2080 - Extended Field Spine Stereotactic Body Radiation Therapy with CT-Guided Adaptive Radiation Therapy System

02:30pm - 04:00pm PT

Hall F

Screen: 1

POSTER

Presenter(s)

Beatriz Guevara, MS - University Hospitals Cleveland Medical Center, Cleveland, OH

B. Guevara¹, R. K. Patel¹, T. Arsenault¹, N. Butka¹, G. C. Pereira¹, R. Kashani², A. Baydoun¹, A. Y. Jia¹, D. E. Spratt¹, L. E. Henke², and A. T. Price²; ¹Department of Radiation Oncology, University Hospitals Cleveland Medical Center/ Seidman Cancer Center, Cleveland, OH, ²Department of Radiation Oncology, University Hospitals Seidman Cancer Center, Case Western Reserve University, Cleveland, OH

Purpose/Objective(s): Spine metastases are common, and stereotactic body radiotherapy (SBRT) can improve pain and local control. However, eligibility for spine SBRT often depends on the number of involved vertebrae, e.g. the NRG/RTOG 0631 trial limited treatment to two adjacent vertebral levels because of setup reproducibility and uncertainties in the spinal cord’s radiation tolerance. This study aimed to determine whether online adaptive radiation therapy (ART) with a CT-guided system can safely permit SBRT treatment over extended consecutive vertebral levels.

Materials/Methods: Five patients were randomly selected who were treated with ART using the CT-guided system for abdominal cancer. For each patient, their simulation CT (simCT) was used to create pre-plans, with all visible spine levels delineated individually as targets. Extended-field HyperSight CBCTs (hCBCT) were used to generate adaptive plans and targets from the simCT were registered using a sixdegreeoffreedom tool to simulate the adaptive process. The non-adaptive plans (nAP) were created by registering the hCBCT to the simCT and transferring the pre-plans and structure sets into the hCBCTs. Prescription was 24 Gy in 2 fractions. Clinical coverage goals included CTV: V24 Gy = 99% and PTV: V 24 Gy = 95%. Institutional standard constraints were applied for the spinal cord and nearby organs at risk (OARs). Target coverage between the nAP and adaptive techniques was evaluated. A centroid analysis determined the magnitude of positional change between the simCT and hCBCT target sets. Clinical goal variation for OARs was compared between the two techniques using paired t-tests. Patient QA was performed on adaptive plans and analyzed standard gamma criteria.

Results: The target coverage ranges for adaptive and nAPs are shown in the table below. The median centroid displacement was 5.0 mm (range: 1.0–9.0 mm) for the thoracic spine and 5.0 mm (range: 0.3–11.0 mm) for the lumbar spine. A paired t-test revealed a significant difference in spinal cord constraint violations between adaptive and nAPs (p=0.019), with ART meeting all priority 1 OAR constraints. Patient QA yielded an average passing rate of 96.7% (range: 94.9%–97.8%).

Conclusion: This study indicates that adaptive replanning with a high-quality CBCT-guided system may enable a dosimetrically optimized delivery of spine SBRT beyond the standard 2–3 consecutive vertebral levels. Future work includes testing this innovative approach in a Phase I trial.

Abstract 2080 - Table 1

Dataset	Target Group	Number of Consecutive Vertebral Levels	Coverage Adaptive V24Gy (%)	Coverage Non-Adaptive V24Gy (%)
1	CTV	7	99.1– 99.8	93.7 – 99.9
1	PTV	7	95.2– 96.2	86.9 – 96.7
2	CTV	6	99.6 – 99.8	96.1 – 99.9
2	PTV	6	95.5 – 96.3	92.5 – 97.7
3	CTV	6	98.7 – 99.7	81.3 – 90.2
3	PTV	6	91.0 – 95.2	65.4 – 78.9
4	CTV	8	99.5 – 99.8	95.0 – 99.9
4	PTV	8	95.7 – 96.8	88.2 – 96.3
5	CTV	6	99.2 – 99.7	96.7 – 99.6
5	PTV	6	95.4 – 96.5	87.7 – 96.4