Incorporation of limiting dose for radiotherapy treatment planning: The limiting dose from the above "Dose Response Analysis" will be used for IMRT re-planning considering the functionally critical brain regions. The optimization goal is to minimize the dose to functionally critical brain regions while maintaining similar PTV (planning target volume) coverage and keeping dose to the critical structures within accepted tolerance. DVHs of the functionally critical brain regions, PTV and all other critical structures will be compared for both treatment plans with and without considering the functionally critical brain regions. A Wilcoxon matched pair signed rank test will be performed to compare the plans in terms of calculated NTCP of critical organs. The McNemar test will be used to compare plans with and without dose constraints of functional areas in terms of yield rate (i.e., the proportion of patients for whom the IMRT plan was successfully devised).