GATE Monte Carlo approach to heterogeneity dose distribution in small fields used in radiation therapy.

The Accurate dosage prediction in Radiation Therapy is challenging, prompting a need for precision beyond conventional clinical Treatment Planning Systems (TPS). Monte Carlo-based methods are sought for their superior accuracy. The aim of this study is to compare dose distributions between the ACUROS algorithm and the GATE platform in various tissue densities and field sizes, focusing on smaller fields. This study was initiated with a homogeneous validation of the TrueBeam STX system, using measurements obtained from the Centre Hospitalier Interregional Edith Cavell (CHIREC) in Brussels. The validation compared dosimetric functions (Percentage Depth Dose (PDD), Dose profile (DP) and Collimator scatter fraction (CSF)) employing the GAMMA index with a 2% / 2 mm criterion tolerance. Following this, heterogeneous studies examined dose distributions between the ACUROS algorithm and the GATE platform in various tissue densities and field sizes, with a specific focus on smaller fields. Simulations were conducted using both platforms on chest phantoms with heterogeneous slabs representing bone, lung, and heart, each housing a central tumor. The impact of electronic equilibrium on tumors for different small field sizes was evaluated. Results showed a remarkable 99% agreement between measurements and GATE calculations in the homogeneous validation of the TrueBeam STX system. However, in heterogeneous studies, ACUROS consistently overestimated lung doses by up to 8% compared to GATE simulation, especially evident with a flattening filter and smaller beam sizes at density interfaces. This highlights significant dose estimation discrepancies between ACUROS and GATE, emphasizing the need for precise calculations. The findings support exploring Monte Carlo-based methods for enhanced accuracy in Radiation Therapy treatment planning.

Prevalence and risk factors of hepatitis B and C among hemodialysis patients in Tunisia.

OBJECTIVE: Hemodialysis patients are at increased risk of infection by hepatitis C and B viruses, which are significant causes of mortality and morbidity. Prevention of their transmission in hemodialysis units remains a challenge worldwide. We aimed to investigate the prevalence of these two infections and to explore major risk factors among patients on chronic hemodialysis. MATERIALS AND METHODS: We performed a cross-sectional study of 109 hemodialysis patients (mean duration of hemodialysis of seven years) between 2012 and 2014 in a Teaching Hospital of Monastir, Tunisia. Hepatitis B and C serological markers were searched for using a chemiluminescent assay. Genome detection was performed using a commercially available quantitative real-time PCR test. RESULTS: A total of 109 hemodialysis patients were enrolled (75 males and 34 females). Ages ranged from 21 to 81 years. Six (5.5%) of these 109 patients had HBV infection defined by a positive HBsAg in four (3.7%) patients and by a detectable DNA associated with an "isolated anti-HBc" profile in the remaining two patients. Hepatitis C was observed in eight patients (7.3%) and five of them had detectable RNA. Hemodialysis duration ˃5years was the main risk factor for hepatitis C infection (P=0.01; OR: 3.11; 95% CI [1.57-13.71]). CONCLUSION: Our findings confirm the downward trend of the prevalence of both hepatitis B and C infections among Tunisian hemodialysis patients. Hemodialysis duration remains the main risk factor for hepatitis C infection. Occult hepatitis B infection should be suspected and investigated, especially among patients with an "isolated anti-HBc" profile.

SU-E-T-393: Using TG119 to Assess RapidArc at Hamad Medical Corporation.

PURPOSE: To provide a confidence level within our clinic relating to the implementation and administration of RapidArc, the AAPM TG1 19 has been implemented. This task group provides a sound and relatively simple methodology for determining the accuracy of the overall IMRT process administered in the day-to-day clinicMethods: Six different test plans, of varying complexity, were created on mock structure sets, downloaded from AAPM, and delivered. The treatment planning system results were then compared with the delivered results. Plans were created and delivered on a solid water phantom, using 25×25cm water equivalent slabs of varying thicknesses. Delivered point and planar dose measurements were obtained using an ionization chamber and film, respectively. RESULTS: The confidence limit (CL), averaged for all test plans, was calculated for the high dose point in the PTV and for the low dose point in the avoidance structure. This was used as an indicator of the uncertainty of the average difference between measured and planned dose. Where the precision of the delivery is based on how small the CL value is.For both the high and low dose points, the local CL's were determined to be 0.036 and 0.011, respectively. The range of results for the CL presented in TG1 19 varies from 0.015 to 0.098 for the high dose point, and from 0.014 to 0.086 for the low dose point. CONCLUSIONS: Our results indicate the accurate implementation of RapidArc within our clinic, especially when compared to the results of other institutions, published in TG1 19. Furthermore, the CL value for the low dose measurements is lower than any of the results published in TG119. We recommend that any clinic conducting IMRT should implement this task group. This will not only provide a greater understanding of the delivery and its limitations, but will also give the overall accuracy and consistency of the technique as it applies to the various treatment sites.

SU-E-T-649: Evaluation of RapidArc- Based Stereotactic Cranial Radiotherapy Plans with MU Objective Using Multiple Non Coplanar Arcs in Comparison with Conventional Dynamic Conformal Arc Technique.

PURPOSE: Previous researches reported that RapidArc plans for stereotactic cranial radiotherapy have two to three times more MUs as compared to Conventional Dynamic Conformal Arc (DCA) Technique. This study aims to evaluate RapidArc plans using multiple non- coplanar arcs, developed with MU objective constraint in the optimization stage. METHODS: Five single brain metastasis and three multiple metastases cases previously planned using DCA techniques in BrainLab iPlan Version 4.1 were investigated in this study. For each case, the target was defined on CT-MR fused images in iPlan. The CT images and contours of these patients were exported from iPlan to Varian Eclipse TPS Version 8.6. For each case, a DCA plan and a RapidArc plan with multiple non-coplanar arcs with and without using MU objective in the optimization stage were generated using Varian Trilogy machine with Millennium 120 MLC keeping the same prescription and critical structure dose limits. All plans were evaluated according to Conformity Index (CI-modified Paddick) Homogeneity Index (HI), and the normal tissue volume receiving various dose levels (V80%, V50%, V25% and V10%). RESULTS: In all the plans, the target objectives were met and dose to OARs was within tolerance dose constraints. RapidArc plans with and without MU objective showed better CI and HI as supposed to DCA plans. V80%, V50%, V25% and V10% of normal tissue for RapidArc plans are equal or lesser than DCA plans. Single isocentre RapidArc plan for closely spaced multiple metastases cases showed better dose fall off between the lesions as supposed to DCA plans. RapidArc plans with MU objective resulted in comparable MUs as that of DCA plans. CONCLUSIONS: Our study showed RapidArc plans done with and without MU objective have no significant dosimetric difference in plan objectives. Therefore, multiple non-coplanar RapidArc plans with MU objective is clinically feasible and can provide better treatment plans than conventional DCA plans, especially for complicated cases.

SU-E-T-169: Initial Investigation into the Use of Optically Stimulated Luminescent Dosimeters (OSLDs) for In-Vivo Dosimetry of TBI Patients.

PURPOSE: To report on an initial investigation into the use of optically stimulated luminescent dosimeters (OSLDs) for in-vivo dosimetry for total body irradiation (TBI) treatments. Specifically, we report on the determination of angular dependence, sensitivity correction factors and the dose calibration factors. METHODS: The OSLD investigated in our work was InLight/OSL nanoDot dosimeters (Landauer Inc.). Nanodots are 5 mm diameter, 0.2 mm thick disk-shaped Carbon-doped Al2O3, and were read using a Landauer InLight microstar reader and associated software.OSLDs were irradiated under two setup conditions: a) typical clinical reference conditions (95cm SSD, 5cm depth in solid water, 10×10 cm field size), and b) TBI conditions (520cm SSD, 5cm depth in solid water, 40×40 cm field size,). The angular dependence was checked for angles ranging ±60 degree from normal incidence. In order to directly compare the sensitivity correction factors, a common dose was delivered to the OSLDs for the two setups. Pre- and post-irradiation readings were acquired. OSLDs were optically annealed under various techniques (1) by keeping over a film view box, (2) Using multiple scan on a flat bed optical scanner and (3) Using natural room light. RESULTS: Under reference conditions, the calculated sensitivity correction factors of the OSLDs had a SD of 2.2% and a range of 5%. Under TBI conditions, the SD increased to 3.4% and the range to 6.0%. The variation in sensitivity correction factors between individual OSLDs across the two measurement conditions was up to 10.3%. Angular dependence of less than 1% is observed. The best bleaching method we found is to keep OSLDs for more than 3 hours on a film viewer which will reduce normalized response to less than 1%. CONCLUSIONS: In order to obtain the most accurate results when using OSLDs for in-vivo dosimetry for TBI treatments, sensitivity correction factors and dose calibration factors should all be determined under clinical TBI conditions.

The effects of extended-release niacin on carotid intimal media thickness, endothelial function and inflammatory markers in patients with the metabolic syndrome.

BACKGROUND: Niacin is an agent that significantly increases high-density lipoprotein cholesterol (HDL-C), but its effects on surrogate markers of atherosclerosis and inflammatory markers are less clear. We studied the effects of niacin on carotid intimal media thickness (IMT), brachial artery reactivity as well as markers of inflammation and the metabolic profile of patients with metabolic syndrome. METHODS AND RESULTS: Fifty patients with the metabolic syndrome (Adult Treatment Panel (ATP) III criteria) were randomised to either extended-release niacin (1000 mg/day) or placebo. After 52 weeks of treatment, there was a change of carotid IMT of +0.009 +/- 0.003 mm in the placebo group and -0.005 +/- 0.002 mm in the niacin group (p = 0.021 between groups). Endothelial function improved by 22% in the group treated with niacin (p < 0.001), whereas no significant changes were seen in the placebo group. High sensitivity C-reactive protein decreased by 20% in the group treated with niacin for 52 weeks (p = 0.013). Niacin increased HDL-C (p < 0.001) and decreased low-density lipoprotein cholesterol and triglycerides (p < 0.001) significantly, and there were no adverse effects on fasting glucose levels after 52 weeks of treatment. CONCLUSION: Extended-release niacin therapy effects a regression in carotid intimal medial thickness and improvement in metabolic parameters (increased HDL and reduced triglycerides). Furthermore, extended-release niacin may demonstrate an anti-atherogenic effect in the metabolic syndrome by improving endothelial function and decreasing vascular inflammation.

The superoxide dismutase mimetic MnTBAP prevents Fas-induced acute liver failure in the mouse.

BACKGROUND & AIMS: Acute liver failure (ALF) of viral origin results from massive hepatocyte apoptosis induced by the interaction between Fas expressed on hepatocytes and Fas ligand on activated T lymphocytes. Because Fas-induced apoptosis of hepatocytes involves mitochondrial damages and potential reactive oxygen species (ROS) overproduction, we investigated whether manganese III tetrakis (5,10,15,20 benzoic acid) (MnTBAP), a nonpeptidyl mimic of superoxide dismutase (SOD), can inhibit Fas-induced ALF. METHODS: An agonist anti-Fas monoclonal antibody was used to induce hepatocyte apoptosis in vitro and ALF in vivo. RESULTS: Preventive and curative treatments by MnTBAP significantly increased survival rates and significantly reduced aspartate aminotransferase levels and parenchymal lesions. ROS generation was suggested by those beneficial effects and significant increases in SOD and Gpx activities after anti-Fas injection. Flow cytometry of isolated hepatocytes incubated with anti-Fas monoclonal antibody showed that ROS production was associated with the collapse of transmembrane potential and loss of cardiolipin content. After injection of anti-Fas monoclonal antibody, mitochondrial Bcl-2 was decreased, cytochrome c released, and caspase-3 activated. Mitochondrial alterations and their consequences were abrogated by MnTBAP. CONCLUSIONS: ROS are key executioners in Fas-induced hepatocyte apoptosis. This finding explains why a nonpeptidyl mimic of SOD can cure ALF in a model of viral hepatitis, pointing out the potential interest of this molecule in humans.

Detoxification of reactive oxygen species by a nonpeptidyl mimic of superoxide dismutase cures acetaminophen-induced acute liver failure in the mouse.

Drug-induced acute liver failure (ALF) is a devastating and often fatal disease mainly caused by poisoning by acetaminophen (APAP). The toxic metabolite, N-acetyl-p-benzoquinone-imine (NAPQI), that leads to gluthatione depletion has been suspected to be the main effector of hepatocyte apoptosis during APAP-induced ALF. We have investigated whether reactive oxygen species (ROS) also play a role in APAP-induced ALF, and whether manganese III tetrakis (5,10,15,20 benzoic acid) (MnTBAP), a mimic of superoxide dismutase (SOD) with catalase-like activity, can treat the disease in mice. The effects of MnTBAP were tested on APAP-intoxicated mice and on isolated hepatocytes incubated with APAP. MnTBAP preventively and curatively administered significantly improved survival times, and dramatically reduced serum transaminase activity levels and parenchymal lesions in APAP-intoxicated mice. Whereas pretreatment with N-acetyl-L-cysteine (NAC) prevented ALF in a dose-dependent manner, the molecule was ineffective when curatively administered. The significant increase in glutathione peroxidase (Gpx) activity following APAP administration, and the beneficial effects of MnTBAP suggested that ROS were produced during APAP-induced ALF. A direct evidence of ROS generation was provided by flow cytometry of isolated hepatocytes incubated with APAP. In vitro, ROS production was associated with mitochondrial damage characterized by the collapse of transmembrane potential and the loss of cardiolipin content. In livers of intoxicated mice, ALF was associated with cytochrome c release that led to the activation of caspases-9 and -3. The capacity of MnTBAP to abrogate all those alterations suggests that ROS play a role in APAP-induced apoptosis of hepatocytes, and explains the beneficial effects of MnTBAP, which could be of interest in APAP-induced ALF in humans.

Laparoscopic liver resections: a feasibility study in 30 patients.

OBJECTIVE: To assess the feasibility and safety of laparoscopic liver resections. SUMMARY BACKGROUND DATA: The use of the laparoscopic approach for liver resections has remained limited for technical reasons. Progress in laparoscopic procedures and the development of dedicated technology have made it possible to consider laparoscopic resection in selected patients. METHODS: A prospective study of laparoscopic liver resections was undertaken in patients with preoperative diagnoses including benign lesion, hepatocellular carcinoma with compensated cirrhosis, and metastasis of noncolorectal origin. Hepatic involvement had to be limited and located in the left or peripheral right segments (segments 2-6), and the tumor had to be 5 cm or smaller. Surgical technique included CO2 pneumoperitoneum and liver transection with a harmonic scalpel, with or without portal triad clamping or hepatic vein control. Portal pedicles and large hepatic veins were stapled. Resected specimens were placed in a bag and removed through a separate incision, without fragmentation. RESULTS: From May 1996 to December 1999, 30 of 159 (19%) liver resections were included. There were 18 benign lesions and 12 malignant tumors, including 8 hepatocellular carcinomas in cirrhotic patients. Mean tumor size was 4.25 cm. There were two conversions to laparotomy (6.6%). The resections included 1 left hepatectomy, 8 bisegmentectomies (2 and 3), 9 segmentectomies, and 11 atypical resections. Mean blood loss was 300 mL. Mean surgical time was 214 minutes. There were no deaths. Complications occurred in six patients (20%). Only one cirrhotic patient developed postoperative ascites. No port-site metastases were observed in patients with malignant disease. CONCLUSION: Laparoscopic resections are feasible and safe in selected patients with left-sided and right-peripheral lesions requiring limited resection. Young patients with benign disease clearly benefit from avoiding a major abdominal incision, and cirrhotic patients may have a reduced complication rate.

[Abdominal surgical emergencies in human immunodeficiency virus (HIV) infected patients. Apropos of 34 cases]. / Les urgences abdominales chirurgicales chez les patients infectés par le virus d'immunodéficience humaine (VIH). A propos de 34 observations.

From September 1986 to September 1994, 34 emergency laparotomies were performed in human immunodeficiency virus (HIV) seropositive patients. Patients were divided into 2 groups. Group A included 11 HIV seropositive patients without acquired immunodeficiency syndrome (AIDS). In these patients, indications for exploration included right lower quadrant pain consistent with appendicitis in 6 patients, right upper quadrant pain consistent with cholecystitis in 3 patients, small bowel obstruction in 1 patient, and blunt abdominal trauma in 1 patient. No postoperative deaths were observed. Group B included 23 AIDS patients. Indications for exploration were diffuse peritonitis in 8 patients, right lower quadrant pain consistent with appendicitis in 6 patients, right upper quadrant pain consistent with cholecystitis in 5 patients, bowel obstruction in 2 patients, diffuse abdominal pain in 1 patient, and massive rectal hemorrhage in 1 patient. The mortality rate in this group was 35% (8 out of 23 patients). Five of the 8 patients with diffuse peritonitis died postoperatively (62%). The importance of early diagnosis and prompt surgery is emphasized to improve the prognosis in AIDS patients, because of their poor general condition and the severity of abdominal complications.

Can pulse oximetry and end-tidal capnography reflect arterial oxygenation and carbon dioxide elimination during laparoscopic cholecystectomy?

An investigation was carried out on 13 ASA class 1 or 2 adult patients undergoing laparoscopic cholecystectomy. Throughout laparoscopy, the end-tidal PCO2 was continuously monitored by capnography and the arterial hemoglobin oxygen saturation by pulse oximetry. Also, repeated measurements of arterial blood gases were done. Ventilation was controlled using an inspired oxygen concentration of 33% and tidal volume of 10 to 15 ml/kg at a rate of 10-14/min. The report showed that both the mean end-tidal PCO2 and arterial PCO2 progressively increased following carbon dioxide insufflation, to reach a maximal value after 30 min, with no significant change in the arterial-alveolar PCO2 gradient. Also, the arterial PO2 significantly decreased, and the hemoglobin oxygen saturation was always above 98% whether monitored by arterial blood gas analysis or by pulse oximetry. The results suggest that end-tidal capnography and pulse oximetry can be used as noninvasive techniques for monitoring arterial oxygenation and carbon dioxide elimination during laparoscopic cholecystectomy.

End-tidal carbon dioxide tension during laparoscopic cholecystectomy. Correlation with the baseline value prior to carbon dioxide insufflation.

An investigation of end-tidal carbon dioxide tension changes was carried out in 19 healthy adult patients undergoing laparoscopic cholecystectomy. Following induction of anaesthesia, and throughout surgery, the end-tidal carbon dioxide tension was continuously monitored by capnography. The value following carbon dioxide insufflation increased with time to reach a maximum value after 40 min. Correlation of the individual maximum end-tidal carbon dioxide tension during laparoscopy with the corresponding baseline value prior to carbon dioxide insufflation showed a positive linear relationship (correlation coefficient 0.86). The correlation showed that an end-tidal carbon dioxide tension of 5.32 kPa (40 mmHg) can be achieved during laparoscopy when the baseline value is adjusted to around 4.0 kPa (30 mmHg).