Dose-Decreasing Effect of the First Reversed Laser Beam Collimator for C-Arm Type Angiographic Equipment

This is a study on the dose-decreasing effect of the first reversed laser beam collimator (RLBC) for C-arm type angiographic equipment. A laser beam was located at the center of each plane at an oblique angle to the angiographic equipment detector. A field of view, which could be seen with the naked eye, was made by focusing the laser beam in the direction of the X-ray source. The height of the table was fixed at 75 cm and the iron balls were located within 2 mm of the top, bottom, left, and right edges of the output image. The time needed for location fixing, fluoroscopy, and measurement of dose area product (DAP) were compared by having 30 radiologists perform location fixing by looking at the fluoroscopic image while performing location fixing (no radiation) and while the RLBC was turned on. In the next test, the time needed for location fixing, fluoroscopy, and DAP were compared when varying the location of the iron balls from 2 to 10 mm from the edges of the output image. The results showed that the time needed for location fixing, the time needed for fluoroscopy, and DAP decreased, both in the first test and the second test. This study confirmed that the use of a RLBC for C-arm type angiographic equipment decreases both the time needed to perform the procedure and the radiation dose received. It is expected that continuous advancement of RLBC technology will contribute greatly to decreasing the dose of radiation needed and improving convenience during angiography.

Ciclofotocoagulación transescleral de contacto, una opción válida en el tratamiento del glaucoma neovascular / Contact transscleral cyclophotocoagulation, a valuable option for treatment of the neovascular glaucoma

Objetivo: describir los resultados de la ciclofotocoagulación tranescleral de contacto como opción de tratamiento en el glaucoma neovascular. Métodos: se realizó un estudio descriptivo, longitudinal prospectivo, en 100 pacientes con glaucoma neovascular atendidos en la Consulta Provincial de Glaucoma de la provincia de Pinar del Río, que cumplían con las indicaciones de la ciclofotocoagulación transescleral con láser. Resultados: el 69 por ciento de los pacientes tratados se encontraron entre los 61 y 80 años de edad. Hubo un predominio del sexo masculino. La agudeza visual se mantuvo estable posterior al tratamiento y hubo una reducción de la presión intraocular en el 91 por ciento de los casos. En el 62 por ciento se reportaron cifras inferiores a los 21 mmHg a los 3 meses posoperatorio; en el 89 por ciento de los pacientes se logró alivio del dolor y en el 75 por ciento hubo regresión de los neovasos. Conclusiones: la ciclofotocoagulación transescleral de contacto proporciona una reducción de la presión intraocular con alivio del dolor y regresión de los neovasos en los pacientes con glaucoma neovascular, y no se produce variación de la agudeza visual(AU)

Objective: to describe the results of contact transscleral cyclophotocoagulation as therapeutical alternative in the neovascular glaucoma. Methods: prospective, longitudinal and descriptive study of one hundred patients with neovascular glaucoma, who had been seen at the provincial glaucoma service of Pinar del Rio province and met the criteria for transscleral cyclophotocoagulation using laser. Results: sixty nine percent of treated patients were 61-80 years old. Males predominated. Visual acuity remained stable after treatment and the intraocular pressure lowered in 91 percent of cases. Sixty two percent reported figures lower than 231 mmHg three months after surgery, 89 percent of patients relieved their pain and the regression of neovessels occurred in 75 percent of cases. Conclusions: contact transscleral cyclophotocoagulation achieves the reduction of the intraocular pressure with pain relief and regression of neovessels in patients with neovascular glaucoma; the visual acuity does not change(AU)

Determination of laser energy density threshold leading to glare-induced blindness by pattern visual evoked potential in guinea pigs / 解放军医学杂志

Objective To explore the application of pattern visual evoked potential (PVEP) in examination of energy density threshold of laser beam that may lead to glare-induced blindness in guinea pigs. Methods Stainless steel bolts (5mm in length, 1.2mm in diameter), as reference electrode and recording electrode for the PVEP measurement, were implanted into skulls of 27 guinea pigs, located in 6mm proximal to bregma and 10mm distal to bregma. These guinea pigs were randomly divided into three groups with 9 (18 eyes) for each group, and they were exposed to laser beam at wave length of 635nm, 660nm and 690nm, respectively. The PVEP was recorded in each group before and immediately after laser irradiation, and also on day 2 and day 4 after laser irradiation in guinea pigs blinded immediately after laser exposure. The latency and amplitude of P wave in PVEP before irradiation was considered as control value for each group. When PVEP could not be recorded instantly after laser irradiation, the intensity of electric current applied at that time was considered as threshold value of each laser beam. The power of electricity(P) values was then calculated, and energy density threshold that led to glare-induced blindness was figured out according to currentpower curve (P-I curve). On day 2 and day 4 after irradiation, PVEP was additionally recorded, and latency and amplitude of P wave were compared with that of control values to examine the recovery of visual function of the blind guinea pigs. Results The energy density thresholds of the three laser beams at wave length of 635nm, 660nm, 690nm respectively were 356.36 10-9J/cm2, 349.58 10-9J/cm2 and 343.93 10-9J/cm2. In guinea pigs became blind after exposure to laser beams at wave length of 635nm, 660nm, 690nm, the latencies of P wave recorded 2 days after blindness were not significantly different with control value of each group(t=-0.356, P=0.729; t=0.492, P=0.633; t=-0.445, P=0.666), while the difference in amplitudes was statistically significant (t=11.01, P=0.000; t=5.223, P=0.000; t=5.702, P=0.000). Four days after blindness, the latencies and amplitudes of P wave recorded on the guinea pigs were also compared with the control values, but no statistically significant difference was found (latency: t=1.329, P=0.213; t=2.040, P=0.069; t=-0.894, P=0.392; amplitude: t=-3.030, P=0.768; t=0.194, P=0.850; t=-0.948, P=0.365). Conclusions The energy density threshold of laser beams, at length wave of 635nm, 660nm, 690nm, may lead to glare-induced blindness in guinea pigs is around 350 10-9J/cm2. PVEP examination is a useful and harmless way to determine the energy density threshold of laser beam which will cause blindness.

A Study on Design and Application of Tissue Compensator for 6MV X-rays / 대한치료방사선과학회지

A radiation beam incident on an irregular or sloping surface produces the non-uniformity of absorbed dose. The use of a tissue compensator can partially correct this dose inhomogeneity. The tissue compensator is designed based on the patient's three dimensional contour. After required compensator thickness was determined according to tissue deficit at 25 cmx 25 cm field size, 10 cm depth for 6MV x-rays, tissue deficit was mapped by isoheight technique using laser beam system. Compensator was constructed along the designed model using 0.5 mm lead sheet or 5 mm acryl plate. Dosimetric verification were performed by film dosimetry using humanoid phantom. Dosimetric measurements were normalized to central axis full phantom readings for both compensated and non-compensated field. Without compensation, the percent differences in absorbed dose ranged as high as 12.1% along transverse axis, 16.8% along vertical axis. With the tissue compensators in place, the difference was reduced to 0~4.3% Therefore, it can be concluded that the compensator system constructed by isoheihnt technique can produce good dose distribution with acceptable inhomogeneity, and such compensator system can be electively applied to clinical radiotherapy.