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Analysis of Setup Error for Craniospinal Irradiation Using Helical TomoTherapy

J Lee1, E Kim2, N Kim1, HK Byun1, CO Suh1,3, Y Chung2*, HI Yoon1, (1) Yonsei Cancer Center, Yonsei University College of Medicine, Seoul, KR, (2) Hanyang University, Seoul, KR, (3) Bundang CHA Medical Center, CHA University, Seongnam, KR


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Helical TomoTherapy (HT) has been utilized for crainospinal irradiation (CSI) because of several advantages including homogeneous dose distribution, comfortable supine treatment position, and daily setup verification using megavoltage CT (MVCT). Since physicians still concern setup uncertainty due to relatively short MVCT scan range compared to long treatment range, we analyzed setup errors for HT-CSI in this study.

Methods: We retrospectively reviewed 83 patients receiving HT-CSI between 2014 and 2018. Interfractional setup errors in mediolateral (ML), craniocaudal (CC), and anteroposterior (AP) directions were assessed using pre-treatment MVCT scans (zygomatic arch-C4 spine). Intrafractional movements were evaluated using post-treatment MVCT scans (T12-L4 spine). Significant intrafractional displacement was defined as greater than 10 mm change in any axis at any fraction when considering target margins. Logistic regression analysis was used to identify risk factors of setup error.

Results: Median HT-CSI dose was 36 Gy (range, 12-45) and median fraction number was 20 (range, 8-30). Median beam-on-time was 538.1 seconds (range, 310.6-964.8). Average of interfractional setup errors in total patients were 2.1±1.2 mm in ML, 2.8±2.8 mm in CC, and 3.5±1.8 mm in AP. Significant intrafractional displacement was revealed in 7 patients (8.4%) ranging from 1 to 10 fractions throughout treatment course. Among total 1443 fractions of all patients, significant intrafractional displacement occurred at 0.35% for ML, 0.77% for CC, and 1.26% for AP. Weight loss grade 1+ during treatment (OR: 9.67, 95% CI: 1.36-68.77, p = 0.023) was identified as an independent related factor for significant intrafractional displacement. Also, nausea grade 2+ (OR: 5.47; 95% CI: 1.44-20.73; p = 0.012) was a significant factor associated with weight loss grade 1+.

Conclusion: HT-CSI showed acceptable setup errors when applying adequate target margins. The delicate monitoring during treatment would be necessary for patients who experienced nausea or weight loss.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (KRF) funded by the Ministry of Education (NRF-2018R1D1A1B07049228).


Not Applicable / None Entered.


TH- External Beam- Photons: tomotherapy

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