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Objective:To evaluate the accuracy of measurement of the output factor of high-energy photon small field (Scp) using commercial semi-diodes and ionization chambers in small fields in accordance with the IAEA-483 report, which has been proposed that all kinds of detectors should be revised for small field Scp measurement in clinical practice.Methods:EGSnrc of Monte Carlo (MC) software was utilized to simulate the treatment head of Varian Novalis Tx linear accelerator, and the profile curve and relative dose value were generated by simulation in DOSXYZnrc based on derived phase space file. Measurement of PDD and Profiles was used to adjust and validate the simulation mode. Detectors including ionization chambers A16, A14 sL, CC01, CC13, PFD and EFD and semi-diodes PFD, EFD and Razor under different radiation field settings (0.5 cm to 10.0 cm) were employed to measure the profile curves and Scp of FWHM equivalent rectangular fields, which were compared with data of Monte-Carlo simulation. The measurement of Scp was revised by data given in the IAEA-483 report. The data with or without correction were compared with the data of MC simulation.Results:A curve deviation o F<2.0% between MC simulation and PFD measurement was accepted. MC simulated Profiles were consistent with PFD, EFD and Razor measurements, when the field was<3.0 cm. Razor response in the out-field region was 2.3% higher than those of MC and PFD, and it increased with the increment of field and was 3.0% at 10.0 cm. The maximum 20.0%-80.0% penumbra width was detected as 3.0 mm for CC13 at 10.0 cm rectangular field. With the decrease of the radiation field, the deviation relative to MC simulation was increased as for Scp mean values of 7 detectors before correction. The standard deviation (SD) of the measured value was increased rapidly when it was close to 1.0 cm, ranging from 0.009-0.014 for the field of 5.0 cm-1.5 cm to 0.030-0.089 for the field of 1.0 cm-0.5 cm. The mean value of SD for the whole measurement before correction was 0.030. The mean SD of Scp measured by the six probes was 0.008, 0.013 at 0.8 cm and 0.021 at 0.6 cm after correction. When the equivalent field was ≥1.0 cm, the corrected Scp and MC simulation deviation was ranged from -3.6% to -0.5%. The error was between -6.9% and -1.3% when the radiation field was<1.0 cm. Conclusion:The SD of Scp measured by different detectors after correction in accordance to the IAEA-483 report is small, which is in good agreement with the data of MC simulation, suggesting that it could be applied in clinical dosimetry.
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Objective To investigate the commissioning and testing of the Eclipse model of an Edge accelerator with high-definition muhi-leaf collimator (HD-MLC).Methods The percentage depth dose (PDD),profile,output factor measured by Razor and CC13 were statistically compared with the standard data.Penumbra,transmission factor (TF),leakage,concave-convex groove,accuracy of movement and dosimetry leaf gap (DLG) were measured with EBT3,electronic portal image device (EPID) and PTW SRS1000&SRS1500.The optimal DLG/TF was acquired when the γ pass rate of test cases was the highest.The point dose of regular fields,intensity-modulated radiation therapy (IMRT) and volume-modulated radiation therapy (VMAT) was verified with FC65-G.The planar dose of these case was verified with Octavius 4D and EBT3.Results The measured PDD data were consistent with the standard data.The measured penumbra of 3 cm and 4 cm square fields was smaller,whereas that of 6 cm square field was larger than the standard values.The left and right edge,field size,center of the field were distributed within the range of-1.0-0.4 mm、0.2-1.7 mm,-0.3-1.9 mm and-0.1-0.8 mm,respectively.The mean penumbra of the left and right MLC in different positions were (2.5±0.042) mm and (2.7±0.005) mm.The leakage of MLC was 0.009-0.016.The measured DLG/TF was 0.1861 cm/0.0116 and the optimal DLG/TF was 0.015 cm/0.014.The differences of point dose of all the test cases except the one which was in the low-dose area were within ±3％.Local and global γ pass rates of all IMRT were 79.81％-100％ and 96.3％-100％ (3％/3 mm),71.3％-98.9％ and 94.3％-99.8％ for VMAT cases.Conclusions This method can accurately test and commission the Eclipse treatment planning model of Edge Linac equipped with HD-MLC.
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Objective The IAEA report No.483 describes the latest method of small field dosimetry.The field output factor measurement and correction methods are used to improve the accuracy and consistency of the measurement results for different type detectors.Methods The field output factors from 0.6 cm×0.6 cm to 10 cm× 10 cm were measured using IBA's CC13 ionization chamber,CC01 ionization chamber,PFD semiconductor detector,EFD semiconductor detector and Razor semiconductor detector,respectively.The field output correction factors were used to correct the measurement result.Results Compared with the corrected data,the results of ionization chamber are mainly affected by the volume averaging and the fluence perturbation effect,lead to the measurement result which is 4.70％ lower at 0.6 cm × 0.6 cm;The results of Shielded semiconductors are mainly affected by fluence perturbation effect,lead to the measurement result which is 4.80％ higher at 0.6 cm × 0.6 cm.The results of unshielded semiconductors are mainly affected by energy response and fluence perturbation effect,resulting in lower measurement results at the field size＞0.8 cm×0.8 cm,2.10％ lower at field size of 1.5 cm× 1.5 cm,higher measurement results at field size＜0.8 cm×0.8 cm and 1.1％ higher at field size of 0.6 cm×0.6 cm.Before the correction,the measurement results from different types of detectors are quite different,average standard deviation is 0.016 6.After the correction,the difference among the detectors is significantly reduced,average standard deviation is 0.006 6.Conclusions For detectors such as ionization chambers and semiconductors,the field output correction factors can be used to correct the output factors of the small field to improve the accuracy and consistency of the measurement results.
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Objective To analyze the diagnostic value of computed tomography (CT) enhanced angiography of pancreatic artery with thin slice target scanning of field of view (FOV) for pancreatic cancer. Methods Clinical data of 36 patients with pancreatic cancer confirmed by postoperative pathology were collected. All patients received CT enhanced angiography of pancreatic artery with thin slice target scanning of FOV before operation, and the accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of the CT enhanced angiography of pancreatic artery with thin slice target scanning of FOV in evaluating tumor size, vascular invasion, arterial origin variation, and node metastasis were calculated with pathological results being the “gold standard”. The Kappa test was used to evaluate the diagnostic value of CT enhanced angiography of pancreatic artery with thin slice target scanning of FOV for pancreatic cancer. Results The diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of CT enhanced angiography of pancreatic artery with thin slice target scanning of FOV for tumor size were all 1.00; the diagnostic accuracy and sensitivity for vascular invasion and arterial origin variation were all 1.00, and the specificity was 0.97 or more; the diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value for lymph node metastasis were 0.89, 0.75, 1.00, 1.00, and 0.83, respectively. The consistency of pathology and CT enhanced angiography of pancreatic artery with thin slice target scanning of FOV was good in evaluating pancreatic cancer (all Kappa0.75). Conclusion CT enhanced angiography of pancreatic artery with thin slice target scanning of FOV is a comprehensive method in evaluating pancreatic tumors, tumor margin, relationship between tumor and peripheral vessels, and peripheral lymph node metastasis, and it can improve the accuracy of surgical resectability evaluation of pancreatic cancer.
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Objective To investigate the dosimetric properties of PTW 60019 synthetic diamond detector in small photon beams.Methods A PTW 60019 synthetic diamond detector was tested under 6 and 10 MV photon beams,respectively.Linearity with dose,dose rate dependence and off-axis ratio were measured and compared to those measured by an IBA SFD.Percentage depth doses were measured and compared to those measured by an IBA SFD and a PTW 31010 semiflex chamber.Total scatter factors were measured and compared to those measured by an IBA SFD and a PTW 31016 PinPoint chamber.Results The dose response of a PTW 60019 synthetic diamond detector showed a good linear behavior as a function of dose,with observed deviations below 0.2％ over a dose range from 100 to 1 000 MU.The dose rate response was almost independent,with deviations below 0.2％ in the dose rate range from 37 to 614 MU/min.For the fields of 20-100 mm in diameter,there were dose differences in percentage depth doses within 1％ as compared to an IBA SFD and a PTW 31010 semiflex chamber.For the 10 mm diameter field,the differences were up to 5.8％ in the build-up region.Off-axis ratios measurements showed a good agreement among the involved detectors (＜ 1％).The higher differences appeared in the penumbra region.A good agreement was also found in terms of total scatter factor measurements for the related detectors.Conclusions The observed dosimetric properties of the PTW 60019 synthetic diamond detector indicate that it is a suitable candidate for small photon beam dosimetry.
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Objective To compare five different detectors in output factor(OF)measurement for the CyberKnife(CK)system,and to select a suitable detector. Methods OFs for 12 different sizes of CK collimators were measured by EBT3films and 5 different commercially available detectors,consisting of diode detectors PTW 60017 and PTW 60018,ionizing chamber detectors PTW 31010 and PTW 30013,and diamond detector PTW 600019.OF was compared between different detectors and different measurement orientations. Results When the size of collimator was larger than 30 mm,the OF deviation among five detectors was less than 1%.When the size of collimator was smaller than 30 mm,however,the OF deviation among five detectors became large and obviously increased with the decrease in the size of collimator. With a OF deviation less than 2%,PTW 60019 achieved the best agreement with films. Compared with films,diode detectors gave slightly higher OFs,while ionizing chamber detectors gave much smaller OFs. The OF measurement was also affected by measurement orientation. PTW 60019 gave a smaller OF in the direction parallel to the central axis than in the direction perpendicular to the central axis of the radiation field,while PTW 31010 had an opposite result. Conclusions When the size of collimator is larger than 30 mm,PTW 31010,PTW 60017,PTW 60018,and PTW 60019 can be directly used for the OF measurement. When the size of collimator is smaller than 30 mm,correction is needed for the OF measurement using the above detectors. PTW 30013 is not suitable for the OF measurement in the small radiation field.
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Objective To compare the relative dose of small fields measured by clinically common detectors and those obtained from Monte Carlo simulation in order to obtain the accurate measurement method, and to modify the inappropriate detectors.Methods The percentage depth-dose distribution curve and profile (flatness and symmetry) curves were collected at 2 cm×2 cm, 3 cm×3 cm, and 4 cm×4 cm under 6-MV X-ray of Trilogy linear accelerator by CC13, PFD, SFD, and blue phantom.The results were compared with the stimulation results from Monte Carlo method (the current gold standard).The correction factors for the detectors with large error were calculated to provide reference data for clinical practice.Results The results measured by SFD detector were most close to the results from Monte Carlo simulation.The measurement errors of CC13 and PFD detectors were large.The correction factor in the penumbra for CC13 and PFD detector was 0.664-1.499.Conclusions SFD detector is better than CC13 and PFD detector in the measurement of small fields, but CC13 and PFD detector can provide reference data for clinical practice after the corresponding correction.
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Objective To investigate muli-leaf collimator (MLC)-defined small field output factors calculated by the treatment planning system (TPS), and to study the measuring method of small field output factors verified by 0.015 cc PinPoint ionization chamber.Methods Eight medical accelerators for intensity-modulated radiation therapy (IMRT) were investigated in Henan province, and TPS-calculated output factors for various small fields (6 cm ×6 cm,4 cm ×4 cm,3 cm ×3 cm and 2 cm ×2 cm) were compared with published values recommended by IAEA.If the relative deviation was more than ± 3％ for the 2 cm ×2 cm field size and ±2％ for the fields of 6 cm ×6 cm, 4 cm ×4 cm and 3 cm ×3 cm, which was beyond the scope of IAEA allowed, the output factors will be measured and verified using 0.015 cc PinPoint ionization chamber and Unidos electrometer.Results TPS-calculated small field output factors for eight medical accelerators were compared with published values.The relative deviation of small field output factors for five pieces of equipment, which accounted for 62.5％ of the total, met the IAEA's requirement, while the other three, which accounted for 37.5％ of the total, did not.After measuring with PinPoint ionization chamber, the results from only three pieces of equipment met minimum IAEA's requirement.Conclusions MLC-defined small field output factors calculated by TPS for some medical accelerators in Henan need to be measured and corrected using micro-ionization chamber, and the measured values could be taken as the basis of radiation treatment planning.
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Objective To develop the methods for using 0.015 cc pinpoint chambers, 0.007 cc miniature chambers and diode detector to measure Multi-leaf collimator (MLC) small field in IMRT.Methods MAX4000 and Unidos electrometers were connected with different types of small chambers and diode detectors.MLC shaped fields of10 cm×10 cm, 6 cm×6 cm, 4 cm×4 cm, 3 cm×3 cm, 2 cm× 2 cm were defined at 100 cm SSD.The field sizes for the Varian accelerator were defined by the tertiary MLC, while the secondary jaws were kept at 10 cm × 10 cm field, with the monitor units of 250 MU.Each field was measured three times to obtain the average value.The readings of all small fields were normalized to 10 cm × 10 cm field values for comparison of measured and published output factors.Results The relative deviations of the MLC small field output factors from the published outputs are 1.0％ , 1.7％ , 1.5％ and 2.4％, respectively, for Unidos electrometer connected with 0.015 cc pinpoint chamber;0.2％, 0.8％, 0.8％ and 1.4％, respectively, for Unidos electrometer connected with 0.007 cc miniature chamber;and 0.1％, 0.5％, 0.5％ and 0.9％, respectively, for MAX4000 electrometer connected with 0.007 cc miniature chamber.Conclusions The 0.015 cc chamber-measured MLC output factors for 3 cm × 3 cm and 2 cm × 2 cm fields are excellent.As required by IAEA, the relative deviations of the measured output factor from the published output factor are within ± 2％ for 2 cm × 2 cm fields and ± 3％ for larger fields.The results measured using 0.007 cc chamber are better than those measured using 0.015 cc chamber.The measured results using the diode detector, normalized to the 10 cm × 10 cm field, are consistent with the minimum requirements and excellent when being normalized to the 4 cm × 4 cm field.For dosimetric consideration, MLC small field output factor should be measured using small chamber and diode detector.The method is accurate and reliable, therefore, all measured output factors for MLC small fields should be input into radiation treatment plan system.
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Objective The beam data is compared with those obtained from Monte Carlo (MC)simulation and measurement to investigate their feasibility and reliability for X-ray small fields.MethodsThe beam data,including the total scatter factor (Scp),percentage depth dose (PDD) was acquired byneasurement and calculation with the field size ranging from 0.5 cm × 0.5 cm to 10 cm x 10 cm.The resultswere compared and analyzed.Results All the data is most consistent for the fields size of ≥3.5 cmx 3.5cm,but they are obvious different for the fields size of ≤ 3.0 cm × 3.0 cm.The measurements seem toreliable using the chambers of CC04 and CC13 for the fields size of ≥2.0 cm x 2.0 cm.Conclusions It isdemonstrated that the accurate measurements and calculations of Scp and PDD can be obtained for the fieldssize of ≥2.0 cm ×2.0 cm,but they needed morc rcscarchcs for thc smaller fields.
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A polymer gel dosimeter was fabricated. A 3-dimensional dosimetry experiment was performed in the small field of the photon of the cyberknife. The dosimeter was installed in a head and neck phantom. It was manufactured from the acrylic and it was used in dosimetry. By using the head and neck CT protocol of the CyberKnife system, CT images of the head and neck phantom were obtained and delivered to the treatment planning system. The irradiation to the dosimeter in the treatment planning was performed, and then, the image was obtained by using 3.0T magnetic resonance imaging (MRI) after 24 hours. The dose distribution of the phantom was analyzed by using MATLAB. The results of this measurement were compared to the results of calculation in the treatment planning. In the isodose curve on the axial direction, the dose distribution coincided with the high dose area, 0.76mm difference on 80%, rather than the low dose area, 1.29 mm difference on 40%. In this research, the fact that the polymer gel dosimeter and MRI can be applied for analyzing a small field in a 3 dimensional dosimetry was confirmed. Moreover, the feasibility of using these for the therapeutic radiation quality control was also confirmed.
Subject(s)
Antineoplastic Combined Chemotherapy Protocols , Cytarabine , Head , Magnetic Resonance Imaging , Neck , Polymers , Quality Control , ThioguanineABSTRACT
Recently PTW developed a MicroLion liquid ionization chamber which is water_equivalent and has a small sensitive volume of 0.002 cm3. The aim of this work is to investigate such dosimetric characteristics as dose linearity, dose rate dependency, spatial resolution, and output factors of the chamber for the external radiotherapy photon beam. The results were compared to those of Semiflex chamber, Pinpoint chamber and Diode chamber with the sensitive volumes of 0.125 cm3, 0.03 cm3 and 0.0025 cm3, respectively and evaluated to be suitable for small fields. This study was performed in the 6MV photon energy from a Varian 2300 C/D linac accelerator and the MP3 water phantom (PTW, Freiburg) was used. Penumbras in the varios field sizes ranged from 0.5x0.5 cm2 to 10x10 cm2 were used to evaluate the spatial resolution. Output factors were measured in the field sizes of 0.5x0.5 to 40x40 cm2. Readings of the chamber was linearly proportional to dose. Dose rate dependency was measured from 100 MU/min to 600 MU/min, showed a maximum difference of 5.0%, and outputs decreased with dose rates. The spatial resolutions determined with comparing profiles for the field sizes of 0.5x0.5 cm2 to 10x10 cm2 agreed between every detector except the Semiflex chamber to within 2%. Outputs of detectors were compared to that of Semiflex chamber and showed good agreements within 2% for every chamber. This study shows that MicroLion chamber characterized by a high signal-to-noise ratio and water equivalence could be suitable for the small field dosimetry.
Subject(s)
Dependency, Psychological , Reading , Signal-To-Noise Ratio , Spatial Analysis , WaterABSTRACT
Cyberknife with small field size is more difficult and complex for dosimetry compared with conventional radiotherapy due to electronic disequilibrium, steep dose gradients and spectrum change of photons and electrons. The purpose of this study demonstrate the usefulness of Geant4 as verification tool of measurement dose for delivering accurate dose by comparing measurement data using the diode detector with results by Geant4 simulation. The development of Monte Carlo Model for Cyberknife was done through the two-step process. In the first step, the treatment head was simulated and Bremsstrahlung spectrum was calculated. Secondly, percent depth dose (PDD) was calculated for six cones with different size, i.e., 5 mm, 10 mm, 20 mm, 30 mm, 50 mm and 60 mm in the model of water phantom. The relative output factor was calculated about 12 fields from 5 mm to 60 mm and then it compared with measurement data by the diode detector. The beam profiles and depth profiles were calculated about different six cones and about each depth of 1.5 cm, 10 cm and 20 cm, respectively. The results about PDD were shown the error the less than 2% which means acceptable in clinical setting. For comparison of relative output factors, the difference was less than 3% in the cones lager than 7.5 mm. However, there was the difference of 6.91% in the 5 mm cone. Although beam profiles were shown the difference less than 2% in the cones larger than 20 mm, there was the error less than 3.5% in the cones smaller than 20 mm. From results, we could demonstrate the usefulness of Geant4 as dose verification tool.
Subject(s)
Electronics , Electrons , Head , Photons , Radiosurgery , Resin Cements , WaterABSTRACT
In this study, we estimated inhomogeneity correction factor in small field. And, we evaluated accuracy of treatment planning and measurement data which applied inhomogeneity correction factor or not. We developed the Inhomogeneity Correction Phantom (ICP) for insertion of inhomogeneity materials. The inhomogeneity materials were 12 types in each different electron density. This phantom is able to adapt the EBT film and 0.125 cc ion chamber for measurement of dose distribution and point dose. We evaluated comparison of planning and measurement data using ICP. When we applied to inhomogeneity correction factor or not, the average difference was 1.63% and 10.05% in each plan and film measurement data. And, the average difference of dose distribution was 10.09% in each measurement film. And the average difference of point dose was 0.43% and 2.09% in each plan and measurement data. In conclusion, if we did not apply the inhomogeneity correction factor in small field, it shows more great difference in measurement data. The planning system using this study shows good result for correction of inhomogeneity materials. In radiosurgery using small field, we should be correct the inhomogeneity correction factor, more exactly.
Subject(s)
Electrons , RadiosurgeryABSTRACT
In case of radiation treatment using small field high-energy photon beams, an accurate dosimetry is a challenging task because of dosimetrically unfavorable phenomena such as dramatic changes of the dose at the field boundaries, dis-equilibrium of the electrons, and non-uniformity between the detector and the phantom materials. In this study, the absorbed dose in the phantom was measured by using an ion chamber and a diode detector widely used in clinics. GAFCHROMIC(R) EBT films composed of water equivalent materials was also evaluated as a small field detector and compared with ionchamber and diode detectors. The output factors at 10 cm depth of a solid phantom located 100 cm from the 6 MV linear accelerator (Varian, 6 EX) source were measured for 6 field sizes (5x5 cm2, 2x2 cm2, 1.5x1.5 cm2, 1x1 cm2, 0.7x0.7 cm2 and 0.5x0.5 cm2). As a result, from 5x5 cm2 to 1.5x1.5 cm2 field sizes, absorbed doses from three detectors were accurately identified within 1%. Wheres, the ion chamber underestimated dose compared to other detectors in the field sizes less than 1x1 cm2. In order to correct the observed underestimation, a convolution method was employed to eliminate the volume averaging effect of an ion chamber. Finally, in 1x1 cm2 field the absorbed dose with a diode detector was about 3% higher than that with the EBT film while the dose with the ion chamber after volume correction was 1% lower. For 0.5x0.5 cm2 field, the dose with the diode detector was 1% larger than that with the EBT film while dose with volume corrected ionization chamber was 7% lower. In conclusion, the possiblity of GAFCHROMIC(R) EBT film as an small field dosimeter was tested and further investigation will be proceed using Monte Calro simulation.
Subject(s)
Electrons , Particle Accelerators , WaterABSTRACT
Total scatter factor (Scp), head scatter factor (Sc) and phantom scatter factor (Sp) are very important for accurate radiation therapy at stereotactic radiosurgery (SRS) with irregular field shape using micro-MLC and intensity modulated radiation therapy (IMRT) including many small field sizes. In this study we measured and compared Scp with reference ion chamber, pinpoint chamber and diode detector and adapted the resuls form diode detector. Head scatter factors for small field sizes were also measured with diode detector covered 1.5 cm-thick solid water build-up cap. Some errors like as electron contamination of 1~3% were included in the values of Sc but trend of total results of Sc was coincided with basic theory. Phantom scatter factors for small field sizes were calculated form Scp and Sc. The results of Sp were compared and were well-agreed with those of other authors.
Subject(s)
Electrons , Head , Hepatocyte Growth Factor , Radiosurgery , WaterABSTRACT
Objective To evaluate the radiation method and resuh of 450 patients received TBI(total body irradiation).Methods Single-dose Measurement was used to mark dose of TLD(thermo luminescence dosimeter).The values of actual dose in body midline were evaluated by calculating and correcting mean dose of incidence and emergence.Radiation methods:In four-field Irradiation.diagonals of fields coinside with the longitudinal axis of the patients,patient in supine and lateral positions received two pairs of parallel opposite radiation.Scheme of TBI came from a preparative radiation about one week before,and this four-field and equal-in-dose(about 10%of TBI)preparative radiation offered US the optimal scheme with aminimal dose non-uniformity by adjusting different dose proportion of supine and lateral position.In small field irradiation,patients received one pair of parallel opposite radiation from lateral side sitting on a special stool with backrest,the stool can be rotated CW or CCW,pedals can be move forward or backward and fixed.In opposite lateral irradiation,similar to four-field irradiation,patients received one pair of horizontal opposite radiation only in supine position.Five of these patients received FTBI(Fractional TBI). Results The average non-uniformity in midline of patients in four-field irradiation group(87 patients).small field irradiation group(91patients)and opposite lateral irradiation group(272 patients)is respectively ±8.1%,±7.4% and ±4.9%. Conclusions It iS a important process for QA and Qc to measure the dose of incidence and emergence real-timely with TLD or semiconductor dosimeter.We can adopt small field irradiation when the field iS not large enough to contain the patient from head to foot,and it showed advantages over four-field irradiation in treatment process and outcomes.We found the uniformity in body midline would be much better in supine position with diagonal＞180 cm than that in four-field irradiation and small field irradiation with diagonal＜110 cm.We compared supine position irradiation with opposite lateral irradiation,only to find which has its strong point.And actually we considered that FTBI treatment booth can be used more often in anterior and posterior parallel fields irradiation,patient semi-sitted,repeatedly received forward and backward radiation. In spit of not possessing radio-biological advantages as FTBI,STBI(Single TBI)is still a practical form of TBI.
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PURPOSE: In order to obtain basic data for treatment plan in radiosurgery, we measured small fields of 6 MV X-rays and compared the measured data with our Monte Carlo simulations for the small fields. MATERIALS AND METHODS: The small fields of 1.0, 2.0 and 3.0 cm in diameter were used in this study. Percentage depth dose (PDD) and beam profiles of those fields were measured and calculated. A small semiconductor detector, water phantoms, and a remote control system were used for the measurement. Monte Carlo simulations were performed using the EGS4 code with the input data prepared for the energy distribution of 6 MV X-rays, beam divergence, circular fields and the geometry of the water phantoms. RESULTS: In the case of PDD values, the calculated values were lower than the measured values for all fields and depths, with the differences being 0.3 to 5.7% at the depths of 2.0 to 20.0 cm and 0.0 to 8.9% at the surface regions. As a result of the analysis of beam profiles for all field sizes at a depth of 10cm in water phantom, the measured 90% dose widths were in good agreement with the calculated values, however, the calculated penumbra radii were 0.1 cm shorter than measured values. CONCLUSION: The measured PDDs and beam profiles agreement with the Monte Carlo calculations approximately. However, it is different when it comes to calculations in the area of phantom surface and penumbra because the Monte Carlo calculations were performed under the simplified geometries. Therefore, we have to study how to include the actual geometries and more precise data for the field area in Monte Carlo calculations. The Monte Carlo calculations will be used as a useful tool for the very complicated conditions in measurement and verification.
Subject(s)
Radiosurgery , Semiconductors , WaterABSTRACT
Radiosurgery requires integral procedure where special devices and computer systems are needed for localization, dose planning and treatment. The aim of this work is to verify the overall mechanical accuracy of our LINAC and develop dose calculation algorithm for LINAC radiosurgery. The alignment of treatment machine and the performance testing of the entire system were extensively carried out and the basic data such as percent depth dose, off-axis ratio and output factor were measured. A three dimensional treatment planning system for stereotactic radiosurgery has been developed. We used an IBM personal computer with C programming language (IBM personal system/2, Model 80386, 1BM Co., USA) for calcu1ating the dose distribution. As a result, deviations at isocenter on gantry and table rotation for our treatment machine were acceptable since they were less than 2 mm. According to the phantom experiments, the focusing isocenter were successful by the error of less than 2 mm. Finally, the mechanical accuracy of our three dimensional planning system was confirmed by film dosimetry in sphere phantom.
Subject(s)
Humans , Computer Systems , Film Dosimetry , Microcomputers , Programming Languages , RadiosurgeryABSTRACT
The work suggested in this paper addresses a method for collecting beam data for small circular fields. Beam data were obtained from Philips 6 and 8 MV LINAC at Dept. Radiation Therapy at Gainesville Incorporated and Shands Teaching Hospital. Specific quantities measured include tissue maximum ratio (TMR), off-axis ration (OAR) and relative output factor (ROF). In small field irradiation, special collimators were used to produce circular fields of 1 cm to 3 cm diameter in 2 mm steps, measured at SAD (soura axis distance) of 100 cm. Diode detector was chosen for primary beam measurement and compared with measurements made with photographic film and TLD dosimeters. The measured TMRs and OARs were formulated from limited measurements to generate basic beam data for reference set-up. The empirical formula were later, extended and generalized for any possible set-up using the trends of fitting parameters. The measured TMRs and OARs were well represented by the fitting formula developed.