AbstractID: 7559 Title: Comparison Study of IMRT Treatment with 3D-RTP in Treating Ethmoid Cancer
The step-and-shoot IMRT treatment technique is implemented to treat various cancer sites in our department using Varian 2100CD with
dynamic MLCs. Comparison studies of IMRT vs. 3D-RTP were carried out. Here, the case of ethmoid cancer was selected for presentation.
In 3D planning, different beam angles were carefully evaluated in order to provide optimal tumor coverage and critical organ sparing. Five
non-coplanar fields of AP, RPO, LPO, IAO, and SAO were used, with MLC and wedge in each beam to provide an optimal plan. For
prescribed dose of 180 cGy per fraction, the maximal dose to the lens is of 19 cGy and mean is 17 cGy. The same five beams were also
chosen for IMRT optimization. The region of interests of lens, eye, optical nerve, chiasm, and brainstem are all entered as objectives in
optimization. The intensity modulated beams resulted in lower lens dose as compared with 3D-RTP: maximal dose of 10 cGy and mean dose
of 5 cGy. The intensity pattern of each beam was then converted to dynamic MLC segments for beam delivery. After conversion, the lens
has a maximal dose of 16 cGy and mean of 8 cGy. The conformity of the PTV was reduced due to the physical limitations of the existing 80leaf configuration, where 1-cm leaf width is used.
The above study demonstrated that while using more treatment fields in 3D-RTP may improve the tumor coverage and critical organ sparing,
IMRT is clearly superior in terms of organ sparing, as compared with 3D-RTP.