Increasing Source-Object Distance: A Computed Radiographybased Strategy to Reducing Radiation Dose in Occipital-Frontal Skull X-Ray

@#Introduction: Exploring potential optimization strategies and developing evident practices is critical. Previous studies show that radiation dose can be reduced by increasing the source-image distance (SID). Although most studies use digital radiography, many hospitals in underdeveloped countries still use computed radiography (CR). Therefore, research will investigate the relationship between SID and Entrance surface dose (ESD) using the CR. Methods: This study involved the measurement of radiation dose and image quality of a radiological procedure performed at a reference SID; 100cm and the tested SIDs; 110cm, 120cm, and 130cm, using constant technical factors (70kVp, 25mAs, grid). A LiF; Mg Ti thermoluminescence dosimeter (TLD-100) chip was placed in the center of the radiation field of the OF10° skull radiography examination to measure ESD. Image quality was assessed using the European Commission guidelines and graded using relative visual assessment analysis (VGA). Results: Significant ESD reduction from 21% and 45% when SID was increased from 100cm to 130cm (p <0.001), where SID was negatively correlated with ESD (r= - 0.98). The VGA scores showed no statistical difference in the image quality of the OF10° skull radiography examination for the tested and reference images (p=0.21). VGA scores for 120cm images showed the highest image quality among the SIDs tested with a dose reduction of 37%. Conclusion: ESD was statically reduced when SID was increased from 100cm to 130cm, while image quality was diagnostically acceptable. The study suggests that 120cm is the optimal SID when both dose and image quality are considered.

Research progress on bolus materials used for radiotherapy / 中华放射肿瘤学杂志

It is necessary to place bolus on skin to increase the surface dose when using high-energy rays to treat superficial lesions because of its build-up effect. It is well known that the set-up reproducibility of hand-made bolus is poor, and the main concern of commercialized bolus is the inadvertent air gap between the bolus and irregular skin. Owing to the advantage of making individualized and complex-shaped bolus, 3D-printing technology is playing an important role in making the bolus. The aim of this review is to summarize the current research status of hand-made, commercialized and 3D-printed bolus materials and future development trend of the bolus, providing reference for clinical application.

Clinical implementation of brass mesh bolus for chest wall postmastectomy radiotherapy and film dosimetry for surface dose estimates

Objective: This study presents the dosimetric data taken with radiochromic EBT3 film with brass mesh bolus using solid water and semi-breast phantoms, and its clinical implementation to analyze the surface dose estimates to the chest wall in postmastectomy radiotherapy (PMRT) patients. Materials and Methods: Water-equivalent thickness of brass bolus was estimated with solid water phantom under 6 megavoltage photon beam. Following measurements with film were taken with no bolus, 1, 2, and 3 layers of brass bolus: (a) surface doses on solid water phantom with normal incidence and on curved surface of a locally fabricated cylindrical semi-breast phantom for tangential field irradiation, (b) depth doses (in solid phantom), and (c) surface dose measurements around the scar area in six patients undergoing PMRT with prescribed dose of 50 Gy in 25 fractions. Results: Water-equivalent thickness (per layer) of brass bolus 2.09 ± 0.13 mm was calculated. Surface dose measured by film under the bolus with solid water phantom increased from 25.2% ±0.9% without bolus to 62.5% ± 3.1%, 80.1% ± 1.5%, and 104.4% ± 1.7% with 1, 2, and 3 layers of bolus, respectively. Corresponding observations with semi-breast phantom were 32.6% ± 5.3% without bolus to 96.7% ± 9.1%, 107.3% ± 9.0%, and 110.2% ± 8.7%, respectively. A film measurement shows that the dose at depths of 3, 5, and 10 cm is nearly same with or without brass bolus and the percentage difference is <1.5% at these depths. Mean surface doses from 6 patients treated with brass bolus ranged from 79.5% to 84.9%. The bolus application was discontinued between 18th and 23rd fractions on the development of Grade 2 skin toxicity for different patients. The total skin dose to chest wall for a patient was 3699 cGy from overall treatment with and without bolus. Conclusions: Brass mesh bolus does not significantly change dose at depths, and the surface dose is increased. This may be used as a substitute for tissue-equivalent bolus to improve surface conformity in PMRT

A comparative study for surface dose evaluation in conventional treatment of carcinoma breast patients irradiated with Co-60 and 6 MV radiation beam

Aim: In the present study, surface doses within the target area and contralateral breast (CLB) received during conventional treatment of carcinoma breast are evaluate and compared for treatment on two different beam energies, i.e., Co-60 γ-ray and 6 MV X-ray beams with thermoluminescent dosimeter, LiF:Mg, Ti (TLD-100). Materials and Methods: The study includes a group of 23 patients comprising 11 patients treated with Co-60 γ-ray beam and 12 patients by 6 MV X-ray beam. Results and Discussion: The treatment using Co-60 γ-ray and 6 MV X-ray beams contributes an average percentage dose of 8.15% ± 0.56% and 4.73% ± 0.94%, respectively, to CLB in mastectomy patients. The contribution of tangential fields (mastectomy) to the CLB doses ranges between 12.71 and 16.40 cGy (5.45%–7.03%) for treatment with Co-60 γ-ray beam and 6.33–10.95 cGy (1.86–4.69%) for treatment with 6 MV X-ray beam. The supraclavicular field (SCF) contributes 1.45%–1.93% and 1.02%–1.43% for treatment with Co-60 γ-ray and 6 MV X-ray beams, respectively. The average surface dose (normalized with breast dose) 89.1% ± 8.5% for Co-60 beam in the SCF region differs significantly from the 60.2% ± 13.0% value for 6 MV X-ray beam. Conclusion: The CLB doses for mastectomy patients are higher for Co-60 beam as compared to 6 MV X-ray beam, and better dose homogeneity is achieved within the irradiated breast from 6 MV X-ray beam. The CLB doses are slightly higher for patients treated with breast conservative radiotherapy or lumpectomy. The average surface dose to SCF decreases by ~30% of treated breast dose for treatment with 6 MV X-ray beam

Investigation on entrance surface doses to patients from medical X-ray diagnosis in Inner Mongolia autonomous region / 中华放射医学与防护杂志

Objective@#To analyze the levels of entrance surface dose (ESD) to patients from diagnostic medical X-ray examinations in Inner Mongolia autonomous region.@*Methods@#The investigation of diagnostic medical X-ray examinations was completed in 30% of the number of hospitals under the requirement of the program plan of the national survey on frequency and dose from medical exposure. The investigation of ESDs to patients from general diagnostic X-ray examinations was carried out in terms of the scale of annual outpatients in different levels of hospital. The difference in ESDs to patients was compared for different equipments, different grade hospitals and different exposure sites, with the comparison result being subjected to rank sum test.@*Results@#In all types of diagnostic medical X-ray equipment, DR photography equipment accounted for the majority. During various routine diagnostic X-ray examinations, the average ESDs was lumbar vertebral 3.39 mGy, pelvic and hip 1.65 mGy, cervical spine 0.90 mGy, extremities 0.38 mGy and thorax 0.37 mGy, respectively. In the diagnostic examinations of chest, lumbar and cervical spine, the ESDs caused by the use of screen film photography equipment were higher than those by DR photography equipment, with statistically significant difference (Z=-3.229, -4.820, -5.265, P<0.05).@*Conclusions@#Screen film photography equipment results in higher ESD than DR photography equipment. The doctor′s operation behavior is an important factor that affects the ESD.

Investigation on entrance surface doses to patients from medical X-ray diagnosis in Inner Mongolia autonomous region / 中华放射医学与防护杂志

Objective To analyze the levels of entrance surface dose (ESD) to patients from diagnostic medical X-ray examinations in Inner Mongolia autonomous region.Methods The investigation of diagnostic medical X-ray examinations was completed in 30％ of the number of hospitals under the requirement of the program plan of the national survey on frequency and dose from medical exposure.The investigation of ESDs to patients from general diagnostic X-ray examinations was carried out in terms of the scale of annual outpatients in different levels of hospital.The difference in ESDs to patients was compared for different equipments,different grade hospitals and different exposure sites,with the comparison result being subjected to rank sum test.Results In all types of diagnostic medical X-ray equipment,DR photography equipment accounted for the majority.During various routine diagnostic X-ray examinations,the average ESDs was lumbar vertebral 3.39 mGy,pelvic and hip 1.65 mGy,cervical spine 0.90 mGy,extremities 0.38 mGy and thorax 0.37 mGy,respectively.In the diagnostic examinations of chest,lumbar and cervical spine,the ESDs caused by the use of screen film photography equipment were higher than those by DR photography equipment,with statistically significant difference (Z =-3.229,-4.820,-5.265,P＜0.05).Conclusions Screen film photography equipment results in higher ESD than DR photography equipment.The doctor's operation behavior is an important factor that affects the ESD.

Investigation and analysis on entrance surface dose of patients in radiography procedures in China / 中华放射医学与防护杂志

Objective To investigate the entrance surface dose to the examined patients in radiography using digital and screen-film system in hospitals at different levels in 15 provinces and municipalities in China,in order to provide data for developing diagnostic reference level of radiography suitable for our national physical characteristics.Methods According to the requirements of the Technical Study on Medical Radiation Hazard Assessment and Control,the examined patients aged 20-70 years were selected,with body weight ranging from 55 to 80 kg for male and 50 to 70 kg for female.TLDs were used to measure the entrance surface dose to adult patients in radiography.No less than 10 examined patients were required at each body position,with examined locations including head (PA,LAT),chest (PA,LAT),abdomen (AP),pelvis (AP),lumbar (AP,LAT),and thoracic vertebra (AP,LAT).Results A total of 19 975 individuals undergoing radiography and 1 813 radiographic equipment of different types including screen-film radiography,computed radiography (CR) and digital radiography (DR),were investigated in 342 hospitals in 15 provinces and municipalities throughout the country.For these three types of equipment,the average entrance surface dose to the examined were 1.75,1.9,and 1.15 mGy in head (PA),1.69,1.46and 1.03 mGy in head (LAT),0.75,0.65 and 0.36 mGy in chest (PA),1.81,1.26 and 0.88 mGy in chest (LAT),4.37,3.77 and 2.15 mGy in abdomen (AP),3.73,3.56 and 2.75 mGy in pelvis (AP),5.49,5.84 and 4.17 mGy in lumbar (AP),12.01,9.37 and 6.82 mGy in lumbar (LAT),4.53,3.65 and 2.49 mGy in thoracic vertebra (AP),and 6.91,6.43 and 4.15 Gy in thoracic vertebra (LAT).Conclusions Entrance surface dose caused by radiography examination varies dependent on different exposure locations.Entrance surface doses caused by digital radiography are all lower than by screen-film radiography;those caused by digital radiography are lower than by computed radiography,except for thoracic vertebra (AP).In all examinations,no difference of statistical significance is found between CR and screen-film radiography in entrance surface dose.

Comparison of digital radiography's entrance surface doses computed from DICOM file or directly from TLDs / 中华放射医学与防护杂志

Objective To make comparison of consistency between the ESD's informationcalculated values and TLD readout values based on PHILIPS DigitalDiagnost so as to provide reference for realizing information management of medical exposure radiation dose during DR diagnosis and treatment.Methods TLDs were used to obtain the ESD values on chest,abdomen,vertebral body,pelvis and limbs.The exposure parameters were collected from the DICOM files,and the information value of ESD were calculated through the dose area product (DAP) method and the exposure parameter method.The consistency between information value and TLD readout value was compared by intraclass correlation coefficient and the Bland-Altman method.Results The ESD values obtained from DAP method,exposure parameter method and TLD method are,respectively,(0.730 ± 0.870) mGy,(0.720 ± 0.863) mGy and (0.770 ±0.948) mGy.ICC was 0.988 for ESDDAP-TLD and 0.982 for ESDParameters-TLD,respectively.The Bland-Altman map showed that the D-value of ESD obtained from DAP-TLD and Parameters-TLD beyond the 95％ consistency interval was 6.7％.Conclusions The PHILIPS DR daily diagnosis and treatment process is based on fixed-mode programmed diagnosis and treatment.Under the premise of qualified equipment quality control,the information calculated value based on DICOM files has a good consistency with TLD readout value.

Optimization of exposure parameters for chest digital radiography in infants and young children / 中华放射医学与防护杂志

Objective To optimize the exposure parameters and reduce the irradiation dose level in infants and young children during digital radiography (DR) chest radiography under the premise of satisfied image quality.Methods The thoracic thickness of 100 patients were measured.Determined the aluminum equivalent of the thoraxes of the infants and young children by comparing the grayscale value and the aluminum step wedge.Another 100 infants and young children of experimental exposure were performed with the aluminum step wedge as a phantom,under AEC control,kV was the only variant to explore the optimal exposure parameters with dose monitor simultaneously.At last,clinical validation was performed.Images quality was compared with x2 test.The radiation dose of two groups was compared with t test.Results The maximum,minimum,average thoracic thickness and their correspondent aluminum equivalent were 13.5 and 2.3 cm,8.0 and 1.4 cm,(10.6 ± 1.3) and 2.0 cm,respectively.The average thoracic thickness of experimental group was (10.1 ± 2.2) cm.The range of entrance surface dose was 0.068-0.056 mGy while the tube voltage range was 55-65 kV.The exposure index range was 0.60-0.74.The visual inspection of aluminum step wedge was from grades 8 to 11 with satisfying image quality at lower radiation.The infant chest X-ray photography exposure parameters formula have been optimized,that was kV =thoracic thickness (cm) × 2 + 38 (constant),mAs (0.8-1.0) with SID =100 cm,without filter grid.Compare to the conventional parameters,the image quality of new method had no significant differences (P ＞ 0.05).The actual average entrance surface dose was (0.048 ± 0.007) mGy,lower than AEC group (0.066 ± 0.008) mGy.The difference was statistically significant (t =16.781,P ＜ 0.001).Conclusions The optimized formula kV =thoracic thickness (cm) ×2 + 38(constant),mAs (0.8-1.0) with SID =100 cm was credible for lowering the radiation exposure with good image quality for clinical diagnosis.

The influence of different ceiling-mounted shield positions on operators' radiation dose in percutaneous coronary intervention / 中华放射医学与防护杂志

Objective To discuss the influence of the change in ceiling-mounted shield positions on the radiation doses to the first and second operators during percutaneous coronary intervention.Methods In this study,the entrance surface dose (ESD) rates were measured for the first and second operators at 125 cm and 155 cm height on different ceiling-mounted shield positions separately through transradial approach.Measurements were repeated 20 times for each position and T test was used for statistical analysis of dose rate arithmetic mean values.Results For the first operator,the effective dose values were obtained only on left foot position.The ESD rate values at ceiling-mounted shield position close to patient were higher than that close to operators (t125 =46.9,t155 =4.1,P ＜0.05).For the second operator,the ESD rate values on his foot position,right foot position,left anterior oblique position and right anterior oblique position at ceiling-mounted shield position close to the operator,were higher than that close to the patient separately (t125 =11.9,24.4,11.2,2.7,t155 =16.1,2.8,14.4,28.8,P ＜ 0.05).The ESD rate values on head position,left foot position,left head position at ceiling-mounted shield position close to the operator,were lower than that close to the patient (t125 =-4.3,-2.4,-80.4,t155 =-10.2,-6.7,-152.6,P ＜ 0.05).Conclusions The change in the ceiling-mounted shield positions gave rise to change in radiation dose to the operators.The changes in radiation doses caused by the changes in ceiling-mounted shield positions are different in various angiographic positions.Ceiling-mounted shield should be used in a reasonable way in agreement with different positions in percutaneous coronary intervention so as to effectively reduce operators radiation dose.

Assessment of radiation dose in dual energy X-ray absorptiometry scanner / 中华放射医学与防护杂志

Objective To evaluate the radiation dose from a dual energy X-ray absorptiometry (DXA) study. Methods A Radcal multifunctional dosimeter (1800 cc ionization chamber, USA) was used, for purpose of comparison, to measure the entrance surface doses (ESD) from Norland XR-800 DXA ( pencil beam scan, 100/46. 8 kVp, 1. 3 mA) and from Hologic Discovery A DXA ( fan beam scan, 140/100 kVp, 5. 0 mA) . Ambient dose equivalent rate at 1 m away from studied phantom center and at 1 m above floor was measured using the US 451P ionizaion chamber survey meter ( Fluke, USA). Results The ESD measured using a Radcal dosimeter for Norland XR-800 DXA was 0. 43 μGy in high speed mode and 0. 73 μGy in standard mode ( AP spine ) , 1. 93 μGy ( hip ) , 0. 40 μGy ( wrist ) and 1. 06 μGy ( mandible) . The ESD measured for Hologic Discovery A DXA was 65. 6 μGy ( AP spine) and 63. 9 μGy ( hip) . The ESD measured for Norland XR-800 at different scan types and scan speeds was <2 μGy while Hologic Discovery A DXA showed a result of <66 μGy ( AP spine and hip scan ) , which were both consistent with the data given in their own respective operational manual. A comparison of DXA scanners with fan beam and pencil beam indicated that ambient equivalent dose rate, measured with 451P survey meter, from fan beam scan was 65 times that from pencil beam scan. Conclusions Compared with other medical X-ray studies, the ESD to the phantom undergoing a DXA study is relatively low. DXA pencil beam scan doses to lumbar spine and hip were about 1/153-1/33 of those from DXA fan beam scan. Pencil beam scan dose to DXA staff was negligible and fan beam scan dose to DXA staff was lower than the personal dose limits of 20 mSv per year.

Experimental study of correlation between the focus-to-flat panel detector distance and entrance surface dosed in digital radiography of lumbar spine / 中华放射医学与防护杂志

Objective To investigated the correlation between the focus-to-flat panel detector distance and entrance surface dosed in digital radiography of lumbar spine.Methods The spine phantom used for bone mineral density(BMD) calibration was radiographed at different value of FFD (100 ～ 240 cm with the interval 10 cm,totally 15 times) using 70 kV and 90 kV with the automatic exposure control (AEC) mode without anti-scatter grid.The parameters measured by QUART dido 2100K type X-ray dose meter.So record the value parameters of the tube current (mAs) and entrance surface dose (ESD).The relation curve were counted between FFD,ESD,mAs and Exposure index (EI) use excle.Pearson correlation analysis and related coefficient difference analysis were performed using the SPSS 19.0 software (P ＜0.05 for the statistically significant level).The FFD and ESD values of regression equation were obtained with regression analysis.Results (1) When the tube voltage was 70 kV:FFD and ESD were negative correlation (r =-0.922,P ＜ 0.001),FFD and mAs were positive correlation (r =0.991,P ＜0.001),FFD and EI negative correlation (r =-0.938,P ＜ 0.001).(2) When the tube voltage was 90 kV:FFD and ESDwere negative correlation (r=-0.955,P ＜0.001),FFD and mAs were positive correlation (r=0.994,P ＜0.001),FFD and EI showed no significant correlation (r=-0.523,P＞0.05).(3) Different position correlation coefficient analysis of the difference was not statistically significant difference.(4) The regression analysis results:The regression equation of the lumbar anteriorposterior position FFD and the ESD at 70 kV:y=0.805 x + 319.731 (F=74.175,P ＜0.001).The regression equation of the lumbar lateral position FFD and the ESD at 90 kV:y =3.152 x + 457.613 (F =133.524,P ＜ 0.001).Conclusions The FFD and ESD in the lumbar spine X-ray radiography were relevant and highly negative correlation.It can effectively reduce the radiographic ESD of lumbar spine with the increasing of the FFD.

Study on correlation between exposure dose and image quality of X-ray chest radiography / 中华放射医学与防护杂志

Objective To investigate optimal radiation dose for digital radiography by researching the correlation between radiation dose and image quality of high kV chest radiography.Methods The kV of chest radiography was setted on 120 kV while mAs was changed.The chest radiography phantom and the contrast detail phantom CDRAD2.0 were exposed by DR with different mAs from 1 to 25 mAs.The entrance doses were measured for all exposures and the images were read independently by 5 observers on a higher resolution monitor of diagnosis work station.The image quality figure (IQF) was measured for each image.Comparison of the mean IQFs with different exposure doses were conducted in order to determined which was the optimal exposure condition for high kV radiography.The image quality of normal adult using different mAs,4 and 10 mAs for high KV chest radiography was compared.Results When the mAs was increased from 1 to 25 mAs,the entrance doses varied from 0.067 to 1.468 mGy.With the entrance doses increasing,the value of IQF was decreased (F =31.00,P ＜ 0.05).The values of IQF were statistically different between 1 and 4 mAs(F =15.3,P ＜0.05),and between 10 and 25 mAs(F =9.74,P ＜0.05).At 4 and 10 mAs with the entrance dose 0.250 and 0.606 mGy,the synthesis score of chest high kV radiography from two kinds of exposure dose was (24.8 ± 1.64),(25.8 ± 2.05),with no statistically significant difference.Conclusions For digital radiography,increasing radiation dose can improve image information.The optimal entrance dose of high kV chest radiography for standard body was about 0.250 mGy.

A survey and analysis of dose level for adults undergoing posteroanterior chest X-rays photography in Shanghai / 中华放射医学与防护杂志

Objective To survey the current dose level for adults undergoing posteroanterior (PA) chest X-ray photography in Shanghai,and to analyze the main factors affecting the dose level.Methods The thermoluminescence dosimeters (TLDs) were deployed to measure entrance surface dose (ESD) in the center of radiated fields.According to the numbers of three types of X-ray equipment and their distribution among different grade hospitals in Shanghai,the ESDs were surveyed for 1032 adults undergoing examination of PA chest X-ray photography from 2008 to 2010,and the relevant information was also recorded.The differences of the mean ESDs among different grade hospitals,equipment types and photographic parameters were statistically analyzed.Results The arithmetic mean of the ESDs for adults undergoing examination of PA chest X-ray photography in Shanghai was 0.23 mGy,and the 75th percentile value was 0.29 mGy,which were all below the current China diagnostic reference level (0.40 mGy).The averaged ESDs were significantly correlated with the grade of hospital,the equipment types and the photographic parameters.Conclusions Compared with the value in the last century,the ESD for adults undergoing PA chest X-ray photography in Shanghai obviously decreases,and there are the potentials for further reduction.

Estimation of the entrance surface dose from the dose indicator in computed radiography system / 中华放射医学与防护杂志

Objective To study the relationship between the dose indicator of computed radiography (CR) and the entrance surface dose (ESD),and to build a model for estimating ESD based on this relationship.Methods Taking Kodak CR system as the research object,a theoretical model for estimating the ESD was established according to theoretical derivations,and the key parameters in the model were determined through experiments in a CR system.Further experiments in another CR system were also conducted to verify the model.Results The ESDs were not only dependent on the dose indicator provided by the CR system,but also influenced by other factors,such as tube potential,patient's body thickness and energy response of the imaging plate.The estimation results of the model agreed well with the experiment results,and the relative deviation was confirmed within 20％.Conclusions The dose indicator based model can provide a relatively fast and easy way for evaluating the doses of patients undergoing X-ray diagnoses with the CR system.

Effects of source to image receptor distance on image quality and entrance surface dose of chest digital radiography for infants / 中华放射医学与防护杂志

Objective To investigate the effects of source to image receptor distance (SID) on the image quality and entrance surface dose (ESD) in the chest digital radiography (DR) for infants.Methods Anthropomorphic chest phantoms were exposed to 60 kVp and different values of SID ( 150 -80 cm with the interval of 10 cm,totally 8 groups) so as to record the values of mAs and ESD.The SID values of 110 cm and 90 cm with the moderate and low ESD values were selected for clinical test.Forty-two hospitalized infants,aged 12 months (8 months to 2 years) underwent chest DR with the SID of 110 cm before admission and 90 cm before discharge respectively.The values of ESD were recorded and compared.Three experienced experts assessed the quality of 84 pieces of images.Results The values of mAs and ESD decreased gradually along with the decrease of the SID from 150 cm to 80 cm.All the 84 images from the 42 infants met the demands for diagnosis.There was no significant difference in the score of image quality of the group with the SID of 110 cm (4.4±0.3) and 90 cm(4.2±0.4) (t=0.453,P＞0.05).The value of ESD of the group with the SID of 90 cm was significantly lower than that of the group of SID of 110 cm by 0.003 4 mGy ( t =12.001,P ＜ 0.05 ).Conclusions The image quality of chest DR could meet the demands for diagnosis in spite of the value of SID,however,the SID value in chest DR significantly might influence the ESD.The SID value of 90 cm shoud be recommended in chest DR for infants.

Comparison of Three Different Methods to Measure the Surface Dose of Intra-operative Radiotherapy / 中国医学物理学杂志

Objective:To analyze and compare the results and precision of three different methods to measure the surface dose of Intra-operative radiotherapy,and conclude some experience of clinical application in Intra- operative radiotherapy.Methods:The study compared the results of measurement surface dose in phantom through three ways:cylindrical ionization chamber with 3D water scanner,plane-parallel ionization chamber,and MOSFET detector.Results:the measurement results of plane-parallel-chamber and MOSFET detector have a better consistency,and the maximum deviation is -1.13%.The method with cylindrical ionization chamber and 3D water scanner has larger deviation compare to the other two methods,the deviation range from-5.55%to 4.55%.Conclusion:The methods of plane-parallel chamber and MOSFET detector to measure the surface dose of Intra-operative radiotherapy can obtain accurate results.

Superficial Dosimetry for Helical Tomotherapy / 대한방사선종양학회지

PURPOSE: To investigate the feasibility of helical tomotherapy on a wide curved area of the skin, and its accuracy in calculating the absorbed dose in the superficial region. MATERIALS AND METHODS: Two types of treatment plans were made with the cylinder-shaped 'cheese phantom'. In the first trial, 2 Gy was prescribed to a 1-cm depth from the surface. For the other trial, 2 Gy was prescribed to a 1-cm depth from the external side of the surface by 5 mm. The inner part of the phantom was completely blocked. To measure the surface dose and the depth dose profile, an EDR2 film was inserted into the phantom, while 6 TLD chips were attached to the surface. RESULTS: The film indicated that the surface dose of the former case was 118.7 cGy and the latter case was 130.9 cGy. The TLD chips indicated that the surface dose was higher than these, but it was due to the finite thickness of the TLD chips. In the former case, 95% of the prescribed dose was obtained at a 2.1 mm depth, while the prescribed does was at 2.2 mm in the latter case. The maximum dose was about 110% of the prescribed dose. As the depth became deeper, the dose decreased rapidly. Accordingly, at a 2-cm depth, the dose was 20% of the prescribed dose. CONCLUSION: Helical tomotherapy could be a useful application in the treatment of a wide area of the skin with curvature. However, for depths up to 2 mm, the planning system overestimated the superficial dose. For shallower targets, the use of a compensator such as a bolus is required.

Consideration of Surface Dose and Depth of Maximum Dose Using Various Detectors for High Energy X-rays / 대한방사선종양학회지

PURPOSE: It is difficult to exactly determine the surface dose and the dose distribution in buildup region of high energy X-rays by using the conventional ion chamber. The aim of this study is to evaluate the accuracy of widely used dosimetry systems to measure the surface dose and the depth of maximum dose (dmax). MATERIALS AND METHODS: We measured the percent depth dose (PDD) from the surface to the dmax in either a water phantom or in a solid water phantom using TLD-100 chips, thimble type ion chamber, diode detector, diamond detector and Markus parallel plate ion chamber for 6 MV and 15 MV X-rays, 10 10 cm2, at SSD=100 cm. We analysed the surface dose and the dmax. In order to verify the accuracy of the TLD data, we executed the Monte Carlo simulation for 6 MV X-ray beams. RESULTS: The surface doses in 6 MV and 15 MV X-rays were 29.31% and 23.36% for Markus parallel plate ion chamber, 37.17% and 24.01% for TLD, 34.87% and 24.06% for diamond detector, 38.13% and 27.8% for diode detector, and 47.92% and 36.01% for thimble type ion chamber, respectively. In Monte Carlo simulation for 6 MV X-rays, the surface dose was 36.22%, which is similar to the 37.17% of the TLD measurement data. The dmax in 6 MV and 15 MV X-rays was 14~16 mm and 27~29 mm, respectively. There was no significant difference in the dmax among the detectors. CONCLUSION: There was a remarkable difference in the surface dose among the detectors. The Markus parallel plate chamber showed the most accurate result. The surface dose of the thimble ion chamber was 10% higher than that of other detectors. We suggest that the correction should be made when the surface dose of the thimble ion chamber is used for the treatment planning for the superficial tumors. All the detectors used in our study showed no difference in the dmax.

Reduction of Electron ContaminationUsing a Filter for 6MV Photon Beam / 대한치료방사선과학회지

PURPOSE: Secondary electrons generated by interaction between primary X-ray beam and block tray in megavoltage irradiation, result in excess soft radiation dose to the surface layer. To reduce the surface dose from the electron contamination, electron filters were attached under the tray when a customized block was used. MATERIALS AND METHODS: Cu, Al or Cu/Al combined plate with different thickness was used as a filter and the surface dose reduction was measured for each case. The measurement to find optimal filter was performed with 10cm x 10cm field size and 78.5cm source to surface distance. The measurement points are positioned with 2mm intervals from surface to maximum build-up point. To acquire the effect of field size dependence on optimal electron filter, the measurement was performed from 4cm x 4cm to 25cm x 25cm field sizes. RESULTS: The surface dose was slowly increased by increasing irradiation field but rapidly increased beyond 15cm x 15cm field size. Al plate was found to be inadequate filter because of the failure to have surface dose kept lowering than the dose of deep area. Cu 0.5mm plate and Cu/Al= 0.28mm/1.5mm combined plate were found to be optimal filters. By using these 2 filters, the absorbed dose to the surface layer was effectively reduced by 5.5%, 11.3%, and 22.3% for the field size 4cm x 4cm, 10cm x 10cm, and 25cm x 25cm, respectively. CONCLUSION: The surface dose attributable to electron contamination had a dependence on field size. The electron contamination was increased when tray was used. Specially the electron contamination in the surface layer was greater when the larger field was used. 0.5mm Cu plate and Cu/Al=0.28mm/1.5mm combined plates were selected as optimal electron filters. When the optimal electron filter was attached under the tray, excessive surface dose was decreased effectively. The effect of these electron filters was better when a larger field was used.