No. I would check your employment contract or speak to your HR dept. I would be very surprised if you could take additional leave rather than sick leave. They probably give extra time off for hospital/drs appointments or treatment.

I work for an MS related organisation and they didn’t have treatment leave in place until I asked for it and pointed out that they should have a policy in place for people with chronic conditions. I now get my ocrevus treatment and recovery covered by work and it means I don’t have to ration my sick leave