deviations in positioning on the dose administered by BNCT for brain tumors at the Tsing Hua open-pool reactor (THOR). For these studies, a simulated head model was generated based on computed tomography (CT) images of a patient with a brain tumor. A cylindrical brain tumor 3 cm in diameter and 5 cm in length was modeled at distances of 6.5 cm and 2.5 cm from the posterior scalp of this head model (T6.5 cm and T2.5 cm, respectively). Radiation doses associated with positioning errors were evaluated for each distance, including left and right shifts, superior and inferior shifts, shifts from the central axis of the beam aperture, and outward shifts from the surface of the beam aperture. Rotational and tilting effects were also evaluated. The dose prescription was 20 Gray-equivalent (Gy-Eq) to 80 % of the tumor. The treatment planning system, NCTPlan, was used to perform dose calculations. The average decreases in mean tumor dose for T6.5 cm for the 1 cm, 2 cm, and 3 cm lateral shifts composed by left, right, superior, and inferior sides, were approximately 1 %, 6 %, and 11 %, respectively, compared to the dose administered to the initial tumor position. The decreases in mean tumor dose for T6.5 cm were approximately 5 %, 11 %, and 15 % for the 1 cm, 2 cm, and 3 cm outward shifts, respectively. For a superficial tumor at T2.5cm, no significant decrease in average mean tumor dose was observed following lateral shifts of 1 cm. Rotational and tilting up to 15° did not result in significant difference to the tumor dose. Dose differences to the normal tissues as a result of the shifts in positioning were also minimal. Taken together, these data demonstrate that the mean dose administered to tumors at greater depths is potentially more vulnerable to deviations in positioning, and greater shift distances resulted in reduced mean tumor doses at the THOR. Moreover, these data provide an estimation of dose differences that are caused by setup error or intra-fractional motion during BNCT, and these may facilitate more accurate predictions of actual patient dose in future treatments.

This work evaluated the neutron spectra induced by a medical used cyclotron. The neutrons were induced during the 18 F-radioisotope productions due to the 9.6 MeV proton beam hit 18 O-water target and induced (p, n) reactions in this SK Cyclotron. To evaluate the induced neutron doses in the cyclotron room, dual-TLD chips and gold foils with bare and 113 Cd covered were used separately to measure thermal neutron doses and fluence rates at positions outside the self-shielding of cyclotron, in the cases of using different targets. Besides, a 6 LiI (Eu) detector with Bonner spheres were used and were placed at the specific locations in the cyclotron room to estimate the neutron spectra of using different operation parameters. In the results, the thermal neutron doses at the locations outside the self-shielding of cyclotron in the case of using target 1 were less than that using target 2. However, thermal neutron doses inside the self-shielding in the case of using target 1 were higher than that using target 2. The evaluated neutron spectra inside and outside the self-shielding confirmed the dose results. The impact of the volume of 18 O-water target was discussed in this study. In conclusion, the large target volume (target 1) caused the higher production yield of 18 F-radioisotope and induced lower dose and softer spectra of neutrons than the small target, under the same operation parameters which were adopted for validation in this study.

Computed Tomography (CT) becomes more and more important and is frequently used in modern diagnostic techniques. CT offers an effective diagnosis on lesion and pathology; however, it also delivers a radiation dose to patients. Besides, in some special emergency cases, the patient may require someone to help him in the examination room to perform the head CT, due to the patient lost intellectual and operational capacity. This study evaluated the delivered radiation dose and the risk of radiation-induced cancer for the patient and for the helper after carrying out the emergent head CT examination. A Rando phantom with thermoluminescent dosimeter (TLD) chips inside relevant organs was used to simulate the patient during head CT examination. An effective dose of 2.06 ± 0.16 mSv and 1.46 ± 0.07 mSv without and with wearing the lead apron were found respectively, considering ICRP 60 recommendation. ICRP 103 recommendations the readings would have been 1.29 ± 0.15 mSv and 0.71 ± 0.04 mSv. The effective dose determined from the dose-length product (DLP) method (2.19 mSv) was similar to the value (2.06 ± 0.16 mSv) estimated by TLD method considering the ICRP 60 recommendation (without lead apron). Assuming a 5% total risk for fatal cancer per Sv in the general population, risk of radiation-induced cancer for patients were 1.03 × 10 −2 % (without lead apron) and 7.80 × 10 −3 % (with lead apron) for ICRP 60, and were 6.45 × 10 −3 % (without lead apron) and 3.55 × 10 −3 % (with lead apron) for ICRP 103. The dose received by the helper was assessed by wearing a personal badge. The helper during emergent head CT examination may receive a personal dose equivalent ( H p (10)) of 19.36 ± 5.89 μSv and 138.81 ± 101.28 μSv with and without lead apron, respectively, at distance of 0.3–1 m from the center of CT scanner. Based on the observed dose reduction of a factor of 7.17 we recommend that helpers wear lead apron in the CT examination room.

The epithermal neutron beam of the Tsing Hua Open-pool Reactor (THOR) was constructed for the study of boron neutron capture therapy (BNCT). The THOR epithermal neutron beam was mainly composed of thermal neutrons, fast neutrons, and photons. For fast neutrons and photons, the absorbed dose and the relative biological effectiveness (RBE) were used to characterize radiation dose and radiation quality. The short-ranged alpha particles and lithium ions produced from 10 B(n,α) 7 Li reactions in the BNCT required cellular- and micro-dosimetry characterizations. Due to the non-uniform microdistribution of boron in cells, these characterizations should depend on the source–target geometry. In this case, the geometry-dependent specific cellular dose and lineal energy could be used to describe radiation dose and radiation quality. In the present work, cellular- and micro-dosimetry were studied for the THOR epithermal neutron beam. The specific cellular dose and lineal energy were calculated for thermal neutron-induced α-particles and 7 Li-ions with different source–target geometry and various cell sizes. Applying the linear energy dependent-biological weighting function, the geometry-dependent RBE of thermal neutron-induced heavy particles was determined. Finally, the effective RBE of the THOR epithermal neutron beam was estimated for tumors and normal tissues of specified 10 B concentrations. This effective RBE should be multiplied by the total absorbed dose to determine the corresponding biological dose required in the treatment planning.

The quality assurance of digital mammogram has been included in the Standards of Medical Exposure Quality Assurance in Taiwan since July, 2008. According to the Standards, determination of the half-value layer (HVL) is an integral part of mammographic dosimetry which requires the evaluation of patient's glandular dose. The purpose of this study was to develop a simple method to help hospitals determine the HVL. A compact device, accommodating Harshaw TLD-100H (LiF:Mg,Cu,P) chips and aluminum sheets in a small holder, was designed to determine the HVL under clinical exposure conditions (tube voltage, target/filter) of a digital mammographic unit. This device was used to determine the HVL ranging from 0.3- to 0.5-mm Al. Air KERMA measured by the TLDs were corrected for scatter radiation and energy dependence caused by the aluminum sheets. Once scatter and energy dependence were corrected, the agreement of determined HVLs was within ±7% with measured data using the ionization chamber. This device provides a simple, inexpensive and remote means to reliably audit the HVL of a mammography unit on a periodic basis.

THORplan is a treatment planning system developed at Tsing Hua University, Taiwan, for boron neutron capture therapy (BNCT) purpose. It is recently developed with user-friendly interface using Interactive Data Language. In this article the accuracy of THORplan is verified by comparing results of Snyder phantom calculation with the analytical model results of MCNP. Neutron source from THOR epithermal neutron beam is used as the source for the calculation. The thermal neutron flux calculated by THORplan is very close to the reference results. SERA overestimates thermal neutron flux by 2-5%. NCTPlan underestimates thermal neutron flux by 4-9% in most locations. The total weighted dose calculated by THORplan is accurate to within 3% except at the tissue interface. SERA overestimates the total weighted dose at depth >1.5 cm by 2-5%. NCTPlan underestimates the total weighted dose by approximately 10% at depth >1cm.

Dual detector dosimetry using the paired detectors, TLD-600 and TLD-700 chips, were selected in this study to distinguish the doses of neutrons and photons in Tsing Hua Open-pool Reactor (THOR) boron neutron capture therapy (BNCT) preclinical test. Since the neutron response of TLD is dependent on the neutron spectrum, responses of TLD-600 and TLD-700 for neutrons and photons were estimated by irradiation methods and in addition the effect of the neutron spectrum on the TLD response was studied by Monte Carlo simulations in present work. A sectional ART head phantom was used to be irradiated with the THOR BNCT beam. TLD-600 and TLD-700 chips were placed inside the phantom to measure and distinct the doses of neutrons from photons. Besides, dual TLD chips were placed in plane of the room space area to estimate the spatial dose distributions in the THOR BNCT treatment room. A cube water phantom was used to consider the deviation between the two algorithms used in this work. In the results, neutron and photon dose distributions in phantom and the spatial dose distributions in THOR BNCT treatment room were estimated; characteristics and the treatment indexes for BNCT were also assessed.

The Cyclotron Center in Shin Kong Wu Ho-Su Memorial Hospital (SK Cyclotron Center) produced the 18 F-FDG compound and provided it to the Positron Emission Tomography (PET) center for diagnosis services. The works in SK Cyclotron Center are distinguished into three procedures including production, dispensation, and carry of the compound. As the medical cyclotron was operated to produce the radioactive compounds, secondary radiations such as neutrons and γ -rays were also induced. To estimate the exposure for the staffs working in the SK Cyclotron Center, the dual-TLD (TLD-600/700) chips were used to measure the doses contributed from photons and neutrons during the operation of the cyclotron, and the doses contributed from photons during dispensation and carry of the nuclear compounds. In the results, the mean H p (10) and H p (0.07) of the finger for a worker were 2.11 mSv y −1 and 96.19 mSv y −1 , respectively. Results estimated by the regular personal chest badges and finger ring dosimeters which considered only the doses of photons were compared. By means of the results of this work, doses contributed from different working procedures and from different types of radiation to the workers in the SK Cyclotron Center were realized.

This paper discussed the neutron doses induced by the high energy medical linear accelerator (Linac). Thermoluminescent dosimeter (TLD) pairs are usually chosen to distinguish the doses of neutrons from photons in mixed radiation field. In this work, TLD-600 and TLD-700 chips were used to investigate the dose contributions of neutrons induced by 15 MV photon beam of the medical Linac used in radiotherapy. A Rando phantom filled with these dual-TLD chips was irradiated in the 15 MV photon beam to assess the doses contribution of the induced neutrons. Besides, dual-TLD chips were also placed in the treatment room to estimate the spatial dose distribution of neutrons. In the results, dose contributions of neutrons in phantom are less than 0.1% compared with the maximum dose of photons. The dose distribution of neutrons in the treatment room was also revealed.

In radiodiagnosis, optimization is defined as a method of reducing the patient-absorbed doses without affecting image quality. In this study, we aimed to determine the parameters of a multi-slice CT (MSCT) scanner (LightSpeed VCT 64; General Electric) that ensure the least organ dose with the best image quality (i.e., optimization) for chest examinations, which are the most frequently used radio diagnostic investigations. Organ doses of an anthropomorphic phantom were measured during MSCT chest scans by using GR-100 (LiF: Mg, Ti) thermo-luminescent dosimeters (TLDs) attached to various parts of the organs. The accumulated equivalent doses were calculated to evaluate the radiation risk to sensitive organs by using different scan conditions and measuring the absorbed doses, because different scan parameters (e.g., pitch, tube current, scan type, etc.) may affect the dose contribution to these organs. By means of the radiation and tissue weighting factors recommended in the International Commission on Radiological Protection (ICRP) 103 report, the effective dose was then estimated. The pitch value and tube current were the main parameters affecting the organ doses of the phantom: increase in the pitch value and reduction of the tube current decreased the absorbed doses without impacting the image resolution and diagnostic information. Consequently, radiologists can establish an optimization protocol in MSCT and acquire high-resolution images with adequate diagnostic information while using the lowest exposure dose for chest examinations.

Stereotactic radiosurgery (SRS) is designed for patients with small lesion areas that are not suitable for actual surgery. SRS delivers high dose to the lesion with high gradient on the irradiation margin area. In this study, radiophotoluminescent glass dosemeter (RPLGD) and radiochromic film were used to measure the output factor of a gamma knife. Also, a Monte Carlo code (OMEGA/BEAM) was applied to simulate the output factor. For 14 and 8 mm sizes of helmet collimators, the variations of output factors determined with RPLGD, radiochromic film, the Monte Carlo code and Elekta were all within 0.5 %. When helmet collimator size was 4 mm, the output factors detected from RPLGD, radiochromic film and Monte Carlo simulation were all within 3.2 % when compared with Elekta. Taken together, RPLGD, radiochromic film and Monte Carlo simulation will be used as precise tools to measure the output factor of a gamma knife.

Purpose: To estimate the lung and other critical organ doses of the patients in total body irradiation before bone marrow transplant which is a general protocol for curing leukemia. Method and Materials: Total body irradiation was performed using the photo beam produced by the linear accelerator in the conditions of 415 cm source‐to‐surface distance (SSD), 40×40 cm2field size and 15 MV beam energy in parallel opposed irradiation in this work. A Rando phantom, a diode detector and thermoluminescent dosimeter(TLD) chips were selected to perform the dose investigation. The diode detector has small volume, and can provide real‐time reading and high accuracy. TLD chips were placed inside the Rando phantom to get the dose distributions along the longitude of the phantom and the critical organs suggested by the ICRP‐60 report. In the meantime, a diode detector and TLD chips were also placed at the entrance surface point to evaluate the dose conversion factors for the critical organs to the entrance surface dose (ESD).Results: The doses of upper mediastinum lung in the Rando phantom are about 20 % higher than the prescribed doses at the center in field. The doses of thyroids, gonad glands and eyes are lower than prescribed doses. The organ‐dose conversion factors for the critical organs to the entrance surface dose were evaluated. Conclusion: The increased doses of lung should be considered in clinical practice. The organ‐dose conversion factors established in this work can be used to estimate the critical organ doses, by means of measuring only the entrance surface dose of the patient in clinical irradiation. The diode detector is accurate and convenient to be used in the evaluation of real‐time ESD of the patient in the clinical total body irradiation.