Purpose: To apply on‐boardmdash;image (OBI) guided amplitude gating for breath‐hold treatment and to assess treatment margin adequacy by analyzing the isocenter placement based on orthogonal 2D kV radiographs and 3D cone‐beam CT (CBCT) acquired under amplitude‐gated breath‐hold. Method and Materials: 25 patients with liver, pancreas, bile duct, or adrenal lesions were treated by using amplitude‐gated breath‐hold technique during the last 18 months. 2D orthogonal kV and 3D CBCT images were acquired under amplitude‐gated breath‐hold and matched to the corresponding DRRs and planning CT images, respectively, for isocenter placement. A total of 438 sets of 2D kV images and 70 sets of CBCT images were analyzed. The margin of 95% probability, which warrants that the target will be within the treatment fields with a probability of 95%, was used to quantify the margin reduction of using image‐guidance for the breath‐hold treatment. Results: The average isocenter shifts based on 2D kV OBI matching over the breath‐hold laser alignment were 0.31 ± 0.27 cm, 0.28 ± 0.28 cm and 0.29 ± 0.28 cm along the lateral (LR), longitudinal (SI) and vertical (AP) directions, respectively. After the patients were moved to the isocenter based on 2D images, the additional shifts based on 3D CT‐CBCT matching were 0.28 ± 0.28 cm, 0.30 ± 0.37 cm and 0.32 ± 0.27 cm along LR, SI, and AP directions, respectively. The 95% probability margins of daily 2D OBI matching with respect to the 3D CBCT matching were 0.6 cm, 1 cm and 0.9 cm along LR, SI and AP directions. If image guidance technique was not used, the required margins of 95% probability increased to 1.1, 1.3 and 1.2 cm along the LR, SI and AP directions. Conclusion: Amplitude gated breath‐hold technique is useful for the treatment of upper abdominal lesions. Image‐guidance technique substantially reduced treatment margin.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging