Small and non-standard fields are used in modern radiotherapy techniques including Intensity Modulated Radiation Therapy (IMRT), Volumetric Modulated Arc Therapy (VMAT) and Stereotactic Radiosurgery (SRS). Dosimetry measurements in these fields are associated by increased uncertainties due to several factors including volume averaging effects, electron fluence perturbations by the presence of non-water equivalent dosimeters, beam quality changes and partial source occlusion especially in the smaller fields.
Quality assurance procedures are essential in modern radiotherapy techniques to verify and maintain the accuracy of the delivered dose.
After a short review of the experimental dosimetry principles, the available dosimetric systems and their limitations in dosimetry measurements of small and non-standard fields will be discussed.