Image guided radiation therapy (IGRT) has become the standard of care in radiotherapy. Modern day IGRT, first introduced in late 1990s, has evolved over the past two decades by introduction of new techniques, often involving multiple modalities. During a daily treatment fraction, the patient may be imaged more than once in order to position the patient and to confirm repositioning if necessary. Image guidance is also employed for intrafraction motion management and adaptive radiotherapy. These imaging procedures, if x ray based, expose additional radiation dose to healthy tissues outside radiotherapy targets. Therefore, understanding the magnitude of this extra dose and the risks associated with these doses are important. Both AAPM TG-75 and TG-180 reports were developed to address the concerns and to provide guidelines and strategies for minimizing imaging dose while improving treatment delivery.
This lecture reviews advances in image guidance during the radiotherapy procedures with emphasis on x ray-based modalities. The evolution of IGRT and currently available IGRT tools and techniques will be reviewed with emphasis on x ray-based ones. Newer specialty radiation delivery units like proton therapy often employ customizable IGRT devices that may need attention, especially with regard to radiation dose. These devices will also be reviewed during this session. The session also provides an overview of the AAPM TG-180 report as well as the recommendations of the report on managing image guidance doses.
The session further discusses techniques for reducing the imaging dose and explains the recommended threshold beyond which imaging dose should be considered in the treatment planning process. It addresses the techniques and methods that can be used in clinical practice to estimate imaging dose resulting from different kV and MV imaging procedures. It explains two recommended methods of estimating patient imaging dose during treatment planning. The lecture also presents a perspective view of radiation dose to healthy tissues resulting from the sources such as leakage, out-of-field dose, etc. and from image-guidance procedures. While the commonly adopted radiation protection safety philosophy of As Low As Reasonably Achievable (ALARA) is applicable to imaging guidance dose, minimizing imaging doses by employing reasonable methods should not compromise target localization. Therefore, balancing ALARA principles with the requirement for effective target localization requires that imaging dose be managed based on the consideration of weighing risks and benefits to the patient.
1. Learn the latest advances in IGRT modalities and techniques
2. Learn the applications of IGRT in specialty delivery units
3. Learn the magnitude of typical organ doses resulting from different imaging procedures and modalities
4. Learn available techniques to reduce the imaging dose in daily clinical practice and how to account for kV and MV imaging dose.
5. Develop a perspective view of radiation to sensitive organs between imaging dose and unintended dose from therapeutic beams.
6. Understand weighing the risks and benefits of imaging guidance for effective target localization.
Not Applicable / None Entered.
Not Applicable / None Entered.