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PQA 07 - PQA 07 Gastrointestinal Cancer and Sarcoma/Cutaneous Tumors Poster Q&A

3098 - Evaluation of Fiducial Motion during Treatment of Upper Abdominal Lymph Nodes with Stereotactic Body Radiation Therapy

Tuesday, October 1, 2024
12:45 PM – 2:00 PM ET
Location: Hall C

Screen: 24

J. Willcox1, M. Hurwitz1, and M. J. Abrams2; 1Department of Radiation Oncology, Beth Israel Deaconess Medical Center, Boston, MA, 2Department of Radiation Oncology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA

Purpose/Objective(s): At our institution, stereotactic body radiation therapy (SBRT) to upper abdominal lymph nodes is performed on a frameless robotic radiosurgery system with implanted fiducial markers and respiratory motion modeling. In this study, we evaluated their motion with SBRT to determine whether fiducials remain necessary for the treatment and the accuracy of the correlative model compared to recorded fiducial motion.

Materials/

Methods: Nine patients who had an upper abdominal lymph node treated with SBRT from 2019 to 2022 were included in this retrospective analysis. Treatment sites included: 3 portacaval, 5 portal, and 1 retrocrural. Centroid fiducial positions and correlation error values were extracted from respiratory motion models at the beginning and end of each fraction, and the tumor motion amplitude for each of these models was calculated. The average amplitude was determined for each patient across all fractions in the superoinferior (SI), anteroposterior (AP), and lateral (LR) directions, as well as intrafractional and interfractional changes in amplitude. The average correlation error, or difference between the predicted fiducial centroid position from the respiratory model and the actual fiducial centroid position, was determined for each patient.


Results: The median age of patients in this study was 66 years (range 35-69). Average tumor motion amplitude across all fractions for the cohort in the SI, AP, and LR directions was 10.4 mm, 4.1 mm, and 2.6 mm, respectively. The maximum intrafractional and interfractional changes in amplitude were 14.1 mm and 15 mm, respectively, in the SI direction. The average correlation error was 1.1 mm, averaged across all nine patients, and 1.7 mm for the patient with the highest average correlation error.


Conclusion: The degree of interfractional and intrafractional change in tumor motion amplitude within this cohort suggests that real-time gated treatment is critical, and motion may be unaccounted for with a single static simulation scan. Therefore, fiducials remain an integral part of the treatment of upper abdominal lymph nodes with SBRT. Additionally, the correlation model was highly predictive of measured motion, lending further support to the continued use of real-time fiducial-based motion tracking for the treatment of lymph nodes in the upper abdomen. Abstract 3098 - Table 1: Motion Amplitude Details

Patient

Average motion amplitude over all fractions

Largest intrafractional change in amplitude

SI (mm)

AP (mm)

LR (mm)

SI (mm)

AP (mm)

LR (mm)

1

7.9

2.2

1.7

4.1

0.9

0.8

2

8.4

2.8

2.5

3.3

1.0

1.9

3

13.3

5.1

2.6

11.9

1.0

0.9

4

12.2

7.2

2.7

8.1

6.2

2.8

5

12.4

6.0

2.3

4.9

2.9

1.1

6

11.5

3.6

3.4

4.3

2.0

2.4

7

8.0

6.2

2.8

3.2

1.1

0.5

8

3.9

2.3

2.4

0.6

0.6

0.6

9

15.1

2.6

3.5

14.1

0.9

3.7