Factors influencing the absorbed dose in intraoral radiography

OBJECTIVES: The aim of the present study was to find out whether it was more effective to achieve a dose reduction in intraoral radiography with an increase in the tube potential setting (and a decrease of milliampere seconds) by an additional attenuation of the X-ray beam behind the film plane or by the use of digital radiography. A second aim was to find out if there were differences between the integral doses determined by two different detectors and two different phantoms. METHODS: The X-ray attenuation in this in vitro study was carried out using additional lead foils from the dental film packet fixed behind the film plane and with a metal film holder. The dose measurements were performed with two semiconductor detectors (Quart, Diados). Patient simulation was achieved by the Alderson phantom or by the use of a filter (6Al+0.8Cu). The absorbed doses were calculated by integrating an exponential function between the entrance dose and the body exit dose. In addition, organ doses were measured and the effective dose was determined according to the Implementation of the 1990 Recommendations of the ICRP (ICRP-60). RESULTS: The increase in tube potential levels did not provide a substantial reduction of the absorbed dose (90 kVp instead of 60 kVp: reduction to 92.4%), only a reduction of the entrance dose (by 30% to 35% at 90 kVp compared with 60 kVp). The use of three lead foils behind the film plane instead of one resulted in a 14.0% reduction of the absorbed dose (60 kVp); the use of a metal film holder resulted in a 27.8% reduction (60 kVp). When tube potential settings were increased, the dose reduction decreased. The absorbed dose was reduced to 52% when a storage phosphor plate was used instead of a film (60 kVp). It was possible to determine the amount of dose reduction with both the calculated absorbed dose and the effective doses. The integral doses obtained from the Alderson phantom showed values 5% higher than those obtained by the filter (r(2)=96.7%). For the comparison of the integral doses, the measurements performed with Quart had values higher by a factor of 1.139 than those performed with Diados. CONCLUSIONS: Instead of increasing the tube voltage or using additional lead foils or metal film holders, a substantial dose reduction is provided by digital radiography or more sensitive films while a low tube potential level is maintained and the milliampere seconds setting is reduced.     

Thermoplastic wrapped lead sheet to reduce cardiac device cumulative dose

The objective of this project is to evaluate the percentage dose reduction in cardiac implantable electronic devices (CIEDs) using a thermoplastic wrapped lead sheet. The dose to CIED is evaluated in various situations with and without a lead shield. The efficiency of this type of shielding is supported by measurements made with a commercial plastic scintillation detector (PSD). Percentage depth dose (PDD) curve and lateral dose measurements (LDMs) were made with and without shielding for photon and electron beams. Photon LDMs were made at a depth of 0.5 cm. PSD measurements were compared with dose calculation from the treatment planning system (TPS). The benefit of shielding is greater at 23 MV than at 6 MV, with an average reduction of 71% and 59% of dose, respectively, for out-of-field distance range between 3 and 15 cm. Measurement of posterior beams shows there is no significant increase in skin dose due to backscatter from the lead sheet even when the field intercepts it. Large deviations between TPS calculation and measurements have been observed. The use of lead shielding with an anterior field is advised and provides an easy way to decrease the cumulative dose to CIEDs. Interception of shielding by an electron beam would increase significantly the cumulative dose to CIED for high energies or decrease the quality of the treatment. For a posterior out-of-field, shielding does not have a significant impact on CIED dose.     

Dose comparison between screen/film and full-field digital mammography

The study purpose was the comparison between doses delivered by a full-field digital mammography system and a screen/film mammography unit, both using the same type of X-ray tube. Exposure parameters and breast thickness were collected for 300 screen/film (GE Senographe DMR) and 296 digital mammograms (GE Senographe 2000D). The entrance surface air kerma (ESAK) was calculated from anode/filter combination, kV_p and mAs values and breast thickness, by simulating spectra through a program based on a catalogue of experimental X-ray spectra. The average glandular dose (AGD) was also computed. Results showed an overall reduction of average glandular dose by 27% of digital over screen/film mammography. The dose saving was about 15% for thin and thick breasts, while it was between 30% and 40% for intermediate thicknesses. Full-field digital mammography dose reduction is allowed by wider dynamic range and higher efficiency of digital detector, which can be exposed at higher energy spectra than screen/film mammography, and by the separation between acquisition and displaying processes.     

Characteristics of Movement-Induced Dose Reduction in Target Volume: A Comparison Between Photon and Proton Beam Treatment

We compared the main characteristics of movement-induced dose reduction during photon and proton beam treatment, based on an analysis of dose-volume histograms. To simulate target movement, a target contour was delineated in a scanned phantom and displaced by 3 to 20 mm. Although the dose reductions to the target in the 2 treatment systems were similar for transverse (perpendicular to beam direction) target motion, they were completely different for longitudinal (parallel to beam direction) target motion. While both modalities showed a relationship between the degree of target shift and the reduction in dose coverage, dose reduction showed a strong directional dependence in proton beam treatment. Clinical simulation of target movement for a prostate cancer patient showed that, although coverage and conformity indices for a 6-mm lateral movement of the prostate were reduced by 9% and 16%, respectively, for proton beam treatment, they were reduced by only 1% and 7%, respectively, for photon treatment. This difference was greater for a 15-mm target movement in the lateral direction, which lowered the coverage and conformity indices by 34% and 54%, respectively, for proton beam treatment, but changed little during photon treatment. In addition, we found that the equivalent uniform dose (EUD) and homogeneity index show similar characteristics during target movement. These results suggest that movement-induced dose reduction differs significantly between photon and proton beam treatment. Attention should be paid to the target margin in proton beam treatment due to the distinct characteristics of heavy ion beams.     

Monte Carlo simulations of occupational radiation doses in interventional radiology

Occupational radiation doses in interventional radiology can potentially be high. Therefore, reliable methods to assess the effective dose are needed. In the present work, the relationship between the personal dose equivalent, H(p)(10), the reading of a personal dosimeter and the effective dose of the radiologist were studied using Monte Carlo simulations. In particular, the protection provided by a lead apron was investigated. Emphasis was placed on sensitivity of the results to changes in irradiation conditions. In our simulations a 0.35 mm thick lead apron and thyroid shield reduced the effective dose, on average, by a factor of 27 (the range of these data was 15-41). Without the thyroid shield the average reduction factor was 15 (range 6-22). The reduction sensitively depended on the projection and the X-ray tube voltage. The dosimeter reading, when the dosimeter was worn above the apron and a thyroid shield was used, overestimated the effective dose on average by a factor of 130 (range 44-258) when the dosimeter was located on the breast closest to the primary X-ray beam. Without the thyroid shield the average overestimation was 69 (range 32-127). If the dosimeter was worn under the apron its reading generally underestimated the effective dose (on average by 20% with the thyroid shield). Our study indicates that, even though large variations are present, the often used conversion coefficient from the dosimeter reading above the apron to the effective dose, around 1/30, generally overestimates the effective dose by a factor of two or more.     

Radiation doses in the UK trial of breast screening in women aged 40-48 years

Although data have been published on the radiation doses involved in screening women in the UK in the age range 50-64 years, data have not been published for the screening of younger women, when one might expect higher doses and a different risk benefit balance. Therefore, data on the radiation doses arising from screening younger women (age range 40-48 years) as part of the UK age trial have been collected and reviewed. Each of the screening centres participating in the trial was asked to submit measurements of doses for samples of approximately 50 or 100 women. The doses for 2296 women were received. The dose estimates were corrected to take account of variations in composition with age and breast thickness and in the spectra used. The average received dose was 2.5 mGy per oblique film and 2.0 mGy per craniocaudal film. Although these doses are about 7% higher than those calculated for the screening of older women, this was owing to differences in equipment rather than age of the women. Age itself was not found to be a significant factor affecting the dose to screened women aged over or under 50 years. An identifiable sub-group of women with larger breasts who were screened using higher dose systems received doses that were about 4.2 times the average, and should be considered in any risk benefit analysis. Where modern mammography systems with automatic beam quality selection and alternative target and filter materials had been introduced, there was a 15% reduction in average received dose and up to a 50% reduction in received dose for large breasts.     

High-contrast radiographs for field control and field documentation in radiotherapy with high-energy photons

In ambitious radiotherapy with individually shaped irradiation fields, high-contrast field radiography is necessary for fine adjustment, control and field documentation. If intensification foils made of materials with medium or high atomic numbers such as copper, iron and lead are used, the film lying between the foils is mainly darkened by the secondary electrons released from the material of the front foil. Within the range of 1 MeV to 15 MeV, high-contrast radiographs are produced by means of copper or steel foils which are clearly superior to lead foils. Steel foils are to be preferred to copper foils because of their rigidity and the firmness of the polished surface. Usual X-ray diagnosis films with steep graduation can be used as film material for field control radiography performed in double exposure technique. A new insensitive film not applied hitherto in X-ray diagnosis allows to prepare field documentation images of high quality which are exposed during the whole irradiation time. This is also important for perpetuation of evidence.     

湖北省调强放疗多叶光栅野光子线束吸收剂量和二维剂量分布验证研究

目的 用热释光剂量计（TLD）和放射性免冲洗胶片测量调强放疗（IMRT）多叶光栅（MLC）野光子线束吸收剂量并验证二维剂量分布。方法 选择湖北省7家三级甲等医院的7台不同型号医用直线加速器,使用国际原子能机构（IAEA）提供的15 cm×15 cm×15 cm聚苯乙烯专用模体,TLD和放射性免冲洗胶片,在源皮距90 cm,照射深度10 cm,照射野5 cm×5 cm,6 MV X射线,6 Gy吸收剂量照射条件下制定IMRT计划并实施照射,比较TLD和胶片吸收剂量测量值与放疗计划系统（TPS）预估剂量之间的偏差。同时,使用医院配备的30 cm×30 cm均质固体模体,在模体表面下5 cm处放置25 cm×25 cm放射性免冲洗胶片,并将IMRT计划中单个射野移植到模体中胶片层面上并实施照射,通过胶片剂量分析系统验证二维剂量分布。结果 所检医用直线加速器中,1号加速器TLD吸收剂量相对偏差和胶片吸收剂量相对偏差分别为-8.5%和-1.9%;7号加速器TLD吸收剂量相对偏差和胶片吸收剂量相对偏差分别为5.4%和0.5%;其余加速器TLD和胶片吸收剂量相对偏差均在±5%范围以内。所有加速器的二维剂量分布通过率均在90%以上。结论 TLD和胶片核查调强放疗剂量质量方法,操作简单,科学性强,TLD和胶片便于邮件方式寄送,该方法可运用于对放疗机构调强放疗剂量大范围的质量核查。     

Efficiency of a lead-containing tie for radiation protection of the thyroid gland.

During fluoroscopy the examiner is usually protected by a radiation-reducing body shield, leaving the thyroid unprotected. The fact that the thyroid is located in a region of the neck usually covered by the shirt collar led to the idea of designing a tie with lead core, providing easy and "decorative" reduction of the radiation dose. Sonographic examinations were carried out in 20 volunteers (10 men, 10 women) to determine the size of the gland and its coverage by such a tie. The reduction of the surface and organ dose was assessed using film dosimetry with scattered radiation, the body of the examiner being simulated by an Alderson phantom. On average 88% of the thyroid gland surface area was covered. Surface dose was reduced to 1%, and organ dose to 10% of the value without the protection tie.     

辐射着色胶片XR-RV3和EDR2的剂量学性能比较

目的 比较两种用于介入放射学程序中患者峰值皮肤剂量测量的胶片性能,包括胶片的灰度随时间变化、灵敏度、能量响应、剂量响应等特性。方法 分别在60、80、100、120和140 kV 5档管电压下自由空气中照射GafChromic XR-RV3 胶片和KODAK EDR2胶片800 mGy剂量,测量结果归一到80 kV分析胶片的能量响应。在模体上用80 kV管电压分别照射两种胶片0.025~10 Gy剂量,分析胶片的灵敏度和剂量响应。采用Epson V750平板扫描仪对两种胶片进行扫描分析,分别测量图像的红、绿、蓝3色通道的像素值。结果 在灰度随时间变化上,XR-RV3胶片在照射后的24 h内灰度的变化为2%,在72 h内为4%,在6周内为6%;低剂量时EDR2胶片比XR-RV3胶片更灵敏;能量响应方面,在放射诊断能量范围内,XR-RV3胶片的能量响应在9%以内,EDR2胶片的能量响应在23%以内;在0.025~10 Gy的剂量范围内,对于XR-RV3胶片,红光通道随剂量的变化曲线的响应最明显。对于EDR2胶片,3种颜色通道的像素值曲线重合,EDR2胶片在接受剂量超过500 mGy时达到饱和。结论 XR-RV3胶片在灰度变化、能量响应、剂量响应等方面要优于EDR2胶片,非常适和用于介入放射学程序中患者峰值皮肤剂量的测量和分析。     

A preliminary study on using the radiochromic film for 2D beam profile QC/QA at the THOR BNCT facility

The GAFCHROMIC^® EBT2 dosimetry film has been studied as a rapid QC/QA tool for 2D dose profile mapping in the BNCT beam at THOR. The pixel values of the EBT2 film image were converted to the 2D dose profile using a dose calibration curve obtained by 6-MV X-ray. The reproducibility of the 2D dose profile measured using the EBT2 film in the PMMA phantom was preliminarily found to be acceptable with uncertainties within about ±2 to ±3.5%. It is found that the EBT2 measured dose profile consisted of both gamma-ray components and neutron contributions. Therefore, the dose profile measured using the EBT2 film is significantly different from the neutron flux profile measured using the indirect neutron radiography method. Further study of the influence of neutrons to the response of the EBT2 film is indispensible for the absolute dose profile determination in a BNCT beam.     

Radiation doses received in the UK Breast Screening Programme in 2001 and 2002

The mean glandular doses (MGD) to samples of women attending for mammographic screening are measured routinely at screening centres in the UK Breast Screening Programme (NHSBSP). This paper reviews a large representative sample of dose measurements collected during screening in the NHSBSP in 2001 and 2002 for 53 218 films, using 290 X-ray sets, for 16 505 women. The average MGD was 2.23 mGy per oblique film and 1.96 mGy per craniocaudal film; similar to those found previously in the NHSBSP for the years 1997 and 1998. Increasing use of sophisticated units with automatic beam quality selection has reduced the radiation dose received by large breasts, with only 2% of oblique mammograms having doses in excess of 5 mGy. The increasing use of large format film has also reduced the doses to this sub-group. However the total dose per woman has increased due to the introduction of two view screening at every visit. The MGD to the standard breast was found to vary from 0.76 mGy to 2.29 mGy, with 97% of units below the recommended upper limit of 2 mGy, illustrating the benefit of strict quality control. A reduction in dose of 3% was observed between the age bands 50-54 years and 60-64 years. This study has confirmed that the proposed national diagnostic reference level (NDRL) of 3.5 mGy for 55 mm thick breasts is an appropriate value to identify systems giving unusually high doses, with just 3.5% of systems exceeding this level. In most cases these higher doses were explained by the design of one particular make of X-ray set and its mode of operation. Average doses for oblique views of average sized breasts were fairly well correlated with the dose to the standard breast, and typically 42% higher. This highlights the need for a revised definition of the standard breast used in the UK to better reflect the exposure factors and doses received in clinical practice.     

Radiation dose reduction to the male gonads during MDCT: the effectiveness of a lead shield

OBJECTIVE: Our study was designed to quantify the effect of a standard gonad shield on the testicular radiation exposure due to scatter during routine abdominopelvic MDCT. SUBJECTS AND METHODS: Routine abdominopelvic MDCT was performed in 34 patients with gonadal lead shielding and 32 patients without this shielding; the testes were not exposed to the direct beam during the examination. We estimated the testicular dose administered with thermoluminescent dosimetry, taking into account each patient's body weight and body mass index (BMI). RESULTS: With a 1-mm lead shield, the mean testicular dose was reduced from 2.40 to 0.32 mSv, a reduction of 87%. The difference was found to be statistically significant (p < 0.0001). No correlation between testicular dose and body weight or BMI was found. CONCLUSION: Shielding the male gonads reduces the testicular radiation dose during abdominopelvic MDCT significantly and can be recommended for routine use.     

Evolution of radiation exposure to operator in diagnostic and interventional radiology procedures and reduction of radiation exposure to operator with protective device

A study was performed to evaluate operator dose during diagnostic and interventional radiology procedures (IVR) and to establish methods of operator dose reduction with a radiation protective device. Operator dose was measured by glass dosimeters worn on the neck and on the abdomen outside the lead apron. In addition, the dose of the primary beam at the collimator surface was measured, which made it possible to define the correlation between the entrance air kerma, measured with Skin Dose Monitor, and operator dose exposed during the monitored procedure. IVR protectors were developed to decrease the amount of scatter radiation received by operators performing the procedures, and their effects were evaluated in abdominal and cardiac angiography procedures. The average effective dose and doses of the neck and abdomen outside the lead apron, estimated for individual procedures, were as follows: abdominal angiography procedures: effective dose, 0.07 mSv; neck area, 0.18 mSv; abdominal area, 0.51 mSv; cardiac angiography procedures: effective dose, 0.07 mSv; neck area, 0.13 mSv; abdominal area, 0.68 mSv. Operator doses were well correlated with exposure dose in abdominal angiography procedures (diagnostic procedure r=0.84, IVR r=0.77). It was found that 68.0% of the effective dose in abdominal angiography procedures and 43.0% of the effective dose in cardiac angiography procedures could be reduced by the use of IVR protectors. Operator and patient doses in interventional radiology were interdependent. The minimization of operator doses is particularly important during interventional radiology, and it is necessary to be aware of practical radiation protection procedures. Measures that reduce patient dose will also reduce occupational exposure. Moreover, operator dose could be substantially reduced by the use of IVR protectors in addition to wearing a protective lead apron during IVR. It was suggested that IVR protectors are effective radiation protective devices in interventional radiology procedures.     

EBT3和EDR2胶片对扫描束碳离子剂量的响应研究

目的 研究EBT3和EDR2胶片对于不同传能线密度和剂量碳离子响应。方法 EBT3和EDR2胶片采用两种方法进行光密度-剂量校准：一是将胶片放置在固体水与束流垂直测量深度,每张胶片接受同能量不同剂量碳离子照射;二是将多张完整胶片放置与束流垂直固体水不同深度,采用碳离子单次照射,在胶片不同区域形成不同物理剂量校准野。结果 在测量范围内,EBT3胶片光密度-剂量校准曲线（下称校准曲线）呈双曲线型,不同传能线密度校准曲线间最大差异为±17%;而EDR2校准曲线呈直线形,不同传能线密度间差异为±27.4%;两种胶片剂量响应均受碳离子在胶片测量深度传能线密度影响,传能线密度越大,胶片光密度响应越低;EBT3胶片灵敏度与剂量呈反比,但EDR2胶片灵敏度则与剂量无关。结论 EBT3胶片响应受传能线密度和剂量双重影响,限制了其在碳离子剂量测量方面的应用。EDR2胶片响应虽受传能线密度影响更大,但受单能碳离子照射时,由于其灵敏度与剂量无关,可用于单能碳离子剂量测量。     

Traditional and MLC based dose compensator design for patients with hip prostheses undergoing pelvic radiation therapy.

Perturbations in the dose distribution caused by a hip prosthesis when treating pelvic malignancies can result in unacceptable dose inhomogeneities within the target volume. Our results, obtained by in vivo exit dose measurements with diodes, showed a 55% reduction in the dose at the exit dmax of a lateral 15 MV photon beam after passing through a bilateral cobalt-chrome alloy hip prosthesis. Such an inhomogeneous dose distribution may decrease the curability. Solutions such as treatment techniques to avoid the prosthesis are often not the best choice as the dose to the rectum may be unacceptably high. In this work an alternative method of dose compensator is presented. Two types of dose compensators were designed based on a 3-D treatment planning system and CT images of a pelvic phantom containing a hip prosthesis: one was fabricated from a polyethylene-lead slab in the representation of step fringes and placed on a tray in the path of the beam while the other was produced by the use of several fields shaped with a multileaf collimator. The calculation procedures developed by the authors for generating the compensators are described. Results of film measurements performed in a phantom with and without the compensators in place are discussed.     

Experimental measurements and Monte Carlo simulations of dose perturbation around a nonradioactive brachytherapy seed due to 6- and 18-MV photons

PurposeRadioactive seeds used in permanent prostate brachytherapy are composed of high-Z metals and may exceed 100 in a patient. If supplemental external beam treatment is administered afterward, the seeds may cause substantial dose perturbation, which is being investigated in this article.Methods and MaterialsFilm measurements using 6-MV beam were primarily carried out using Kodak XV2 film layered above and below a nonradioactive iodine-125 (¹²⁵I) seed. Monte Carlo simulations were carried out using DOSXYZnrc. Other experimental comparisons looked at changing beam energy, depth, and field size, including two opposing fields’ pair. Effect of multiple seeds spatially spaced 0.5 cm vertically was also studied.ResultsFor a single ¹²⁵I seed, on XV film, there is a localized dose enhancement of 6.3% upstream and ?10.9% downstream. With two opposing fields, a cold spot around the seed of ～3% was noticed. Increasing beam energy and field size decreased the magnitude of this effect, whereas the effect was found to increase with the increasing Z of material. DOSXYZnrc and EBT-2 film verified maximum dose enhancement of +15% upstream and ?20% downstream of the ¹²⁵I seed surface.ConclusionsIn general, the dose perturbation because of the seeds was spatially limited to ～2 mm upstream and ～5 mm downstream to the incident beam. Similar to other heterogeneities, the seeds perturbation depends on incident beam energy, field size, and its Z. With multiple seeds spatially apart and multiple radiation fields routinely used in external beam radiotherapy, the cumulative effect may not result in clinically significant dose perturbation.     

Radiation dose to neonates on a Special Care Baby Unit

Neonates on a Special Care Baby Unit often require radiography to monitor the progress of their treatment and as a result can have a large number of radiographs taken during their stay in hospital. The skin entrance dose was estimated from a knowledge of the technique factors, X-ray tube output and backscatter factors. Normalized organ dose data were employed to estimate the radiation dose to a number of critical organs. A number of methods of reducing the radiation dose to neonates were investigated. Initially, this involved changing the radiographic technique factors and introducing a lead rubber adjustable collimator, placed on top of the incubator, in addition to the light beam diaphragms on the X-ray tube. It was deduced from the results of calculations that these modifications to the radiographic examination technique had reduced the average entrance dose per radiograph from 92 mu Gy to 58 mu Gy, a reduction of 37%. Later, a rare-earth film-screen combination was introduced to replace the existing fast calcium tungstate screens. This enabled the average entrance dose per radiograph to be reduced to 39 mu Gy, a further reduction of 33%. The mean radiation dose to a neonate is mainly determined by the number of radiographs taken and this is dependent on the clinical symptoms.     

Study on surface dose generated in prostate intensity-modulated radiation therapy treatment

The surface doses of 6- and 15-MV prostate intensity-modulated radiation therapy (IMRT) irradiations were measured and compared to those from a 15-MV prostate 4-beam box (FBB). IMRT plans (step-and-shoot technique) using 5, 7, and 9 beams with 6- and 15-MV photon beams were generated from a Pinnacle treatment planning system (version 6) using computed tomography (CT) scans from a Rando Phantom (ICRU Report 48). Metal oxide semiconductor field effect transistor detectors were used and placed on a transverse contour line along the Phantom surface at the central beam axis in the measurement. Our objectives were to investigate: (1) the contribution of the dynamic multileaf collimator (MLC) to the surface dose during the IMRT irradiation; (2) the effects of photon beam energy and number of beams used in the IMRT plan on the surface dose. The results showed that with the same number of beams used in the IMRT plan, the 6-MV irradiation gave more surface dose than that of 15 MV to the phantom. However, when the number of beams in the plan was increased, the surface dose difference between the above 2 photon energies became less. The average surface dose of the 15-MV IMRT irradiation increased with the number of beams in the plan, from 0.86% to 1.19%. Conversely, for 6 MV, the surface dose decreased from 1.33% to 1.24% as the beam number increased from 7 to 9. Comparing the 15-MV FBB and 6-MV IMRT plans with 2 Gy/fraction, the IMRT irradiations gave generally more surface dose, from 15% to 30%, depending on the number of beams in the plan. It was found that the increase in surface dose for the IMRT technique compared to the FBB plan was predominantly due to the number of beams and the calculated monitor units required to deliver the same dose at the isocenter in the plans. The head variation due to the dynamic MLC movement changing the surface dose distribution on the patient was reflected by the IMRT dose-intensity map. Although prostate IMRT in this study had an average higher surface dose than that of FBB, the more even distribution of relatively lower surface dose in IMRT field could avoid the big dose peaks at the surface positions directly under the FBB fields. Such an even and low surface dose distribution surrounding the patient in IMRT is believed to give less skin complication than that of FBB with the same prescribed dose.