Three years experience in the development of a dynamic quality management concept in a digitized radiotherapy department.

BACKGROUND: This article addresses general procedures for dynamic quality management and offers some practical suggestions to control an electronic radiotherapy system. The review of data takes place additionally to and completely independent of visual opportunities such as the approval of port images. MATERIAL AND METHODS: The radiotherapy procedure was split up into individual processes, all steps were analyzed with respect to their potential of being influenced by human mistakes or system malfunction. RESULTS: Relating the mistakes to the absolute number of treated fields, we can show that the percentage of fields that is related to an error was 0.22% in 1997 and could be decreased to 0.18% in 1999. For an average number of about 90-100 patients per day the time to verify the electronic data were: 6-8 h for the routine weekly control, 4 h/week to check the first treatments and manually calculated treatment fields, 6 h/week for physicists to check the 3D plans and 12 h/week for senior oncologists to check the 3D plans and data approval in the verification system. CONCLUSIONS: Meticulous monitoring and the currently available level of automation ensure that even clinically irrelevant errors and mistakes can be detected so that patients can be offered patient-oriented efficient radiotherapy in a routine hospital setting.

Corneal lathing using the excimer laser and a computer-controlled positioning system: Part II--Variable trephination of corneal buttons.

A new system is presented that allows a variable trephination of donor corneas for the preparation of corneal buttons used in penetrating keratoplasty. With the help of a computer-controlled positioning system that uses high-precision micropositioning elements (both translation and rotational stages) the donor cornea is removed, epithelial side up, in a fixation device in front of a focused excimer laser beam (ArF, lambda = 193 nm). User friendly computer software allows the surgeon to select a variety of parameters (diameter, shape, angle of trephination) of the corneal graft. Histological and electron microscopical data of human corneas trephined with this "Excimer Laser Corneal Shaping System" are presented.

Corneal lathing using the excimer laser and a computer-controlled positioning system: Part I--Lathing of epikeratoplasty lenticules.

Precise lathing of epikeratoplasty lenticules is difficult to achieve with the cryolathe due to unpredictable expansion of the lathing tools and the corneal tissue during the freezing process. In addition, the procedure destroys all viable cells in the transplant thereby possibly contributing to the prolonged period of visual rehabilitation. Non-freezing techniques using the microkeratome or the rotor-trephine, on the other hand, are technically demanding, can cause mechanical damage during cutting or fixation, and, have not given consistently reproducible refractive results. A new system is presented that allows a variable laser ablation of donor corneas into lenticules for aphakic and myopic epikeratoplasty, as well as for lamellar keratoplasty. With the help of a computer-controlled positioning system that uses high-precision micropositioning elements (both translation and rotational stages) the donor cornea is moved, epithelial side down, in a holding device in front of a focused excimer laser beam (ArF, lambda = 193 nm). This photoablation lathing process assures the viability of the stromal cells in the lenticule in close approximation to the treated surface. The user friendly computer software allows the fast and convenient selection of a variety of parameters, such as the diameter of the optical zone, the shape of the wing zone, the refractive power, the central thickness of the lenticule and the overall contour of the transplant. The first laboratory data of lenticules prepared from human corneas with this "Excimer Laser Corneal Shaping System" are presented.