IGRT: How and When
This chapter gives an overview of IGRT techniques employed in prostate cancer. The described techniques include portal imaging using Megavoltage sources (porta films and electronic portal imaging devices), Kilovoltage radiographs (room-based or gantry-based systems, transabdominal ultrasound, and in-room CTs. An ideal IGRT system would allow for daily prostate imaging without possible introduction of errors due to image acquisition itself, it would do so within a reasonable time frame, without the necessity for implanted radio-opaque markers and preferentially without exposing the patient to radiation. A solution that combines all these features is inexistent so far. For the existing IGRT techniques, there is a considerable lack of data whether they lead to a reduced acute and chronic toxicity profile in comparison with the non-IGRT approach, or if they are associated with an improved local control. Nevertheless, given the increasingly higher doses and smaller treatment margins utilized, combined with the trend to hypofractionate radiation therapy, daily IGRT for prostate cancer has become a necessity as an accurate and precise way of delivering the intended dose to the PTV and the OARs. The problem of interfractional prostate movement and the possibility of setup errors are optimally accounted for.
KeywordsPlanning Target Volume Transabdominal Ultrasound Electronic Portal Imaging Device Hypofractionate Radiation Therapy Planning Target Volume Margin
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