Electrovaporization as a treatment modality for transurethral resection of the prostate: influence of generator type.

OBJECTIVES: To study the influence of the electrosurgical generator on the vaporization efficacy during electrovaporization (EVAP) using different vaporization elements. METHODS: Electrical properties of human prostatic (in vivo) and bovine myocardium (in vitro) tissue were measured under electroresection and electrovaporization conditions. The effective output power of four different generators ("old generation" Force 4 and Force 40 and "new generation" Force 300 and Force FX) was measured at different impedance loads. In vitro, the coagulation and vaporization capabilities of the electrosurgical generators in combination with resection and vaporization elements were studied on homogeneous tissue (bovine myocardium). RESULTS: The electrical impedance of human prostatic tissue and bovine myocardium increases from 400 to 1000 ohms when coagulated. The effective output power of the old generation electrosurgical devices depends strongly on tissue impedance. This implies that working on already coagulated tissue using such devices is not well controlled and not reproducible. By contrast, new generation electrosurgical devices correct for the higher impedance of coagulated tissue, thus delivering constant output power and corresponding tissue effects. CONCLUSIONS: For an effective application of the EVAP technique, the use of a new generation impedance independent electrosurgical unit is highly recommended.

Sharpening the penumbra of high energy electron beams with low weight narrow photon beams.

BACKGROUND AND PURPOSE: High energy (20-50 MeV) electron beams, available from the MM50 Racetrack Microtron, can be used for the treatment of deep-seated tumors. A disadvantage is the increasing penumbra width as a function of depth. By the addition of a narrow (typically 1 cm wide) photon beam near the field edge, the 50-90% penumbra width of the electron beam is reduced, yielding a significantly increased effective field size. MATERIALS AND METHODS: For rectangular electron beams in a water phantom (energies 25 and 40 MeV, field sizes 5 x 5-15 x 15 cm2) a computer program was used to optimize the photon beam parameters (position, weight and width) to obtain a combined beam with the sharpest penumbra at the optimization depth and a beam flatness within certain constraints. The study furthermore included penumbra sharpening of an irregular multileaf collimator-shaped field. RESULTS AND CONCLUSION: At optimization depths near R90, photon beam addition reduces the penumbra width by 40-50% (from 15-20 mm to 8-10 mm). Beam flatness at the optimization depth is within +/-5% and hot-spots are < or =120% for all depths. By the addition of narrow photon beams around the rectangular or irregular field, the electron field width can be reduced by 1-3 cm, while the effective field size is maintained.

Side-firing devices for laser prostatectomy. An overview.

Transurethral laser coagulation of the prostate has become an accepted treatment for benign prostatic hyperplasia (BPH). The most common method is the use of a sideward-firing fiber that, once inserted in the prostatic area, irradiates the abundant prostatic tissue with Nd:YAG laser light. In this study, eight different side-firing fibers that are commercially available were evaluated. The devices can be characterized by the way laser light is deflected sideward and by their thermal behavior. Most of the eight devices differ with regard to the angle at which the laser beam is deflected, the spot size on the irradiated tissue surface, and the heating of the device itself. Implementation of the optical and thermal characteristics of each device in the treatment protocol will contribute to the optimal use of laser energy for prostatectomy.