Inter- and intrafraction motion assessment and accumulated dose quantification of upper gastrointestinal organs during magnetic resonance-guided ablative radiation therapy of pancreas patients

Dose Escalation for Pancreas SBRT: Potential and Limitations of using Daily Online Adaptive Radiation Therapy and an Iterative Isotoxicity Automated Planning Approach

“…In previous studies, doses of 70 to 100 Gy BED 10 (ie, BED with α:β ratio of 10) are required for an ablative effect and increase overall survival. 23 , 24 , 25 Current SBRT dose regimens of 35 to 40 Gy in 5 fractions (59.5-72 Gy BED 10 ) do not achieve this dosimetric threshold, but increasing BED without increasing normal structure toxicity could be achieved with our approach because of the inter- and intrafraction bowel and target motions, 6 although intrafraction tumor motion can be managed by adapting the breath hold technique with a more generous CTV-to-PTV margin, 26 as well as utilizing OAR margins to generate planning organ-at-risk volume. We have shown that DE-ART can achieve 110 to 125 Gy BED 10 for the GTV and TVI, and DE-PTV can achieve 85 Gy BED 10 .…”

“…Although a higher biological effective dose (BED) to the primary tumor may improve LAPC outcomes, 5 the prescription dose for pancreatic SBRT is restrained by the nearby radiosensitive organs at risk (OARs) (ie, small and large bowel, duodenum, and stomach), and limitations in image guidance techniques. Furthermore, as the interfractional motion of the abdominal OARs can usually exceed a few centimeters, 6 small inaccuracies in patient positioning can result in large localization errors in high-dose gradients near the target/OAR interface, ultimately affecting outcomes. Consequently, the verification of tumor and OAR positions before each treatment becomes a standard procedure for pancreas SBRT.…”

Patient specific contouring region of interest for abdominal stereotactic adaptive radiotherapy

“…Due to the empirical nature of our method, the CRoI can be quickly updated during the adaptive process if there are significant changes to patient anatomy. In the setting of stereotactic abdominal ART, there are expected changes in the luminal structures’ positions from day to day such as an approximate median and max displacement of both the small and large bowel of approximately 0.6–1.0 cm and 3.5 cm-4.8 cm, respectively [24] . Due to this high inter-fractional mobility of the luminal OARs, we would expect the dose distributions to change from fraction to fraction.…”

Quality Assurance Assessment of Intra-Acquisition Diffusion-Weighted and T2-Weighted Magnetic Resonance Imaging Registration and Contour Propagation for Head and Neck Cancer Radiotherapy

“…The ground-truth volume difference was defined as the deformed contour volume minus the original T2W contour volume. Generally, the Jacobian integral measures the net local volume change, and good agreement between the Jacobian integral and volume changes indicate a reliable DVF 11 . As shown, most algorithms showed reasonable correlation for most structures, with the exception Demons (particularly low value for primary tumor).

Figure E1. Percentage of negative values in Jacobian determinants for each deformable image registration method.

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