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Treatment planners frequently modify beam arrangements and use IMRT to improve target dose coverage while satisfying dose constraints on normal tissues. The authors herein analyze the limitations of these strategies and quantitatively assess the extent to which dose can be redistributed within the patient volume. Specifically, the authors hypothesize that (1) the normalized integral dose is constant across concentric shells of normal tissue surrounding the target (normalized to the average integral shell dose), (2) the normalized integral shell dose is constant across plans with different numbers and orientations of beams, and (3) the normalized integral shell dose is constant across plans when reducing the dose to a critical structure. Using the images of seven patients previously irradiated for cancer of brain or prostate cancer and one idealized scenario, competing three-dimensional conformal and IMRT plans were generated using different beam configurations. Within a given plan and for competing plans with a constant mean target dose, the normalized integral doses within concentric "shells" of surrounding normal tissue were quantitatively compared. Within each patient, the normalized integral dose to shells of normal tissue surrounding the target was relatively constant (1). Similarly, for each clinical scenario, the normalized integral dose for a given shell was also relatively constant regardless of the number and orientation of beams (2) or degree of sparing of a critical structure (3). 3D and IMRT planning tools can redistribute, rather than eliminate dose to the surrounding normal tissues (intuitively known by planners). More specifically, dose cannot be moved between shells surrounding the target but only within a shell. This implies that there are limitations in the extent to which a critical structure can be spared based on the location and geometry of the critical structure relative to the target.

Because of this evidence gap, we wanted to compare Microperc and Miniperc with an ultimate purpose to determine which modality is preferred for different stone characteristics. Our hope is that these findings may help guide which technique is most suitable for a given renal stone burden.METHODS: This is a retrospective collaborative multi-institutional study between Dortmund Clinic (Germany) and Modena University Hospital (Italy) in which we compare 2 matched groups of patients. The first group (32 patients) underwent miniperc for medium-sized renal stones in Dortmund Clinic and the second group (19 patients) underwent microperc in Modena University Hospital. Both groups were matched according to Age, Sex, BMI and maximum stone diameter according to preoperative plain KUB films.RESULTS: The primary stone free rates in the miniperc and microperc groups were similar (93.8% vs 84.2%, P ¼ 0.262). Mean operative time for miniperc was significantly shorter than that of microperc (45.6AE 18.9 vs 68.7 AE 35.2 minutes, P ¼ 0.004). The overall complication rate was 11.7 % with no significant difference between the 2 groups (12.5 % for miniperc vs 10.5 % for microperc, P ¼ 0.604). Mean hospital stay in miniperc was significantly longer than that of microperc (4.7 AE 1.6 vs 3 AE 1.5 days, P < 0.001).CONCLUSIONS: Our current data show that microperc is emerging as an effective and safe treatment option for intermediatesized kidney stones, with outcomes comparable even to miniperc which is already a well established treatment with high safety profile in experienced hands.

INTRODUCTION AND OBJECTIVE: Symptomatic urinary stone disease is a common cause for emergency department (ED) visits; for some patients, ED revisits often occur before cessation of a stone episode. Little is known regarding how non-clinical factors such as patient race, ethnicity, or insurance status contribute to ED revisit for stone disease. We sought to identify associations between ED revisit and patient race/ethnicity.METHODS: This was a retrospective cohort study of patients in Florida, Georgia, and Maryland who had initial ED treat-and-release visits for urinary stone disease utilizing the state-specific Healthcare Cost and Utilization Project (HCUP) databases between 2016-2017. A repeat ED visit for urinary stones within 30 days of an initial ED encounter was the primary outcome. A generalized estimating equation with a logit link that accounted for hospital-level clustering was employed, using race/ethnicity as the primary predictor and adjusting for other covariates such as age, sex, and primary payer. Race and ethnicity were reported as a single variable by HCUP, with ethnicity taking precedence over race in the assignment; categories were White, Hispanic, Black, and Other/Unknown. RESULTS: Of the 209,309 patients who had an initial treat-andrelease ED visit for symptomatic urinary stones, 14,853 (7.1%) had at least one additional ED encounter for symptomatic stones within 30 days of their initial ED visit. Revisit percentages differed among racial/ ethnic groups (White 7.5%, Hispanic 6.8%, Black 5.7%, p < 0.001). Black (adjusted odds ratio (aOR) 0.72, 95% confidence interval (CI) 0.67 to 0.76) and Hispanic (aOR 0.88, 95% CI 0.82 to 0.94) individuals were less likely to revisit than White individuals. Primary insurance coverage with Medicaid compared to private insurance (aOR 1.49, 95% CI 1.41 to 1.57), and rural residence compared to large metropolitan (aOR 1.13, 95% CI 1.02 to 1.25) were associated with increased odds of revisit.CONCLUSIONS: In this cohort, repeat emergency care for symptomatic urinary stones affects 7.1% of patients after initial stone management in the ED setting. Race/ethnicity was associated with stone-related ED revisit. To understand the revisit discrepancies, further investigation into potential explanations of observed race/ethnicityassociated care patterns following initial ED encounters for urinary stones is warranted.

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