R1 provides thermal stability to the BJT. It helps to reduce the leakage current due to minority carriers at elevated temperatures.
Although it can be removed, its good to use it.
If the circuit is always in the active region then R1 serves no purpose and can be removed. Any transistor base leakage current will be absorbed by the op amp (rail-rail) output.
to improve precision i recommend to use a mosfet instead of BJT,
With a MOSFET there is about no gate current. But with BJT you have an bas current.
The Feedback is with R49. R49 sees load current + base current. So base current causes error.
Additionally the R1 causes current through R49 giving additional errors.
To improve stability, i´d replace the R1 with a c (best a foil c). An additional resistor between this C and R49 may further improve stability.
The OPAMP needs to be unity gain stable.
PS. look for 4..20mA constant current circuits.
I'm with Klaus on this one, a Mosfet will yield more accurate results.
Although the current is low, and therefore the Mosfet's channel does not require too much enhancement, I would still use a logic level Mosfet.
The circuit will work equally well with or without R1.When R1 will work?And how it works?