Room: Exhibit Hall
Purpose: To investigate clinically useful cone beam CT (CBCT) protocols for obese patients under image guided radiation treatment (IGRT) of abdominal or pelvic cancer.
Methods: It is challenging to take CBCT for patients weighing more than 400 pounds for image guided radiation treatment of abdominal or pelvic cancer. The quality of CBCT image taken with standard pelvis protocol, such as 125 kVp, 80 mA, and 13 ms from a Varian Trilogy radiotherapy unit, is generally poor and not clinically useful. To acquire clinically useful CBCT images, an â€œobeseâ€? pelvis phantom, which is a combination of three sections of Rando phantoms with diameter about 50 cm that matches one obese patient treated in our clinic, is used to establish an optimum protocol. Three machines, Varian Trilogy, Varian TrueBeam, and Elekta Synergy, are used in this investigation. The following CBCT protocols were established and tested: Trilogy: 125 kVp, 80 mA, and 26 ms; TrueBeam: A. 140 kVp and 1687.5 mAs, B. 140 kVp and 3600.0 mAs; and Synergy: 140 kVp and 1689.6 mAs. CBCT images taken with these protocols were compared with regular CBCT protocols from Trilogy (125 kVp, 80 mA, and 13 ms), TrueBeam (A. 125 kVp and 1080.0 mAs, B. 125 kVp and 4050.0 mAs), and Synergy (120 kVp and 1056 mAs), respectively.
Results: The quality of CBCT images scanned with the obese pelvis protocols is significantly improved and clinically accepted for patient positioning alignment before treatment.
Conclusion: IGRT for obese patient is clinically challenging from every aspect. CBCT imaging quality is one of the most affected by obesity. Through carefully selection of CBCT protocols, improved and clinically useful images can be acquired and used for image guided radiotherapy.