Dad has Grade 4 Glioblastoma

Hi my dad was told on March 9th he had a large mass on his brain. One week later they said its in both hemispheres too deep to safely try a resection. He is 75 and wont ask about prognosis. Since then had a biopsy and started 3 weeks of radiotherapy and 21 days of Temozolomide, he won’t ask any questions - I think I need to know how quick this thing could take him? 

He’s thankfully staying positive but i’m struggling to know how to give him best help. He lives with us at home.