2010 AAPM Annual Meeting
Dr. Jean Pouliot, PhD, UC San Francisco, San Francisco, CA, 94143-1708
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The primary purpose of in-room CBCT volumetric 3D verification images is to verify patient
position and target localization in real-time. However, they are also used for clinical treatment
evaluation or plan modification for adaptive radiation therapy. Daily positioning variation, organ
deformation, or tumor shrinkage incur variations in delivered doses to targets as well as critical
structures. The evaluation plan calculated based on the verificationCBCT images presents the
actual dosimetric information with the patient anatomy and position achieved just before the
treatment, thus,representing the actual or near treatment delivery.
Unlike helical CT, CBCT involves drawbacks such as limited field-of-view and artifacts affecting
accuracy and reproducibility of HU linearity and homogeneity. Studies have shown that CBCT
images are being used in volumetric dose calculations for the purpose of evaluation planning and
the purpose of planning or adaptive re-planning. Nevertheless, the in-room CBCT is still not
optimized for treatment planning purpose and whether CBCT can provide accurate dose
calculation results is limited within certain conditions. Such conditions should be addressed for
proper use of CBCT in treatment planning. Limitations related to field-of-view and image quality
should be emphasized to ensure accuracy and quality in clinical practices. In order to properly
and safely utilize the verification in-room CBCT for treatment planning, users should be aware of
limitations and concerns of using CBCT for dose calculation. Users also should perform a set of
tests to validate use of CBCT for dose calculation and understand the limits fort he applications.
This session will review the needs of CBCT-based dose calculation for plan evaluation and plan
modification first. Following presentations will present the current status, limitation and concerns
of CBCT-based dose calculation for currently available commercial CBCT systems.
1. needs of CBCT-based dose calculation – plan evaluation and/or plan generation modification for adaptive radiation therapy
2. the current status of CBCT image quality and artifacts, and their impact on CBCT-based dose calculation accuracy
3. limitations and concerns in clinical practice
4. future possibilities of in-situ dose calculation.