In vivo dosimetry with thermoluminescent dosimeters in external photon beam radiotherapy

The ultimate check of the actual dose delivered to a patient in radiotherapy can only be achieved by using in vivo dosimetry. This work reports a pilot study to test the applicability of a thermoluminescent dosimetric system for performing in vivo entrance dose measurements in external photon beam radiotherapy. The measurements demonstrated the value of thermoluminescent dosimetry as a treatment verification method and its applicability as a part of a quality assurance program in radiotherapy. (c) 2009 Elsevier Ltd. All rights reserved.

The use of different types of thermoluminescent dosimeters to measure extremity doses in nuclear medicine

Depth-dose curves in LiF detectors of different effective thicknesses, together with their responses, were calculated for typical nuclear medicine radiation fields with 99mTc, 18F and 90Y sources. Responses were analysed in function of the radionuclide, detector effective thickness and irradiation geometry. On the other hand the results of the nuclear medicine measurement campaign of the ORAMED project were presented focussing on the dose distribution across the hand and on the appropriate position to wear the dosimeter.According to the results, thin LiF detectors provide better responses in all cases. Its use is essential for 18F, since thick dosimeters can underestimate Hp(0.07) up to a 50% because of the very inhomogeneous dose deposition on the active layer. The preliminary results of the measurement campaign showed that the index tip of the non-dominant hand is usually the most exposed position among the 22 monitored positions. It was also found that, in average, wrist dosimeters are likely to underestimate the maximum skin dose by a factor of the order of 20. This factor is reduced to around 6 for a ring dosimeter worn on the base of the index of the non-dominant hand. Thus, for typical nuclear medicine procedures, the base of the index of the non-dominant hand is recommended as the best monitoring option.

Factors affecting the use of CaF2 : Mn thermoluminescent dosimeters for low-level environmental radiation monitoring /

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Outpatient Radioiodine Therapy for Thyroid Cancer A Safe Nuclear Medicine Procedure

Purposes: To evaluate the dosimetric effect of outpatient radioiodine therapy for thyroid cancer in members of a patient`s family and their living environment, when using iodine-131 doses reaching 7.4 GBq. The following parameters were thus defined: (a) whole-body radiation doses to caregivers, (b) the production of contaminated solid waste, and (c) radiation potential and surface contamination within patients` living quarters. Methods: In total, 100 patients were treated on an outpatient basis, taking into consideration their acceptable living conditions, interests, and willingness to comply with medical and radiation safety guidelines. Both the caregivers and the radiation dose potentiality inside patients` residences were monitored by using thermoluminescent dosimeters. Surface contamination and contaminated solid wastes were identified and measured with a Geiger-Muller detector. Results: A total of 90 monitored individuals received a mean dose of 0.27 (+/- 0.28) mSv, and the maximum dose registered was 1.6 mSv. The mean value for the potential dose within all living quarters was 0.31(+/- 0.34) mSv, and the mean value per monitored surface was 5.58 Bq/cm(2) for all the 1659 points measured. The overall production of contaminated solid wastes was at a low level, being about 3 times less than the exemption level indicated by the International Atomic Energy Agency. Conclusions: This study indicates that the treatment of thyroid cancer by applying radioiodine activities up to 7.4 GBq, on an outpatient basis, is a safe procedure, especially when supervised by qualified professionals. This alternative therapy should be a topic for careful discussion considering the high potential for reducing costs in healthcare and improving patient acceptance.

Quality control of blood irradiation with a teletherapy unit: damage to stored red blood cells after cobalt-60 gamma irradiation

BACKGROUND: Previous publications have documented the damage caused to red blood cells (RBCs) irradiated with X-rays produced by a linear accelerator and with gamma rays derived from a Cs-137 source. The biologic effects on RBCs of gamma rays from a Co-60 source, however, have not been characterized. STUDY DESIGN AND METHODS: This study investigated the effect of 3000 and 4000 cGy on the in vitro properties of RBCs preserved with preservative solution and irradiated with a cobalt teletherapy unit. A thermal device equipped with a data acquisition system was used to maintain and monitor the blood temperature during irradiation. The device was rotated at 2 r.p.m. in the irradiation beam by means of an automated system. The spatial distribution of the absorbed dose over the irradiated volume was obtained with phantom and thermoluminescent dosimeters (TLDs). Levels of Hb, K+, and Cl- were assessed by spectrophotometric techniques over a period of 45 days. The change in the topology of the RBC membrane was investigated by flow cytometry. RESULTS: Irradiation caused significant changes in the extracellular levels of K+ and Hb and in the organizational structure of the phospholipid bilayer of the RBC membrane. Blood temperature ranged from 2 to 4 degrees C during irradiation. Rotation at 2 r.p.m. distributed the dose homogeneously (92%-104%) and did not damage the RBCs. CONCLUSIONS: The method used to store the blood bags during irradiation guaranteed that all damage caused to the cells was exclusively due to the action of radiation at the doses applied. It was demonstrated that prolonged storage of Co-60-irradiated RBCs results in loss of membrane phospholipids asymmetry, exposing phosphatidylserine (PS) on the cells` surface with a time and dose dependence, which can reduce the in vivo recovery of these cells. A time- and dose-dependence effect on the extracellular K+ and plasma-free Hb levels was also observed. The magnitude of all these effects, however, seems not to be clinically important and can support the storage of irradiated RBC units for at last 28 days.

Study of the spatial distribution of the absorbed dose in blood volumes irradiated using a teletherapy unit

Blood irradiation can be performed using a dedicated blood irradiator or a teletherapy unit. A thermal device providing appropriate storage conditions during blood components irradiation with a teletherapy unit has been recently proposed. However, the most appropriated volume of the thermal device was not indicated. The goal of this study was to indicate the most appropriated blood volume for irradiation using a teletherapy unit in order to minimize both the dose heterogeneity in the volume and the blood irradiation time using these equipments. Theoretical and experimental methods were used to study the dose distribution in the blood volume irradiated using a linear accelerator and a cobalt-60 therapy machine. The calculation of absorbed doses in the middle plane of cylindrical acrylic volumes was accomplished by a treatment planning system. Experimentally, we also used cylindrical acrylic phantoms and thermoluminescent dosimeters to confirm the calculated doses. The data obtained were represented by isodose curves. We observed that an irradiation volume should have a height of 28 cm and a diameter of 28 cm and a height of 35 cm and a diameter of 35 cm, when the irradiation is to be performed by a linear accelerator and a cobalt-60 teletherapy unit, respectively. Calculated values of relative doses varied from 93% to 100% in the smaller volume, and from 66% to 100% in the largest one. A difference of 5.0%, approximately, was observed between calculated and experimental data. The size of these volumes permits the irradiation of blood bags in only one bath without compromising the homogeneity of the absorbed dose over the irradiated volume. Thus, these irradiation volumes can be recommend to minimize the irradiation time when a teletherapy unit is used to irradiate blood. (C) 2010 Elsevier Ltd. All rights reserved.

Avaliação da dose efetiva recebida pelo técnico de radiologia no contexto ocupacional

Introdução – As funções a desempenhar pelos técnicos de radiologia (TR) envolvem exposição ocupacional às radiações ionizantes, podendo acarretar potenciais efeitos biológicos. Metodologia – De modo a avaliar a dose efetiva recebida pelo TR nos diferentes métodos de estudo radiológico em que este trabalha, procedeu-se à realização de um estudo exploratório-descritivo. Efetuaram-se medições com dosímetros termoluminescentes em cinco valências radiológicas e foram aplicados questionários aos TR para determinar o tempo total de trabalho, bem como as medidas gerais de proteção radiológica utilizadas durante o período de medições. Resultados – Verificou-se que as doses efetivas, calculadas por hora, foram mais elevadas na valência de radiologia de intervenção, com os dados obtidos sobre a proteção plumbínea, sendo que a valência com menor dose efetiva calculada por hora foi a de mamografia, que apresentou um valor de medição igual a zero. Conclusões – Com o presente estudo conclui-se que existem diferenças de dose efetiva recebida de acordo com a função desempenhada pelo TR. Pela extrapolação dos valores calculados para doses efetivas anuais, verificou-se que os valores correspondentes a cada valência se encontram muito abaixo do limite anual legal de 20mSv.

Fetal dose reduction in head and neck radiotherapy of a pregnant woman.

BACKGROUND AND PURPOSE: A pregnant woman was referred for post-operative radiotherapy of a malignant schwannoma in the head and neck region. A best-treatment plan was devised in order to minimize the fetal dose. MATERIAL AND METHODS: The fetal dose resulting from radiological examinations was determined according to international protocols, that resulting from radiotherapy was calculated according to Recommendation 36 of the American Association of Physicists in Medicine (AAPM) Task Group. Pre-treatment dosimetry was performed with an anthropomorphic phantom. Several alternative treatment plans were evaluated. The use of a multileaf collimator (MLC) and a virtual wedge (VW) was compared to cerrobend blocks (CB) and physical wedge (PW). In-vivo dosimetry was performed using a vaginal probe containing thermoluminescent dosimeters (TLD). RESULTS: The total fetal dose resulting from diagnostic and radiotherapy procedures was estimated to be 36 mGy. The technique based on MLC and VW was elected for patient treatment. Measurements for this configuration resulted in afetal dose reduction of 82%. The shielding of the patient's abdomen further reduced the fetal dose by 42%. CONCLUSION: The use of VW and MLC for the treatment of a pregnant woman is highly recommended. Each case should be individually studied with pre-treatment and in-vivo dosimetry.

Accuracy of out-of-field dose calculation of tomotherapy and cyberknife treatment planning systems: A dosimetric study.

PURPOSE: Late toxicities such as second cancer induction become more important as treatment outcome improves. Often the dose distribution calculated with a commercial treatment planning system (TPS) is used to estimate radiation carcinogenesis for the radiotherapy patient. However, for locations beyond the treatment field borders, the accuracy is not well known. The aim of this study was to perform detailed out-of-field-measurements for a typical radiotherapy treatment plan administered with a Cyberknife and a Tomotherapy machine and to compare the measurements to the predictions of the TPS. MATERIALS AND METHODS: Individually calibrated thermoluminescent dosimeters were used to measure absorbed dose in an anthropomorphic phantom at 184 locations. The measured dose distributions from 6 MV intensity-modulated treatment beams for CyberKnife and TomoTherapy machines were compared to the dose calculations from the TPS. RESULTS: The TPS are underestimating the dose far away from the target volume. Quantitatively the Cyberknife underestimates the dose at 40cm from the PTV border by a factor of 60, the Tomotherapy TPS by a factor of two. If a 50% dose uncertainty is accepted, the Cyberknife TPS can predict doses down to approximately 10 mGy/treatment Gy, the Tomotherapy-TPS down to 0.75 mGy/treatment Gy. The Cyberknife TPS can then be used up to 10cm from the PTV border the Tomotherapy up to 35cm. CONCLUSIONS: We determined that the Cyberknife and Tomotherapy TPS underestimate substantially the doses far away from the treated volume. It is recommended not to use out-of-field doses from the Cyberknife TPS for applications like modeling of second cancer induction. The Tomotherapy TPS can be used up to 35cm from the PTV border (for a 390 cm(3) large PTV).

Ambient radiation levels in positron emission tomography/computed tomography (PET/CT) imaging center

Objective: To evaluate the level of ambient radiation in a PET/CT center. Materials and Methods: Previously selected and calibrated TLD-100H thermoluminescent dosimeters were utilized to measure room radiation levels. During 32 days, the detectors were placed in several strategically selected points inside the PET/CT center and in adjacent buildings. After the exposure period the dosimeters were collected and processed to determine the radiation level. Results: In none of the points selected for measurements the values exceeded the radiation dose threshold for controlled area (5 mSv/year) or free area (0.5 mSv/year) as recommended by the Brazilian regulations. Conclusion: In the present study the authors demonstrated that the whole shielding system is appropriate and, consequently, the workers are exposed to doses below the threshold established by Brazilian standards, provided the radiation protection standards are followed.

Dosimetric evaluation of X-ray examinations of paranasal sinuses in pediatric patients

Abstract Objective: To estimate the entrance surface air kerma (Ka,e) and air kerma in the region of radiosensitive organs in radiographs of pediatric paranasal sinuses. Materials and Methods: Patient data and irradiation parameters were collected in examinations of the paranasal sinuses in children from 0 to 15 years of age at two children's hospitals in the city of Recife, PE, Brazil. We estimated the Ka,e using the X-ray tube outputs and selected parameters. To estimate the air kerma values in the regions of the eyes and thyroid, we used thermoluminescent dosimeters. Results: The Ka,e values ranged from 0.065 to 1.446 mGy in cavum radiographs, from 0.104 to 7.298 mGy in Caldwell views, and from 0.113 to 7.824 mGy in Waters views. Air kerma values in the region of the eyes ranged from 0.001 to 0.968 mGy in cavum radiographs and from 0.011 to 0.422 mGy in Caldwell and Waters views . In the thyroid region, air kerma values ranged from 0.005 to 0.932 mGy in cavum radiographs and from 0.002 to 0.972 mGy in Caldwell and Waters views. Conclusion: The radiation levels used at the institutions under study were higher than those recommended in international protocols. We recommend that interventions be initiated in order to reduce patient exposure to radiation and therefore the risks associated with radiological examination of the paranasal sinuses.

Entrance surface dose measurements in pediatric radiological examinations

A survey of pediatric radiological examinations was carried out in a reference pediatric hospital of the city of Sao Paulo. in order to investigate the doses to children undergoing conventional X-ray examinations. The results showed that the majority of pediatric patients are below 4 years, and that about 80% of the examinations correspond to chest projections. Doses to typical radiological examinations were measured in vivo with thermoluminescent dosimeters (LiF: Mg, Ti and LiF: Mg, Cu, P) attached to the skin of the children to determine entrance surface dose (ESD). Also homogeneous phantoms were used to obtain ESD to younger children, because the technique uses a so small kVp that the dosimeters would produce an artifact image in the patient radiograph. Four kinds of pediatric examinations were investigated: three conventional examinations (chest, skull and abdomen) and a fluoroscopic procedure (barium swallow). Relevant information about kVp and mAs values used in the examinations was collected, and we discuss how these parameters can affect the ESD. The ESD values measured in this work are compared to reference levels published by the European Commission for pediatric patients. The results obtained (third-quartile of the ESD distribution) for chest AP examinations in three age groups were: 0.056 mGy (2-4 years old); 0,068 mGy (5-9 years old)-. 0.069 mGy (10-15 years old). All of them are below the European reference level (0.100mGy). ESD values measured to the older age group in skull and abdomen AP radiographs (mean values 3.44 and 1.20mGy, respectively) are above the European reference levels (1.5mGy to skull and 1.0 mGy to abdomen). ESD values measured in the barium swallow examination reached 10 mGy in skin regions corresponding to thyroid and esophagus. It was noticed during this survey that some technicians use, improperly, X-ray fluoroscopy in conventional examinations to help them in positioning the patient. The results presented here are a preliminary survey of doses in pediatric radiological examinations and they show that it is necessary to investigate the technical parameters to perform the radiographs. to introduce practices to control pediatric patient`s doses and to improve the personnel training to perform a pediatric examination. (c) 2007 Elsevier Ltd. All rights reserved.

Occupational exposure to radon and natural gamma radiation in the La Carolina, a former gold mine in San Luis Province, Argentina

Radon and gamma radiation level measurements were carried out inside the La Carolina mine, one of the oldest gold mining camps of southern South America, which is open for touristic visits nowadays. CR-39 track-etch detectors and thermoluminescent dosimeters of natural CaF(2) and LiF TLD-100 were exposed at 14 points along the mine tunnels in order to estimate the mean (222)Rn concentration and the ambient dose equivalent during the summer season (November 2008 to February 2009). The values for the (222)Rn concentration at each monitoring site ranged from 1.8 +/- 0.1 kBq m(-3) to 6.0 +/- 0.5 kBq m(-3), with a mean value of 4.8 kBq m(-3), indicating that these measurements exceed in about three times the upper action level recommended by ICRP for workplaces. The correlations between radon and gamma radiation levels inside the mine were also investigated. Effective doses due to (222)Rn and gamma rays inside the mine were determined, resulting in negligible values to tourists. Considering the effective dose to the mine tourist guides, values exceeding 20 mSv of internal contribution to the effective doses can be reached, depending on the number of working hours inside the mine. (C) 2009 Elsevier Ltd. All rights reserved.

Thermoluminescence measurements of entrance surface skin dose in exams of dog's chest in veterinary radiology

This study aims to determine the entrance surface skin doses in dogs (with suspected pulmonary metastasis) submitted to chest X-rays using the technique of thermoluminescence (TL) dosimetry. Twenty seven radiologic exams of dogs of different breed and sizes were performed. The radiation doses were assessed using thermoluminescent dosimeters of calcium sulphate doped with dysprosium (CaSO(4):Dy) produced at Instituto de Pesquisas Energeticas e Nucleares (IPEN-CNEN). The entrance surface skin dose range evaluated in this type of procedure was between 0.43 mGy to small size dogs and 4.22 mGy to big size dogs with repeated exams. The obtained results indicate that is extremely important the assessment of radiation doses involved in veterinary diagnostic radiology procedures, to evaluate the delivered doses to the animals, to be used as a parameter in the individual monitoring of pet's owners, who assist the animal positioning, and to protect occupationally exposed workers at the Veterinary Radiology Clinics. (C) 2010 Elsevier Ltd. All rights reserved.