Main Session
Sep 28
PQA 04 - Breast Cancer, Patient Reported Outcomes/QoL/Survivorship, Functional Radiation Medicine, Hematologic Malignancies, Palliative Care, and International/Global Oncology

2751 - Investigation of Clinical Availability of the Halcyon CBCTp Workflow for Palliative Radiotherapy

03:00pm - 04:00pm ET
Poster Hall - Exhibit Hall A
Screen: 22
POSTER

Presenter(s)

Ryutaro Higashi, MD Headshot
Ryutaro Higashi, MD - Sagara Hospital, Kagoshima, MIyazaki

R. Higashi1, N. Kuga2, K. Uezono2, J. Shidooka2, Y. Ueda3, R. Nishimura3, and Y. Sagara4; 1Department of Radiology, Sagara Hospital Miyazaki, Miyazaki-City, Japan, 2Department of Radiological Technology, Sagara Hospital Miyazaki, MIyazaki, Japan, 3Department of Breast Surgery, Sagara Hospital Miyazaki, MIyazaki, Japan, 4Department of Radiology and Department of Breast Surgery, Sagara Hospital Miyazaki, Miyazaki, Japan

Purpose/Objective(s):

Our hospital has introduced Varian Halcyon 4.0 with HyperSight imaging system. HyperSight Cone Beam CT (HS-CBCT) can acquire higher-quality images in a shorter time than conventional CBCT images, and a function called CBCT for planning (CBCTp) has been added to enable a new treatment planning workflow that uses CBCT images as treatment planning images.

This study explores the clinical availability of a CBCTp workflow for palliative radiation therapy planning.

Materials/Methods:

From January to August 2025, 13 patients(17 sites) who underwent palliative radiotherapy were subjected to retrospective imaging and dose distribution analysis. The breakdown of the sites was 2 cases of brain, 5 cases of thoracic spine (including 2 cases of stereotactic irradiation), 5 cases of lumbar spine, and 5 cases of pelvic bone. In the IGRT of the first treatment, the HS-CBCT images acquired in iCBCT Acuros mode were registered in a rigid body registration in a three-axis translational direction.

In order to reduce the calculation error due to the difference in body contour between the two images, the missing air area was replaced with the adipose tissue(-100HU). The treatment plan image was replaced with HS-CBCT and calculated under the same dose normalization conditions, and the dose distribution of planning CT(pCT) and HS-CBCT was evaluated.

Results:

Gamma analysis was evaluated at 3%/2mm, 2%/2mm, 1%/1mm within the area of dose distribution (Threshold 80%) in the three cross-sections of the isocenter. The gamma pass rate was more than 95% at 2 mm. In addition, the error rate (%Diff) of the total MU value was within ±1.5% in all cases, but the variance was significantly greater in the thoracic and lumbar spine cases than in the brain and pelvic bones, and that variance might be affected with artifact caused with respiratory motion and/or intestinal peristalsis.

Conclusion:

CBCTp workflow is considered to be fully clinically available, but measures such as respiratory suppression and breath hold are necessary for areas affected by artifact caused with respiratory motion and intestinal peristalsis.