M.A. Elshaikh

Adjuvant vaginal brachytherapy decreases the risk of vaginal recurrence in patients with stage I non-invasive uterine papillary serous carcinoma. A multi-institutional study

OBJECTIVES To investigate the impact of adjuvant vaginal brachytherapy on vaginal recurrence in stage I non-invasive uterine papillary serous carcinoma (UPSC). METHODS This is a retrospective multi-institutional study from 2000-2012. 103 patients who underwent surgical treatment with non-invasive stage IA UPSC were included. RESULTS 85% and 55% underwent staging lymphadenectomy and omentectomy respectively. 28.2% (29/103) developed recurrence. Vaginal, pelvic and extra-pelvic recurrences developed in 7.8% (8/103), 3.9% (4/103) and 16.5% (17/103) respectively. Among patients who were observed or received only chemotherapy, the rate of vaginal recurrence was 10.9% (7/64) compared to 2.6% (1/39) among those who received vaginal brachytherapy +/- chemotherapy (p=0.035). The rate of vaginal recurrence was not different between those who were observed and those who received only chemotherapy (9.3% vs. 14.3%, p=0.27). The 5-year progression free survival (PFS) and overall survival (OS) for the entire cohort were 88.3% and 90.6%. Patients who underwent surgical staging had longer PFS (p=0.001) and OS (p=0.0005) compared to those who did not. In multivariable analysis controlling for age, histology, chemotherapy, brachytherapy, and staging lymphadenectomy, only lymphadenectomy was an independent predictor of PFS (HR 0.28, 95% CI 0.11-0.71, p=0.0037) and OS (HR 0.27, 95% CI 0.10-0.71, p=0.0035). Neither chemotherapy nor brachytherapy were predictors of PFS or OS. CONCLUSIONS This is the largest study reported in stage I non-invasive UPSC. The majority of recurrences were extra-pelvic. Vaginal brachytherapy has a significant role in reducing the risk of vaginal recurrence and surgical staging was the only predictor of outcome. Therefore, both should be considered in these patients.

Racial disparities in uterine clear cell carcinoma: a multi-institution study.

Objective The aim of this study was to evaluate the impact of race on the overall survival (OS) and progression-free survival (PFS) of white and African-American patients with uterine clear cell carcinoma (UCCC). Methods A retrospective review was conducted of all primary UCCC cases treated at 1 of 4 major gynecologic cancer centers between 1982 and 2012. Patients and tumor characteristics were retrieved from the cancer databases of the respective institutions and based on a retrospective review of the medical records. Differences in the OS and PFS between African-American and white women were compared using the Kaplan-Meier curves and log-rank test for univariate analysis. Cox regression models for the multivariate analyses were built to evaluate the relative impact of the various prognostic factors. Results One hundred seventy women with UCCC were included in the study, including 118 white and 52 African-American women. Both groups were comparable with respect to age (P = 0.9), stage at diagnosis (P = 0.34), angiolymphatic invasion (P = 0.3), and depth of myometrial invasion (P = 0.84). In the multivariate analyses for known prognostic factors, OS and PFS were significantly different between white and African-American patients in the early-stage disease (hazard ratio [HR], 5.4; 95% confidence interval [CI], 1.2–23.2; P = 0.023 and HR, 3.5; 95% CI, 1.60–7.77; P = 0.0016, respectively) but not in the advanced-stage disease (HR, 0.83; 95% CI, 0.40–1.67; P = 0.61 and HR, 1.5; 95% CI, 0.84–2.78; P = 0.15, respectively). Conclusions In the current study, African-American patients have a prognosis worse than that of white patients in early-stage UCCC. We could not prove the same difference in advanced-stage disease.

SU-F-18C-06: Prospective Patient Evaluation of Iterative Reconstruction in Radiation Oncology

PURPOSE This work incorporates iterative reconstruction (IR) into a dose reduction study to characterize image quality metrics, delineation, and dosimetric assessment, with the goal of reducing imaging dose in Radiation Oncology. METHODS Three-dimensional noise power spectrum (NPS) analysis characterized noise magnitude/texture (120 kVp, 50-200 mAs, IR levels 1-6 yielding noise reduction of 0.89-0.55 compared to filtered backprojection (FBP)). Task-specific Modulation Transfer Functions (MTFtask) were characterized across varied subject contrasts. A prospective dose reduction study (500 to 150 mAs) was conducted for 12 patients (43 inter-fraction CTs) for high-dose rate brachytherapy. Three physicians performed qualitative image assessment between full-dose FBP (FD-FBP, 500 mAs), low-dose FBP (LD-FBP, 150-250 mAs), and low-dose IRL5-6 (LD-IR) scans for image noise, cuff/bladder interface detectability, spatial resolution, texture, and segmentation confidence. Comparisons between LD-FBP and LD-IR were conducted for the following metrics: delineation (bladder and rectum evaluated via overlap indices (OI) and Dice similarity coefficients (DSC)), noise, boundary changes, dose calculation, and digitally reconstructed radiographs (DRRs). RESULTS NPS showed ∼50% reduction in noise magnitude and ∼0.1 1/mm spatial frequency shift with IRL6. The largest MTFtask decrease between FBP and IR was 0.08 A.U. Qualitative patient image evaluation revealed LD-IR was equivalent or slightly worse than FD-FBP, and superior to LD-FBP for all metrics except low contrast interface and texture. The largest CT number discrepancy from FBP occurred at a bone/tissue interface using IRL6 (-1.2 ± 4.9 HU (range: -17.6 - 12.5 HU)). No significant contour differences (OIs and DSCs = 0.85 - 0.95) and dose calculation discrepancy (<0.02%) were observed. DRRs preserved anatomical detail and demonstrated <2% difference in intensity between LD-FBP and LD-IRL6. CONCLUSION While phantom analysis showed slight noise texture differences with IR, patient results revealed that image quality, contouring ability, and dosimetric parameters were not adversely affected, thus support integrating IR into treatment planning. Research supported in part by a grant from Philips HealthCare.

TU-E-108-06: Investigation of Prostate Deformation and Associated Dosimetric Implications in IMRT of the Prostate

PURPOSE Prostate deformation is generally considered a secondary correction and is consequently often ignored in planning margin design. In this study we estimated prostate deformation and investigate the associated dosimetric impact on target coverage. METHODS A cohort of ten prostate cancer patients were retrospectively selected for the study, each with three fiducial markers implanted in the prostate. All CBCT images were registered to respective planning CT images using the Velocity AI deformable image registration (B-spline-based) software. For cases with accurate prostate registrations (defined by mean marker misalignments of <1.5 mm), deformation-vector-fields (DVFs) of the prostate and seminal vesicles (SVs) were quantified using deformation-volume histograms. For the case with the largest prostate deformation, target coverage degradation was analyzed in each of three treatment plans with PTV margins of 10, 5, and 3 mm. RESULTS Deformation of the prostate and SVs was most significant in the anterior-posterior (AP) direction. Maximum prostate deformation of > 10mm, 5mm, and 3mm occurred in 0.5%, 10.0%, and 68.5% of cases, respectively. Based on the deformation-volume histograms, DVF magnitudes greater than 5mm and 3mm occurred in 2% and 27% of cases, respectively. In general, SV deformation was larger than that of the prostate. For the case with the largest prostate deformation, prostate coverage (D95%) was reduced by 0.5%, 9.0%, and 17.0% for 10mm, 5mm, and 3mm margin plans respectively. CONCLUSION These preliminary results are suggestive that prostate deformation over a course of fractionated prostate radiotherapy may not be insignificant, and thereby that proper margin design may be necessary to account for deformation. A consequence of these results is that use of tight planning margins of (e.g. less than 5 mm) must be viewed with severe caution.

TH-C-141-11: Evaluation of MR Images as the Planning and Reference Dataset for Daily CBCT-Based IGRT of the Prostate

PURPOSE An important question rarely discussed in the CT vs. MRI simulation debate is whether MRI reference images provide an adequate image-set to use with daily localization such as cone-beam CT (CBCT). This study compares clinical couch shifts based on daily CBCT images to shifts measured from MR images as the reference dataset for prostate IMRT treatment. METHODS Eight patients undergoing a pilot study had MR imaging along with CT simulation with the intent of evaluating a MR-simulation process. Patients had T1, T2 and bTFE (balanced Turbo Field Echo) sequences. The remainder of the treatment planning process continued using traditional procedures using CT. Therapists used only the CT scan as a reference for localization. Retrospectively, an observer measured shifts between daily CBCT images and MR reference images. RESULTS The differences in shift positions for the cohort between therapists and the observer are -0.16cm ± 0.25cm (AP), 0.04cm ± 0.19cm (SI), and - 0.01cm ± 0.14cm (LR). The mean group error for the therapists and the observer were less than 2 mm in all directions. Based on these shifts, the calculated margins for the therapists would be 0.87cm (AP), 0.65cm (SI), and 0.71cm (LR) and for the observer would be 1.1cm (AP), 0.66cm (SI), and 0.70cm (LR). For SI and LR directions both sets of margins are very close to one another. An outlier impacted the AP margin difference by 2.3mm and should be investigated further. This initial analysis suggests that each modality can be considered clinically sufficient for daily localization. CONCLUSION The results of this study suggest that MR reference image-sets can be used for daily image-guided localization of prostate cancers with at least the same accuracy as current methods. MR simulation provides substantial soft-tissue contrast and can improve tissue targeting in radiation oncology, as a Result further investigation is warranted.

SU‐FF‐J‐41: Clinical Management of Detected Target Deviations in IGRT: A Geometrical Approach

Purpose: To investigate an efficient method for assessing the impact of target deviations detected by daily image‐guidance on planning volumes. We hypothesize that, using this method, on‐line daily correction may not be warranted. Method and Materials: Geometrical surfacemodels of the CTV and PTV were generated from the respective planning volumes via a surface reconstruction algorithm. Given a set of target deviations, represented by 6‐degree positioning shifts (translation, pitch, roll, yaw) from IGRT systems (e.g. Varians OBI/CBCT), collision detection was performed to find geometric distance between CTV and PTV surfacemodels when the shifts are applied to the CTV. Since the method is based on shifts, which do not incorporate intra‐fraction motion, a criterion was defined such that on‐line shifts are not applied if the CTV and PTV surfaces are greater than a distance defined by a population‐based margin for intra‐fraction motion. Results: A software module was developed to: import IMRT plans, generate surfacemodels, communicate with the IGRT system, and calculate CTV/PTV spatial geometric distances. Surfacemodel generation is performed off‐line. Collision detection between CTV and PTV surfacemodels from daily shifts is done on‐line within minutes on a desktop PC. In the examples shown, “collisions” are defined by minimum distances of 3 mm in any direction (intrafraction motion margin) between the CTV and PTV. If a collision is detected, an on‐line shift is applied; otherwise the treatment proceeds as planned. Conclusions: The proposed method represents a quick and quantitative way to manage target deviations determined during image‐guidance, without the need to apply on‐line corrections. The approach is not limited to target analysis, but may also include normal tissues, such as the bladder and rectum. Adaptive and on‐line treatment planning studies are under way to determine the validity of the hypothesis, and to improve the collision detection criteria.