Fiducial-based image-guided SBRT for pancreatic adenocarcinoma: Does inter-and intra-fraction treatment variation warrant adaptive therapy?

• Published in: Radiation oncology (London, England) Vol. 16; no. 1; p. 53
• Main Authors: Hill, Colin S, Han-Oh, Sarah, Cheng, Zhi, Wang, Ken Kang-Hsin, Meyer, Jeffrey J, Herman, Joseph M, Narang, Amol K
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 19-03-2021; BioMed Central; BMC
• Subjects: Active breathing coordination; Adenocarcinoma - pathology; Adenocarcinoma - radiotherapy; Care and treatment; Development and progression; Fiducial Markers; Humans; Linear Models; Methods; Motion; Motion management; Pancreatic adenocarcinoma; Pancreatic cancer; Pancreatic Neoplasms - pathology; Pancreatic Neoplasms - radiotherapy; Patient outcomes; PTV design; Radiosurgery; Radiotherapy; Radiotherapy, Image-Guided; Radiotherapy, Intensity-Modulated; Respiration; SBRT; United States; Pancreatic adenocarcinoma; Active breathing coordination; Motion management; PTV design; SBRT
• ISSN: 1748-717X; 1748-717X
• DOI: 10.1186/s13014-021-01782-w

Variation in target positioning represents a challenge to set-up reproducibility and reliability of dose delivery with stereotactic body radiation therapy (SBRT) for pancreatic adenocarcinoma (PDAC). While on-board imaging for fiducial matching allows for daily shifts to optimize target positioning, the magnitude of the shift as a result of inter- and intra-fraction variation may directly impact target coverage and dose to organs-at-risk. Herein, we characterize the variation patterns for PDAC patients treated at a high-volume institution with SBRT.
We reviewed 30 consecutive patients who received SBRT using active breathing coordination (ABC). Patients were aligned to bone and then subsequently shifted to fiducials. Inter-fraction and intra-fraction scans were reviewed to quantify the mean and maximum shift along each axis, and the shift magnitude. A linear regression model was conducted to investigate the relationship between the inter- and intra-fraction shifts.
The mean inter-fraction shift in the LR, AP, and SI axes was 3.1 ± 1.8 mm, 2.9 ± 1.7 mm, and 3.5 ± 2.2 mm, respectively, and the mean vector shift was 6.4 ± 2.3 mm. The mean intra-fraction shift in the LR, AP, and SI directions were 2.0 ± 0.9 mm, 2.0 ± 1.3 mm, and 2.3 ± 1.4 mm, respectively, and the mean vector shift was 4.3 ± 1.8 mm. A linear regression model showed a significant relationship between the inter- and intra-fraction shift in the AP and SI axis and the shift magnitude.
Clinically significant inter- and intra-fraction variation occurs during treatment of PDAC with SBRT even with a comprehensive motion management strategy that utilizes ABC. Future studies to investigate how these variations could lead to variation in the dose to the target and OAR should be investigated. Strategies to mitigate the dosimetric impact, including real time imaging and adaptive therapy, in select cases should be considered.