[Composition of 359 kidney stones from the East region of Algeria]. / Détermination de la composition de 359 calculs du haut appareil urinaire collectés dans la région Est-algérien.

PURPOSE: Determine stones composition of the upper urinary tract in the eastern region of Algeria. METHODS: Our study focuses on a set of 359 stones of the upper urinary tract collected between January 2007 and December 2012 at hospitals in the eastern region of Algeria and analyzed by Fourier transform infrared spectroscopy. RESULTS: The male/female ratio was only 1.32. Calcium oxalate prevailed in 68.5% of stones and 49.3% of nuclei, mainly as whewellite (51.8% of stones and 37.9% of nuclei vs 16.7% and 11.4% respectively for weddellite). Carbapatite prevailed in 15% of stones and 29.8% of nuclei. The struvite, identified in 11.1% of calculi, prevailed in 3.9% of stones and 3.1% of nuclei. Among purines, uric acid prevailed with frequencies quite close to 8.9% and 7% respectively in the stone and in the nucleus while the ammonium urate prevailed in only 0.3% of stones and 3.3% of nuclei. The cystine frequency was 3.6% in both stone and nucleus. The frequency of stone with umbilication was 26.2%. Whewellite was the main component of umbilicated stones with Randall's plaque. CONCLUSION: Our results suggest that stones of the urinary tract in the Algerian east region resemble those observed in industrialized countries. Some features such as stones location, the whewellite prevalence, the frequencies of main components in both the stone and the nucleus as well as the formation of stones on renal papilla confirm this trend. LEVEL OF EVIDENCE: 4.

SU-E-T-423: Dosimetric Effect of Rotation on Stereotactic Body Radiotherapy (SBRT) of the Spine.

PURPOSE: To study the dosimetric effects of the residual setup rotation errors in spine SBRT. METHODS: We selected 25 patients with 26 lesions from an IRB approved registry. All patients were setup with Exactrac IGRT and treated with Novalis. Excatrac provided 6D shifts (3 translational, 3 rotational). The translational shifts were corrected by moving the couch. The rotational shifts >2 degrees were corrected by repositioning the patient, while smaller shifts were ignored. For each patient, we rotated the simulation CT rigidly around the CTV center by the recorded residual angles, using the MIM 4.22 software. The resulting rotated CT with all contours were imported into the TPS. The clinical plans used for treatment were mapped onto the rotated CT. Dosimetric endpoints were extracted for the rotated CTV (mean, max, D90) and the rotated cord (D0.1cc, D1cc, V10, max). These endpoints were compared to those from the clinical plan. RESULTS: For the CTV, the average ratio of the mean doses was 1.001 (0.996-1.004), the average ratio of D90 was 1.003 (0.998-1.011), and the average ratio of the maximum doses was 1.005 (0.995-1.029). For the cord, the average ratio of DO.lcc was 1.01 (0.94-1.06), the average ratio of D1cc was 1.036 (0.92-1.23), the average max doses ratio was 1.03 (0.95-1.11), and the average V10 ratio was 1.43 (0.56-2.78). CONCLUSIONS: Rotational errors in patient setup as small as 2 degrees do have dosimetric effects in spine SBRT treatments. The use of a robotic table to eliminate translational and rotational shifts is strongly recommended. It is important to note that, eventhough, the residual rotations resulted in up to 11% variation (cord max dose) from the planned doses, none of these cases violated our clinical treatment plan acceptance criteria (tolerance of the critical organs).

SU-E-T-486: Volume and Location Dependence on the Difference Between Monte Carlo and Pencil Beam Dose Calculations for Lung Stereotactic Body Radiation Therapy.

PURPOSE: Stereotactic body radiotherapy has been an efficacious treatment modality for early stage non-small cell lung cancer. The accuracy of dose calculations is in question due to the presence of inhomogeneity. It was required in several clinical trials to calculate dose without heterogeneity correction. However, to better correlate the outcomes with the planned dose, accurate dose calculation with heterogeneity correction is highly desirable. METHODS: We compared the recalculated dose with Monte Carlo (MC) algorithm to the original Pencil Beam (PB) calculations for clinical lung SBRT plans. Thirty-one clinical plans that followed protocol guidelines were retrospectively investigated. Dosimetric parameters D1, D95 and D99 for the PTV and D1 for organs at risk were compared. Correlations of mean lung dose and V20 of lungs between two calculations were investigated. RESULTS: Compared to the PB calculations without heterogeneity correction in clinical plans, we found that in terms of D95 of PTV, (1) the two calculations resulted in similar D95 for edge tumors with volumes greater than 25.1cc; (2) an average overestimation of 5% in PB calculations for edge tumors with volumes less than 25.1cc; and (3) an average overestimation of 9% or underestimation of 3% in PB calculations for island tumors with volumes smaller or greater than 22.6 cc, respectively. With heterogeneity correction, the PB calculation resulted in an average reduction of 23.8% and 15.3% in D95 for island and edge lesions respectively compared to the MC calculation. For organs at risks, no clinical meaningful differences were found among all the comparisons. Excellent correlations for mean dose and V20 of lungs were observed between the two calculations. CONCLUSIONS: Using a single scaling factor to account for the differences in using heterogeneity correction may not be sufficient. To understand dose-response relation in Lung SBRT, accurate dose calculation such as the Monte Carlo algorithms is highly recommended.

SU-E-J-10: Accuracy of Image Guidance Using Cone-Beam CT with Multiple Breath Hold Using Active Breathing Coordination.

PURPOSE: To complete a CBCT for a treatment using ABC, multiple breath hold (BH) (>3) were used due to the slow gantry rotation and the short BH period. Inter-BH tumor position variability may introduce distortion in the reconstructed images. This study aims to determine a threshold of the inter-BH scan displacement so that the inconsistency can be identified from the CBCT images. METHODS: A numerical phantom was constructed to represent the thorax region of a human body. To simulate the inter-BH displacements, known magnitudes of motion (s = 0, 1, 3, 5 mm) along the longitudinal direction were introduced for the 'tumor' and 'diaphragm' in the phantom. Two different irregular motion patterns (s1=s3=/=s2 and s1=/=s2=/=s3) during CBCT scans were tested. Furthermore, a physical phantom with a movable insert was scanned using a commercial CBCT system. The insert of the phantom was programmed to move in the longitudinal direction according to the same motion patterns as designed in the numerical simulations. Subsequently, nine CBCT's in 'half-fan' mode for the physical phantom were acquired with the insert in various positions. These CBCT images were then fused to the reference CT by aligning to either the body of the phantom or the 'tumor' inside the insert. RESULTS: Based on numerical simulation, position variation >1mm can be observed from the reconstructed CBCT images. Based on acquired CBCTs of the physical phantom, position variations of >3mm or 5mm were observed, depending on the motion pattern during the data acquisition. Because of the use of half-fan mode, we observed the order of position displacements of the tumor during CBCT acquisition drastically affected the outcome of imaging registration. CONCLUSIONS: Using ABC device, the inter-BH variability during a CBCT acquisition affects accuracy of tumor localization. A patient individualized planning margin might be necessary to account for this effect.