A novel position-sensitive mega-size dosimeter for photoneutrons in high-energy X-ray medical accelerators

PurposeA novel position-sensitive mega-size polycarbonate (MSPC) dosimeter is introduced. It provides photoneutron (PN) dose equivalent matrix of positions in and out of a beam of a high energy X-ray medical accelerator under a single exposure.MethodsA novel position-sensitive MSPC dosimeter was developed and applied. It has an effective etched area of 50 × 50 cm², as used in this study, processed in a mega-size electrochemical etching chamber to amplify PN-induced-recoil tracks to a point viewed by the unaided eyes. Using such dosimeters, PN dose equivalents, dose equivalent profiles and isodose equivalent distribution of positions in and out of beams for different X-ray doses and field sizes were determined in a Siemens ONCOR Linac.ResultsThe PN dose equivalent at each position versus X-ray dose was linear up to 20 Gy studied. As the field size increased, the PN dose equivalent in the beam was also increased but it remained constant at positions out of the beam up to 20 cm away from the beam edge. The jaws and MLCs due to material differences and locations relative to the target produce different PN contributions.ConclusionsThe MSPC dosimeter introduced in this study is a perfect candidate for PN dosimetry with unique characteristics such as simplicity, efficiency, dose equivalent response, large size, flexibility to be bent, resembling the patient’s skin, highly position-sensitive with high spatial resolution, highly insensitive to X-rays, continuity in measurements and need to a single dosimeter to obtain PN dose equivalent matrix data under a single X-ray exposure.     

Radiochromic films for dental CT dosimetry: A feasibility study

Dental CT dose evaluations are commonly performed using thermoluminescent dosimeters (TLD) inside anthropomorphic phantoms. Radiochromic films with good sensitivity in the X-ray diagnostic field have recently been developed and are commercially available as GAFCHROMIC XR-QA. There are potential advantages in the use of radiochromic films such as a more comprehensive dosimetry thanks to the adjustable size of the film samples. The purpose of this study was to investigate the feasibility of using radiochromic films for dental CT dose evaluations.Film samples were cut with a width of 5 mm and a length of 25 mm (strips), the same size as the Alderson Rando anthropomorphic phantom holes used in this study. Dental CT dose measurements were performed using simultaneously both TLD and radiochromic strips in the same phantom sites. Two equipment types were considered for dental CT examinations: a 16 slice CT and a cone beam CT. Organ equivalent doses were then obtained averaging the measurements from the sites of the same organ and effective doses were calculated using ICRP 103 weighting factors. The entire procedure was repeated four times for each CT in order to compare also the repeatability of the two dosimeter types.A linear correlation was found between the absorbed dose evaluated with radiochromic films and with TLD, with slopes of 0.930 and 0.944 (correlation r > 0.99). The maximum difference between the two dosimeter’s measurements was 25%, whereas the average difference was 7%. The measurement repeatability was comparable for the two dosimeters at cumulative doses above 15 mGy (estimated uncertainty at 1 sigma level of about 5%), whereas below this threshold radiochromic films show a greater dispersion of data, of about 10% at 1 sigma level. We obtained, using respectively Gafchromic and TLD measurements, effective dose values of 107 μSv and 117 μSv (i.e. difference of 8.6%) for the cone beam CT and of 523 μSv and 562 μSv (i.e. difference of 7%) for the multislice CT.This study demonstrates the feasibility of radiochromic films for dental CT dosimetry, pointing out a good agreement with the results obtained using TLD, with potential advantages and the chance of a more extensive dose investigation.     

Novel 6 MV X-ray photoneutron detection and dosimetry of medical accelerators

PurposeDosimetry of fast, epithermal and thermal photoneutrons in 6 MV X-ray beams of two medical accelerators were studied by novel dosimetry methods.MethodsA Siemens ONCOR and an Elekta COMPACT medical accelerators were used. Fast, epithermal and thermal photoneutron dose equivalents in 10 cm × 10 cm 6 MV X-rays fields were determined in air and on surface of a polyethylene phantom in X and Y directions. Polycarbonate dosimeters as bare or with enriched ¹⁰B convertors (with or without cadmium covers) were used applying a 50 Hz-HV electrochemical etching method.ResultsFast, epithermal and thermal photoneutron dose equivalents were efficiently determined respectively as ∼1145.8, ∼45.3 and ∼170.6 μSv in air and ∼1888.5, ∼96.1 and ∼640.6 μSv on phantom per 100 Gy X-rays at the isocenter of Siemens ONCOR accelerator in air. The dose equivalent is maximum at the isocenter which decreases as distance from it increases reaching a constant level. Tissue-to-air ratios are constants up to 15 cm from the isocenter. No photoneutrons was detected in the Elekta COMPACT accelerator.ConclusionsFast, epithermal and thermal photoneutron dosimetry of 6 MV X-rays were made by novel dosimetry methods in a Siemens ONCOR accelerator with sum dose equivalent per Gy of ∼0.0014% μSv with ∼0.21 MeV mean energy at the isocenter; i.e. ∼150 times smaller than that of 18 MV X-rays. This observation assures clinical safety of 6 MV X-rays in particular in single-mode machines like Elekta COMPACT producing no photoneutrons due to no “beryllium exit window” in the head structure.     

Clinical application of MOSkin dosimeters to rectal wall in vivo dosimetry in gynecological HDR brachytherapy

PurposeThree MOSkins dosimeters were assembled over a rectal probe and used to perform in vivo dosimetry during HDR brachytherapy treatments of vaginal cancer. The purpose of this study was to verify the applicability of the developed tool to evaluate discrepancies between planned and measured doses to the rectal wall.Materials and methodsMOSkin dosimeters from the Centre for Medical Radiation Physics are particularly suitable for brachytherapy procedures for their ability to be easily incorporated into treatment instrumentation. In this study, 26 treatment sessions of HDR vaginal brachytherapy were monitored using three MOSkin mounted on a rectal probe. A total of 78 measurements were collected and compared to doses determined by the treatment planning system.ResultsMean dose discrepancy was determined as 2.2 ± 6.9%, with 44.6% of the measurements within ±5%, 89.2% within ±10% and 10.8% higher than ±10%. When dose discrepancies were grouped according to the time elapsed between imaging and treatment (i.e., group 1: ≤90 min; group 2: >90 min), mean discrepancies resulted in 4.7 ± 3.6% and 7.1 ± 5.0% for groups 1 and 2, respectively. Furthermore, the position of the dosimeter on the rectal catheter was found to affect uncertainty, where highest uncertainties were observed for the dosimeter furthest inside the rectum.ConclusionsThis study has verified MOSkin applicability to in-patient dose monitoring in gynecological brachytherapy procedures, demonstrating the dosimetric rectal probe setup as an accurate and convenient IVD instrument for rectal wall dose verification. Furthermore, the study demonstrates that the delivered dose discrepancy may be affected by the duration of treatment planning.     

Local diagnostic reference levels for intraoral dental radiography in the public hospitals of Cyprus

PurposeThe purpose of this study was to determine local DRLs for children and adults undergoing intraoral dental examinations at the intraoral radiology units of the public hospitals in Cyprus.MethodsMeasurements were made on all the twenty intraoral X-ray units of the public hospitals in Cyprus with the intention to establish the local DRLs for all the possible intraoral X-ray examinations for children and adults. All units are film based. The measurements were made by a Dose Area Product (DAP) meter (GAMMEX RMI 841-RD) placed at the surface of the dental unit’s X-ray shaping cone (FSD 20 cm). A diagnostic radiology dosimeter (Dosimax Plus A) was also placed at an FSD of 100 cm to compare the dose reading between the two dosimeters.ResultsDRLs were established at the 3rd quartile for 7 exposure settings corresponding to 12 types of teeth (Adult and children mandibular and maxillary incisor, premolar and molar) with values of 197, 163, 128, 102, 81, 65 and 49 mGycm⁻² and 7.23, 5.94, 4.75, 3.68, 3.10, 2.41 and 1.88 mGy for benchmark nominal exposure times of 1000, 800, 640, 500, 400, 320 and 250 ms respectively, at a nominal exposure voltage of 70 kVp.ConclusionsThe local DRLs of the present study compare well with other similar published DRLs.     

Étude dosimétrique de préparations de médicaments radiopharmaceutiques au 68Ga

AimProduction of ⁶⁸Ga-radiopharmaceuticals is a rapidly growing field in France. However, operators may already be involved in other radiopharmaceutical activities. It is thus necessary to know the exposure of this new activity.Material and methodsFor passive dosimetry, a radiophotoluminescent (RPL) dosimeter, a thermoluminescent (TLD) chip, 2 TLD rings and a passive dosimeter for crystalline were used. For active dosimetry, an extremity dosimeter and a whole body dosimeter were used. This study was performed during semi-automatized production of ⁶⁸Ga-investigational medicinal products. Values were normalized to 500MBq manipulated (median activity using a 1850MBq ⁶⁸Ga-generator), 60 radiosynthesis (maximum enrollment ability of our center) and 2 operators. A LB123 proportional counter was used for quantification of external exposition to 10MBq ⁶⁸Ge and internal exposition by inhalation was theoretically assessed. ⁶⁸Ga emission attenuation by collective protection equipments was also discussed.ResultsConsidering passive dosimetry, the equivalent dose to extremities was 21.75 ± 0.34 mSv, the whole-body effective dose was 0.189 ± 0.011 mSv and the dose to crystalline was 0.925 ± 0.009 mSv. Considering active dosimetry, the equivalent dose to extremities was 8,75 ± 0.12 mSv and the whole-body effective dose was 0,088 ± 0.009 mSv. Total exposure to ⁶⁸Ge was 1.75 μSv.ConclusionIn our hands, ⁶⁸Ga is a directly transposable activity in radiopharmacies already equipped for ¹⁸F because of a dosimetry complying with regulatory limits and suitable radiation protection of collective equipments.     

Phantom study quantifying the depth performance of a handheld magnetometer for sentinel lymph node biopsy

PurposeThe use of a magnetic nanoparticle tracer and handheld magnetometer for sentinel lymph node biopsy (SLNB) was recently introduced to overcome drawbacks associated with the use of radioisotope tracers. Unlike the gamma probe, the used magnetometers are not only sensitive to the tracer, but also the diamagnetic human body. This potentially limits the performance of the magnetometer when used clinically.MethodsA phantom, mimicking the magnetic and mechanical properties of the human axilla, was constructed. The depth performance of two current generation magnetometers was evaluated in this phantom. LN-phantoms with tracer uptake ranging from 5 to 500 μg iron were placed at clinically relevant depths of 2.5, 4 and 5.5 cm. Distance-response curves were obtained to quantify the depth performance of the probes.ResultsThe depth performance of both probes was limited. In the absence of diamagnetic material and forces on the probe (ideal conditions) a LN-phantom with high uptake (500 μg iron) could first be detected at 3.75 cm distance. In the phantom, only superficially placed LNs (2.5 cm) with high uptake (500 μg iron) could be detected from the surface. The penetration depth was insufficient to detect LNs with lower uptake, or which were located deeper.ConclusionThe detection distance of the current generation magnetometers is limited, and does not meet the demands formulated by the European Association for Nuclear Medicine for successful transcutaneous SLN localization. Future clinical trials should evaluate whether the limited depth sensitivity is of influence to the clinical outcome of the SLNB procedure.     

Fetal radiation dose in three common CT examinations during pregnancy – Monte Carlo study

PurposeTo determine fetal doses in different stages of pregnancy in three common computed tomography (CT) examinations: pulmonary CT angiography, abdomino-pelvic and trauma scan with Monte Carlo (MC) simulations.MethodsAn adult female anthropomorphic phantom was scanned with a 64-slice CT using pulmonary angiography, abdomino-pelvic and trauma CT scan protocols. Three different sized gelatin boluses placed on the phantom’s abdomen simulated different stages of pregnancy. Intrauterine dose was used as a surrogate to a dose absorbed to the fetus. MC simulations were performed to estimate uterine doses. The simulation dose levels were calibrated with volumetric CT dose index (CTDI_vol) measurements and MC simulations in a cylindrical CTDI body phantom and compared with ten point doses measured with metal-oxide-semiconductor field-effect-transistor dosimeters. Intrauterine volumes and uterine walls were segmented and the respective dose volume histograms were calculated.ResultsThe mean intrauterine doses in different stages of pregnancy varied from 0.04 to 1.04 mGy, from 4.8 to 5.8 mGy, and from 9.8 to 12.6 mGy in the CT scans for pulmonary angiography, abdomino-pelvic and trauma CT scans, respectively. MC simulations showed good correlation with the MOSFET measurement at the measured locations.ConclusionsThe three studied examinations provided highly varying fetal doses increasing from sub-mGy level in pulmonary CT angiography to notably higher levels in abdomino-pelvic and trauma scans where the fetus is in the primary exposure range. Volumetric dose distribution offered by MC simulations in an appropriate anthropomorphic phantom provides a comprehensive dose assessment when applied in adjunct to point-dose measurements.     

Visualization of air and metal inhomogeneities in phantoms irradiated by carbon ion beams using prompt secondary ions

PurposeNon-invasive methods for monitoring of the therapeutic ion beam extension in the patient are desired in order to handle deteriorations of the dose distribution related to changes of the patient geometry. In carbon ion radiotherapy, secondary light ions represent one of potential sources of information about the dose distribution in the irradiated target. The capability to detect range-changing inhomogeneities inside of an otherwise homogeneous phantom, based on single track measurements, is addressed in this paper.MethodsAir and stainless steel inhomogeneities, with PMMA equivalent thickness of 10 mm and 4.8 mm respectively, were inserted into a PMMA-phantom at different positions in depth. Irradiations of the phantom with therapeutic carbon ion pencil beams were performed at the Heidelberg Ion Beam Therapy Center. Tracks of single secondary ions escaping the phantom under irradiation were detected with a pixelized semiconductor detector Timepix. The statistical relevance of the found differences between the track distributions with and without inhomogeneities was evaluated.ResultsMeasured shifts of the distal edge and changes in the fragmentation probability make the presence of inhomogeneities inserted into the traversed medium detectable for both, 10 mm air cavities and 1 mm thick stainless steel. Moreover, the method was shown to be sensitive also on their position in the observed body, even when localized behind the Bragg-peak.ConclusionsThe presented results demonstrate experimentally, that the method using distributions of single secondary ion tracks is sensitive to the changes of homogeneity of the traversed material for the studied geometries of the target.     

Patient doses and occupational exposure in a hybrid operating room

PurposeThis study aimed to characterize the radiation exposure to patients and workers in a new vascular hybrid operating room during X-ray-guided procedures.MethodsDuring one year, data from 260 interventions performed in a hybrid operating room equipped with a Siemens Artis Zeego angiography system were monitored. The patient doses were analysed using the following parameters: radiation time, kerma-area product, patient entrance reference point dose and peak skin dose. Staff radiation exposure and ambient dose equivalent were also measured using direct reading dosimeters and thermoluminescent dosimeters.ResultsThe radiation time, kerma-area product, patient entrance reference point dose and peak skin dose were, on average, 19:15 min, 67 Gy·cm², 0.41 Gy and 0.23 Gy, respectively. Although the contribution of the acquisition mode was smaller than 5% in terms of the radiation time, this mode accounted for more than 60% of the effective dose per patient. All of the worker dose measurements remained below the limits established by law.ConclusionsThe working conditions in the hybrid operating room HOR are safe in terms of patient and staff radiation protection. Nevertheless, doses are highly dependent on the workload; thus, further research is necessary to evaluate any possible radiological deviation of the daily working conditions in the HOR.     

Characteristics of a novel polymer gel dosimeter formula for MRI scanning: Dosimetry,toxicity and temporal stability of response

The present study intended to investigate the composition of a new polymer gel dosimeter. The new composition would be more suitable for a wide range of applications in comparison to polyacrylamide gel dosimeter since its extremely toxic acrylamide has been replaced with less harmful monomer i.e. 2-Acrylamido-2-MethylPropane Sulfonic acid (AMPS). To this end, the PAGAT gel dosimeter formula was used as a basis to test the new formulation of polymer gel dosimeter with a different monomer (AMPS) instead of acrylamide by using the %6 T and %50 C to the formula. The new formulation was named PAMPSGAT (Poly AMPS, Gelatin and THPC) polymer gel dosimeter. Moreover, the MRI response (R₂) of dosimeters was analyzed in terms of different dose range as well as post-irradiation time. The results indicated that the dose-response (R₂) of AMPS/Bis had a linear trend over a wide dose range. Furthermore, the results showed an acceptable temporal stability for the new polymer gel dosimeter.     

Évaluation de l’exposition des travailleurs du service de radioimmunoanalyse du Bénin aux rayonnements ionisants de l’iode 125

Occupational radiation dose of staff handling ¹²⁵I assessment at the Benin radioimmunoassay laboratory, have been undertaken from October 2012 to April 2013 to determine level of radiation safety. Equivalent dose to skin, whole body and extremities, were measured by the mean of thermoluminescence dosimetry. Firstly, three permanent workers and two students were provided with finger ring dosimeters to wear at index finger base of both hands. Ring dosimeters were used for four months. Secondly, three permanent workers and three students were provided with badge dosimeters to wear at the chest level. Badge dosimeters were renewed monthly for six months. The exposed ring and badge dosimeters were evaluated in Ghana. Permanent workers highest average equivalent dose received at index finger base of both hands was 142.75 ± 89.54, microSV/2 months and that of students was 34.69 ± 29.23, microSV/2 months. Workers skin exposure was below one third of prescribed dose limits for permanents workers (500mSv/yr) and students (150mSv/yr). Whole body exposure, expressed in mSv/month, of permanent workers and students, respectively ranged from 0.12 to 0.23 and from 0.11 to 0.16. Radio-immuno-assay laboratory workers are weakly exposed to ionizing radiation. They are safe from deterministic effect risk.     

Eye lens dose correlations with personal dose equivalent and patient exposure in paediatric interventional cardiology performed with a fluoroscopic biplane system

PurposeTo analyse the correlations between the eye lens dose estimates performed with dosimeters placed next to the eyes of paediatric interventional cardiologists working with a biplane system, the personal dose equivalent measured on the thorax and the patient dose.MethodsThe eye lens dose was estimated in terms of H_p(0.07) on a monthly basis, placing optically stimulated luminescence dosimeters (OSLDs) on goggles. The H_p(0.07) personal dose equivalent was measured over aprons with whole-body OSLDs. Data on patient dose as recorded by the kerma-area product (P_KA) were collected using an automatic dose management system. The 2 paediatric cardiologists working in the facility were involved in the study, and 222 interventions in a 1-year period were evaluated. The ceiling-suspended screen was often disregarded during interventions.ResultsThe annual eye lens doses estimated on goggles were 4.13 ± 0.93 and 4.98 ± 1.28 mSv. Over the aprons, the doses obtained were 10.83 ± 0.99 and 11.97 ± 1.44 mSv. The correlation between the goggles and the apron dose was R² = 0.89, with a ratio of 0.38. The correlation with the patient dose was R² = 0.40, with a ratio of 1.79 μSv Gy⁻¹ cm⁻². The dose per procedure obtained over the aprons was 102 ± 16 μSv, and on goggles 40 ± 9 μSv. The eye lens dose normalized to P_KA was 2.21 ± 0.58 μSv Gy⁻¹ cm⁻².ConclusionsMeasurements of personal dose equivalent over the paediatric cardiologist’s apron are useful to estimate eye lens dose levels if no radiation protection devices are typically used.     

Real-time patient radiation dosimeter for use in interventional radiology

There is currently no effective real-time patient dosimeter available for use in interventional radiology (IR). We conducted a feasibility study in a clinical setting to investigate the use of the new dosimeter using photoluminescence sensors during procedures. Reference dosimeters were set at almost the same position of the prototype dosimeter sensors.We found excellent correlations between the reference measurements and those of the prototype dosimeter (r² = 0.950). The sensor of the new dosimeter does not interfere with the IR procedure. The new dosimeter will be an effective tool for the real-time measurement of patient skin doses during IR.     

Implementation and evaluation of a transit dosimetry system for treatment verification

PurposeTo evaluate a formalism for transit dosimetry using a phantom study and prospectively evaluate the protocol on a patient population undergoing 3D conformal radiotherapy.MethodsAmorphous silicon EPIDs were calibrated for dose and used to acquire images of delivered fields. The measured EPID dose map was back-projected using the planning CT images to calculate dose at pre-specified points within the patient using commercially available software, EPIgray (DOSIsoft, France). This software compared computed back-projected dose with treatment planning system dose. A series of tests were performed on solid water phantoms (linearity, field size effects, off-axis effects). 37 patients were enrolled in the prospective study.ResultsThe EPID dose response was stable and linear with dose. For all tested field sizes the agreement was good between EPID-derived and treatment planning system dose in the central axis, with performance stability up to a measured depth of 18 cm (agreement within −0.5% at 10 cm depth on the central axis and within −1.4% at 2 cm off-axis). 126 transit images were analysed of 37 3D-conformal patients. Patient results demonstrated the potential of EPIgray with 91% of all delivered fields achieved the initial set tolerance level of Δ_D of 0 ± 5-cGy or %Δ_D of 0 ± 5%.ConclusionsThe in vivo dose verification method was simple to implement, with very few commissioning measurements needed. The system required no extra dose to the patient, and importantly was able to detect patient position errors that impacted on dose delivery in two of cases.     

Monte Carlo calculation of photo-neutron dose produced by circular cones at 18 MV photon beams

Aim

The aim of this study is to calculate neutron contamination at the presence of circular cones irradiating by 18 MV photons using Monte Carlo code.

Monte Carlo study on the secondary cancer risk estimations for patients undergoing prostate radiotherapy: A humanoid phantom study

AimThe aim of this study was to estimate the secondary malignancy risk from the radiation in FFB prostate linac-based radiotherapy for different organs of the patient.BackgroundRadiation therapy is one of the main procedures of cancer treatment. However, the application the radiation may impose dose to organs of the patient which can be the cause of some malignancies.Materials and methodsMonte Carlo (MC) simulation was used to calculate radiation doses to patient organs in 18 MV linear accelerator (linac) based radiotherapy. A humanoid MC phantom was used to calculate the equivalent dose s for different organs and probability of secondary cancer, fatal and nonfatal risk, and other risks and parameters related to megavoltage radiation therapy. In out-of-field radiation calculation, it could be seen that neutrons imparted a higher dose to distant organs, and the dose to surrounding organs was mainly due to absorbed scattered photons and electron contamination.ResultsOur results showed that the bladder and skin with 54.89 × 10⁻³ mSv/Gy and 46.09 × 10⁻³ mSv/Gy, respectively, absorbed the highest equivalent dose s from photoneutrons, while a lower dose was absorbed by the lung at 3.42 × 10⁻³ mSv/Gy. The large intestine and bladder absorbed 55.00 × 10⁻³ mSv/Gy and 49.08 × 10⁻³, respectively, which were the highest equivalent dose s due to photons. The brain absorbed the lowest out-of-field dose, at 1.87 × 10⁻³ mSv/Gy.ConclusionsWe concluded that secondary neutron portion was higher than other radiation. Then, we recommended more attention to neutrons in the radiation protection in linac based high energy radiotherapy.