EPH 1 International Journal of Health Sciences and Nursing VOL 1 ISSUE 2 December 2015 Paper 1 Impact of segments number reduction in IMRT planning M. ElGohary 1 , G. Kamal 2 , M. Galal 3 , M.Hosini 4 * 1. Biophysics department, Faculty of science, AlAzhar University 2. Biophysics department, Faculty of science, AlAzhar University (Girls), Cairo, Egypt 3. Radiation oncology department (NEMROK), Faculty of Medicine, Cairo University, Cairo, Egypt 4. Radiation oncology department, Faculty of Medicine, Zagazig University, Zagazig, Egypt * mhosini@ksu.edu.sa Purpose: To investigate the planning and dosimetric advantages of direct aperture optimization (DAO) over beamlet optimization in IMRT treatment of head and neck (H/N) and prostate cancers. Materials and methods: a brain metastatic case with multiple lesions, five head and neck, as well as five prostate patients were planned using the beamlet optimizer in Elekta-Xio © ver 4.6 IMRT treatment planning system. Based on our experience in beamlet IMRT optimization, PTVs in brain were prescribed to 66Gy using 5 fields, PTVs in H/N plans were prescribed to 70 Gy delivered by 7 fields, and prostate PTVs were prescribed to 76 Gy using nine fields. In all plans, fields were set to be equally spaced. All cases were re-planed using Direct Aperture optimizer (DAO) in Prowess Panther © ver 5.01 IMRT planning system at same configurations and dose constraints. Plans were evaluated according to ICRU criteria, number of segments, number of monitor units and planning time. Results: In brain case, beamlet optimization was better than DAO for both GTVs and PTVs in 95% isodose coverage, and the hot area was about 7% more in beamlet plan than DAO plan. For OAR, results showed an improvement in OAR sparing up to more than 35% in rt. eye, lt. eye, rt. optic nerve and lt. optic nerve when using DAO for planning, while optic chiasma sparing was about 20% also in beamlet optimizer plan. For H/N plans, the near maximum dose (D2) and the dose that covers 95% (D95) of PTV has improved by 4% in DAO. For organs at risk (OAR), DAO reduced the volume covered by 30% (V30) inspinal cord, right parotid, and left parotid by 60%, 54%, and 53% respectively. This considerable dosimetric quality improvement achieved using 25% less planning time and lower number of segments and monitor units by 46% and 51% respectively. In DAO prostate plans, Both D2 and D95 for the PTV wereimproved by only 2%. The V30 of right femur, left femur and bladder were improved by 35%, 15% and 3% respectively. On the contrary, the rectum V30 got even worse by 9%. However, number of monitor units, and number of segments decreased by 20% and 25% respectively. Moreover the planning time reduced significantly too. Conclusion: DAO introduces considerable advantages over beamlet optimization for different sites of cancer, in regards to organ at risk sparing. While no significant improvement occurred in the PTV ICRU reporting dose. Key words:- DAO, IMRT, Optimization, Prostate, head and neck