“…Furthermore, radiochromic films (Gafchromic EBT3, Ashland) were exposed to selected fields, scanned (Epson 1680 pro), and evaluated using ImageJ. 13 Penumbra width (80%-20%, with 100% defined as max dose for fields <50 × 50 mm 2 , and 100% defined as two times the dose at the penumbra inflection point for field sizes >50 × 50 mm 2 , to account for inhomogeneity in the plateau region caused by the absence of a flattening filter 14 ) was derived from water tank commissioning data (SAD 800 mm, depth 15 mm) and assessed as a function of field size (7.6×7.5 to 97.6×97.5 mm 2 ). In addition, the dependence of penumbra width on off-axis position was determined from exposed EBT3 films (delivering elongated fields of 22.6×97.5 mm 2 for X and 110 × 22.5 mm 2 for Y , SAD 800 mm, depth 50 mm).…”