Monte Carlo simulation is the state-of-the-art for the study of radiation transport problems in radiotherapy, in particular for modeling medical linear accelerators (linacs). PRIMO is a software system based on the Monte Carlo method that simulates linacs and absorbed dose distributions in external beam radiotherapy patients. The software is being used in the clinical practice, in dosimetry, and for educational and research applications. The aim of this workshop was to gather the advances in the aforementioned areas that have been achieved using PRIMO.