Abstract:

Objective A new method of 3⁃dimensional conformal planning design is proposed and itsdosimetric advantages in stereotactic body radiotherapy（SBRT）are evaluated. Methods A retrospective studywas conducted in 30 patients treated with SBRT technology. The conventional 3⁃dimensional conformal planning（CCP） and the deformed target 3⁃dimensional conformal planning （DCP） were designed respectively. Theprescription dose of each plan is defined as the planning target volume（PTV）50 Gy/5 fractions，and the PTVcoverage was required to be ＞95% for prescription dose. The plans were compared by assessing the conformityindex（CI），dose gradient（DG），approximate minimum dose of PTV（D99%），maximum dose at 2 cm from PTV inany direction（D2 cm）and monitor unit（MU）. Results Both groups of plans satisfied all clinical requirements.CI，DG，D99%，and D2 cm in the group DCP were significantly improved（t = 4.55，5.95，4.37，3.86，P < 0.05）andMU decreased（t = 2.82，P < 0.05）compared with the group CCP. Conclusions DCP has obvious dosimetricadvantages，and reduces the number of MU while shortening the treatment time. It can be promoted as a new planningdesign method.

Key words: SBRT, 3?dimensional conformal planning, dose gradient, conformity index