An on-line replanning scheme for interfractional variationsa…
Ergun E. Ahunbay, Cheng Peng, and Guang-Pei Chen
Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
Sreeram Narayanan
Prowess, Inc., Concord, California, 94520
Cedric Yu
Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore,
Maryland, 21201
Colleen Lawton and X. Allen Lib
Department of Radiation Oncology, Medical College of Wisconsin, Milwaukee, Wisconsin 53226
Received 8 February 2008; revised 2 June 2008; accepted for publication 4 June 2008;
published 16 July 2008
Ability of online adaptive replanning is desirable to correct for interfraction anatomic changes. A
full-scope replanning/reoptimization with the current planning techniques takes too long to be
practical. A novel online replanning strategy to correct for interfraction anatomic changes in real
time is presented. The scheme consists of three steps: 1 rapidly delineating targets and organs at
risk on the computed tomography of the day by modifying original planning contours using robust
tools in a semiautomatic manner, 2 online segment aperture morphing SAM adjusting beam/
segment apertures by applying the spatial relationship between the planning target contour and the
apertures to the new target contour, and 3 performing segment weight optimization SWO for the
new apertures if necessary. The entire scheme was tested for direct-aperture-based IMRT on rep-
resentative prostate and abdomen cases. Dose volume histograms obtained with the online scheme
are practically equivalent to those obtained with full-scope reoptimization. For the days of small to
moderate organ deformations, only the SAM is necessary, while for the large deformation days,
both SAM and SWO are required to adequately account for the deformation. Both the SAM and
SWO programs can be completed within 1 min, and the overall process can be completed within 10
min. The proposed SAM-SWO scheme is practically comparable to full-scope reoptimiza