TRUS-probe integrated MOSkin detectors for rectal wall in vivo dosimetry in HDR brachytherapy: In phantom feasibility study

The increasing complexity and high amount of dose per fraction delivered in prostate high dose rate (HDR) brachytherapy treatments call for the implementation of accurate and effective methods for the systematic and independent quality control of the overall treatment procedure. In this study, MOSkin detectors were placed on a trans-rectal ultrasound (TRUS) probe with the aim of performing both imaging and real time rectal wall in vivo dosimetry with the use of just one single instrument. After an adequate calibration of the detectors, which was carried out in a solid water phantom, the use of MOSkins integrated to the TRUS probe was studied in a gel phantom with a typical (simplified) prostate implant. Measured and calculated doses from the treatment planning system were compared, with a resulting very low average discrepancy of −0.6 ± 2.6%. The results are very promising and of particular clinical importance, however, further in vivo investigation is planned to validate the proposed method.     

Treatment verification and in vivo dosimetry for total body irradiation using thermoluminescent and semiconductor detectors

The objective of this work is the characterization of thermoluminescent and semiconductor detectors and their applications in treatment verification and in vivo dosimetry for total body irradiation (TBI) technique. Dose measurements of TBI treatment simulation performed with thermoluminescent detectors inserted in the holes of a “Rando anthropomorphic phantom” showed agreement with the prescribed dose. For regions of the upper and lower chest where thermoluminescent detectors received higher doses it was recommended the use of compensating dose in clinic. The results of in vivo entrance dose measurements for three patients are presented. The maximum percentual deviation between the measurements and the prescribed dose was 3.6%, which is consistent with the action level recommended by the International Commission on Radiation Units and Measurements (ICRU), i.e., ±5%. The present work to test the applicability of a thermoluminescent dosimetric system and of a semiconductor dosimetric system for performing treatment verification and in vivo dose measurements in TBI techniques demonstrated the value of these methods and the applicability as a part of a quality assurance program in TBI treatments.     

In-phantom dose verification of prostate IMRT and VMAT deliveries using plastic scintillation detectors

The goal of this work was to demonstrate the feasibility of using a plastic scintillation detector (PSD) incorporated into a prostate immobilization device to verify doses in vivo delivered during intensity-modulated radiation therapy (IMRT) and volumetric modulated-arc therapy (VMAT) for prostate cancer. The treatment plans for both modalities had been developed for a patient undergoing prostate radiation therapy. First, a study was performed to test the dependence, if any, of PSD accuracy on the number and type of calibration conditions. This study included PSD measurements of each treatment plan being delivered under quality assurance (QA) conditions using a rigid QA phantom. PSD results obtained under these conditions were compared to ionization chamber measurements. After an optimal set of calibration factors had been found, the PSD was combined with a commercial endorectal balloon used for rectal distension and prostate immobilization during external beam radiotherapy. This PSD-enhanced endorectal balloon was placed inside of a deformable anthropomorphic phantom designed to simulate male pelvic anatomy. PSD results obtained under these so-called “simulated treatment conditions” were compared to doses calculated by the treatment planning system (TPS). With the PSD still inserted in the pelvic phantom, each plan was delivered once again after applying a shift of 1 cm anterior to the original isocenter to simulate a treatment setup error.The mean total accumulated dose measured using the PSD differed the TPS-calculated doses by less than 1% for both treatment modalities simulated treatment conditions using the pelvic phantom. When the isocenter was shifted, the PSD results differed from the TPS calculations of mean dose by 1.2% (for IMRT) and 10.1% (for VMAT); in both cases, the doses were within the dose range calculated over the detector volume for these regions of steep dose gradient. Our results suggest that the system could benefit prostate cancer patient treatment by providing accurate in vivo dose reports during treatment and verify in real-time whether treatments are being delivered according to the prescribed plan.     

Characterization of a Ce3+ doped SiO2 optical dosimeter for dose measurements in HDR brachytherapy

Aim of this work was to study the application of a new miniaturized Ce³⁺ doped SiO₂ scintillation detector to in vivo dosimetry in high dose rate brachytherapy. Energy, dose-rate, temperature and angular dependences of the detector response to ¹⁹²Ir HDR brachytherapy fields were investigated, as well as sensitivity reproducibility and linearity. To this aim, two ad hoc phantoms were designed and developed to perform measurements in water. Intra-session reproducibility resulted to be very high, however inter-session reproducibility showed too high statistical variation. Detector response resulted to increase linearly with dose (R² = 0.997), with no evidence of energy and dose-rate dependence. Sensitivity resulted to increase linearly with temperature (R² = 0.995), with a 0.2% increase each °C. Finally, no significant angular dependence for the source moving around a circle in the azimuthal plane centered at the scintillator was observed. The obtained results show that the proposed detector is suitable for in vivo real-time dosimetry in high dose rate brachytherapy.     

Uncertainty and routine use of Aerial l-alanine – Electron spin resonance dosimetry system

Aerial l-alanine pellet dosimeter is characterized by MiniScope MS300 electron spin resonance spectrometer measurements using Aer'EDE Version 2.0.4. software for dose calculation. The measurement traceability is achieved by Aerial dosimetry laboratory where dosimeters for calibration curve were irradiated by electron beam accelerator. Dose determinations in Aerial are traceable to National Physical Laboratory (NPL). The software used for construction of calibration curve gives also the standard deviation of the residuals of measurements for calibration that is used for dose uncertainty calculation. In aim to determine whether this value can actually be taken as absorbed dose uncertainty during usage of this dosimetry system, alanine dosimeters were irradiated with doses between 5 and 32 kGy by ⁶⁰Co laboratory source for internal calibration. The dose rate at the places for irradiation was (20 ± 0.5) mGy s⁻¹ determined by Fricke dosimeter. Measurement of each irradiated dosimeter was repeated ten times in ten days. The results of measurements were analyzed to identify the sources of uncertainty, as well as their quantification in evaluation of total measurement uncertainty. In addition to statistical effects, the very low dose rate that was used for the irradiation of alanine dosimeters affects the measurements of absorbed dose, particularly for higher absorbed doses where the measured dose can be up to 3% lower than the real.     

Dosimetric evaluation of alanine-in-glass dosimeters at clinical dose levels using high-energy X-rays from a linear accelerator

This study presents the first dosimetric evaluation of the alanine-in-glass dosimeter in radiation therapy. The dosimeter is composed of a Pyrex glass tube filled with pure polycrystalline alanine. 6 MV X-ray beams from a linear accelerator were used to irradiate the dosimeter in a solid water phantom to therapy-level doses ranging from 0 to 30 Gy. An X-band electron paramagnetic resonance (EPR) spectrometer was utilized to measure the absorbed dose of the dosimeter. The doses measured by the dosimeter were compared to those from ion chamber dosimetry. It was found that the dosimeter exhibited a linear response in the dose range from 0.1 to 30 Gy. The deviation between measured and delivered doses was 0.11% over the 0.5–30 Gy range, whereas the deviation increased to about 25% at 0.1 Gy. The lowest detectable dose with an acceptable deviation limit of 5% or less was found to be 0.3 Gy. The inaccuracy in measurements at low doses can be attributed to background signals and instrument noise. The accuracy can be improved by proper selection of measurement conditions and better optimization of equipment. The findings of this study show that the alanine-in-glass dosimeter is suitable for dose measurements with acceptable accuracy down to 0.3 Gy. The dosimeter is therefore has the potential to be employed in radiotherapy applications and quality control procedures.     

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.     

Dosimetric verification of treatment planning system superficial dose calculations for proton beam

To investigate the accuracy of Eclipse treatment planning system (TPS) dose calculations at the surface. It is desirable to know the accuracy of the proton treatment planning system in predicting dose at superficial region. All measurements were performed in a clinical proton beam at the National Cancer Center in Korea. Proton treatment plans were developed for a superficial planning target volume (PTV) contoured on a cylindrical polymethylmethacrylate phantom specially designed for this study. Dose was then measured at the surface and also in the PTV for these treatment plans and compared against the TPS calculations. For our study, a model GD-301 glass dosimeters were used. The proton treatment planning system overestimated the superficial dose without use of bolus as much as by 7–14% when compared to glass dosimeter. On the other hand, with use of bolus to cover the superficial region, surface dose between the calculation from Eclipse and measurement using the glass dosimeter are approximately within 3%.     

Bilateral comparison of an alanine/ESR dosimetry system at radiotherapy dose levels

To improve the signal to noise ratio and to reduce the uncertainty for Electron Spin Resonance (ESR) readout of alanine dosimeters irradiated in the dose range of 2–10 Gy, new spectrometer settings have been proposed for microwave power, modulation amplitude, conversion time, sweeps of the spectrum and orientations of the alanine pellets (Garcia et al., 2009). To check the reliability of the new spectrometer settings at radiotherapy dose levels, a bilateral dose comparison in terms of absorbed dose to water was performed between the CEA LIST Laboratoire National Henri Becquerel (LNHB) and the Radiometrology Center of the China Institute of Atomic Energy (RC-CIAE). Eighteen alanine dosimeters were irradiated with 2, 5 and 10 Gy. Each dosimeter was readout with the new spectrometer settings developed within the framework of the collaboration. The results of D_meas/D_nom at both laboratories in the dose range of 2–10 Gy are within the tolerance limits. The maximum deviations observed are within the extended uncertainties (k = 2).     

Temperature dependence of a Ce3+ doped SiO2 radioluminescent dosimeter for in vivo dose measurements in HDR brachytherapy

Fiber-optic-coupled scintillation dosimeters are characterized by their small active volume if compared to other existing systems, and are therefore particularly suited for internal in vivo dosimetry. Due to possible differences between calibration conditions (i.e., room temperature) and conditions of clinical application (i.e., body temperature), their temperature dependence should be accurately studied. In this work, the temperature dependence of a Ce³⁺ doped SiO₂ scintillation detector coupled to a SiO₂ optical fibre was investigated for high dose rate brachytherapy applications. To this aim, two sets of irradiations with two different Ir-192 sources were performed in a water bath phantom at water temperatures ranging between 17 °C and 40.4 °C (Experiment 1). The relative response of the dosimeter was collected and analyzed. The same experiment was repeated with a second optical fibre which was designed without the active Ce³⁺ doped part at its end (Experiment 2) as well as by changing the length of the passive fibre inserted in water (Experiment 3). The two sets of measurements of experiment 1 were in accordance, indicating a linear increase with temperature of the scintillator sensitivity, with an average increase of 0.27 ± 0.2%/°C. In experiment 2, a 0.5%/°C increase of the collected signal resulted for the passive fibre. No significant difference of the temperature coefficient was found by changing the length of the fibre inserted in water (experiment 3). The obtained results show that a temperature-specific correction factor should be adopted at temperatures different than room temperature (e.g. for in vivo internal dosimetry). Further studies are required to understand the observations.     

Organ point dose measurements in clinical multi slice computed tomography (MSCT) examinations with the MOSkin™ radiation dosimeter

This study reports on the application of the MOSkin™ dosimeter in MSCT imaging for the real-time measurement of absorbed organ point doses in a tissue-equivalent female anthropomorphic phantom. MOSkin™ dosimeters were placed within the phantom to measure absorbed point organ doses for 2 commonly applied clinical scan protocols, namely the renal calculus scan and the pulmonary embolus scan. Measured organ doses in the imaged field of view were found to be in the dose range 4.7–9.5 mGy and 16.2–27.4 mGy for the renal calculus scan and pulmonary scan protocols respectively. For the derivation of effective dose, using the more recent ICRP 103 tissue weighting factors (w_T) compared to that of the ICRP 60 w_T resulted in a difference in the derived effective dose by up to 0.8 mSv (−20%) in the renal calculus protocol and up to 1.8 mSv (18%) in the pulmonary embolus protocol. This difference is attributed to the reduced radiosensitivity of the gonads and the increased radiosensitivity of breast tissue in the latest ICRP 103 assigned w_T. The results of this study show that the MOSkin™ dosimeter is a useful real-time tool for the direct assessment of organ doses in clinical MSCT examinations.     

Evaluation of internal occupational exposure by 123I in a radiopharmaceutical production facility

¹²³I is a photon emitter radionuclide (159 keV) used for diagnostic procedures of endocrinal diseases in nuclear medicine. Since 1998 it is produced at the industrial radiopharmaceutical plant operated by the Institute for Nuclear Energy (IEN-CNEN) and supplied to clinics located in the State of Rio de Janeiro, in Brazil. The production of this radionuclide represents a risk of internal occupational exposure. According to international recommendations, workers involved in this activity should be routinely monitored in order to comply with dose limits and keep individual exposures as low and reasonably achievable. The Radiation Protection Plan implemented at the IEN includes annual in vivo measurements of ¹²³I in the thyroid performed at the In Vivo Monitoring Laboratory of the Institute for Radiation Protection and Dosimetry (IRD-CNEN). This work describes a series of improvements on the measurement techniques used for the monitoring of the workers from the facility, including (i) optimization of in vivo measurement of the thyroid using an array of high-purity germanium detectors, (ii) development of a new in vitro bioassay method for the determination of ¹²³I in urine samples using a HPGe germanium detector and (iii) the establishment of a methodology for internal dose assessment, based on bioassay data. The sensitivity of the methods allow detection of ¹²³I activities below derived registry level of 1 mSv for the incorporation scenarios of exposure assumed in this work. Thus, it can be concluded that the methods are suitable for application in routine monitoring of workers occupationally exposed to ¹²³I in this facility.     

Monte-Carlo simulations of Al2O3 dosimetry in uniform MV photon beams: Influence of field and detector size

This work was to evaluate the absorbed dose to different sizes Al₂O₃ dosimeter in uniform MV photon beams using Monte Carlo simulation. The absorbed dose ratio factor f_md of Al₂O₃ dosimeters was calculated. The incident beams included 4 MV–24 MV X-rays using Mohan's spectra with different field sizes. Results show that the maximum variation of f_md due to different dosimeter sizes is 5%. As the field diameter increases from 1 cm to 3 cm, the difference of f_md can be up to 8%. The results of this work show that the effect of dosimeter size and the field size can't be neglected when using Al₂O₃ dosimeter.     

The study on changes of rectum area in proton prostate cancer therapy

The purpose of this study is to determine the changes in the rectum area during treatment and to identify the rectum area within the given field of view in order to reproduce the same pose as that presented during therapy planning to properly deliver the planned dose to the prostate. We obtained digitally reconstructed radiographs after planning treatment for 30 patients out of all patients who had been subjected to proton prostate cancer therapy from August 2012 to November 2014 at this hospital. We then obtained an image using a digital imaging positioning system (DIPS) on the first day of treatment. When planning the digitally reconstructed radiograph treatment, we determined the change in size of the rectum between the actual treatment and treatment planning by measuring the cross section of the rectum and the cross section on the image from the DIPS. The results indicated that the rectum area in the digitally reconstructed radiograph taken during treatment planning and the rectum area obtained from the DIPS image during treatment were different. As a consequence, when region targeted for proton treatment of prostate cancer does not maintain a constant volume, the position of the prostate does not receive an adequate dose due to such changes. Therefore, the results of this study will be useful to determine the corresponding volume during a prostate treatment plan.     

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.     

EPR of gamma-irradiated polycrystalline alanine-in-glass dosimeter

This study attempts to overcome some of the reported discrepancies in alanine-EPR reproducibility that may be related to alanine dosimeter preparation and/or EPR spectrometer settings. The dosimeters were prepared by packing pure polycrystalline $\text{<mi mathsize="small" is="true">L</mi>}\text{-}\alpha \text{-}\mathrm{alanine}$ directly as supplied by the manufacturer in glass tubes. This dosimeter production scheme avoids any possible contribution to the EPR signal from a binding material. The dosimeters were irradiated with gamma ray to low-dose ranges typical for medical therapy (0–20 Gy). Special attention has been paid to the study of minimum detectable dose, measurement repeatability and reproducibility, and post-irradiation stability. The dosimeter exhibited a linear dose response in the dose range from 0.1 to 20 Gy. These positive properties favor the polycrystalline alanine-in-glass tube as a radiation dosimeter.     

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.     

An evaluation of dosimetric characteristics of MAGIC gel modified by adding formaldehyde (MAGIC-f)

PurposeTo evaluate the dosimetric characteristics of a new formulation of MAGIC gel, called MAGIC-f, which contains the addition of 3.3% formaldehyde, resulting in a gel with increased thermal stability.MethodsMAGIC-f gel was prepared and stored in hermetically sealed plastic containers. After irradiation, magnetic resonance images (MRI) were acquired to evaluate dose and dose distribution. Dosimetric characterization was performed by means of depth dose measurements, dose response sensitivity and linearity, temporal stability, energy and dose rate dependence, dose integration using sequential beams, temperature influence during MRI acquisition and dose distribution integrity.ResultsMAGIC-f depth dose measurements are compatible with the dosimetric table data within ±4% uncertainty. The dosimeter's R₂ response varies linearly with dose at least from 0 to 6 Gy. The time–course of the sensitivity of the dosimeter following irradiation, indicated stabilization after 2 weeks. The dosimeter's response to irradiation was altered by 6% when increasing the energy from cobalt beams to 10 MV beams. The dose rate dependence of this new formulation of gel dosimeter is small: less than 2.5% for a variation from 200 to 500 cGy/min, and the dependence with the fractionation scheme is about 50% smaller than for standard MAGIC gel. The dependence on scanning temperature was also verified, and the integrity of the dose distribution was confirmed for a period of 90 days.ConclusionsThe results demonstrate the applicability of this new dosimeter in tridimensional dose distribution measurements.     

食品辐照技术中使用的丙氨酸-ESR剂量测量方法的研究-ESR测量条件的选定

鉴于丙氨酸辐照后形成的自由基很稳定,其总数在食品辐照常用的剂量范围(10²~10⁴Gy)内正比于辐照剂量,我们选定丙氨酸-ESR系统作为我国γ射线大剂量传递剂量计,并对它进行了研究,确定了正常的ESR测量条件。特别修正了波谱仪的增益系数之间的线性关系并计测了旋转样品管对信号幅度的影响。检测吸收剂量的下限为5Gy。在0.05~1k7Gy的范围内,对于以十种不同剂量辐照的丙氨酸样品,ESR波谱主峰幅度h与相应的剂量D之间的线性相关系数大于0.999。     

Verification of radiotherapy doses by EPR dosimetry in patients' teeth

The aim of this work was to verify applicability of electron paramagnetic resonance (EPR) ex vivo dosimetry in teeth enamel for determination of doses absorbed by patients during radiotherapy with radiation fields covering head regions and to examine with what accuracy the doses predicted by radiotherapy treatment plan (RTP) can be confirmed by doses measured ex post by the EPR method. The doses were determined in 22 enamel samples obtained from 11 patients who, after their radiotherapy treatment underwent extraction of teeth due to medical reasons. The delivered doses were determined by measuring EPR signals in enamel samples from the extracted teeth; magnitude of these signals is proportional to concentration of stable free radicals induced by radiation in the hydroxyapatite content of enamel. The measured doses were compared with doses planned in the teeth locations by RTP systems. The relation between the measured (D_m) and the planned (D_p) doses can be described as a linear function: D_m = s·D_p + b, with the slope s = 0.93 ± 0.03 and the intercept b = 0.67 ± 1.26. The deviations between the measured and calculated doses were in the (−12.6%, +1.9%) range with the average deviation of – 4.6%. It is concluded, than more accurate measurements, achievable when using a higher calibration dose than in the present study, are necessary to confirm or to deny the observed bias between the measured and planned doses.