Figure 1. Forward planning method for modified dynamic conformal arcs.

The images show target volume definition consisting of gross tumor volume (GTV) and planning target volume (PTV) (A); PTV covering by prescribed isodose surface (IDS) in general dynamic conformal arcs (DCA) (B); modified GTV (mGTV) compared to the original GTV (C); and PTV covering by prescribed IDS in modified DCA (mDCA) (D).

(B) In this case, when the original GTV is directly used as an object volume for leaf adaptation, the dose conformity of the PTV with the prescribed IDS (dashed line) has room for improvement, that is, over-coverage. (C) To improve the dose conformity, a copy of the original GTV is used to generate a surrogate object for leaf adaptation to be deformed in a desired shape, namely, the mGTV, and then modified according to the over- and/or under-coverage of the PTV with the initial prescribed IDS. (D) When an appropriately modified mGTV is used for leaf adaptation, the dose conformity of the PTV with the prescribed IDS is improved.