Patient Setup Time Research Articles

Three-field isocentric technique for breast irradiation using individualized shielding blocks

The three-field technique is the most common method used for breast and regional node treatment after conservative surgery. Several variants of this technique, which are characterized by complex geometrical problems, have been described. A possible simplification of this technique and the use of individualized shielding blocks both for anterior and for tangential fields is proposed, thus allowing for the simultaneous shielding of the half beam and the critical areas. Advantages of isocentrical techniques are thereby maintained, but the number of mechanical movements required is minimized and collimators and couch rotations are not needed. Patient set-up time is also greatly shortened. The accuracy of this technique has been verified using both photographic methods and thermoluminescent dosimetry.

Physical aspects of a rotational total skin electron irradiation.

A technique for rotational total skin electron irradiation is presented in which the patient stands on a slowly rotating platform (SSD = 285 cm) in a large uniform linear accelerator electron field (Eo = 3.5 MeV). The beam is scattered by the transmission ionization chamber and by a special lead/aluminum scattering filter, and then degraded by a sheet of Lucite. A Farmer chamber is used as a patient dose monitor and a method for absolute dose calibration is presented. The field is uniform to within +/- 5% for dimensions of 180 X 40 cm2. The surface dose for rotational therapy is equal to 45% of the maximum dose in a stationary beam. The rotating beam exhibits a dose maximum on the surface, falls to 80% at 0.5 cm and has an x-ray contamination of approximately 4%. The surface dose rate is about 25 cGy/min for the rotating beam. The rotational beam percentage depth dose distributions, calculated using stationary beam information, agree well with measured data. The stationary beam exhibits a dose maximum at 4 mm in tissue, a surface dose of 93%, 80% dose at a depth of 1 cm, a practical range of 1.75 cm, and an x-ray contamination of 2.5%. The rotational total skin electron irradiation significantly reduces the patient treatment and setup time and solves the problem of beam matching, when compared to standard multiple-beam techniques.