Preliminary application of volumetric-modulated arc therapy dosimetry verification system based on three-dimensional dose reconstruction of patient anatomical structures / 中华放射肿瘤学杂志

Objective:To perform testing and clinical application of a volumetric-modulated arc therapy (VMAT) dosimetry verification system based on three-dimensional dose reconstruction of patient anatomical structures.Methods:ArcCheck array calibration was performed. Then, 200 MU was delivered with a 10 cm×10 cm field when the source to center of ArcCheck was 100 cm to calibrate the absolute dose and the dose was simultaneously measured by a FC65-G detector in the center of the ArcCheck. The absolute dose calibration value or the CT value of ArcCheck was adjusted to minimize the differences between the planning and measurement values of FC65-G, reconstructed value by 3DVH and reconstructed percent depth dose by 3DVH. 10 lung and 10 cervical cancer VMAT cases were selected and measured by ArcCheck and FC65-G under the delivery of a TrueBeam LINAC. The three-dimensional doses of all cases were reconstructed by 3DVH and compared with the planning and measurement values.Results:Different array calibration files of ArcCheck exerted different effect upon the two-dimensional dose measured by ArcCheck and three-dimensional dose reconstructed by 3DVH. The optimal reconstructed dose was obtained when self-calibration file was adopted and 249.96 cGy was regarded as the absolute dose calibration value. The deviations of the mean dose (D mean) and D 95% of the target were within ±4.2% and parameters of some organs at risk significantly differed compared with the reconstructed and planning dose for all cases. A negative mean point dose difference was obtained and the reconstructed dose was closer to the measured value. The γ-passing rate of the target for some cases was low, the proportion of regions irradiated by 50% prescription dose was slightly higher and the proportion of other organs was relatively high. Conclusion:The 3DVH model can be accurately established and tested with the acceptance test method in the present study, which can provide detailed information for dose verification.

Preliminary study on dosimetry verification of VMAT on the basis of TG119 report / 中华放射肿瘤学杂志

Objective To preliminarily verify the feasibility of utilizing TG119 report to commission the volumetric modulated arc therapy (VMAT) plans.Methods Based on the test cases mentioned in TG119 report,7-/9-field intensity-modulated radiation therapy (IMRT) and dual-arc VMAT plans were devised by using two types of beam energy (6 MV and 10 MV) in the Eclipse TPS system according to the requirement of this report.All the plans were verified using 0.125cc semiflex thimble ionization chamber,MatriXX and Delta 4,respectively.The final results were statistically compared with the results measured by multiple institutions in the TG119 report.Results The resuhs of both IMRT and VMAT plans met the requirement of the TG119 report.The discrepancy of point dose in the high/low dose region of VMAT plans using different photon beams was ranged from-2.55％ to 2.55％,and ± 1.85％ for the IMRT plans.The percentage of γ passing points (±3％/3 mm) for the IMRT plans using 6 MV and 10 MV photon beams was 99.38％ and 99.53％,99.32％ and 99.46％ for the VMAT plans.The γ passing rate of the compound field exceeded 98％.Conclusions The VMAT plans with 6 MV and 10 MV photon beams meet the requirement of the TG119 report.TG119 report provides certain guidance for establishing a benchmark for dosimetry verification of the VMAT plans.

Study on dosimetric verification of VMAT treatment planning for chest esophageal carcinoma / 中华放射肿瘤学杂志

Objective To study the dosimetry characteristics of VMAT plan in the esophageal carcinoma radiotherapy.Methods Application of 0.6 cm3 ionization chamber and COMPASS threedimensional dose verification system,20 cases of upper and middle chest esophageal carcinoma on the VMAT plans for absolute dose and relative dose verification.Dose volume histogram (DVH) comparison treatment target,lungs,heart,and differences in the spinal cord irradiation dose and volume,and analyses γpass rate of GTV,CTV,PTV and organs at risks.Results The center dose of upper and middle chest esophageal carcinoma accurate rates were above 99％.Thoracic segment esophageal:GTV,PTV and organs at risks of γ pass rate above 97％.D95％ and Dmean of GTV,CTV and PTV were relatively undervalued within 3％.D1％ of spinal cord is 2.21％ overvalued.Left and right pulmonary V5 were slightly overvalued by about 0.5％,V10-D30,Dmean undervalued within 2％.In period of middle chest esophageal carcinoma:the gamma passed rate of GTV,CTV,PTV and organs at risks of above 97％,GTV,CTV,PTV D95％,Dmean were relatively undervalued within 2％.Spinal cord D1％ is 2.04％ overvalued.Left and right pulmonary V5-D30 to V10 as a trend of gradually to be underestimated,at 1.5％.Heart Dmean was undervalued by 2.68％.Conclusion VMAT technology is applicable in the chest esophageal carcinoma radiotherapy.

Investigation of dose verification of esophageal carcinoma intensity modulated radiotherapy / 中华放射肿瘤学杂志

Objective To compare the results of three dose verification solutions of esophageal carcinoma IMRT plans. Methods Seven esophageal carcinoma cases were planned with Pinnacle 8.0 h.The MATRIXX and Delta4 were chosen as the two-dimensional dosimetry and three-dimensional dosimetry.IMRT plans and Delta4 phantom plans were also recalculated by Monte Carlo. Gamma values were evaluated for MATRIXX and Delta4 with 3 mm/3% gamma criteria. For the comparison of Pinnacle, Delta4 and Monte gamma maps, the dose distribution in central plane, dose profiles and dose-volume histograms were used to evaluate the agreement. Results The gamma maps comparison show that with 3 mm/3% gamma criteria an over 98% pass ratio was obtained by MATRIXX measurement. A 94. 4% gamma pass ratio whicl.contains 4 fields gamma pass ratio lower than 90%, was obtained by Delta4 measurement. A 97.6% and 99. 8% gamma pass ratio was obtained between the Delta4 measurement and Monte Carlo simulation with 2 mm/2% and 3 mm/3% gamma criteria. The dose distribution in central plane and dose profiles from Pinnacle calculation were almost in agreement with both the Monte Carlo simulation and Delta4 measurement. The DVH plot have slightly differences between Pinnacle and Delta4 measurement as well as Pinnacle and Monte Carlo simulation, but have excellent agreement between Delta4 measurement and Monte Carlo simulation. Conclusions It was shown that all the three methods can be used very efficiently to verify esophageal carcinoma IMRT delivery, Delta4 and Monte Carlo simulation no data missed. The primary advantage of Delta4 is the fact it can measure true 3D dosimetry while Monte Carlo can simulate in patients CT images but not in phantom.

Advances in research on clinical use of electronic portal imaging device(EPID) / 中国癌症杂志

Electronic portal imaging device(EPID) is now been used widely.EPID was initially used for the purpose of checking set-up error.There are two ways to verify set-up errors-on-line and off-line.With advanced knowledge about the dosimetry characteristics of EPID,the use of EPID for dosimetry verification was adapted from the research study to the clinic.EPID plays an important role in quality assurance of radiotherapy accessories including multileaf collimator(MLC)that has been most studied in the past couple of years.This article briefly reviews the clinical use of EPID.