Z Chi

SU-E-T-592: Relationship Between Dose of Distribution and Area of Segment Fields Among Different Intensity-Modulated Radiotherapy Planning in Cervix Cancer

PURPOSE In premise of uninfluenced to dose distribution of tumor target and organ at risk(OAR) in cervical cancer,area of segment fields was changed to increase efficacy and optimize treatment method by designing different plan of intensity modulated radiotherapy(IMRT). METHODS 12 cases of cervical cancer were confirmed in pathology and treated with step and shoot IMRT. Dose of PTV was 50Gy/25fractions. Every patient was designed 9 treatment plans of IMRT by Pinnacle 8.0m planning system,each plan was used with 9 beams of uniform distribution and fixing incidence direction(200°,240°,280°,320°,0°,40°,80°,120°and 160°respectively),and designed for delivery on Elekta Synergy linear accelerator. All plans were optimized with the direct machine parameter optimization(DMPO) algorithm using the same set of optimization objectives. Number of maximum segment field was defined at 80 and minimum MU in each segment was 5MU,and minimal segment area was 2*1cm2 ,2*2cm2 ,3*3cm2 ,4*4cm2 ,5*5cm2 ,6*6cm2 ,7*7cm2 ,8*8cm2 and 9*9cm2 ,respectively.Coverage,homogeneity and conformity of PTV,sparing of OAR, MU and number of segment were compared. RESULTS In this group, mean volume of PTV was 916.8±228.7 cm3 . Compared with the area of minimal segment field increased from 2*1cm2 to 9*9 cm2 ,the number of mean MU was decreased from 1405±170 to 490±47 and the number of segment field was reduced from 76±4 to 39±7 respectively(p<0.05). When the limit of minimal segment area was increased from 2*1cm2 to 7*7 cm2 ,dose distribution of PTV,OAR,CI,HI and V23 were not different (p>0.05),but when the minimal segment area was 8*8 cm2 and 9*9 cm2 ,they were changed compared with 7*7 cm2 and below(p<0.05). CONCLUSION The minimal segment field of IMRT plan designed by Pinnacle 8.0m planning system in cervical carcinoma should be enlarge reasonably and minimal segment area of 7*7 cm2 was recommend.

SU-E-P-48: Evaluation of Intensity Modulated Radiotherapy (IMRT) with Three Different Commercial Planning Systems for the Treatment of Cervical Cancer

Purpose: To investigate the performances of three commercial treatment planning systems (TPS) for intensity modulated radiotherapy (IMRT) optimization regarding cervical cancer. Methods: For twenty cervical cancer patients, three IMRT plans were retrospectively re-planned: one with Pinnacle TPS,one with Oncentra TPS and on with Eclipse TPS. The total prescribed dose was 50.4 Gy delivered for PTV and 58.8 Gy for PTVnd by simultaneous integrated boost technique. The treatments were delivered using the Varian 23EX accelerator. All optimization schemes generated clinically acceptable plans. They were evaluated based on target coverage, homogeneity (HI) and conformity (CI). The organs at risk (OARs) were analyzed according to the percent volume under some doses and the maximum doses. The statistical method of the collected data of variance analysis was used to compare the difference among the quality of plans. Results: IMRT with Eclipse provided significant better HI, CI and all the parameters of PTV. However, the trend was not extension to the PTVnd, it was still significant better at mean dose, D50% and D98%, but plans with Oncentra showed significant better in the hight dosage volume, such as maximum dose and D2%. For the bladder wall, there were not notable difference among three groups, although Pinnacle and Oncentra systems provided a little lower dose sparing at V50Gy of bladder and rectal wall and V40Gy of bladder wall, respectively. V40Gy of rectal wall (p=0.037), small intestine (p=0.001 for V30Gy, p=0.010 for maximum dose) and V50Gy of right-femoral head (p=0.019) from Eclipse plans showed significant better than other groups. Conclusion: All SIB-IMRT plans were clinically acceptable which were generated by three commercial TPSs. The plans with Eclipse system showed advantages over the plans with Oncentra and Pinnacle system in the overwhelming majority of the dose coverage for targets and dose sparing of OARs in cervical cancer.

SU-E-T-740: The Optimization in Segment Numbers for Nasopharyngeal Carcinoma (NPC) Treated by Intensity Modulated

Purpose: In premise of uninfluenced to dose distribution of tumor target and organ at risk(OAR) in Nasopharyngeal carcinoma (NPC),the number of segment was changed to increase efficacy and optimize treatment method by designing different plan of intensity modulated radiotherapy(IMRT). Methods: 10 cases of NPC were confirmed in pathology and treated with step and shoot IMRT. The target volumes were defined: GVT-T (the primary tumor); GVT-N (the metastasis lymph nodes in neck) ; CTV-T and CTV-N (the clinical targets of GVT-T and GTV-N) ; and PTV (incidental lymph nodal region). Dose of GTV/CTV/PTV was 70/64/54Gy for 30 fractions.Every patient was designed 7 treatment plans of IMRT by Pinnacle 8.0m planning system,each plan was used with 9 beams of uniform distribution and fixing incidence direction(200°,240°,280°,320°,0°,40°,80°,120°and 160°respectively),and designed for delivery on Elekta Synergy linear accelerator.All plans were optimized with the direct machine parameter optimization(DMPO) algorithm.Minimum MU in each segment was defined at 4MU,and minimal segment area was 4cm2.Number of maximum segment field was defined at 120,110,100,90,80,70,60, respectively.Coverage and conformity of GTV/CTV/PTV,sparing of OARs(spinal cord, brain, parotids, lens and optic nerves) were compared. Results: In this group,mean volume of GTV(GTV-T+GTV-N),CTV(CTV-T+CTV-N)and PTV were 91.39±71.13cm3,177.27±92.16cm3 and 1028.05±167.03cm3,.respectively. Compared with the number of segment decreased from 120 to 60, there were no difference in MU(p>0.05),and the dose distribution of targets(GTV/CTV/PTV),OARs and CI were not different too(p>0.05).But when the segment number was <60, CI of PTV was changed compared with others(p<0.05). Conclusion: The minimal segment number of IMRT plan designed by Pinnacle 8.0m planning system in NPC should be decreased reasonably and the limit of minimal segment number was recommended by 70.

SU‐E‐T‐643: A Comparison of the DTA and Gamma Index Analysis for IMRT/VMAT Plans in Rectal Carcinoma

PURPOSE To investigate the variability of the global gamma index analysis for IMRT and VMAT plans in Rectal Carcinoma, assess the impact of criterion by 3mm/3% or 4mm/4% gamma index and DTA method. METHODS In ten patients, five-field IMRT plans with fixed gantry positions were compared to two dual arcs VMAT plans, each of them was optimized with Oncentra4.3 planning system, and designed by experienced planners using appropriate similar optimization parameters and dose constraints with a number of iterations to meet the clinical acceptance criteria. Plans were normalized so that at least 95% of PTV would receive the prescription dose 50 Gray in 25 fractions. Measurements of the plan dose distribution were performed and analyzed with Delta4 detector array by 3mm/3% or 4mm/4% gamma index and DTA methods. RESULTS All plans passed in the dose verification, for gamma criterion, an average of 93.13% of the detector points passed the 3 mm/3% for VMAT plans while in IMRT verification it was 96% (p=0.017), the lowest pass-rate were 90.2% for VMAT and 91.2% for IMRT; For 4 mm/4% gamma criterion, an average of 97.15% of the detector points passed of VMAT plans compared to 99.36% of IMRT plans (p=0.052), the lowest pass-rate were 91.5% for VMAT and 97.8% for IMRT. For DTA criterion, an average of 88.35% of the detector points passed of VMAT plans compared to 93.53% of IMRT plans(p=0.002). CONCLUSION For the gamma criterion, VMAT and IMRT techniques can both achieve good dose verification with Delta4 detector array. However for the DTA criterion, it showed significant difference. Different criterions resulted in different pass-rate, further studies are needed to evaluate the methods to verify the dose distribution for VMAT/IMRT plans, so appropriate method can be chosen in clinic in the future.

SU-E-T-608: Performance Comparison of Four Commercial Treatment Planning Systems Applied to Intensity-Modulated Radiotherapy

PURPOSE To compare the performances of four commercial treatment planning systems (TPS) used for the intensity-modulated radiotherapy (IMRT). METHODS Ten patients of nasopharyngeal (4 cases), esophageal (3 cases) and cervical (3 cases) cancer were randomly selected from a 3-month IMRT plan pool at one radiotherapy center. For each patient, four IMRT plans were newly generated by using four commercial TPS (Corvus, Monaco, Pinnacle and Xio), and then verified with Matrixx (two-dimensional array/IBA Company) on Varian23EX accelerator. A pass rate (PR) calculated from the Gamma index by OminiPro IMRT 1.5 software was evaluated at four plan verification standards (1%/1mm, 2%/2mm, 3%/3mm, 4%/4mm and 5%/5mm) for each treatment plan. Overall and multiple pairwise comparisons of PRs were statistically conducted by analysis of covariance (ANOVA) F and LSD tests among four TPSs. RESULTS Overall significant (p>0.05) differences of PRs were found among four TPSs with F test values of 3.8 (p=0.02), 21.1(>0.01), 14.0 (>0.01), 8.3(>0.01) at standards of 1%/1mm to 4%/4mm respectively, except at 5%/5mm standard with 2.6 (p=0.06). All means (standard deviation) of PRs at 3%/3mm of 94.3 ± 3.3 (Corvus), 98.8 ± 0.8 (Monaco), 97.5± 1.7 (Pinnacle), 98.4 ± 1.0 (Xio) were above 90% and met clinical requirement. Multiple pairwise comparisons had not demonstrated a consistent low or high pattern on either TPS. CONCLUSION Matrixx dose verification results show that the validation pass rates of Monaco and Xio plans are relatively higher than those of the other two; Pinnacle plan shows slight higher pass rate than Corvus plan; lowest pass rate was achieved by the Corvus plan among these four kinds of TPS.

SU-E-T-39: Analyses of Plan Quality Using Different Gantry Rotation Time On Volumetric Modulated Arc Therapy in Rectal Carcinoma

PURPOSE To compare plan quality of volumetric modulated arc radiotherapy (VMAT) using different gantry rotation times. METHODS In ten rectal carcinoma patients, plans with different gantry rotation times were designed by Oncentra4.3 planning system, each of them was optimized by experienced planners using almost similar parameters and dose constraints except the different gantry rotation time. The gantry rotation time was increased from 30s to 150s by step of 30(30s, 60s, 90s, 120s, and 150s). Plans (VMAT30s, VMAT60s, VMAT90s, VMAT120s and VMAT150s) were normalized so that at least 95% of PTV would receive the prescription dose 50 Gray in 25 fractions. Dose-volume histograms and isodose distributions were evaluated. Conformity indices (CI), homogeneous indices (HI), monitor units (MUs), delivery time were also compared. RESULTS As the increasing of gantry rotation time, VMAT150s provided comparable organs at risk sparing and better target coverage and conformity than VMAT30s. In the normal tissue such as bladder and femurs, the VMAT plans show almost the same V30 and Dmean for them compared with IMRT plans, meanwhile the conformity indices (CI) was better than IMRT plans(p=0.021). However, there was no significant different among the VMAT60s, VMAT90s, VMAT120s and VMAT150s (p=0.054). VMAT150s increased delivery time and monitor units in plans without improving plan quality compared to VMAT60s, VMAT90s and VMAT120s. CONCLUSION VMAT60s, VMAT90s, VMAT120s and VMAT150s achieved comparable treatment plans in rectal carcinoma. Slower gantry movement in VMAT150s only improves slight improvement than the others.

SU-E-J-248: Comparative Study of Two Image Registration for Image-Guided Radiation Therapy in Esophageal Cancer

PURPOSE Image-guided radiation therapy (IGRT) is one of the major treatment of esophageal cancer. Gray value registration and bone registration are two kinds of image registration, the purpose of this work is to compare which one is more suitable for esophageal cancer patients. METHODS Twenty three esophageal patients were treated by Elekta Synergy, CBCT images were acquired and automatically registered to planning kilovoltage CT scans according to gray value or bone registration. The setup errors were measured in the X, Y and Z axis, respectively. Two kinds of setup errors were analysed by matching T test statistical method. RESULTS Four hundred and five groups of CBCT images were available and the systematic and random setup errors (cm) in X, Y, Z directions were 0.35, 0.63, 0.29 and 0.31, 0.53, 0.21 with gray value registration, while 0.37, 0.64, 0.26 and 0.32, 0.55, 0.20 with bone registration, respectively. Compared with bone registration and gray value registration, the setup errors in X and Z axis have significant differences. In Y axis, both measurement comparison results of T value is 0.256 (P value > 0.05); In X axis, the T value is 5.287(P value < 0.05); In Z axis, the T value is -5.138 (P value < 0.05). CONCLUSION Gray value registration is recommended in image-guided radiotherapy for esophageal cancer and the other thoracic tumors. Manual registration could be applied when it is necessary. Bone registration is more suitable for the head tumor and pelvic tumor department where composed of redundant interconnected and immobile bone tissue.

SU-E-T-580: Comparison of Cervical Carcinoma IMRT Plans From Four Commercial Treatment Planning Systems (TPS)

PURPOSE Different treatment planning systems (TPS) use different treatment optimization and leaf sequencing algorithms. This work compares cervical carcinoma IMRT plans optimized with four commercial TPSs to investigate the plan quality in terms of target conformity and delivery efficiency. METHODS Five cervical carcinoma cases were planned with the Corvus, Monaco, Pinnacle and Xio TPSs by experienced planners using appropriate optimization parameters and dose constraints to meet the clinical acceptance criteria. Plans were normalized for at least 95% of PTV to receive the prescription dose (Dp). Dose-volume histograms and isodose distributions were compared. Other quantities such as Dmin(the minimum dose received by 99% of GTV/PTV), Dmax(the maximum dose received by 1% of GTV/PTV), D100, D95, D90, V110%, V105%, V100% (the volume of GTV/PTV receiving 110%, 105%, 100% of Dp), conformity index(CI), homogeneity index (HI), the volume of receiving 40Gy and 50 Gy to rectum (V40,V50) ; the volume of receiving 30Gy and 50 Gy to bladder (V30,V50) were evaluated. Total segments and MUs were also compared. RESULTS While all plans meet target dose specifications and normal tissue constraints, the maximum GTVCI of Pinnacle plans was up to 0.74 and the minimum of Corvus plans was only 0.21, these four TPSs PTVCI had significant difference. The GTVHI and PTVHI of Pinnacle plans are all very low and show a very good dose distribution. Corvus plans received the higer dose of normal tissue. The Monaco plans require significantly less segments and MUs to deliver than the other plans. CONCLUSION To deliver on a Varian linear-accelerator, the Pinnacle plans show a very good dose distribution. Corvus plans received the higer dose of normal tissue. The Monaco plans have faster beam delivery.

SU‐E‐J‐210: Setup Error Effects of Different Cycles During Treatment Process of Esophageal Cancer Radiotherapy

Purpose: The purpose of this study is to measure setup errors before treatment delivery and observe the change of setup errors throughout the entire course of radiotherapy. Methods: There were 23 esophageal cancer patients were treated by Elekta linear accelerator, a total of 405 CBCT scans were analysed. The systematic and random errors were calculated in the X, Y, Z axis. The date of each group was analysed by SNK statistical method. Results: All data can be divided into 6 groups. It is respectively the first to fifth week and general setup errors. The systematic and random errors (cm) in the X axis were 0.33, 0.32, 0.34, 0.37, 0.45,0.35 and 0.28, 0.28, 0.31, 0.32, 0.34, 0.31. The systematic and random errors (cm) in the Y axis were 0.61, 0.62,0.65, 0.66, 0.61, 0.63 and 0.5, 0.5, 0.53, 0.54,0.46, 0.53. The systematic and random errors (cm) in the Z axis were 0.26, 0.26, 0.29, 0.29, 0.37,0.29 and 0.19, 0.2, 0.21, 0.21, 0.24, 0.21. It has found that the systematic error gradually increased with the increase of treatment time in the X, Z axis, setup errors have no obvious change in the Y axis. No significant correlations were found between each group in the Y axis, P value > 0.05. The fifth week and other groups was found to be significant in the X and Z axis, P values 0.05. Conclusion: The first week or previous setup errors can guide subsequent treatment, but in the end of treatment (after at most 20 times) the treatment plan should be redesigned. Because each treatment situation is different, if allows, the CBCT should be used for each treatment.

SU‐E‐T‐513: Evaluation Output Dose of Electron Beams Based On Monte Carlo

Purpose: The purpose of this study is to investigate the influence factor of output dose for electron beams used in radiotherapy by Monte Carlo technique. Methods: MCTP code was used to calculate a group of output dose from Varian Clinac 23EX. According to the contributions, the calculated output dose was divided into four parts which can help to identify the physical reasons for the variation of output dose, dose from direct particles which was arisen from the machine head directly, dose from indirect particles which was arisen from the collimation devices, including jaws, scrapers and shielding. Results: 1. Appling same cones and same jsw settings but different field inserts, considering the 6 Mev beams, due to direct particles as well as indirect particles the output dose increases from the smallest to the largest field insert. 2. Different cones with same jaw settings and field size, for 6MeV electron beams, the use of a wider cone resulted in a higher output dose, which is mainly because of the direct particles. 3. Same field size with different cones and jaw settings, considering the 18 MeV beams, the wider cone exhibits a reduced output dose, which is attributed to indirect particles, and jaw contributes more than others. 4. Open cone, for the 6 MeV beams the wider cones that also has wider jaw settings showed an increased contribution to the output dose majorly from the indirect particles compared with the smaller cones. Similar trends were seen from the 9 MeV beams, although they were diminished. A reverse Result was indicated for the 18 MeV beams. Conclusion: The variation of output dose depends in a complicated manner on the characteristics of the beams and the modifications that the various cone‐insert combinations introduce to these characteristics.