Fast Monte Carlo codes for occupational dosimetry in interventional radiology.

PURPOSE: Interventional radiology techniques cause radiation exposure both to patient and personnel. The radiation dose to the operator is usually measured with dosimeters located at specific points above or below the lead aprons. The aim of this study is to develop and validate two fast Monte Carlo (MC) codes for radiation transport in order to improve the assessment of individual doses in interventional radiology. The proposed methodology reduces the number of required dosemeters and provides immediate dose results. METHODS: Two fast MC simulation codes, PENELOPE/penEasyIR and MCGPU-IR, have been developed. Both codes have been validated by comparing fast MC calculations with the multipurpose PENELOPE MC code and with measurements during a realistic interventional procedure. RESULTS: The new codes were tested with a computation time of about 120 s to estimate operator doses while a standard simulation needs several days to obtain similar uncertainties. When compared with the standard calculation in simple set-ups, MCGPU-IR tends to underestimate doses (up to 5%), while PENELOPE/penEasyIR overestimates them (up to 18%). When comparing both fast MC codes with experimental values in realistic set-ups, differences are within 25%. These differences are within accepted uncertainties in individual monitoring. CONCLUSION: The study highlights the fact that computational dosimetry based on the use of fast MC codes can provide good estimates of the personal dose equivalent and overcome some of the limitations of occupational monitoring in interventional radiology. Notably, MCGPU-IR calculates both organ doses and effective dose, providing a better estimate of radiation risk.

Monte Carlo study of the effects of system geometry and antiscatter grids on cone-beam CT scatter distributions.

PURPOSE: The proliferation of cone-beam CT (CBCT) has created interest in performance optimization, with x-ray scatter identified among the main limitations to image quality. CBCT often contends with elevated scatter, but the wide variety of imaging geometry in different CBCT configurations suggests that not all configurations are affected to the same extent. Graphics processing unit (GPU) accelerated Monte Carlo (MC) simulations are employed over a range of imaging geometries to elucidate the factors governing scatter characteristics, efficacy of antiscatter grids, guide system design, and augment development of scatter correction. METHODS: A MC x-ray simulator implemented on GPU was accelerated by inclusion of variance reduction techniques (interaction splitting, forced scattering, and forced detection) and extended to include x-ray spectra and analytical models of antiscatter grids and flat-panel detectors. The simulator was applied to small animal (SA), musculoskeletal (MSK) extremity, otolaryngology (Head), breast, interventional C-arm, and on-board (kilovoltage) linear accelerator (Linac) imaging, with an axis-to-detector distance (ADD) of 5, 12, 22, 32, 60, and 50 cm, respectively. Each configuration was modeled with and without an antiscatter grid and with (i) an elliptical cylinder varying 70-280 mm in major axis; and (ii) digital murine and anthropomorphic models. The effects of scatter were evaluated in terms of the angular distribution of scatter incident upon the detector, scatter-to-primary ratio (SPR), artifact magnitude, contrast, contrast-to-noise ratio (CNR), and visual assessment. RESULTS: Variance reduction yielded improvements in MC simulation efficiency ranging from ∼17-fold (for SA CBCT) to ∼35-fold (for Head and C-arm), with the most significant acceleration due to interaction splitting (∼6 to ∼10-fold increase in efficiency). The benefit of a more extended geometry was evident by virtue of a larger air gap-e.g., for a 16 cm diameter object, the SPR reduced from 1.5 for ADD = 12 cm (MSK geometry) to 1.1 for ADD = 22 cm (Head) and to 0.5 for ADD = 60 cm (C-arm). Grid efficiency was higher for configurations with shorter air gap due to a broader angular distribution of scattered photons-e.g., scatter rejection factor ∼0.8 for MSK geometry versus ∼0.65 for C-arm. Grids reduced cupping for all configurations but had limited improvement on scatter-induced streaks and resulted in a loss of CNR for the SA, Breast, and C-arm. Relative contribution of forward-directed scatter increased with a grid (e.g., Rayleigh scatter fraction increasing from ∼0.15 without a grid to ∼0.25 with a grid for the MSK configuration), resulting in scatter distributions with greater spatial variation (the form of which depended on grid orientation). CONCLUSIONS: A fast MC simulator combining GPU acceleration with variance reduction provided a systematic examination of a range of CBCT configurations in relation to scatter, highlighting the magnitude and spatial uniformity of individual scatter components, illustrating tradeoffs in CNR and artifacts and identifying the system geometries for which grids are more beneficial (e.g., MSK) from those in which an extended geometry is the better defense (e.g., C-arm head imaging). Compact geometries with an antiscatter grid challenge assumptions of slowly varying scatter distributions due to increased contribution of Rayleigh scatter.

Use of an electron spoiler for radiation treatment of surface skin diseases

OBJECTIVES: Low-energy electron beams are characterised by low surface doses with a pronounced dose build-up and penetration of several centimetres, but often a higher surface dose and a lower penetration range is desired. The purpose of this study was to investigate the use of an electron spoiler to modify these beams for treating surface skin diseases and evaluate the feasibility of this method. MATERIALS AND METHODS: An aluminium foil 4-mm thick covering the end of the electron applicator was used as a spoiler for a 6 MeV electron beam. The dosimetric characteristics of this beam were measured, and Monte Carlo simulations were performed. RESULTS: The spoiler reduced the practical range and increased surface and build-up doses, but it also significantly broadened the penumbra and increased peripheral doses. Nevertheless, the beam was clinically acceptable when skin collimation with lead was employed. Monte Carlo simulations agreed well with all the experimental measurements. CONCLUSIONS: The feasibility of using a low-energy electron beam with a spoiler for treating surface skin diseases was demonstrated. The method is hygienic and avoids some of the disadvantages associated with the bolus technique, but it is valid only for flat surfaces and perpendicular incidence. As a consequence, it can be an alternative to bolus and other reported methods in certain cases, especially when a particular sterility assurance level is required (AU)

[Foreign body simulating kidney tumour]. / Cuerpo extraño simulando tumor renal.

A six cm kidney tumour is found in a prostate control ultrasonography, in a 70 aged men. A chirurgical remove is indicated the tumour presented a very few separation of the kidney. The kidney was only compressed by the mass which contained a chirurgical gauze inside it from a previous surgery 35 years before.

Cuerpo extraño simulando tumor renal / Foreing body simulating kidney tumour

Un tumor renal de seis cm es encontrado en una ecografía prostática de control. Se indica una exéresis quirúrgica. Dicha tumoración presentó una mínima separación con el riñón. El riñón estaba únicamente comprimido por la masa la cual contenía una gasa quirúrgica en su interior de una cirugía previa hacía 35 años (AU)

A six cm kidney tumour is found in a prostate control ultrasonography, in a 70 aged men. A chirurgical remove is indicated the tumour presented a very few separation of the kidney. The kidney was only compresed by the mass which contained a chirurgical gauze inside it from a previous surgery 35 years before (AU)

[Urinary diversions and bladder enlargements]. / Derivaciones urinarias y ampliaciones vesicales.

Overall review that offers an integrated insight of the importance and repercussions of urinary by-pass and bladder replacement. Over the last decades there has been a growing interest in the possibility of reconstructing the urinary system and there are now an almost infinite number of surgical solutions. The history of the development of using the intestine for by-passes and the reconstruction of the urinary system is described. The secondary metabolic alterations, the possibility of secondary intestinal tumours and the rudiments of ureterointestinal anastomosis are dealt with. Bladder substitution techniques are highlighted, and the vast experience of the Urology Department of Hospital Miguel Servet explained, including criteria and conclusions that help to choose from the many urological surgery alternatives headed by urinary by-pass and bladder complications.

Derivaciones urinarias y ampliaciones vesicales / Urinary diversion and bladder replacement

Revisión de conjunto que ofrece una visión integrada de la trascendencia y repercusión de las derivaciones urinarias y sustituciones vesicales. Las últimas décadas han estado presididas por un interés creciente en las posibilidades de reconstrucción del aparato urinario y la oferta de soluciones quirúrgicas reconstructivas es prácticamente ilimitada. Se aborda progresivamente la evolución histórica de la utilización del intestino en las alternativas de derivación y reconstrucción del aparato urinario, las alteraciones metabólicas secundarias, la eventualidad de patología tumoral intestinal secundaria y los principios quirúrgicos básicos de las anastomosis ureterointestinales. Se destaca las técnicas de sustitución vesical y se aporta una extensa experiencia del Servicio de Urología del Hospital Miguel Servet con criterios y conclusiones que facilitan la elección entre las múltiples alternativas de cirugía urológica presidida por la derivación urinaria y las ampliaciones vesicales (AU)

[Retroiliac ectopic ureter opening to the seminal vesicle]. / Desembocadura de uréter ectópico retroilíaco en vesícula seminal.

OBJECTIVE: To describe a case of right retroiliac ectopic ureter opening into the seminal vesicle, an uncommon congenital malformation. METHODS/RESULTS: This anomaly was diagnosed in a 24-year-old male with recurrent acute right epididymitis based on the clinical, ultrasound and CT findings. Cystoscopy and IVP provided no additional information. Surgical exploration showed right renal agenesis and a retroiliac ectopic ureter opening into a dilated right seminal vesicle. These structures were resected. Patient evolution was satisfactory with no recurrence of the infective episodes. CONCLUSIONS: Diagnosis of this anomaly is based on clinical suspicion and the findings of the diagnostic imaging techniques. Surgical exploration, which is only required in symptomatic patients, will establish the correct diagnosis and treatment.

[Analysis of our series of kidney transplants: urologic complications and survival]. / Análisis de nuestra serie de trasplantes renales: complicaciones urológicas y supervivencia.

PURPOSE: To review our series of 416 renal transplants, with special reference to the surgical complications and their management. METHODS: From June, 1986 to October 1997, we are performed 416 heterotopic renal transplants, harvested from cadavers. Reconstruction of the urinary tract reconstruction was by ureteroneocystostomy in practically all the cases. RESULTS: There were some urological complications in 80 patients (19.2%). The most common urological complication was obstruction of the urinary tract arising from stenosis (3.3%), lymphocele (4.3%) and clotting (1.2%). 78.1% of these urological complications were resolved by endourological techniques. Urinary fistula was observed in 12 cases (2.8%). Vascular complications in 22 (6.9%), lithiasis in 5 (1.2%), and eventrations in 11 (2.6%). The treatment of these complications is described. The actuarial survival rates were 87.8% and 77.3% at one and five years respectively for the graft, and 92.4% and 83.5% for the patients. CONCLUSIONS: Our surgical complication rate in patients undergoing renal transplantation was 19.2%. The most common complication was urinary tract obstruction from stenosis (3.3%), lymphocele (4.3%) and clotting (1.6%); 78.1% of these obstructive complications were resolved by endourologic techniques. Percutaneous drainage and esclerotherapy of the lymphoceles resolved 66.6% of them. Renal biopsy performed with a 14G needle caused 5 severe hemorrhagic complications. There were no complications when an 18G needle was utilized.

[Analysis of a series of radical prostatectomies]. / Análisis de una serie de prostatectomías radicales.

OBJECTIVE: Radical prostatectomy (RP) is an elective therapeutical procedure for localized prostate cancer. The paper describes the critical analysis of our 10-year series. MATERIAL AND METHODS: A total of 216 RP have been performed between June 1986 and December 1996 (60 of them in the last year); with the purpose of securing a minimum follow-up of 4 months, the 204 procedures performed up to October 1996 were studied. Mean age was 64.9 years and PSA median 10.8 ng/ml. Intraglandular clinical stage was found in 192 cases versus 12 cases extraglandular. Up to the end of 1993 Walsh's technique with erectors' preservation was being used although the poor results obtained with regard to potency as well as the existence of positive borders have compelled us to perform the standard extracapsular technique since beginning of 1994. RESULTS: Mean follow-up in our series has been 29.62 months. Post-operative complications reached 29.9%, anastomosis fistula (21 cases) among the early ones and anastomosis stenosis (16 cases) among the late ones. 82.04% patients have total continence or minimal incontinence, the percentage of obstruction being 3.58%. Total impotence is estimated at 92.77%. One patient (0.49%) died in the immediate post-operative. Understaging was observed in 36.7%. 84 patients had extracapsular disease. Our percentage of positive surgical borders is of around 43.13%. Progression has been seen in 47 of 204 patients (23.03%): 8 local relapses, 12 metastasis, 3 with both conditions and 24 biological progression. Progression has been related to pathological stage, pre-operative PSA and Gleason's sum of the specimen. Difference was statistically significant. Overall survival at 1 and 5 years is 99.2% and 95.5% respectively while tumour specific survival is 97.8% and 75.8% at 1 and 5 years. CONCLUSIONS: RP is a surgery with minimal mortality but noticeable morbidity (incontinence 14.35%; impotence 92.77%; other complications from surgical technique 29.9%). Our clinical understaging is of around 36.7%. Progression is related to the specimen's pathological stage, and pre-operative PSA and Gleason. Our overall survival at 1 and 5 years is 99.2% and 95.5% respectively while tumour specific survival is 97.8% and 75.8%.

[Surgical complications in kidney transplantation. Analysis of our series (300 transplantations, 1986-1995)]. / Complicaciones quirúrgicas en el trasplante renal. Análisis de nuestra serie (300 trasplantes, 1986-1995).

OBJECTIVES: To review our series of 300 renal transplants, with special reference to the surgical complications and their management. METHODS: From June, 1986 to August, 1995, we performed 300 heterotopic renal transplants harvested from cadavers. Reconstruction of the urinary tract was by ureteroneocystostomy in practically all of the cases. RESULTS: The overall surgical complication rate was 20.3%. The graft was lost in 2 cases (0.66%). The most common urological complication was obstruction of the urinary tract arising from stenosis (3.6%), lymphocele (5.3%) and clotting (1.6%); 78.1% of these obstructive complications were resolved by endourological techniques. Urinary fistula was observed in 9 cases (3%) and lymphocele in 16 (5.3%), which were resolved by percutaneous drainage and sclerotherapy in 81.2% of the cases. Vascular complications were observed in 14 cases (4.6%), lithiasis in 5 (1.66%) and eventration in 6 (2%). The treatment of these complications are described. The actuarial graft and patient survival rates were 90.9% and 84.7% at one and five years, respectively, for the graft and 93.5% and 89% for the patients. CONCLUSIONS: Our surgical complication rate in patients undergoing renal transplantation was 20.3%. The most common complication was urinary tract obstruction from stenosis (3.6%), lymphocele (5.3%) and clotting (1.6%); 78.1% of these obstructive complications were resolved by endourological techniques. Percutaneous drainage of the lymphocele combined with sclerotherapy achieved resolution in 81.2%. Renal biopsy performed with a 14 G needle caused 5 severe hemorrhagic complications. There were no complications when an 18 G needle was utilized.

[Surgical staplers. Urologic surgery with intestines]. / Suturas mecánicas. Cirugía urológica con empleo de intestino.

Since the late 1980s, different reservoirs and bladder substitution techniques have been added to the urological surgical armamentarium. The necessary use of an intestinal segment--generally detubularized--make these surgical procedures complicated and time-consuming. Furthermore, problems are encountered postoperatively due to the important morbidity arising from these procedures. The present article describes our experience with mechanical sutures and resorbable material. Although the results have not been analyzed, our initial experience at the Miguel Servet Hospital has shown that these devices significantly facilitate the operative procedure, thereby reducing the incidence of urinary and intestinal fistulas. Although there is an evident risk of calculi formation, complicated solutions are not required and the biological tolerance to the metal sutures is excellent.

[Renal transplantation: results]. / Trasplante renal: resultados.

Between June 1986 and December 1991, 125 kidneys were transplanted in our hospital. Survival results of patients per annum was 94%, 90% of which represent grafts. Regarding the complications occurred in our series the most frequent ones were medical followed by surgical [urological (4%), vascular (2.4%) and others derived from the surgical procedure (20%)]. It was necessary to perform 5 transplantectomies.

[Current validity of urethroplasty in two stages]. / Vigencia actual de la uretroplastia en dos tiempos.

Review of 18 patients with complex urethral stenosis, who underwent a two-stage urethroplasty in our Unit over the last three years. Clinical results have been favourable in all patients and, from the radiological point of view, there has been only one re-stenosis. Complications rate has been low and can be superimposed to that of any urethroplasty procedure. The paper emphasizes the enormous relevance of the care taken between both surgical stages on the procedure's final result.

[Metastasis in maxillary sinus as presentation form of adenocarcinoma of the prostate]. / Metástasis en seno maxilar como presentación de un adenocarcinoma de próstata.

Presentation of one case of prostate adenocarcinoma its initial clinical manifestation being the appearance of facial tumour secondary to metastatic affectation of left maxillar sinus. After stressing its rarity, the relevance of immunohistochemical studies for the specific prostatic antigen and acid phosphatase in determining the unconnected origin of metastatic lesions is addressed.