External beam radiotherapy is commonly used for patients with cancer. While tumor
shrinkage and palliation are frequently achieved, local control and cure remain
elusive for many cancers. With regard to local control, the fundamental problem
is that radiotherapy-induced normal tissue injury limits the dose that can be
delivered to the tumor. While intensity-modulated radiation therapy (IMRT) allows
for the delivery of higher tumor doses and the sparing of proximal critical
structures, multiple competing plans can be generated based on dosimetric and/or
biological constraints that need to be considered/compared. In this work, an IMRT
treatment plan evaluation and ranking tool, based on dosimetric criteria, is
presented. The treatment plan with the highest uncomplicated target conformity
index (TCI+) is ranked at the top. The TCI+ is a dose-volume-based index that
considers both a target conformity index (TCI) and a normal tissue-sparing index
(NTSI). TCI+ is designed to assist in the process of judging the merit of a
clinical treatment plan. To demonstrate the utility of this tool, several
competing lung and prostate IMRT treatment plans are compared. Results show that
the plan with the highest TCI+ values accomplished the competing goals of tumor
coverage and critical structures sparing best, among rival treatment plans for
both treatment sites. The study demonstrates, first, that dose-volume-based
indices, which summarize complex dose distributions through a single index, can
be used to automatically select the optimal plan among competing plans, and
second, that this dose-volume-based index may be appropriate for ranking IMRT
dose distributions.