Biological and dosimetric effect of the number of beams for radiotherapy plans of breast cancer patients. Z. Mansour1, Ehab M. Attalla 2, Ibrahim A. Awad 3 M.I. Abdel Hamid 4 and A. Sarhan 5

Aim: To evaluate the biologic differences in treatment plans, the dosimetric outcome with different number of beams on 3D conformal radiotherapy for breast cancer patients as well as evaluate the outcome of plans with more number of fields compared with less number of fields for irradiation of breast cancer patients then determine the optimum plan through dosimetric and biological parameters. The study included 13 of the female breast cancer patients who were irradiated, after surgery. The tumor and the organs at risk were delineated. Then for every patient two plans of increasing and decreasing the number of beams were done. The DVH of each plan was analyzed based on the calculating the TCP and NTCP by MATLAB and calculating the dosemetrical parameters such as CI and HI. Results: All the results representing the following parameters V105% , V95% ,V110%, D mean , D max CI, HI and D5% are the same in both more and less number of beams . All the results also showed that the average TCP% of PTV of the plans that contains more numbers of beams is 54.27 % while in other plans 54.65%. Mean± SEM of group (a) is 54.27 ± 1.121 while in group b is 54.65 ± 0.9297 N=13. This show that there is no significance in the group (a) (increasing numbers of beams) versus group (b) (less numbers of beam) means that the tumor control by increasing the number of beams is nearly the same as decreasing the number, b value = ( 0.7964). This occurred in the rest of the parametersRadio oncologist and medical physicist must make a decision about treatment though the accurate values of TCP and NTCP and this achieved via testing plans by MATLAP program not by the number of beams.