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Objective:To introduce the method and result of the modeling and preliminary dose verification of the treatment planning system used in the first domestic proton therapy device of China (Raystation 10B, a system of scientific research version with no available registration certificate) and to verify the modeling accuracy using dose verification result.Methods:The modeling method for a treatment planning system (TPS) mainly included the data acquisition and modeling of integrated depth dose (IDD) curves, the data acquisition and modeling of beam spot profiles in air, and the calibration and modeling of absolute dose by scanning a 10 cm ×10 cm square field with a spot spacing of 2.5 mm. By measuring the dose distributions in three cases with different complexity levels and comparing them with the dose distributions calculated using the TPS, this study verified and analyzed the modeling accuracy and proposed the requirements for beam parameters and the commissioning suggestions of the proton device.Results:The peak values of the IDD curves of low-energy regions fitted using the TPS model were less than the measured values, while those of medium- and high-energy regions fitted using the TPS model approximated the measured values. The range in all energy regions fitted accurately. For the three cases with different complexity levels, the deviation between the average dose calculated by the TPS and that measured was within ±5% (national standard for type tests of medical devices). Moreover, the DTA of high-dose-gradient areas was less than 3 mm.Conclusions:The modeling accuracy of the TPS generally meets the verification requirements. However, due to the low resolution of IDDs obtained by Monte Carlo simulation in the TPS model and the sharp Bragg peaks of low-energy regions, the IDD modeling accuracy of low-energy regions is insufficient.
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The fi rst part of this study was about measurement of dosimetric parameters for small photon beams to be used as input data for treatment planning computer system (TPS) and to verify the dose calculated by TPS in Stereotactic Radiosurgery (SRS) procedure. The beam data required were percentage depth dose (PDD), off-axis ratio (OAR) and scattering factor. Small beams of 5 mm to 45 mm diameter from a circular cone collimator in SRS were used for beam data measurements. Measurements were made using pinpoint ionisation chamber (0.016cc). In the second part of this study, we reported the important of carrying out quality assurance (QA) procedures before SRS treatment which were found to infl uence the accuracy of dose delivery. These QA procedures consisted of measurements on the accuracy in target localization and treatment room laser alignment. The calculated TPS dose for treatment was verifi ed using pinpoint ionisation chamber and thermoluminescent detector (TLD) 100H. The deviation mean between measured and calculated dose was -3.28%. The measured dose obtained from pinpoint ionisation chamber is in good agreement with the calculated dose from TPS with deviation mean of 2.17%. In conclusion, pinpoint ionisation chamber gives a better accuracy in dose calculation compared to TLD 100H. The results are acceptable as recommended by International Commission on Radiation Units and Measurements (ICRU) Report No. 50 (1994) that dose delivered to the target volume must be within ± 5% error.
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RadiosurgeryABSTRACT
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 To investigate the safety and validity of Neptune 3D-RTPS-A treatment planning system compared to Prowess TPS.Methods A total of 30 clinical tumor cases with radiotherapy planning on Prowess TPS from September 2009 to May 2010 were used.The contours, organs at risk and target volumes in Prowess TPS were transported into Neptune TPS, the same parameters setted in the two treatment planning systems.The results of comparison of the two TPS were calculated.Results All cases of clinical treatment planning were completed successfully by Neptune TPS, and the various functions of the design were achieved for fitting tumor conformal radiation therapy.The key parameters on radiation treatment were compared.The results are as follows:the differences of source skin distance ( SSD ) ＜0.5% , differences of Monitor Unites ＜0.5%, the differences of dose at isocenter ＜2%, the differences of five isodose lines surrounding area ＜ 3%, and the mean difference of distances of five isodose lines was 0.43 mm, the differences of the volume of PTV on 90% isodose line ＜ 2%, and the differences in V30of organs at risk ＜ 3%.Conclusions Neptune TPS could be qualified for clinical validity and safety by clinical verification.