Use of segmental boost fields in the irradiation of inguinal lymphatic nodes.

En face electron fields to boost inguinal lymphatics have been used by oncologists for many years. With the introduction of multileaf collimators (MLC) and independent jaws, the practice of creating segmental fields to boost areas of interest has expanded. Typical anterior-posterior opposing field treatment of the pelvis may now be enhanced to include additional anterior segments to boost lymphatic tissue at a predetermined depth. This report illustrates the clinical implementation of one such segmental boost technique. Computer generated isodose plans utilize manual contour and CT-generated data for analysis of inguinal lymphatic depths. Potential areas of field overlap are discussed as well as the use of combined 6 and 15 MV photon energies to reduce areas of inhomogeneous dose. Technical details associated with MLC field size limits and other clinical factors are also discussed in relationship to smooth treatment delivery.

A room-based diagnostic imaging system for measurement of patient setup.

A room-based diagnostic x-ray imaging system for routine measurement of radiotherapy patient orientation has been developed. The system consists of a pair of room-mounted x-ray tubes and a portable imager consisting of an orthogonal pair of phosphor screens, a mirror/lens system, a CCD camera, and computer software for comparing images of the patient to reference images. Orthogonal pairs of images can be acquired quickly and with relatively little exposure, allowing correction of patient setup on a daily basis. This could limit patient setup error to the uncertainty in the measurement and repositioning processes, a potentially significant improvement over the present standard.

Measurement of patient setup errors using port films and a computer-aided graphical alignment tool.

Patient orientations were measured for 49 patients treated in the abdomen, chest, and pelvic regions over the course of 20 months. Setup errors were determined using a curve-matching graphical interface to compare digitized port films to digitized simulation films. Data representing both "initial patient setup" and "patient setup at treatment" are presented and compared. Data were sorted by anatomic area and analyzed both at the population level and on a patient-by-patient basis. For each population, setup errors were observed to be primarily random, with population standard deviations of 5-6 mm for each of three translations and 2-3 degrees for each of two rotations. Rotations about the patients' inferior-superior axes were not measured. For each site, correlations between translations and/or rotations were small. The results are consistent with those from previous studies. The data set is among the largest collected to date.