Preliminary experimental analysis of the feasibility of quartz glass for radiotherapy dosimetry / 中国辐射卫生

Objective To explore the feasibility of quartz glass for radiotherapy dosimetry through the experimental study of the thermoluminescence characteristics of synthetic quartz glass. Methods The thermoluminescence glow curves of quartz glass under different annealing conditions were analyzed, the thermoluminescence characteristics of quartz glass were studied, and the measurement parameters were optimized. Using the Co-60 reference radiation field in the National Secondary Standard Dosimetry Laboratory, the quartz glass samples under different annealing conditions were irradiated following the dose levels of radiotherapy, i.e., 0.5, 1.0, 2.0, 4.0, 6.0, 8.0, and 10.0 Gy, respectively. According to the relationship between the absorbed dose of quartz glass and the relative thermoluminescence signal intensity, the linearity and dispersion of the dose response of quartz glass were obtained, and the feasibility of quartz glass for radiotherapy dosimetry was analyzed. Results The linear correlation coefficient of dose response of quartz glass under annealing condition of 430℃ for 10 min was 0.9984, and the dose response dispersion was 0.97% at the absorbed dose of 2 Gy. The linear correlation coefficient of dose response of quartz glass under annealing condition of 600℃ for 1 h was 0.9911, and the dose response dispersion was 1.4% at the absorbed dose of 2 Gy. Conclusion Preliminary results suggest that quartz glass with annealing condition of 430℃ for 10 min has the potential to be used for radiotherapy dosimetry.

Angular dependence of the optically stimulated luminescent dosimeter / 中国辐射卫生

0bjective To study the angular dependence of optically stimulated luminescent dosimeter (OSLD) with solid phantoms under SSDL radiation level 60Co radiation field, and to discuss the possibility of OSLD in volumetric modulated arc therapy (VMAT) and other rotating irradiation dose audit. Methods OSLDs were embedded in the two phantoms with the same size and material, respectively. The phantom 1 was set to make the first OSLD perpendicular to the beam, and the phantom 2 was set to make the second OSLD parallel to the beam. The OSLDs were irradiated at 8 angles: 0°, 45°, 90°, 135°, 180°, −45°, −90, −135°. The counts of the OSLSs were read and the response of each angle which normalized to 0° were calculated. Results When the OSLDs are perpendicular to the beam, the angular response is between −6.76% ～ +1.5%, with the maximum angular dependence at 90° and −90°. When the OSLDs are parallel to the beam, the angular response is between −1.74%～+1.67%, below 2%. Conclusion It is better to correct the sensitivity of dosimeters by Element Correction Factors (ECF) for dose audit. Under the condition of rotating irradiation, OSLD shoud be set parallel to the beam, which can better reduce the influence of angular dependence and facilitate further application research of VMAT dose audit.

Development of methodology for quality audit of doses in target area and organ at risk and two dimensional dose distribution in intensity modulated radiotherapy / 中华放射医学与防护杂志

Objective To develop the methodology for using TLD and radiochromic film to measure the planned target volume (PTV) and organ at risk (OAR) doses and 2D dose distribution in IMRT,in order to provide technical guidance on the dose quality audit in IMRT at home.Methods China has participated in the research project launched by the international multi-radiotherapy centre (IMRC).IMRT polystyrene phantom provided by IAEA was scanned by CT scanner and then the scanned images were transmitted to TPS to outline prescribed dose to PTV and to OAR.The former was limited to 400 cGy while the latter limited to 200 cGy.IMRT was implemented with the phantom irradiated using 6 MV X-ray.The irradiated TLDs and films were sent to IAEA dosimerty laboratory for measurement and calculation.Jiangsu,Sichuan,Hubei and Henan provinces were selected to engage with this study for their variety of accelerators and highly skilled physicists.The procedures used were the same as in the IMRC and the irradiated TLDs and films were required to send to external audit group for measurement and calculation.Results According to IAEA requirement,the relative deviations of the TLD-measured and TPS planned doses are within ±7.0％ for PTV and OAR.The China's research results at the IMRC have shown that the relative deviation of TLD-measured and TPS-planned values for the upper and lower PTV were-0.2％ and 0.8％,respectively,consistent with the IAEA requirement,and the values for upper and lower OAR were -0.6％ and-1.0％,respectively,consistent with the requirement.As the results have shown in four provinces,the relative deviations of the TLD-measured and TPS-planned were within 0 to 10.6％ for upper and lower PTV and-0.6％ to 20.9％ for upper and lower OAR.According to IAEA requirement,the passing rate should be greater than 90％ for 3 mm /3％ for 2D dose distribution.China's result at the IMRC is 100％,being excellent.The four provinces' results have shown that 2D dose distribution pass rate of 3 mm/3％ was in the range of 45.0％-100.0％.Conclusions The uses of TLD in quality audit for PTV and OAR doses and the radiochromic film in 2D dose distribution pass rate in IMRT are characterized by scientific feasibility,strong operability,easy-to-mail and data realibility.They are can be applied to quality assurance and audit in medical institutions in the country to on a large scale.

Development of methodology for quality audit of doses in target area and organ at risk and two dimensional dose distribution in intensity modulated radiotherapy / 中华放射医学与防护杂志

Objective@#To develop the methodology for using TLD and radiochromic film to measure the planned target volume (PTV) and organ at risk (OAR) doses and 2D dose distribution in IMRT, in order to provide technical guidance on the dose quality audit in IMRT at home.@*Methods@#China has participated in the research project launched by the international multi-radiotherapy centre (IMRC). IMRT polystyrene phantom provided by IAEA was scanned by CT scanner and then the scanned images were transmitted to TPS to outline prescribed dose to PTV and to OAR. The former was limited to 400 cGy while the latter limited to 200 cGy. IMRT was implemented with the phantom irradiated using 6 MV X-ray. The irradiated TLDs and films were sent to IAEA dosimerty laboratory for measurement and calculation. Jiangsu, Sichuan, Hubei and Henan provinces were selected to engage with this study for their variety of accelerators and highly skilled physicists. The procedures used were the same as in the IMRC and the irradiated TLDs and films were required to send to external audit group for measurement and calculation.@*Results@#According to IAEA requirement, the relative deviations of the TLD-measured and TPS planned doses are within ±7.0% for PTV and OAR. The China′s research results at the IMRC have shown that the relative deviation of TLD-measured and TPS-planned values for the upper and lower PTV were -0.2% and 0.8%, respectively, consistent with the IAEA requirement, and the values for upper and lower OAR were -0.6% and -1.0%, respectively, consistent with the requirement. As the results have shown in four provinces, the relative deviations of the TLD-measured and TPS-planned were within 0 to 10.6% for upper and lower PTV and -0.6% to 20.9% for upper and lower OAR. According to IAEA requirement, the passing rate should be greater than 90% for 3 mm /3% for 2D dose distribution. China′s result at the IMRC is 100%, being excellent. The four provinces′ results have shown that 2D dose distribution pass rate of 3 mm/3% was in the range of 45.0%-100.0%.@*Conclusions@#The uses of TLD in quality audit for PTV and OAR doses and the radiochromic film in 2D dose distribution pass rate in IMRT are characterized by scientific feasibility, strong operability, easy-to-mail and data realibility. They are can be applied to quality assurance and audit in medical institutions in the country to on a large scale.

Analysis on eye lens doses and hand doses of working operator in 125I seed source implantation / 中华放射医学与防护杂志

Objective To measure the doses to eye lens and hands of workers,using thermo luminescent dosimeter (TLD) and optically stimulated luminescence dosimeter (OSLD).Methods TLDs in the same batch were annealed,packed and stuck to the flat abdomen of Alderson-Phantom at a distance of about 15 cm from 125I seed source,while irradiated at different doses:1.0,1.5,3.0,5.0,10.0,12.0,20.0,25.0,30.0,50.0 and 60.0 μ Gy.And then TLDs were measured by dosimeters to establish a dose calibration curve.By implanting seed source into the selected lung for 14 cases,belly for 10 cases,pelvic for 5 case and neck for 6 cases while placing calibrated TLDs on the left,middle and right above eyes,left and right hands of the workers to obtain the location-specific kerma values.Finally,the conversion factors Hp (3) and Hp (0.07) were used to calculate the values of dose equivalent to eye lens and hands.Additionally,OSLDs were used to measure the doses to workers in the same way.Results The TLD-measured eye lens dses to the operator and his assistant were 0.8 and 1.6 mSv in lungs,1.3 and 1.2 mSv in bellies,0.9 and 0.6 mSv in pelves,0.3 mSv in necks,respectively.Meanwhile,hand doses to the operator and his assistant were 1.4 and 2.1 mSv in lungs,1.2 and 1.0 mSv in bellies,0.5 and 0.9 mSv in pelves,0.1 mSv in necks,respectively.The maximum doses to eye lens and hands were 1.2 and 1.0 mSv,respectively in a single treatment.OSLD-measured dose equivalents from lung therapy were 0.2 and 0.1 mSv for eye lens of the operator and his assistant and 0.4 and 0.6 mSv for hands.For belly therapy,the accumulated dose equivalent to hands of the operator was 0.1 mSv while those for other types of therapy were 0 mSv.Conclusions TLDs have the capability to measure not only accumulated dose but also dose equivalent from a single therapy According to ICRP 118 publication and as estimated in the present study,the number of therapy should be not more than 17 every year.OSLDs only give the accumulated dose,the accuracy of which needs to be studied in low-dose measurement.

Development of methodology for dose quality audit of multi-leaf collimator in intensity modulated radiotherapy / 中华放射医学与防护杂志

Objective To develop the methodology for using TLDs and films to measure absorbed dose and 2D dose distribution produced by the multi-leaf collimator (MLC) in intensity modulated radiotherapy (IMRT),in order to provide the guidance on dose quality audit in IMRT.Methods A total of 30 different-typed accelerators were selected from 27 hospitals in Jiangsu,Sichuan,Hubei and Henan provinces,including 17 Varian accelerators,10 Elektas and 3 Simens.The same batch of films and TLDs were put in a 2 cm-thick solid plate for fixation and then loaded in a 15 cm × 15 cm × 15 cm polysyrene solid phantom supplied by International Atomic Energy Agency(IAEA) in terms of 90 cm SSD,19 cm depth,10 cm × 10 cm field at different doses.The standard dose curves wcrc established for film and TLD,respectively.The irradiated film was measured and then sent to the External Audit Group (EAG) in China.The TLD-and film-absorbed doses were compared with TPS-calculated doses.The 2D dose distribution on the IRMT MLC field was measured using films.The homogeneous phanton of 30 cn × 30 cm was scanned by CT and the image was transferred to the TPS.The IMRT was implemented with 6 Gy fractionated irradiation by placing a 25 cm × 25 cm film on the phantom surface at 95 cm SSD and at 5 cm depth.The irradiated film was sent to the IAEA dosimetry laboratory for measurement and calculation.2D dose distribution verification was conducted in thc same way consistent with the procedure of international multi-radiotherapy center.The 3 mm/3％ passing rate was calculated for 2D dose distribution and compared with the film-measured and TPS calculated result.Results IAEA requires the relative deviation of TLD and film measured absorbed dose are with in ± 5％.The relative deviation of TLD-and filmmeasured to TPS-calculated absorbed dose was within the range of ±0.7％-± 8.5％ and within ±0.3％ ±7.8％ in Jiangsu,Sichuan,Hubei and Henan provinces,respectively.IAEA requires the 3 mm/3％ passing rate of film-measured 2D distribution to be 90％.The result of the present study were up to 94.0％.The verification result of 2D dose distribution were within 70.0％-99.9％ in Sichuan,Jiangsu,Hubei and Henan provinces.Conclusions The adsorbed dose and 2D distribution can be audited using TLDs and films for MLC in IRMT.The method is scientific and applicable,economical and convenient for development of dose quality audit for a wide range of IRMT.

Monte Carlo Simulation study of LUNA stereotactic body radiotherapy device’s output ;factors / 中国医学装备

Objective:Using Monte Carlo simulation method to study the important dosimetric parameter output factor of the LUNA stereotactic body radiotherapy device. Methods:Following the manufacturer’s technical documentation to establish the LUNA stereotactic body radiotherapy device’s Monte Carlo model and after model validation. After referring to the output factor measurement’s detector provided by manufacturer, set the relevant parameters in Monte Carlo model at last, compare and analyze the difference of output factor which provided between by manufacturer and calculated by Monte Carlo simulation. Results:In the range of 3%deviation, under the different collimator of condition, output factors which provided by manufacturers and calculated by Monte Carlo are in good agreement, and the reasons for the difference are also analyzed. Conclusion:LUNA stereotactic body radiotherapy device’s output factors of Monte Carlo simulated research work provides reference and basis for the clinical use and quality control.

Quality control research of active spot scanning proton and heavy ion accelerator's radiation field uniformity / 中华放射医学与防护杂志

Objective To develop the method for testing the consistency of irradiation field produced by the active spot scanning proton and heavy ion accelerator.Methods Calibration of the EBT3 films were carried out with the calibrated ion beam to establish the dose calibration curve.According to the different proton and carbon ion energies (proton:94.29,150.68,212.62 McV;carbon ion:175.99,283.43,412.54 MeV/u),EBT3 films were located in the solid water phantoms in each therapy room,respectively.Finally,the irradiated EBT3 films were scanned and the radiation field size's deviation and flatness were analyzed.Results In different conditions,radiation field size's deviations were all less than 2 mm and the flatness parameters were all controlled below the 5％.Conclusions EBT3 films can be used to test the active spot scanning proton and heavy ion accelerator's radiation field uniformity.

Research on quality testing for active spot scanning proton and heavy ion accelerator / 中华放射医学与防护杂志

Objective To study the quality testing of dose delivery system of the active spot scanning proton and heavy ion accelerator,in order to provide the reference for the quality control of related equipment.Methods In the four therapy rooms,both 0.6 cc chambers and Gafchromic EBT3 films were used,respectively,to test the accelerator for dose reproducibility,dose linearity,dose stability,depth dose distribution,beam scanning position deviation and radiation field uniformity in each therapy room.Results Dose reproducibility variation coefficients are all less than 1.5％,dose linearity's maximum deviations less than 2％,dose stability's deviations less than 2％,depth dose distribution stability within 2％,beam scanning position deviation less than 1 mm,consistency of irradiation field's deviation less than 2 mm,and flatness within ± 5％.Conclusions The indicators about quality testing for the active spot scanning proton and heavy ion accelerator are all in line with the requirements of IEC standards draft.

Verification of dose parameters under reference and non-reference conditions for radiotherapy in Liaoning province / 中华放射医学与防护杂志

Objective To verify the reliability of dose parameters of radiotherapy under reference and non-reference conditions by using TLD.Methods Dose parameters were verified by using TLDs under reference and non-reference conditions,including the maximum dose in axel of 5 electron beams with energy of 9 MeV and the variations of dose by depth,source-skin distance,exposure field and 45° wedge for 10 photon beams with energy of 6 MV in 5 hospitals.Results The average relative deviation of 6 MV photon beam measured between TLDs and finger ionization chambers were 4.45％,within ± 7％ as required by IAEA.The average relative deviation of 9 MeV electron beam measured between TLDs and plane parallel chambers were 2.45％,within ± 5％ was required by IAEA.Conclusions Measuring dosimetric parameters by using TLDs under reference and non-reference conditions was reliable and feasible.

Development of measurement method using TLD for workers occupation personally exposed to 125Ⅰ seed source in the implant / 中华放射医学与防护杂志

Objective To explore the method for measuring and calculating both absorbed dose and effective dose received in organ and tissues of occupational workers by using TLDs for the implantation of 125Ⅰ seed sources.Methods The experiments with 60Co γ-rays were carried out for the stability.A group of TLD chips was exposed to 125Ⅰ seed sources to establish standard dose curve for air kerma.During the 125Ⅰ seed implantation, the TLD chips were pasted to 13 locations like thyroid inside and outside the lead aprons worn by occupational workers to measure average absorbed dose and calculate the absorbed doses and effectives to organs and tissues.Results For 3 cases of prostate cancers with implantation of 125Ⅰ seeds, the worker's organs and tissues received the absorbed dose 0.02 -3.80 μ Gy and effective dose 0.06- 1.81 μSv outside lead aprons and the highest absorbed dose 2.35 μ Gy and effective 0.02 μSv inside lead aprons, respectively, with more than 65.9% of rays shielded.For 3 cases of brain cancers with implantation of 125Ⅰ seeds, the workers received the absorbed dose 0.23 - 11.31 μGy and effective dose 0.88 - 4.07 μSv outside lead aprons and the highest absorbed dose 2.22 μ Gy and effective dose 0.09 μSv inside lead aprons, respectively, with more than 54.5% of rays shielded.For 3 cases of lung cancers with implantation of 125Ⅰ seeds, the workers received the absorbed dose 0.03 - 14.78 μGy and effective dose 0.35 -7.59 μSv outside lead aprons and the highest absorbed dose 4.09 μGy and effective 0.22 μSv inside lead aprons, respectively, with more than 58.4% of rays shielded.For 2 cases of mediastinum cancers with implantation of 125Ⅰseeds, the workers received the absorbed dose 0.06 - 74.91 μGy and effective dose 0.83 - 17.96 μSv outside lead aprons and the highest absorbed dose 10.29 μGy and effective 0.5 μSv inside lead aprons, respectively, with more than 85% of rays shielded.For one case of ovary cancer with implantation of 125Ⅰ seeds, the worker received the absorbed dose 0.09 - 14.29 μGy and effective dose 2.40 - 4.50 μSv outside lead aprons and the highest absorbed dose 7.77 μGy and effective 0.12 μSv inside lead aprons, respectively, with more than 34% of rays shielded.For one case of eye cancer with implantation of 125Ⅰ seeds, the workers received the absorbed dose 2.2 -39.84 μGy and effective dose 4.48 - 10.06 μSv outside aprons and the highest absorbed dose 5.19 μGy and effective 0.16 μSv inside aprons, respectively, with more than 54.6 % of rays shielded.Conclusions The method of using TLDs to measure the doses to the occupational workers in the course of the implantation of 125Ⅰ seed sources is simple and easy to operate.It would be an effective approach to protecting medical workers in the case of brachytherapy.

Development of the Diode method for patient's dose measurement in radiotherapy / 中华放射医学与防护杂志

Objective To explore the measurement method of the treatment dose of the patient with Diode for photon beam in radiotherapy,and to validate the treatment dose by comparing with the treatment planning system (TPS).Methods Experiments of the reproducibility,dose rate dependence,non-linearity dose response,and calibration factor in 60Co γ and 6 MV X beams were carried out with Diode on the surface of solid phantom and in water phantom.According to the needs of clinic treatment,different conditions were chosen to observe the dose changes with the angle of incidence,energy response,distance of source to skin,field size,wedge angle,block and tray using ionization chamber and water phantom.The Diode was placed on the surface of the solid phantom to obtain the correction factors.The doses of the chest,abdomen,and head and neek were verified with the Alderson phantom and Diode.Diode doses of the pelvis,head and neck at 14 points on the patient were measured.Results The Diode was irradiated at the points of the Alderson phantom,such as AP,RL and LL of the pelvis,with and without wedges,RL and LL junction of the neck and chin,with and without mask,the maximum relative deviation of doses was within ± 3% between Diode and TPS.The Diode was placed in different locations on the patient,including chest,abdomen and head and neck.The relative maximum deviation of doses was within ±5% between Diode and TPS.Conclusions The Diode method is reliable for measuring the exposure doses of the patient in radiotherapy.

Development on Monte Carlo methodology with scatter correction factor of afterloading 192Ir source / 中华放射医学与防护杂志

Objective To facilitate activity measurement by using the thimble ionization chamber in hospitals,to obtain air kerma scatter correction factor of medical afterloading of 192Ir source by developing an available and convenient calculation method.Methods According to International Atomic Energy Agency (IAEA) 1079 Report to calculate the scatter correction factor of 192 Ir source,to measure air kenna of 192Ir source with and without lead shield using thimble ionization chamber.Simulation measurement conditions were used to calculate scatter correction factor of 192Ir source and comparison was made between experimental results and literature records.At the same time,the different ionization chamber models were simulated at different room sizes to obtain scattering correction factor of 192 Ir source.ResultsComparison was made between the simulation scatter correction factors of 192Ir source and experiment by the shadow shield,and the relative deviation was 0.8%.The deviation of the 192 Ir activity calculated according to the simulated scatter correction factor and measured by well type ionization chamber was 2.4%.By comparison between the calculated results by using two kinds of spherical ionization chamber and those ones deduced by IAEA 1079 Report,the relative deviations ranged within 0.3%-0.4%.Five different types of thimble ionization chamber and different room sizes were simulated and calculated by MC simulation,with the relative deviation within 3%.Conclusions Monte Carlo simulation method for calculating afterloading 192 Ir source's scatter correction factor is feasible,and this method is convenient for use in the thimble chamber for brachytherapy QA work in the hospital.