3). selleck chemicals These sectors were created by dividing the CTV (for volumetric analysis) or PTV (for dosimetric analysis) into superior, midgland, and inferior sections, respectively (0.3 cm, 0.4 cm, and 0.3 cm of the base–apex length of the CTV

or PTV), which were then partitioned into posterior, anterior, or lateral portions of the gland. The motivation behind such a division was to identify whether there was a region-specific variability in the results, given that there may be different consequences to treatment from segmentation errors in different regions of the implantation volume [20] and [21]. For example, overcontouring the posterior region of the gland may increase the risk of severe rectal complications. A similar sector-based study was performed by Bice et al. (22) for a more localized dose–volume histogram analysis of postimplant dose distributions. The four volumetric comparison measures, which we described in our earlier reports (17) are summarized in Table 1 and illustrated in Fig. 4. For evaluation of the dose distribution, the following parameters were computed. The volume of the PTV receiving 100% or more of

the prescribed dose, was computed for the nine sectors of the PTV and the whole PTV. These values were calculated by the VariSeed software. To characterize extraprostatic dose, the external index (EI) (24), defined in Eq. 5, measures RG7422 ic50 the amount of tissue external to the PTV that receives doses of 150% or more of the prescribed dose. equation(5) EI150=(isoV150−V150)/V isoV150 is the total volume of the 150% isodose surface, V150 is the

volume of the PTV receiving 150% or more of the prescribed dose (the volume of the intersection between the isoV150 and PTV surfaces) and V is the volume of the PTV. Ideally, EI150 is zero. A 3D extension of the conformity index (CI) defined by Otto and Clark (25) is used, which measures BCKDHA both the undercoverage of the target as well as the overtreatment of the normal tissues. equation(6) CI100%=100×volume of region−(volume of region underdose+volume of healthy tissue dose)volume of region In Eq. 6, volume of region is the volume of the PTV (or one of its nine sectors), volume of region underdose is the volume of the PTV (or one of its nine sectors) that is receiving less than 100% of the prescribed dose, and volume of healthy tissue dose is the volume of the region outside the PTV (or one of its nine sectors) that is receiving 100% or more of the prescribed dose. A maximum conformity value of 1 shows perfect conformity of the 100% isodose to the region being observed. We would like to note that although the above-mentioned dose parameters are computed to evaluate the TES method, our planning process places quantitative constraints only on the whole prostate and whole PTV and CTV V100 and V150.