Dads been diagnosed with DLBCL

My dad’s (67/M) been diagnosed with stage 4 DLBCL. He’s got low platelets and haemoglobin. No bleeding manifestations. We were supposed to start on Chemo today (R EPOCH) But they’re suspecting infection so they might start in a day or two. Doctors recommending switching to R CHOP. He was at 100% function till 2 weeks ago when he suddenly developed low back ache but I’ve seen him deteriorate over the last week( in terms of strength and mobility) Just looking for support and answers to random queries here. Like how long before his platelets stabilise. Funnily enough I’m a doctor and don’t have a lot of answers to these myself.

Update Dad tolerated the second attempt at rituximab well yesterday. His platelets are very low 3k. That’s worrisome for me.