Use of 3D transabdominal ultrasound imaging for treatment planning in cervical cancer brachytherapy: Comparison to magnetic resonance and computed tomography

PURPOSE: To evaluate if the addition of 3D transabdominal ultrasound (3DTAUS) imaging to computed tomography (CT) can improve treatment planning in 3D adaptive brachytherapy when compared with CT-based planning alone, resulting in treatment plans closer to the ones obtained using magnetic resonance imaging (MRI)-based planning. METHODS AND MATERIALS: Five patients with cervical cancer undergoing brachytherapy underwent three imaging modalities: MRI, CT, and CT-3DTAUS. Volumes were delineated by a radiation oncologist and treatment plans were optimized on each imaging modality. To compare treatment plans, the dwell times optimized on MRI were transferred on CT and CT-3DTAUS images and dose parameters were reported on volumes of the receiving imaging modality. The plans optimized on CT and CT-3DTAUS were also copied and evaluated on MRI images. RESULTS: Treatment plans optimized and evaluated on the same imaging modalities were clinically acceptable but statistically different (p < 0.05) from one another. MR-based plans had the highest target coverage (98%) and CT-based plans the lowest (93%). For all treatment plans evaluated on MRI, the target coverage was equivalent. However, a decrease in target coverage (V100) was observed when MR-based plans were applied on CT-3DTAUS (6%) and CT (13%) with p < 0.05. An increase in the rectum/sigmoid dose (D2cc) was observed with both CT-3DTAUS based (0.6 Gy) and CT-based planning (1 Gy) when compared with MR-based plans, whereas bladder dose stayed similar. CONCLUSIONS: When compared with CT-based planning, the addition of 3DTAUS to CT results in treatment plans closer to MR-based planning. Its use reduces the high-risk clinical target volume overestimation typically observed on CT, improving coverage of the target volume while reducing dose to the organs at risk. (C) 2017 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.