TU-E-213CD-01: Image Guided Adaptive Brachytherapy for Cervical Cancer

Image-guidance plays an important role in modern radiation therapy, predominantly in external beam planning and delivery. In contrast, brachytherapy is still largely based on systems originally developed in the early 20th century. In recent years, with the advent of high/pulsed dose rate (HDR/PDR) afterloading technology, advanced treatment planning systems and CT and MRI compatible applicators, image-guided adaptive brachytherapy treatments are now achievable. With image guidance, the target can be delineated more precisely, resulting in delivering more controlled doses of radiation to the target while sparing surrounding healthy tissue. GEC-ESTRO guidelines are crucial for implementing robust and standardized image guided adaptive brachytherapy (IGABT). They rely on MRI-guided planning for cervical cancer. MRI can be performed for each brachytherapy (BT) fraction to adaptively plan and deliver the desired radiation dose with less toxicity to surrounding tissues. MR imaging has its advantages, but also challenges and limitations (image artifacts and distortion related to magnetic nonlinearity, MR sequence selection, accuracy of 3D applicator reconstruction) that need addressed. Moreover, MRI technology is not readily available in most Radiation Oncology departments, making its implementation hard. In such settings, CT or US-based planning can be used despite lacking the desired soft tissue resolution to accurately depict the target. Hybrid approaches have been proposed, where a first BT fraction is planed based on MRI, and subsequent fractions are performed with CT-guidance. Moreover, new intracavitary/interstitial applicators are becoming available and data from centers using existent applicators is maturing. Regardless of the type of adaptive image guided and applicators used, there are still ongoing debates regarding the prescription, the relevance of point A dose, treatment planning in general, and the use of inverse planning in particular, role of model-based dose calculation algorithms, adaptive strategies, intrafraction variability, in-vivo dosimetry, dose summation with external beam treatments, to mention just some of the challenges raised by implementing this treatment technique. This symposium is proposing to address all of these issues and update the community at large on the status of image guided adaptive brachytherapy for cervical cancer.

1. To discuss the physics perspective of role of IGABT in management of cervical cancer. 2. To compare IGABT approaches: MRI, CT, US, and Hybrid 3. To present the advantages, challenges, and limitations of MRI for IGABT. 4. To discuss hot topics in IGABT including planning strategies, role of model-based dose calculation algorithms, new applicators, dose specification.