Skin Dosimeters Research Articles

Molecular disruptions in PTFE as the basis of a therapy-level skin dosimeter

75 μm thick PTFE tape attracts interest, forming the basis of a potential skin dosimeter capable of utilization in radiotherapeutic external beam applications. The medium is readily available, for instance in the form of ordinary plumber's tape as used herein, typically of 12 mm width mounted on a spool. A60Co (mean energy 1.25 MeV) irradiator has been used to deliver doses in the range 0.1- to 10 Gy, with disrupted molecular bonds inspected via Raman spectrometry. The peak of greatest magnitude, at a wavenumber of ∼734 cm−1, corresponds to the difluoromethylene (CF2) symmetric stretching mode. Reduction in the peak intensity is seen to occur over the range 0.1- to 5 Gy, covering the values of skin dose typically arising in a single fractionated radiotherapeutic treatment. Results from these preliminary investigations point to a technique offering viability for radiotherapy skin dosimetry, utilizing a soft, low atomic number medium of particularly low-cost, also available in hypoallergenic form.

Is the use of gonad protection protectors necessary during infants chest radiography?

Introduction and objectivesTo compare gonad doses with and without a gonad protector and to optimize the use of gonadal protectors in infants thorax radiography. Materials and methodsTwo pediatric anthropomorphic phantoms are used: an X-ray system for KXO-50SS/DRX-3724HD, and a digital radiography system for CALNEO Smart C12, with and without a gonad protector during infants thorax radiography. A real time skin dosimeter is placed on the X-ray system, and a real time skin dosimeter is inserted on the front side of the mammary gland, the front and back sides of the true pelvis level, and on the ovaries and testes. The X-ray system is irradiated 15 times using phantoms with and without a gonad protector. The measured entrance patient doses values of for the real time skin dosimeter are compared for each phantom, with and without the gonad protector. ResultsThe medium of measured entrance patient doses values for front side dose of the true pelvis level with and without the protector are 10.00 and 5.00 μGy at newborn, and 10.00 and 0.00μGy at one year, respectively. The medium of measured entrance patient doses values for the back side dose of the true pelvis level with and without the protector are 0.00 and 0.00 μGy at both newborn one year, respectively. The measured entrance patient doses cannot be detected in the ovaries and testes with or without the protector. No significant differences are observed in the measured entrance patient doses values for the front and back side doses of the pelvis, ovaries, and testes at newborn and one year, with and without the protector (p>0.05). ConclusionsNo significant difference was observed in gonad dose measurements with and without the gonad protector during infants chest radiography. We believe that gonadal protector wearing is not necessary.

Carbon rich media for luminescence-based surface dosimetry and study of associated surface defects

The present study continues research into the utilisation of carbonaceous media for medical radiation dosimetry, focusing on the effects of surface area-to-volume ratio and carbon content on structural interaction alterations and dosimetric properties in sheet- and bead-type graphitic materials (with the respective carbon content of ∼98 wt% and ∼90 wt%). Using 60Co gamma-rays and doses from 0.5 Gy to 20 Gy, the study has been made of the response of commercially available graphite in the form of 0.1 mm, 0.2 mm, 0.3 mm and 0.5 mm thick sheets, also of activated carbon beads. Confocal Raman and photoluminescence spectroscopy have been employed, examining radiation-induced structural interaction alterations. Dose-dependent variation in the Raman intensity ratio ID/IG relates to the varying dominance of defect generation and dose-driven defect annealing. Of the various thickness graphite sheets, the 0.1 mm thick medium possesses the greatest surface area-to-volume ratio. Perhaps unsurprisingly, it also exhibits the greatest thermoluminescence (TL) yield compared to that of the other carbonaceous sheet foils used herein. Moreover, the second greatest mass-normalised TL yield has been observed to be that of the porous beads, reflected in the greater defect density (ID/IG > 2) when compared to the other media, due in part to their inherent feature of large internal surface area. Considering the challenge posed in matching skin thickness with skin dose, the near tissue equivalent graphite sheets show particular promise as a skin dosimeter, sensitive as a function of depth.

Usefulness of the superior orbitomeatal line without the lens included in the scan range at different tube voltage during pediatric head CT

Introduction and objectivesTo compare the real time skin dosimeter values at lens between with the lens included in the scan range (orbitomeatal base line [OML]) or without the lens included in the scan range (superior orbitomeatal line [SOML]) at different tube voltages. Materials and methodsWe used three pediatric anthropomorphic phantoms with a 64 detector-row computed tomography (CT) scanner with the OML- or SOML-protocol at different tube voltages during the head CT. A real time skin dosimeter was inserted into the phantom center of the head, and surfaces of the lens. We compared the real time skin dosimeter values at lens between the OML- and SOML-protocol. ResultsThere were no significant differences in the real time skin dosimeter values for the head in the scan area for each phantom at different tube voltages between the OML- and SOML-protocol (p > 0.05 for all phantom). Compared with the OML protocol, it is possible to reduce the real time skin dosimeter values at lens by approximately 80% by using the SOML protocol (p < 0.05) at all tube voltages. Compared with the OML protocol, it is possible to reduce the real time skin dosimeter values at mammary gland by approximately 20% by using the SOML protocol (p < 0.05) at all tube voltages. ConclusionsDuring the pediatric head CT examination, SOML protocol was possible to reduce the real time skin dosimeter values at lens by approximately 80% compared with OML protocol at all tube voltages.

Utilidad de la línea orbitomeatal superior sin incluir los cristalinos en la exploración con diferentes voltajes del tubo en la TC craneal pediátrica

Introduction and objectivesTo compare the real time skin dosimeter values at lens between with the lens included in the scan range (orbitomeatal base line [OML]) or without the lens included in the scan range (superior orbitomeatal line [SOML]) at different tube voltages. Materials and methodsWe used three pediatric anthropomorphic phantoms with a 64 detector-row computed tomography (CT) scanner with the OML- or SOML-protocol at different tube voltages during the head CT. A real time skin dosimeter was inserted into the phantom center of the head, and surfaces of the lens. We compared the real time skin dosimeter values at lens between the OML- and SOML-protocol. ResultsThere were no significant differences in the real time skin dosimeter values for the head in the scan area for each phantom at different tube voltages between the OML- and SOML-protocol (P>.05 for all phantom). Compared with the OML protocol, it is possible to reduce the real time skin dosimeter values at lens by approximately 80% by using the SOML protocol (P<.05) at all tube voltages. Compared with the OML protocol, it is possible to reduce the real time skin dosimeter values at mammary gland by approximately 20% by using the SOML protocol (P<.05) at all tube voltages. ConclusionsDuring the pediatric head CT examination, SOML protocol was possible to reduce the real time skin dosimeter values at lens by approximately 80% compared with OML protocol at all tube voltages.

Flexible real-time skin dosimeter based on a thin-film copper indium gallium selenide solar cell for electron radiation therapy.

Various dosimeters have been proposed for skin dosimetry in electron radiotherapy. However, one main drawback of these skin dosimeters is their lack of flexibility, which could make accurate dose measurements challenging due to air gaps between a curved patient surface and dosimeter. Therefore, the purpose of this study is to suggest a novel flexible skin dosimeter based on a thin-film copper indium gallium selenide (CIGS) solar cell, and to evaluate its dosimetric characteristics. The CIGS solar cell dosimeter consisted of (a) a customized thin-film CIGS solar cell and (b) a data acquisition (DAQ) system. The CIGS solar cell with a thickness of 0.33mm was customized to a size of 10×10mm2 . This customized solar cell plays a role in converting therapeutic electron radiation into electrical signals. The DAQ system was composed of a voltage amplifier with a gain of 1000, a voltage input module, a DAQ chassis, and an in-house software. This system converted the electrical analog signals (from solar cell) to digital signals with a sampling rate of ≤50kHz and then quantified/visualized the digital signals in real time. We quantified the linearity/ sampling rate effect/dose rate dependence/energy dependence/field size output factor/reproducibility/curvature/bending recoverability/angular dependence of the CIGS solar cell dosimeter in therapeutic electron beams. To evaluate clinical feasibility, we measured the skin point doses by attaching the CIGS solar cell to an anthropomorphic phantom surface (for forehead, mouth, and thorax). The CIGS-measured doses were compared with calculated doses (by treatment planning system) and measured doses (by optically stimulated luminescent dosimeter). The normalized signals of the solar cell dosimeter increased linearly as the delivered dose increased. The gradient of the linearly fitted line was 1.00 with an R-square of 0.9999. The sampling rates (2, 10, and 50kHz) of the solar cell dosimeter showed good performance even at low doses(<50 cGy). The solar cell dosimeter exhibited dose rate independence within 1% and energy independence within 3% error margins. The signals of the solar cell dosimeter were similar(<1%) when penetrating the same side of the CIGS cell regardless of the rotation angle of the solar cell. The field size output factor measured by the solar cell dosimeter was comparable to that measured by the ion chamber. The solar cell signals were similar between the baseline (week 1) and the last time point (week 4). Our detector showed curvature independence within 1.8% (curvatures of<0.10mm- ) and bending recovery (curvature of 0.10mm-1 ). The differences between measured doses (CIGS solar cell dosimeter vs. optically stimulated luminescent dosimeter) were 7.1%, 9.6%, and 1.0% for forehead, mouth, and thorax, respectively. We present the construction of a flexible skin dosimeter based on a CIGS solar cell. Our findings demonstrate that the CIGS solar cell has a potential to be a novel flexible skin dosimeter for electron radiotherapy. Moreover, this dosimeter is manufactured with low cost and can be easily customized to various size/shape, which represents advantages over other dosimeters.

Usefulness of large beam-shaping filters at different tube voltages of newborn chest CT.

To investigate optimizing the use of different beam shaping filters (viz. small, medium and large) when using different tube voltages during the newborn chest computed tomography (CT) on a GE Lightspeed VCT scanner. We used pediatric anthropomorphic phantoms with a 64 detector-row CT scanner while scanning the chest. A real-time skin dosimeter (RD - 1000; Trek Corporation, Kanagawa, Japan) was positioned into the phantom center of the body, the surface of the body back, and the right and left mammary glands. We performed and compared six scan protocols using small, medium, and large beam shaping filters at 80 and 120 kVp protocols. There were no significant differences in the image noise for the chest scan among the different beam shaping filters. By using the large beam shaping filter at 80 kVp, it was possible to reduce the exposure dose by 5% in comparison with the small beam shaping filter, and by 10% in comparison with the medium beam shaping filter. By using the large beam shaping filter at 120 kVp, it was possible to reduce the exposure dose by 15% in comparison with the small beam shaping filter and by 20% in comparison with the medium beam shaping filter (p < 0.01). The large beam shaping filter had the most dose reduction effect during newborn chest CT on a GE Lightspeed VCT scanner. The additional copper filtration being present in the large bowtie filter of the GE Lightspeed CT scanner when using different tube voltages is more effective in reducing radiation exposure in children.

¿Es necesario utilizar protectores de gónadas durante la realización de radiografías de tórax en los lactantes?

Introduction and objectivesTo compare gonad doses with and without a gonad protector and to optimize the use of gonadal protectors in infants thorax radiography. Materials and methodsTwo pediatric anthropomorphic phantoms are used: an X-ray system for KXO-50SS/DRX-3724HD, and a digital radiography system for CALNEO Smart C12, with and without a gonad protector during infants thorax radiography. A real time skin dosimeter is placed on the X-ray system, and a real time skin dosimeter is inserted on the front side of the mammary gland, the front and back sides of the true pelvis level, and on the ovaries and testes. The X-ray system is irradiated 15 times using phantoms with and without a gonad protector. The measured entrance patient doses values of for the real time skin dosimeter are compared for each phantom, with and without the gonad protector. ResultsThe medium of measured entrance patient doses values for front side dose of the true pelvis level with and without the protector are 10.00 and 5.00μGy at newborn, and 10.00 and 0.00μGy at one year, respectively. The medium of measured entrance patient doses values for the back side dose of the true pelvis level with and without the protector are 0.00 and 0.00μGy at both newborn one year, respectively. The measured entrance patient doses cannot be detected in the ovaries and testes with or without the protector. No significant differences are observed in the measured entrance patient doses values for the front and back side doses of the pelvis, ovaries, and testes at newborn and one year, with and without the protector (p>0.05). ConclusionsNo significant difference was observed in gonad dose measurements with and without the gonad protector during infants chest radiography. We believe that gonadal protector wearing is not necessary.

An investigation on quantitative detector characteristics of novel flexible skin dosimeter using Monte Carlo simulation method

Novel lead oxide-based flexible dosimeters with superior performance were experimentally tested for electron therapy. However, absorbed/transmitted primary particle fraction and secondary radiation distribution from the dosimeter surface have not been reported. These features should be specified to improve the dosimeter’s reliability for medical applications. Hence, the absorbed primary particle fraction, transmitted particle and secondary radiations distributions of lead oxide-based flexible skin dosimeter under the incident 6 MeV electron radiation have been investigated by pyPenelope Monte Carlo Simulation. The results have demonstrated that the generated secondary irradiation probabilities are not significantly high to enhance the therapeutic dose abnormally. In addition, the angular distribution of the scattered secondary irradiations is low. No abnormal changes were observed in the fraction and energy distribution of the transmitted primary electrons. Hence, it can be concluded that the designed structure has promising potential to be used as dosimeters in electron beam therapy.

Development and evaluation of a lead oxide flexible skin dosimeter with a silicon passive layer

Normal tissues are also exposed during radiation therapy. In particular, the skin is highly sensitive to radiation. Therefore, care should be taken regarding excessive exposure, and the dose irradiated to the skin should be measured accurately. In this study, a skin dosimeter that can be attached to the human body was manufactured using a silicone binder, and a new type of passive layer using silicon was applied. In addition, the manufactured dosimeter was evaluated to establish whether it could be used with a skin dosimeter. The observation of the surface of the dosimeter through SEM analysis showed that cracks did not occur on the surface of the silicon passive layer PbO dosimeter when it was bending. The bending silicon passive layer PbO dosimeter's relative standard deviation was 1.45%, meeting the evaluation criteria of 1.5%. The linearity evaluation showed that the R 2 of the bending silicon passive layer PbO dosimeter was 0.9996, satisfying the evaluation criterion R 2 of 0.9990. The PDD measurements showed that the D_max points matched. As the silicon passive layer PbO dosimeters showed no cracks when bending, high signal stability, and accuracy in reproducibility, linearity, and PDD measurement results, it could be suitable for application as skin dosimeters.

Commercial photodiodes and phototransistors as dosimeters of photon beams for radiotherapy.

The response to radiation typically used in radiotherapy treatments has been experimentally evaluated for three samples of two phototransistors (BPW85B and OP505A) and two PIN photodiodes types (VTB8440BH and BPW34S). To that end, a staggered irradiation cycle has been applied which included dose rate values from 0.81 to 4.87cGy/s, achieving a total absorbed dose of 21.4Gy. The samples have been irradiated with a linear accelerator and the relations between the induced photocurrent and the average and instantaneous dose rates, and between the accumulated charge and the absorbed dose, have been determined. The radiation-induced output currents were measured by means of an external interface of the devices to a previously designed readout unit. Experimental results of Si PIN photodiode BPW34S have shown a sensitivity of (13.9±0.5) nC/cGy, slight sensitivity dependence on dose rate, and a high linearity of the current with the average and instantaneous dose rate, requiring only 10V of reverse bias voltage. This device thermal drift has characterized and modeled for temperature effect compensation. Silicon PIN photodiode BPW34S, previously tested for X-rays and Co-60 gamma ray source, can also be a reliable candidate for dose rate and absorbed skin dose determination in typical radiotherapy treatments irradiations. A low sensitivity loss below 2% up to 21.4Gy has been measured, allowing its use as an affordable reusable skin dosimeter. Moreover, no significant difference has been observed between its response to dose-per-pulse and changing pulse repetition frequency in terms of sensitivity and dependence with dose-rate value.

USE OF VACUUM MATTRESSES CAN REDUCE THE ABSORBED DOSE DURING PEDIATRIC CT.

To evaluate and compare the absorbed dose and image quality when applying a commercially produced fixation device (group A) and a vaccum mattress fixation device to pediatric patients (group B). We compared the absorbed dose and image noise between the groups at the phantom and clinical study. For phantom study, the measurement absorbed dose for a real time skin dosimeter was 3.0mGy at the group A and 1.9mGy at the group B (p<0.05). For clinical study, computed tomography dose index product, dose-length and effective radiation dose were significantly lower with the group B compared to the group A, (3.4mGy, 27.0mGy-cm, and 2.2mSv vs 4.4mGy, and 36.7mGy-cm, and 3.0mSv), p<0.05 for all comparisons. Compared to the commercially produced fixation device, the vaccum mattress fixation device composed of a less absorptive material enabled a reduction in the absorbed dose while maintaining the image quality during pediatric CT examinations.

Development and evaluation of a monoxide-based flexible skin dosimeter for radiotherapy at photon energies

Radiation therapy uses high-energy radiation that can cause various side effects depending on the patient's exposure. In particular, the radiation exposure of the skin to reach the target volume produces side effects. Therefore, side effects as skin damage can be reduced during clinical trials using various skin dosimeters such as films and glass detectors to determine the skin dose exposure. However, accurately measuring the doses using these dosimeters is challenging due to human body curvature. In this study, a flexible skin dosimeter was developed using the photoconductor materials mercury oxide (HgO) and lead oxide (PbO). The performance of the proposed dosimeter was evaluated by measuring reproducibility, linearity, dose rate independence according to dose, and percent depth dose (PDD) at photon energy beam. The results showed that the flexible skin dosimeter using HgO material has high applicability as a skin dosimeter due to its stability compared to PbO. The results also provided useful insights for the radiation therapy field, particularly in areas where radiation measurement is difficult, depending on the human curvature. The proposed apparatus could serve in various radiation detection areas as a flexible, functional material.

Evaluation of monoxide film-based dosimeters for surface dose detection in electron therapy.

Generally, electron therapy is applied to tumors on or close to the skin surface. However, this causes a variety of skin-related side effects. To alleviate the risk of these side effects, clinical treatment uses skin dosimeters to verify the therapeutic dose. However, dosimeters suffer from poor accuracy, because their attachment sites are approximated with the help of naked eyes. Therefore, a dosimeter based on a flexible material that can adjust to the contours of the human body is required. In this study, the reproducibility, linearity, dose-rate dependence, and percentage depth ionization (PDI) of PbO and HgO film-based dosimeters are evaluated to explore their potential as large-scale flexible dosimeters. The results demonstrate that both dosimeters deliver impressive reproducibility (within 1.5%) and linearity (≥ 0.9990). The relative standard deviations of the dose-rate dependence of the PbO and HgO dosimeters were 0.94% and 1.16% at 6 MeV, respectively, and 1.08% and 1.25% at 9 MeV, respectively, with the PbO dosimeter outperforming the 1.1% of existing diodes. The PDI analysis of the PbO and HgO dosimeters returned values of 0.014 cm (–0.074 cm) and 0.051 cm (–0.016 cm), respectively at 6 MeV (9 MeV) compared to the thimble chamber and R50. Therefore, the maximum error of each dosimeter is within the allowable range of 0.1 cm. In short, the analysis reveals that the PbO dosimeter delivers a superior performance relative to its HgO counterpart and has strong potential for use as a surface dosimeter. Thus, flexible monoxide materials have the necessary qualities to be used for dosimeters that meet the requisite quality assurance standards and can satisfy a variety of radiation-related applications as flexible functional materials.

Skin dose assessment at diagnostic and therapeutic photon energies: A Monte Carlo study on TLDs

In radiotherapy but also as a part of quality assurance in diagnostic imaging, assessment of radiation dose to the skin of the patient is of particular importance. While skin dose is recommended to be measured at a reference depth of 70 μm, in practice in both diagnostic radiology as well as therapeutic applications, the dosimeter is placed on the skin surface, the measured dose depending in large part on dosimeter thickness. Thermoluminescent dosimeters (TLDs) are commonly applied as skin dosimeters, most of the commercial forms being thicker than 140 μm, also with a density greater than that of soft tissue, accordingly representing in effective point of measurement deeper than 70 μm. On the other hand, Monte Carlo (MC) simulations can be used to accurately calculate the dose at an intended depth. In this work we first validate our MC simulations, comparison being made with a previously published correction factor for LiF TLD of dimensions 3 × 3 × 0.1 mm3. Then correction factors to convert the dose measured by various commercial LiF-based TLDs (with thicknesses ranging from 0.15 to 1 mm) to skin dose at 70 μm depth are calculated for RQR reference diagnostic photon spectra and some common MV photon therapy spectra. These results are useful for correction of TLD responses in various clinical situations.

Evaluation of the Attenuation Rate for Clinical Application of a Flexible Skin Dosimeter in Radiotherapy

During radiotherapy, some patients owing to the variability in skin sensitivities, may experience adverse skin reactions for doses at which other patients are asymptomatic. Hence, when abnormal symptoms appear on a patient’s skin, the etiology should be verified. Accordingly, a surface dosimeter on the skin can help ascertain whether accurate doses are irradiated. Furthermore, surface doses are measured in the field junction gaps during craniospinal irradiation or during large-area radiotherapy to avoid adverse reactions due to cumulative skin doses from multiple beams. However, the point dose measurement errors of surface dosimeters exceed approximately 10% and have low-positional accuracies because the attachment sites are approximated with the help of the naked eye. Moreover, accurate information on field junction gaps cannot be obtained. Therefore, in clinical practice, a flexible array dosimeter is required as it can measure the dose distribution on the body surface by adapting its shape to the body curvatures. In this study, we implemented a flexible array dosimeter and, based on its constituent materials, evaluated the attenuation rate associated with its use. A polyester (PET) film was used as the underlying substrate. HgI2 and PbI2 photoconductors were used for their good performances in films. Furthermore, the measurement accuracy was verified through comparisons with Monte Carlo simulation outcomes. The resulting PET film had an attenuation rate of 2.22% at a 50-µm thickness. At the minimum material thickness of 25 µm, the attenuation rates for HgI2 and PbI2 were 4.69% and 5.72%, respectively. Further research is needed to fabricate HgI2-based digital skin dosimeters with a thickness under 25 µm. Radiation detection and pixel resolution should be evaluated to accurately confirm the field junction gap.

Effectiveness of a novel real-time dosimeter in interventional radiology: a comparison of new and old radiation sensors

Radiation dose management is important in interventional radiology (IR) procedures, such as percutaneous coronary intervention, to prevent radiation-induced injuries. Therefore, radiation dose should be monitored in real time during IR. This study evaluated the fundamental characteristics of a novel real-time skin dosimeter (RTSD) developed at our institution. In addition, we compared the performance of our new and old radiation sensors and that of a skin dose monitor (SDM), with ion chamber reference values. We evaluated the fundamental characteristics (e.g., energy dependence, dose dependence, and angular dependence) of the RTSD developed by us in the diagnostic X-ray energy range. The performance of our RTSD was similar to that of the SDM. In particular, the new radiation sensor of our RTSD demonstrated better dose rate dependence compared to the old sensor. In addition, the new sensor had the advantage of being small in size and thus minimally affecting the X-ray images compared to the old sensor. Therefore, the developed skin dosimeter and radiation sensor may be useful in real-time measurement of patients' exposure to and multi-channel monitoring of radiation in IR procedures. The new dosimeter system can be recommended for visualization and management of the radiation dose to which the patients' skin is exposed.

Application of MOSkin detector for in vivo dosimetry on total skin electron therapy (TSET)

Currently, TLDs and Gafchromic EBT3 film are commonly used for skin dose measurement during Total Skin Electron Therapy. However, measurements using these dosimeters are time consuming due to post-irradiation processing requirements. The MOSkin has advantages of being a small physical size with a 0.55 μm thick gate oxide and a water equivalent depth of 0.07 mm while providing real-time dosimetry. Measurements of the MOSkin’s dosimetric characteristics were performed using a 6 MeV electron beam with an Elekta Infinity linear accelerator. For the TSET measurements, doses measured with the MOSkin were directly compared to TLDs and Gafchromic EBT3 film using a 6 MeV high dose rate electron beam. A 6 mm Perspex spoiler was placed and aligned perpendicularly to the beam in order to lower the effective beam energy and improve dose homogeneity. The MOSkin showed good dose linearity (R2 = 0.9986) and dose rate independence for a 6 MeV electron beam and behaved very similarly to the other types of dosimeters that are commonly used in vivo dosimetry. For the TSET measurements, all three detector types showed a very similar trend of dose readings over the range of measurement points. Therefore, the MOSkin is an effective skin dosimeter for TSET dosimetry.

Red-emission phosphor’s brightness deterioration by x-ray and brightness recovery phenomenon by heating

There are no feasible real-time and direct skin dosimeters for interventional radiology. One would be available if there were x-ray phosphors that had no brightness change caused by x-ray irradiation, but the emission of the Y2O3:Eu, (Y, Gd, Eu)BO3, and YVO4:Eu phosphors investigated in our previous study was reduced by x-ray irradiation. We found that the brightness of those phosphors recovered, and the purpose of this study is to investigate their recovery phenomena. It is expected that more kinds of phosphors could be used in x-ray dosimeters if the brightness changes caused by x-rays are elucidated and prevented. Three kinds of phosphors—Y2O3:Eu, (Y, Gd, Eu)BO3, and YVO4:Eu—were irradiated by x-rays (2 Gy) to reduce their brightness. After the irradiation, brightness changes occurring at room temperature and at 80 °C were investigated. The irradiation reduced the brightness of all the phosphors by 5%–10%, but the brightness of each recovered immediately both at room temperature and at 80 °C. The recovery at 80 °C was faster than that at room temperature, and at both temperatures the recovered brightness remained at 95%–98% of the brightness before the x-ray irradiation. The brightness recovery phenomena of Y2O3:Eu, (Y, Gd, Eu)BO3, and YVO4:Eu phosphors occurring after brightness deterioration due to x-ray irradiation were found to be more significant at 80 °C than at room temperature. More kinds of phosphors could be used in x-ray scintillation dosimeters if the reasons for the brightness changes caused by x-rays were elucidated.

SU‐F‐T‐654: Pacemaker Dose Estimate Using Optically Stimulated Luminescent Dosimeter for Left Breast Intraoperative Radiation Therapy

Purpose:To assess and report the in vivo dose for a patient with a pacemaker being treated in left breast intraoperative radiation therapy (IORT). The ZEISS Intrabeam 50 kVp X‐ray beam with a spherical applicator was used.Methods:The optically stimulated luminescent dosimeters (OSLDs) (Landauer nanoDots) were employed and calibrated under the conditions of the Intrabeam 50 kVp X‐rays. The nanoDots were placed on the patient at approximately 15 cm away from the lumpectomy cavity both under and above a shield of lead equivalence 0.25 mm (RayShield X‐Drape D‐110) covering the pacemaker area during IORT with a 5 cm spherical applicator.Results:The skin surface dose near the pacemaker during the IORT with a prescription of 20 Gy was measured as 4.0±0.8 cGy. The dose behind the shield was 0.06±0.01 Gy, demonstrating more than 98% dose reduction. The in vivo skin surface doses during a typical breast IORT at a 4.5 cm spherical applicator surface were further measured at 5, 10, 15, and 20 cm away to be 159±11 cGy, 15±1 cGy, 6.6±0.5 cGy, and 1.8±0.1 cGy, respectively. A power law fit to the dose versus the distance z from the applicator surface yields the dose fall off at the skin surface following z^‐2.5, which can be used to estimate skin doses in future cases. The comparison to an extrapolation of depth dose in water reveals an underestimate of far field dose using the manufactory provided data.Conclusion:The study suggests the appropriateness of OSLD as an in vivo skin dosimeter in IORT using the Intrabeam system in a wide dose range. The pacemaker dose measured during the left breast IORT was within a safe limit.