[Measurements of dose distribution in small fields of 10 MV X-rays]

Dose distribution measurement in small fields include: 1. Field size factor, 2. Percentage depth dose, 3. Isodose curves charts, 4. Tissue-phantom ratio, and 5. Penumbra width. Field size factor was measured by using different detectors and it was found that the dimension of detector must be less than half of the field size to avoid under-estimation. If a 0.6 cc cylindrical ion chamber was used for small fields measurement, it would under-estimate the field size factor by 19.7% for a 2x2 cm2 field. The percentage depth dose and the tissue-phantom ratio increased with increasing the field size. The penumbra width increased with increasing the field size which was larger for a square field than the corresponding circular field by less than 1 mm.