Dosimetry of photon pencil beams is affected by two main detector-related issues: (i) resolution and (ii) water-equivalency. If a detector has poor resolution, the measured dose profile is wider than the real dose profile as a result of a convolution between the real profile and the detector point spread function (PSF). If a detector is not water-equivalent, its response changes with increase in the off-axis distance because of lack of charged particle equilibrium in the lateral direction. Off-axis measurements for three small circular photon fields with diameters of 1.5 mm, 3 mm, and 5 mm are presented in this work. A 10 MV beam from a Clinac-18 linac (Varian, Palo Alto, CA) was used as a radiation source. Dosimetric measurements were carried out with two different dosimeters: a micro parallel-plate ionization chamber (Exradin A14P) and radiochromic film
(Gafchromic
TM
HS). The profiles obtained with the A14P chamber were first corrected using (D wat
/D air
) EGSnrc Monte Carlo-calculated correction factors. These factors were determined for different positions of the ionization chamber in each particular field. Then the corrected profiles were subjected to a 2-D deconvolution to eliminate the blur due to the relatively poor resolution of the A14P chamber. The radiochromic film has an adequate resolution and is also considered water-equivalent. The measured profiles and Monte Carlo simulations with the EGSnrc code were in agreement within
±
3% of the central axis value, confirming the usefulness of our techniques for measuring dose profiles for photon pencil beams on the order of 2 mm diameter.