  The purpose of this study was to use various dosimetrical indices to
determine the best IMRT modality technique for treating patients with prostate
cancer. Ten patients with prostate cancer were included in this study.
Intensity modulated radiation therapy plans were designed to include different
modalities, including the linac step and shoot, Tomotherapy, RapidArc, and
Proton systems. Various dosimetrical indices, like the prescription isodose to
target volume (PITV) ratio, conformity index (CI), homogeneity index (HI),
target coverage index (TCI), modified dose homogeneity index (MHI),
conformation number (CN), critical organ scoring index (COSI), and quality
factor (QF) were determined to compare the different treatment plans.
Biological indices such as the generalized equivalent uniform dose (gEUD),
based tumor control probability (TCP), and normal tissue complication
probability (NTCP) were also calculated and used to compare the treatment
plans. The RapidArc plan attained better PTV coverage, as evidenced by its
superior PITV, CI, TCI, MHI, and CN values. Regarding OARs, proton therapy
exhibited superior dose sparing for the rectum and bowel in low dose volumes,
whereas the Tomotherapy and RapidArc plans achieved better dose sparing in high
dose volumes. The QF scores showed no significant difference among these plans
(p=0.701). The average TCPs for prostate tumors in the RapidArc, Linac, and
Proton plans were higher than the average TCP for Tomotherapy (98.79%, 98.76%,
and 98.75% vs. 98.70%, respectively). Regarding the rectum NTCP, RapidArc
showed the most favorable result (0.09%), whereas Linac resulted in the best
bladder NTCP (0.08%).
