Genitourinary Cancer

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SU_23_2239 - Characterizing Intrafraction Target Rotation Correction for Patients Undergoing SBRT for Prostate Cancer

Sunday, October 21
1:15 PM - 2:45 PM
Location: Innovation Hub, Exhibit Hall 3

Characterizing Intrafraction Target Rotation Correction for Patients Undergoing SBRT for Prostate Cancer
S. R. Blacksburg1, M. R. Witten1, M. Core2, A. Theriault2, L. Perry2, R. Sheu3, A. Mirza1, G. Demircioglu1, T. J. Carpenter1, J. Morgenstern1, and J. A. Haas1; 1NYU Winthrop Hospital, Mineola, NY, 2Accuray Incorporated, Sunnyvale, CA, 3Icahn School of Medicine at Mount Sinai, New York, NY

Purpose/Objective(s): Prostate intrafraction translation is a well-described phenomenon during the course of radiotherapy. There is a paucity of literature which characterizes the accompanying rotation, which is often uncorrected during the course of treatment. Robotic-based Stereotactic Body Radiation Therapy (SBRT) has the ability to correct for intrafraction rotations and translations, with time stamps and movement recorded. The purpose of this investigation was to assess the magnitude of prostate intrafraction rotation, as well as to determine the predictors thereof.

Materials/Methods: We queried the data management system of 172 patients receiving robotic-based SBRT for localized prostate cancer. From September 28, 2015 to January 12, 2018, 13,368 intrafraction prostate rotation corrections occurred for this cohort. Patients were treated with a median dose of 3500cGy (2100-3625) over 5 (3-5) fractions. The mean age was 66 (41-93). The mean CTV, PTV, and Bladder sizes were 75cc’s (17.8-215.2), 129.7cc’s (34.7-320.8), and 143.9cc’s (36.4-408.8), respectively. Based on NCCN risk categories, 16.1%, 65.7% and 18.2% had low, intermediate, and high risk disease. 19.8% of patients received neoadjuvant and concurrent Androgen Deprivation Therapy (ADT) during treatment.

Results: The mean intrafraction rotation corrections in the Yaw, Pitch, and Roll planes were 0.6° (0-5.2), 1.3° (0-14.1), and 0.9° (0-8.9). The mean treatment time per fraction was 19.3 minutes (9-59). 60.5%, 37.2%, and 21.5% of patients experienced prostate rotation ≥4°, 5°, or 6° during the course of treatment. The mean time to rotation ≥5° was 16 minutes (1-57). Patients aged ≥65 were more likely to experience prostate rotation ≥5° during treatment (44.4% vs. 26.4%, p=.016). This also occurred for men receiving ADT (58.8% vs. 27.8%, p=.001) and for those with CTV sizes <35cc’s (85.7% vs. 32.6%, p=.004). On multivariate analysis, age ≥65 (OR 2.314, CI 1.073-4.990, p=.032) and the use of ADT (OR 3.611, CI 1.590 -8.200 p=.002) predicted for prostatic rotation ≥5° during treatment.

Conclusion: This study represents the largest series characterizing intrafraction prostate rotation during the course of robotic-based SBRT. Prostate rotation independent of translation can be significant during the course of treatment, with a high percentage of patients experiencing rotations ≥5°. This can occur early during the course of treatment. Patients aged ≥65 and those receiving ADT have the highest likelihood of significant intrafraction prostate rotation. Radiation facilities administering SBRT for patients with prostate cancer should remain cognizant of the likelihood and magnitude of significant intrafraction prostate rotation during treatment.

Author Disclosure: S.R. Blacksburg: None. M.R. Witten: Consultant; accuray. M. Core: None. A. Theriault: None. L. Perry: None. G. Demircioglu: None. J.A. Haas: None.

Seth Blacksburg, MD, MBA

NYU Winthrop Hospital

Disclosure:
Employment
none: none

Compensation
Accuray: Speaker's Bureau

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