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Objective To investigate the feasibility and plan quality of the image-guided volumetric modulated arc therapy (VMAT) based voluntary deep exhale breath-holding technique in the stereotactic ablative body radiotherapy (SABR) for liver tumors.Methods Fifteen patients with liver tumors were involved in this study.All patients were immobilized with voluntary deep exhale breath hold (vDEBH) combined with real-time position management (RPM) respiratory gating system.Treatment was planned using VMAT with 2 modified partial arc and re-planned using intensity modulated radiation therapy (IMRT) technique for comparison.Dosimetric parameters were calculated for plan quality assessment.Quality assurance studies included absolute dose and multiple planar dose verifications,total monitor units and delivery time analysis.Daily cone beam computed tomography imaging was used to verify the motions.Results There were no significant dosimetric differences between VMAT and conventional IMRT plans (P ＞0.05).Both techniques were able to minimize doses to organs at risk including normal liver,kidneys,spinal cord,and stomach.However,the average monitor units with VMAT were significantly lower 28.1％ than those with IMRT(t =3.064,P ＜0.05).The average beam-on time in VMAT plans was 31.6％ shorter than that in IMRT plans(t =2.278,P ＜ 0.05).Conclusions The utilization of VMAT in the treatment planning of SABR for liver tumors under breath control mode has better dosimetrics.In comparison to conventional IMRT plans,VMAT plans have higher efficiency and feasibility.
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Objective To study the effect of the respiratory amplitude on the dose distribution of volumetric modulated arc therapy (VMAT).Methods Respiratory motion simulation phantom (QUASAR) was used to simulate the respiratory movement from head to toe,and a two-dimensional ionization chamber matrix was used to collect the dose distribution in isocenter with different respiratory amplitude.Verisoft software and absolute dose analysis were used to analyze dose distribution,percentage errors of absolute dose in isocenter,passing rates of radiation field for the data collected,and results were compared to planned dosage.Results The effect on isocenter target dose of respiratory motion was below dose tolerance 5％ (t =-22.614--10.756,P ＜ 0.05).The respiratory movement made the dose on the edge of the target area higher,with fewer hot spots and more cold spots in the target area.As the respiratory amplitude increased,the effect of respiratory movement on the overall dose distribution in the target area was greater.The difference of the whole beam γ passing rate between 6,8,10 mm and stationary state was significant (t =3.095,8.685,14.096,P ＜ 0.05).The difference of target γ passing rate between 8,10 mm and stationary state was significant (t =6.081,9.841,P ＜0.05).Conclusions The respiratory movement could cause the dose transmission errors of VMAT,the error increased with increased range of motion.The actual radiation dose for normal tissues along the direction of respiratory movement on the target edge was higher than what was planned.
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Objective To analyze the biophysical dosimetric characteristics and clinical application ability of VMAT technology for breast cancer post-mastectomy.Methods 28 patients with breast cancer (10 at left side and the other at right side) were planned in different ways respectively.One was two 90 degree arc VMAT plan and the other were 5 beam IMRT plan.The dosimetric parameters of two different plans including tumor control probability (TCP),conformity index(CI),homogeneity index (HI),V95and V110 in target,normal tissue complication probability (NTCP),V5,V20,V30 for ipsilateral lung,NCTP,D V25 for heart,D for the contralateral breast in OARs,MU and times were compared.Results The average tumor control probability (TCP) in VMAT and IMRT group was(96 ±2)％ and (90 ±2)％ (t =-6.28,P ＜ 0.01),respectively.The PTV dose average homogeneity index (HI) of VMAT plans was better than that of IMRT plan (0.15 ±0.04 vs 0.22 ±0.02,t =13.29,P ＜0.01).For cancer position in left side,the mean dose of heart was decreased by 433.24 cGy in the VMAT plan.The NTCP of the hearts in VMAT plans had statistically significant difference compared with IMRT plans [(1.00±0.12)％ vs (1.70±0.13)％,t =2.14,P ＜0.05].For plans of right breast cancer,the average mean dose of hearts in two control group was (3.27 ± 0.26) Gy and (6.00 ± 0.47) Gy (t =9.21,P＜0.01).The total monitor unit (MU) was 530.7 in the VMAT arm and 693.9 in the IMRT arm (t =9.58,P ＜0.01).The treatment time was shorter in VMAT arm (t =8.40,P ＜0.05).Conclusions VMAT plans have better clinical value and more superior biophysical dosimetric characteristics for breast cancer post-mastectomy.
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Objective To dosimetrically compare three delivery techniques of VMAT,IMRT and 3D-CRT in the treatment of accelerated partial breast irradiation (APBI).Methods Twenty patients with T1/2N0M0breast cancer were treated with VMAT.These cases were subsequently re-planned using static gantry IMRT and 3D-CRT technology to evaluate dosimetric differences.Dosimetric parameters including dose conformity index (CI),dose volume histogram (DVH) analysis of normal tissue coverage,dose parameters of PTV and normal tissues were evaluated,the delivery parameters including MU and delivery time were also analyzed.Results The IMRT and VMAT plans provided lower maximum dose,better mean dose and more conformal target dose distributions than the 3D-CRT plans (F =14.86,8.57,18.23,P ＜0.05).The volume of ipsilateral breast receiving 5 Gy for VMAT technique was significantly less than that of3D-CRTor IMRT(F=5.83,P＜0.05).The ipsilateral lung volume receiving 20 Gy (V20),5 Gy(V5) and the 5％ volume dose (D5) of IMRT were superior to those of 3D-CRT and VMAT(F =16.39,3.62,4.81,P ＜ 0.05).The low volume dose distributions of D5 in contralateral lung for IMRT was better than that of VMAT and 3D-CRT(F =3.99,3.43,P ＜ 0.05).The total mean MUs for VMAT,3D-CRT and IMRT were 621.0 ± 111.9,707.3 ± 130.9 and 1161.4 ± 315.6,respectively (F =31.30,P ＜ 0.05).The average machine delivery time was(1.5 ± 0.2)min for the VMAT plans,(7.0 ± 1.6)min for the 3D-CRT plans and (11.5 ± 1.9)min for the IMRT plans.Conclusions VMAT and IMRT techniques offer improved dose conformity as compared with 3D-CRT techniques without increasing dose to the ipsilateral lung.In terms of MU and delivery time,VMAT is more efficient for APBI than conventional 3D-CRT and static beam IMRT.
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Objective To evaluate the sensitivity of patient-specific volumetric-modulated arc therapy (VMAT) quality assurance (QA) to minor multileaf collimator (M LC) positioning errors.Methods Systematic multileaf collimator (MLC) positioning errors (+0.5 mm,+ 1 mm and +2 mm) were introduced into the clinical VMAT patient plans with 2 types of MLC positioning errors:systematic MLC gap width errors and systematic MLC shift errors for 6 cases,including 3 cases with prostatic cancer and 3 cases with nasopharyngeal cancer.The planar dose distributions of the original and modified plans were measured using ArcCheck array.The coincidence between the measured results and the calculated results was evaluated using both absolute distance-to-agreement (AD-DTA) analysis with 3％/3 mm and 2％/2 mm criteria.Results The average passing rate of the 6 original VMAT plans was 96.0％ with the ADDTA criteria of 3％/3 mm which was commonly adopted in clinical practice.For the MLC gap width errors of + 1 mm,+2 mm,and-2 mm and the MLC shift errors of 2 mm,the drop levels in average passing rate with the AD-DTA criteria of 3％/3 mm were 8.8％,15.5％,6.1％ and 7.9％,respectively.The + 2 mm MLC positioning errors and + 1 mm MLC gap width errors could be detected by the patient-specific VMAT QA procedure.The AD-DTA criteria of 2％/2 mm was more sensitive compared with the criteria of 3％/3 mm.Conclusions Patient-specific VMAT QA is not sensitive enough to detect the systematic MLC positioning errors within 1 mm.Additional MLC QA is needed to guarantee the accuracy of VMAT delivery.
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The aim of this study is to evaluate plan quality and dose accuracy for Volumetric Modulated Arc Therapy (VMAT) on the TG-119 and is to investigate the effects on variation of the selectable optimization parameters of VMAT. VMAT treatment planning was implemented on a Varian iX linear accelerator with ARIA record and verify system (Varian Mecical System Palo Alto, CA) and Oncentra MasterPlan treatment planning system (Nucletron BV, Veenendaal, Netherlands). Plan quality and dosimetric accuracy were evaluated by effect of varying a number of arc, gantry spacing and delivery time for the test geometries provided in TG-119. Plan quality for the target and OAR was evaluated by the mean value and the standard deviation of the Dose Volume Histograms (DVHs). The ionization chamber and Delta4PT bi-planar diode array were used for the dose evaluation. For treatment planning evaluation, all structure sets closed to the goals in the case of single arc, except for the C-shape (hard), and all structure sets achieved the goals in the case of dual arc, except for C-shape (hard). For the variation of a number of arc, the simple structure such as a prostate did not have the difference between single arc and dual arc, whereas the complex structure such as a head and neck showed a superior result in the case of dual arc. The dose distribution with gantry spacing of 4degrees was shown better plan quality than the gantry spacing of 6degrees, but was similar results compared with gantry spacing of 2degrees. For the verification of dose accuracy with single arc and dual arc, the mean value of a relative error between measured and calculated value were within 3% and 4% for point dose and confidence limit values, respectively. For the verification on dose accuracy with the gantry intervals of 2degrees, 4degrees and 6degrees, the mean values of relative error were within 3% and 5% for point dose and confidence limit values, respectively. In the verification of dose distribution with Delta4PT bi-planar diode array, gamma passing rate was 98.72+/-1.52% and 98.3+/-1.5% for single arc and dual arc, respectively. The confidence limit values were within 4%. The smaller the gantry spacing, the more accuracy results were shown. In this study, we performed the VMAT QA based on TG-119 procedure, and demonstrated that all structure sets were satisfied with acceptance criteria. And also, the results for the selective optimization variables informed the importance of selection for the suitable variables according to the clinical cases.