Abstract
PurposeVariation 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.MethodsWe 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.ResultsThe 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.ConclusionsClinically 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.
Highlights
Pancreatic adenocarcinoma (PDAC) carries a grim prognosis and is estimated to become the second leading cause of cancer death by 2030 [1]
We aim to characterize inter-fraction and intra-fraction variation in tumor positioning in patients treated with stereotactic body radiation therapy (SBRT) for PDAC at a high-volume institution
Patient selection and treatment course We reviewed 30 consecutive patients with borderline resectable or locally advanced PDAC who underwent 5-fraction SBRT to 33 Gy with volumetric-modulated arc therapy (VMAT) using alpha-cradle (Smithers Medical Products Inc., North Canton, OH, USA) or Vak-lok (CIVCO Medical Solutions, Coralville, IA, USA) immobilization with a wingboard (CIVCO Medical Solutions, Coralville, IA, USA); active breathing coordination (ABC, Elekta, Stockholm, Sweden); hexapod for rotational shifts; and daily image-guidance (IG) with cone beam computed tomography (CBCT)
Summary
Pancreatic adenocarcinoma (PDAC) carries a grim prognosis and is estimated to become the second leading cause of cancer death by 2030 [1]. Despite the high propensity for distant spread, local progression contributes significantly to the morbidity of the disease. Local progression may significantly contribute to hospitalizations and inhospital mortality, further highlighting the potential importance of local control [3]. Radiation therapy is playing a larger role in the neoadjuvant and definitive setting [5,6,7,8,9,10,11]. Radiation may improve outcomes with exploration in the setting of vascular involvement, both with respect to margin sterilization and local recurrence risk reduction [11,12,13]. Radiation can add to local progression-free survival and prevent local obstructive complications as referenced above
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