Significant trends between the volume of tumor and change in tumor volume after therapy on CE T1-weighted subtraction maps were found for both PFS and OS ( pretreatment volume < 15 cm ( 3 ) , P < .003 ; posttreatment volume < 7.5 cm ( 3 ) , P < .05 ; percentage change in volume > 25 % , P = .004 for PFS and P = .053 for OS ) .