Could Disorientation And Confusion Be Due To Tumors In Brain?

Hello, My father is 61 years old and was recently diagnosed with metastatic lung cancer. It traveled to his brain and had 2 tumors. One tumor was removed surgically and the other was treated with the Gamma Knife radiation...A few months later his MRI showed good results on original tumors but showed 11 new tumors(very small). We did the gamma knife again. He then started chemotherapy for the lung cancer. After his 2nd round(14 days after) he was feeling terrible, no energy and fatigue. We then took him to the emergency room and they said that his hemoglobin was at 5.9. They then admitted him into the hospital and did a blood transfusion. Throughout this process he was having headaches and such. The doctor gave him an IV of dexamethesone(which he has used quite a bit before) but I noticed that dad was not acting normal and seemed very disoriented/confused/not speaking clearly/not understanding. We left the hospital when the doctor said that if he felt ok he was ok with discharging him. Dad wanted to leave and he was prescribed dexamethesone for the headaches. We then went back to the neurologist for an MRI and the MRI showed 8 new spots. I have no idea on exact placement but would his confusion and forgetfulness be from dexamethesone side effects of tumor adema on certain parts of his brain?