I had the same treatment protocol as you mention, but many more than 7 rounds of high dose MTX. For the first several months, I want to say I was in the hospital every 2 weeks for four to five days depending how quickly the MTX passed. After doing every other week, I did every four weeks. The whole thing went on for eleven months. I was 55 when I was diagnosed, so slightly younger. I guess the biggest thing is that I was tired all the time. I think every medication I took either gave me constipation or diarrhea. They discussed a stem cell initially, but I responded really well to treatment. It was confirmed by a few different docs that it was not required, and they wanted stem cell as a back up in the event of reoccurrence. As a former patient, I recommend that you are there for him and be positive. The best thing I ever heard from Mayo was that this CNS NHL is curable, so I always knew in the back of my head I’d make it through despite how miserable I may have been on any particular day. Let him do for himself as much as he can as well. There is a lot I don’t remember because I was so very sick. My husband filled in many blanks for me. As a Cancer patient, i just wanted to feel normal and have people treat me normally and not pity me. I also felt guilty because my husband had to give up part of his life to help me. He never said a word about it, so it was a burden I placed upon myself. I know it was unfounded. I hit my five year mark in 2021. Good luck to you and your dad. Feel free to be in touch if you want to talk about anything more specifically.

The stem cell transplant is not used for patients above 65 and it depends on the physical condition.
My wife had an HDM-RVP treatment: 8 times for 4 days in hospital with 2 weeks in between the treatments . The methotrexate infusion lasts only 2 hours but the flushing takes 3 days to bring down the methotrexate level below 80.
(High dose Methotrexate, Rituximab, vincristine, procarbazine)
She was given anti nausea medication (Zofran) but did not need it.
After 4 treatments a brain MRI was taken and it showed a complete response to the therapy. No lesions visible anymore.
She then was given a break of 1 month and thereafter started the outpatient consolidation therapy ( to prevent short term relaps) with cytarabine: 2 infusions (2hours)with 2 weeks in between them. Steroids are added to reduce the neurotoxicity. Every 3 days a blood draw is taken to monitor blood counts and platelets. My wife had to get a platelet transfusion once because levels had dropped to very low levels after a week of the first cytarabine infusion(risk of internal bleeding). The treatment had a negative impact on motor skills/ gait-balance). Fall risk!
The treatment is followed up by ‘expectant observation’ with contrast MRI every 2 months with probably reduced frequency after a year without recurrence.

There is not much information on progression free survival. I saw randomized trial data which indicated 5 years on average.
Oncologists are careful using the term cured.