In addition to the two dosimeters you have mentioned, you can also use subminiature TLDs, OSL(photo luminescent) dosimeters, MOSFET dosimeters, diamond dosimeters, plastic scintillators(active type), dosimeters used in CR and DR, etc. One obvious requirement  is that they should be of mm size. The water phantom dosimetry also called Radiation Field Analyzer systems provided with miniature ion chamber or silicon diodes(pin diodes are better) can be used for on-line acquisition of  Dosimetric data. Several companies are marketing these systems. There are many publications available which one manufacturer also provides on request. Pl see in this ResearchGate website two of my publications relating to this topic. The best way depends on the resources available with you (related instruments/equipments). For manual measurements, you may use the MOSFET since the associated measurement(threshold voltage changes) may be obtained with an inexpensive reader. PIN diodes requires a sensitive electrometer. OSL readers may be cheaper than TLD readers. Small plastic scintillators require a light guide with an associated Photomultiplier tube. Pl note the Linacs have extremely short focus giving rise to a short penumbra. Beam profile measurement in water with a PIN diode will enable to measure the sharp fall-off at the edges of the beam 

After sending the above answer, I happened to come across an ad in the current Journal of Medical Physics of a 1mm spatial resolution water-equivalent Extradin W1 scintillator-based instrument for small field dosimetry,  marketed by Standard Imaging company. The instrument has built-in automatic correction for Cherenkov Effect in the light guide.

I hope this instrument may be ideal for your work. 

I believe that by computational method is the best way, but if you need anything experimental dosimeters TDLs and OSLs are a good alternative for the small size compared to ionization chambers.

radiochromic films