Boron neutron capture enhancement (BNCE) of the fast neutron irradiations use thermal neutrons produced in depth of the tissues to generate neutron capture reactions on 10B within tumor cells. The dose enhancement is correlated to the 10B concentration and to thermal neutron flux measured in the depth of the tissues, and in this paper we demonstrate the feasibility of Monte Carlo simulation to study the dosimetry of BNCE. The charged particle FLUKA code has been used to calculate the primary neutron yield from the beryllium target, while MCNP-4A has been used for the transport of these neutrons in the geometry of the Biomedical Cyclotron of Nice. The fast neutron spectrum and dose deposition, the thermal flux and thermal neutron spectrum in depth of a Plexiglas phantom has been calculated. The thermal neutron flux has been compared with experimental results determined with calibrated thermoluminescent dosimeters (TLD-600 and TLD-700, respectively, doped with 6Li or 7Li). The theoretical results were in good agreement with the experimental results: the thermal neutron flux was calculated at 10.3 X 10(6) n/cm2 s1 and measured at 9.42 X 10(6) n/cm2 s1 at 4 cm depth of the phantom and with a 10 cm X 10 cm irradiation field. For fast neutron dose deposition the calculated and experimental curves have the same slope but different shape: only the experimental curve shows a maximum at 2.27 cm depth corresponding to the build-up. The difference is due to the Monte Carlo simulation which does not follow the secondary particles. Finally, a dose enhancement of, respectively, 4.6% and 10.4% are found for 10 cm X 10 cm or 20 cm X 20 cm fields, provided that 100 micrograms/g of 10B is loaded in the tissues. It is anticipated that this calculation method may be used to improve BNCE of fast neutron irradiations through collimation modifications.
The model's application permitted us to analyze precisely the link between lateral impact trauma of the pelvic ring and lesions of the posterior urethra and to identify an urethra stretching prior to visualization of a pelvic fracture. Utilization of the model with other mechanisms of injury should allow for better comprehension of this associated trauma, improved prevention, iatrogenic aggravation of, and care for, these serious injuries.
Case reportThe tension-free vaginal tape (TVT) is a minimally invasive polypropylene monofilament mesh sling that is known to be an effective treatment for female urinary incontinence.
1The efficacy and the simplicity of the technique have made of it the treatment of choice for this common condition.1 Infection is an extremely rare complication of the TVT usually presenting with leucorrhea and/or purulent collections in the retropubic space. 2 We report a case of TVT infection due to actinomycosis presenting as recurrent vaginal erosions of the mesh.A 46-year-old woman presented with dyspareunia and vaginal discharge. She had had a TVT (Gynecare) inserted two years before for urinary stress incontinence. Pelvic examination revealed the exposure of a 1 Â 0.5 cm portion of mesh within the vagina. She underwent transvaginal excision of the exposed part of the mesh. Postoperative course was uneventful, and bacterial cultures were sterile. Two months later, a pelvic examination revealed a new area of mesh erosion away from the previous one. The patient underwent a transvaginal removal of the entire sling, and multiple biopsies of vaginal tissue around the eroded area were taken and sent for histological examination. Postoperative course was uneventful. Histology of the biopsy specimen and mesh revealed PAS-positive granules with structures radiating from the periphery, characteristic of Actinomyces sp infection, although cultures remained sterile. The patient received a one-month course of intravenous penicillin G (10 7 IU/day) followed by a four-month course of oral amoxicillin (3 g/day). At six-month follow-up, she was well with no signs of urinary incontinence and pelvic examination was normal.
DiscussionVaginal erosion is a rare complication of TVT device occurring in 0.7% of the cases.3 It is reasonable to believe that erosion may occur in the presence of multiple factors, such as inadequate vaginal incision suturing, impaired wound healing, wound infection or foreign body rejection.3 One theory suggests that subclinical infection of mesh results in wound separation that presents as exposure of the mesh.
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