Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Biophysics

Purpose of work: to study the best planning techniques for post-operative breast radiotherapy, either forward intensity modulated radiation therapy (FIMRT), or inverse intensity modulated radiation therapy (I-IMRT), and volumetric modulated arc therapy (VMAT). Another strategy is to check the dosimetric difference between using 6 or 10 MV energies for both I-IMRT and VMAT. The present study aims to check the impact of shape parameters on organs at risk doses. Materials and Methods: In the present study, four different inverse plans and one forward plan of randomly selected twenty left breast cancer patients were compared dosimetrically. Plans were done on Monaco's (5.1) treatment planning system, and data analyses were accomplished using IBM SPSS (20) data editor software. Results: Inverse planning achieved superior target coverage over forward planning (p-value =0.001,0.07) by about 2-4 % compared to forward planning. Conformity index (p-value <0.05) also improved 0.7 to 0.85 maintaining adequate homogeneity index (p-value = 0.461, 0.138). Left lung and heart high dose levels decreased using I-IMRT, VMAT (p-value <0.05) at the cost of increasing volume irradiated by low doses (p-value <0.05). For contralateral lung, VMAT increased scattered dose over F-IMRT (p< 0.05), but I-IMRT showed a non-significant increase of V5 Gy (p-value = 0.14). For contralateral breast, both I-IMRT and VMAT increased absorbed dose over F-IMRT (P < 0.05). Using high energy for inverse planning increases scattered low dose to organs at risk, and this effect becomes more significant for healthy tissues away from the target than that near it

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