Dosimetric and radiobiological comparison of different treatment plans which are using at applications of intensity modulated radiation therapy (IMRT) for prostate cancer

Objective: The starting point of this study, investigation of radiobiological and dosimetric results of 7 field and 9 field IMRT plans for prostate cancer in order to show differences between them. Method: The IMRT treatment plans for 11 prostate cancer patients that previously treated were created with 7 and 9 fields for PTV46, PTV56 and PTV74 target structures along three phases by 6 MV photon energy. The prescribed dose was determined 74 Gy. Targets and OARs contours are created under the guidance of RTOG. The dosimetric values of targets' such as Dmak, Dmin etc. are obtained and HI and CI parameters calculated from DVH datas. EUD, TCP and NTCP radiobiological metrics are calculated using related parameters in gEUD base with MATLAB software. Results: It should be noted that the IMRT plans with 7 and 9 fields isn't established supremacy over each other regarding targets. It was appeared that PTV74 CI values of 7 fields are more close to 1 (p<0,05). Also PTV56 and PTV74 HI values of 9 fields are lower than 7 fields' (p<0,05). There were no significant difference appeared between two plan types related to target structures. It was shown that V50 of rectum was provided objective criteria for both of two plan types and NTCP values of 9 field plans are more superior than 7 fields' (p<0,05). Standard deviation of rectum EUD values which were calculated according to selected optimum plan with 7 fields are lower than 9 fields'. Lower NTCP values of bladder obtained for 7 field plans (p<0,05). There were no significant difference coincided for femour heads' NTCP values. Conclusion: Generally there is significant difference between two IMRT plan types related to target structures. In the main, the IMRT plans with 7 fields had much more adequate results related to rectum and bladder. Radiobiological comparison of different treatment plans would be provided more valuable clinical outcome. Key words: prostate, IMRT, EUD, TCP, NTCP.