Improved dose homogeneity to the intact breast using three-dimensional treatment planning: technical considerations.

The current consensus is that breast-conservative treatment is superior to mastectomy because it provides survival equivalent to total mastectomy and axillary dissection while preserving the breast. This technique still has several technical issues that can adversely influence the successful outcome of breast-conservative treatment. Specifically, dose coverage and homogeneity must be maintained throughout the breast while reducing the hot-volume magnitude and normal tissue complications. A random retrospective three-dimensional treatment-planning study was conducted using computed tomography scans of 20 female patients with early-stage breast cancer. Two- and three-dimensional homogenous and heterogeneous treatment planning was conducted using all possible hard-wedge combinations and effective photon energies, with the goal of reducing the hot volumes in the breast below 110 percent of the prescribed dose. The hard-wedge combination that minimized the hot volumes uses either 15-degree wedges on the medial and lateral beams or a 30-degree wedge on the medial beam and a 15-degree wedge on the lateral beam. For patients with bridge distances less than 20 cm, this wedge combination reduces the hot volumes below 110 percent of the prescribed dose. For patients with bridge distances greater than 20 cm, low- and high-energy photon beams must be mixed to lower the maximum dose below 110 percent of the prescribed dose. The hot volumes in the breasts of 20 random patients was reduced below 110 percent of the prescribed dose without a significant reduction in tumor coverage.

Clinical application of digitally-reconstructed radiographs generated from magnetic resonance imaging for intracranial lesions.

PURPOSE: The purpose of this work is to demonstrate the clinical utility of magnetic resonance (MR) imaging-based digitally reconstructed radiographs (DRRs) for the setup and verification of patients with intracranial lesions. METHODS AND MATERIALS: MR images of 16 patients with various intracranial lesions were obtained for treatment planning and virtual simulation. Five-millimeter-thick contiguous T1-weighted postcontrast transverse slices were obtained using a standard head coil in a General Electric Signa 1.5T MR scanner. MR-DRRs were generated using the "pseudo density" technique on an existing treatment planning computer without any special modifications. Anterior and lateral verification films were taken for each patient for visual comparison with MR-based DRRs. RESULTS: Visual alignment with bony landmarks, including the orbits, frontal sinus, sphenoid sinus, auditory meatus, nasal bone, vomer bone, mastoid process, and the cranium were used by physicians, physicists, and therapists to verify patient positioning. Misalignments from 3 to 10 mm were visually identified and corrected using this technique. CONCLUSION: A method for visually utilizing MR-based DRRs during simulation has been developed and clinically implemented. The quality of MR-DRRs generated using this technique is such that physicians, physicists, and therapists can easily and routinely compare MR-DRRs side-by-side with simulation films.

Clinical efficacy of respiratory gated conformal radiation therapy.

One major limitation of three-dimensional conformal radiation therapy that has not been adequately addressed is respiration-induced organ motion. During respiration, tumors in the abdomen can typically move from 1 to 3 centimeters. Because the size and shape of external radiation treatment fields do not change during treatment, the field size of the x-ray beam must be enlarged to encompass the tumor through the entire respiration cycle. Several manufacturers are developing respiratory gating systems. These systems allow the selective delivery of absorbed doses to moving target volumes in the abdomen during time intervals when the target volume is within the intended location. Before respiratory gated radiotherapy can be implemented clinically, the efficacy of the procedure must be justified. The magnitude of dosimetric and geometric uncertainties associated with respiratory motion must be identified to determine if gating can provide an advantage over conventional treatment techniques. In addition, clinical situations and specific types of cancer that could benefit from respiratory gating must also be identified.