To quantify interfraction esophagus motion during thoracic SBRT using MRI-guided radiation therapy (RT). We reviewed computed tomography (CT) simulation and on-treatment MR datasets of 7 patients obtained using a 0.3-T MR-guided RT system. Image registration was based on bony anatomy from the cricoid to the gastroesophageal junction and defined as upper, mid, and lower esophagus. The planning CT was compared to 3 treatment MRI scans obtained during initial, middle, and final fractions at slice intervals of 0.9 cm. Esophageal motion was quantified by measuring expansion and displacement in both the right-left (RL) and anterior-posterior (AP) directions and corrected for RL and AP shift. RL shift was defined as the distance between right lateral esophagus on planning CT and on-treatment MR scan. AP shift was defined as distance between posterior aspect of esophagus on planning CT and on-treatment MRI. Expansion was defined as additional length in RL or AP direction. Displacement was defined as movement of central point of RL or AP diameter and was calculated by subtracting CT radius from the sum of the MRI radius and RL or AP shift. Sample means were compared by analysis of variance (ANOVA) and Fisher protected least significant difference test. Twenty-eight imaging datasets from 7 patients undergoing SBRT for primary lung cancer (3) and metastatic lung disease (4) were analyzed. Gross tumor volume locations included right hilum (3), left upper lobe (2), left lower lobe (1), and mediastinum (1). Mean RL expansion was 0.36±0.02 cm and displacement was 0.29±0.02 cm, favoring leftward motion (58.2% and 51.3%). Mean AP expansion was 0.37±0.03 cm and displacement was 0.39±0.03, favoring anterior motion (68.7% and 71.1%). Magnitude of AP expansion and displacement was less than 0.5 cm in 74.3% and 69.9% of observations, respectively. Motion was greatest in lower esophagus (RL expansion 0.44±0.04 cm, RL displacement 0.34±0.03 cm, AP expansion 0.46±0.04 cm, AP displacement 0.49±0.04 cm). The difference was significant compared to mid and upper esophagus (P<.0001). A total of 34% of lower esophageal MRI contours showed motion >0.5 cm in either the RL or AP directions. The 95th percentiles of expansion for leftward, rightward, anterior, and posterior directions were 0.68 cm, 0.84 cm, 1.32 cm, and 1.07 cm, respectively. As previously reported, lower esophagus motion is of significantly greater magnitude than mid and upper esophagus. Preliminary analysis of MRI on-treatment imaging of the lower esophagus during thoracic SBRT suggests a margin expansion of 0.68 cm left, 0.84 cm right, 1.32 cm anterior, and 1.07 cm posterior would account for 95% of measurements. Additional work to define individualized esophageal normal tissue structures from personalized observations is ongoing.

Purpose: To quantify inter‐fraction esophagus‐variation. Methods: Computed tomography and daily on‐treatment 0.3‐T MRI data sets for 7 patients were analyzed using a novel Matlab‐based (Mathworks, Natick, MA) rapid computational method. Rigid registration was performed from the cricoid to the gastro‐esophageal junction. CT and MR‐based contours were compared at slice intervals of 3mm. Variation was quantified by “expansion,” defined as additional length in any radial direction from CT contour to MR contour. Expansion computations were performed with 360° of freedom in each axial slice. We partitioned expansions into left anterior, right anterior, right posterior, and left posterior quadrants (LA, RA, RP, and LP, respectively). Sample means were compared by analysis of variance (ANOVA) and Fisher's Protected Least Significant Difference test. Results: Fifteen fractions and 1121 axial slices from 7 patients undergoing SBRT for primary lung cancer (3) and metastatic lung disease (4) were analyzed, generating 41,970 measurements. Mean LA, RA, RP, and LP expansions were 4.30±0.05 mm, 3.71±0.05mm, 3.17±0.07, and 3.98±0.06mm, respectively. 50.13% of all axial slices showed variation > 5 mm in one or more directions. Variation was greatest in lower esophagus with mean LA, RA, RP, and LP expansion (5.98±0.09 mm, 4.59±0.09 mm, 4.04±0.16 mm, and 5.41±0.16 mm, respectively). The difference was significant compared to mid and upper esophagus (p<.0001). The 95th percentiles of expansion for LA, RA, RP, LP were 13.36 mm, 9.97 mm, 11.29 mm, and 12.19 mm, respectively. Conclusion: Analysis of on‐treatment MR imaging of the lower esophagus during thoracic SBRT suggests margin expansions of 13.36 mm LA, 9.97 mm RA, 11.29 mm RP, 12.19 mm LP would account for 95% of measurements. Our novel algorithm for rapid assessment of margin expansion for critical structures with 360° of freedom in each axial slice enables continuously adaptive patient‐specific margins which may reduce overlap with high‐dose regions.

PURPOSE To demonstrate the feasibility of a rapid computational algorithm for generating esophageal margin expansions. METHODS Inter-fraction MRI allows visualization of relative variations of the esophagus and other critical structures when compared to planning CT. We have developed a rapid computational method for quantifying this motion. CT simulation and on-treatment MR data sets of seven patients were obtained using a 0.3 T MR-guided RT system. Rigid registration guided by bony anatomy from the cricoid to the gastro-esophageal junction was used for transferring CT contours to MR volumes. CT- and MR-based contours were re-sampled to form boundaries - BCT and BMR respectively - that densely sample the image grid. Centroids CCT and CMR were calculated slice-by-slice from BCT and BMR respectively. For each CT boundary point BCT(i) within an area enclosed by the MR boundary points, the intersection BMR(j) was calculated between the MR boundary and a line defined by BCT(i) and CCT. The length of the vector defined by BCT(i) and BMR(j) provides a margin expansion within a given slice for that vector orientation. This procedure is repeated for every slice to characterize margin expansions along the esophagus. RESULTS Expansions were determined for in-plane quadrants along the length of the esophagus. With the analysis relying on simple geometry, the non-negligible time constraint in the procedure is manual contouring. Given the soft tissue contrast on MR volumes, systematic margin uncertainties are ultimately determined by in-plane spatial resolution (1.5×1.5 mm2 in most cases). CONCLUSION We demonstrate a rapid method for assessing inter-fractional variation for the sake of suggesting thorough treatment margins (applied to the esophagus). Ongoing work aims to assess intra-fractional esophageal motion.

PURPOSE:18F-fluorodeoxyglucose (FDG) positron emission tomography-(PET)/computed tomography (CT) imaging is used for staging and treatment planning of patients with anal cancer. Quantitative pre- and posttreatment metrics that are predictive of recurrence are unknown. We evaluated the association between pre- and posttreatment FDG-PET/CT parameters and outcomes for patients with squamous cell carcinoma of the anus (SCCA).METHODS AND MATERIALS:The records of 110 patients treated between 2003 and 2013 with definitive radiation therapy for SCCA were reviewed under an institutional review board-approved protocol. The median radiation therapy dose was 50.4 Gy (range, 35-60 Gy). Concurrent chemotherapy was administered for 109 of 110 patients and generally consisted of 5-fluorouracil and mitomycin C (n = 94). All patients underwent pretreatment FDG-PET/CT and 101 of 110 underwent posttreatment FDG-PET/CT 3 months after completion of radiation therapy. The maximum standard uptake value (SUVmax) was analyzed, in addition to multiple patient and treatment factors, by univariate and multivariate Cox regression for correlation with local recurrence (LR) and overall survival (OS).RESULTS:The median follow-up was 28.6 months. LR occurred in 1 of 15 (6.7%), 5 of 47 (10.6%), and 6 of 48 (12.5%) patients with stage I, II, and III disease, respectively. On univariate analysis, a significant association was observed between reduced LR and posttreatment SUVmax <6.1 (P = .0095) and between increased OS and posttreatment SUVmax <6.1 (P = .0086). On multivariate analysis, a significant association was observed between reduced LR and posttreatment SUVmax <6.1 (P = .0013) and the use of intensity modulated radiation therapy (P < .001). A significant multivariate association was observed between increased OS and posttreatment SUVmax <6.1 (P = .0373) and the use of 5-fluorouracil/mitomycin C chemotherapy (P = .001).CONCLUSION:Posttreatment SUVmax <6.1 is associated with reduced LR and increased OS after chemoradiation therapy for SCCA independent of T and N stage on multivariate analysis. Greater follow-up is required to confirm this association with late patterns of failure.