John,
My job is a data scientist/programmer, so I'm used to collecting all available data on systems I manage and analysing it. I turned that on myself as the subject to be analysed.
I've kept a very detailed records, in different forms, but all as Excel spreadsheets...
A very detailed diary which records everything relevant on a day-to-day basis. It now gets an entry less than once a week as I'm close to finishing treatment and nothing much is changing, although that might increase as I get my testosterone back during puberty Mk II. During radiotherapy treatment, there's at least one entry a day, and sometimes more. It also records:
All my clinician meetings, who was there, what the discussion and outcome was;
All changes in medication, and for hormone therapy jabs I record injection site, batch no, expiry date (I was doing my own HT jabs, and I pass that data back to my GP to record in my patient records, just as they normally would).
PSA and testosterone test levels.
This covers almost 2½ years and runs to 12 A4 sheets when printed out.
A summary version of above with just the clinical records. It did get given to clinicians a few times, and I can see it made its way into my hospital records. My consultant would always ask me things like how long I'd been on hormone therapy, what my PSA was, etc, because he knew I could find it faster than he could in the hospital records.
3 A4 sheets when printed out.
Detailed body weight taken daily using body composition scales, so I can also see how my muscle and fat have been impacted by hormone therapy. Didn't start until a month after starting HT. I actually measured and recorded everything about me I could which might be impacted by the treatments. This included blood pressure (patchy record), blood glucose (monthly), penis size, testicle size, breast size. Some things I didn't know about at the start, and added later, such as urine peak flow rate and bladder capacity.
A few clinicians have have looked through my data and found it amazing, including England's top urologist at a conference. He said "If you were my patient, I'd be asking for a presentation - we never get this sort of detail back from patients". My consultant radiographer was very interested in the effect of brachytherapy on sexual function - he said he's often asked by patients, but there's no data they can refer to. At my 12 month review, I graphed the incidence of rectal bleeding I have (very minor) for my consultant - that's worth a thousand words and more precisely conveys the situation, so I get better guidance back.
I've used the data quite extensively in presentations that I do to patients, and for answering patient questions. I mentioned one here quite recently where a patient asked some questions after a talk including how long did it take to lose my body hair on hormone therapy, and I could look it up and say I first noticed it at 17 weeks (and it's still continuing 2 years later). There's no way I'd remember that 2 years later if I hadn't recorded it.
Another table I keep is a giant spreadsheet with all my blood test results, so it's easy to see how any particular one changes over time. Often gave a copy to a clinician, as they found it so useful.
For me, I'm pretty sure it was a psychological factor too, of me being in charge of my disease, and something that helped me mentally to handle it.
So go for it!
By the way, one thing I wished I asked for was a testosterone test before I started hormone treatment, so I know what my normal testosterone level is, and thus how much of it I get back afterwards. I will never know now.