[en] Highlights: • Normal tissue conformal avoidance can be achieved through prostate immobilization. • A 150 cm³ air-inflated endorectal balloon renders prostate motion mitigation. • Uneventful planned treatment delivery during the first 15 min. • Gradually increasing probability of target motion > 2 mm after 15 min. • Quantitated setup accuracy and target motion corroborate tight PTV margins. To quantitate the accuracy, reproducibility and prostate motion mitigation efficacy rendered by a target immobilization method used in an intermediate-risk prostate cancer dose-escalated 5×9Gy SBRT study.