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

Abstract

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*8cm2and 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 V2 3 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.

Implementation of Constant Dose Rate and Constant Angular Spacing Intensity-modulated Arc Therapy for Cervical Cancer by Using a Conventional Linear Accelerator

“…IMRT plans were designed using seven gantry angles, i.e., 257°, 308°, 0°, 51°, 103°, 154°, and 206°. The optimization parameters adopted were recommended by Qiu et al .,[ 12 ] i.e., the minimum segment area of 7 cm × 7 cm, the minimum segment MU of 5, and the maximum number of segments of <55. All the CDR-CAS-IMAT treatment plans consisted of only a single arc with 358° gantry rotation.…”