Defining the role of radiosurgery in the management of brain metastases.

The role of stereotactic radiosurgery in the management of recurrent and newly diagnosed brain metastases was evaluated prospectively. From December 1988 to March 1991, 58 lesions in 40 patients were treated with accelerator-based stereotactic radiosurgery. All patients were followed for a minimum of 6 months or to death. The primary purpose was to determine the impact of radiosurgery on local control and its subsequent effects on quality of life. An overall tumor control rate of 82% with a complete response rate of 43% were achieved. As anticipated, the response rate for smaller tumors was substantially better than that for larger tumors (78% for lesions < 2 cm3; 50% for lesions > or = 10 cm3). Although the overall in-field progression rate was 18.5%, only 1/23 (4%) complete responders subsequently recurred. The in-field failure rate is highly comparable with recently published surgical data. Progression outside the brain was noted in two-thirds of patients. One quarter of the deaths were neurologic. The median survival for this minimally selected patient population was 6.5 months. Stereotactic radiosurgery was also associated with improved quality of life as measured by Karnofsky score, neurologic function, and steroid dependence. Long-term steroid dependence was encountered in only four patients. We conclude that stereotactic radiosurgery can be used effectively in patients with brain metastases. In this series, a high tumor response rate was achieved which was associated with improved quality of life.

3D rendering of SAR distributions from Thermotron RF-8 using a ray casting technique.

A comprehensive 3D visualization package developed for CT-based 3D radiation treatment planning has been modified to volume-render SAR data. The program accepts data from sequential thermographic thermometry measurements as well as calculated data from thermal models. In this presentation sample data obtained from a capacitive heating system 'Thermotron-RF8' is presented. This capability allows the generation of accurate standardized volumetric images of SAR and provides a valuable tool to better preplan hyperthermia treatments.

A three-dimensional volume visualization package applied to stereotactic radiosurgery treatment planning.

A comprehensive software package has been developed for visualization and analysis of 3-dimensional data sets. The system offers a variety of 2- and 3-dimensional display facilities including highly realistic volume rendered images generated directly from the data set. The package has been specifically modified and successfully used for stereotactic radiosurgery treatment planning. The stereotactic coordinate transformation is determined by finding the localization frame automatically in the CT volume. Treatment arcs are specified interactively and displayed as paths on 3-dimensional anatomical surfaces. The resulting dose distribution is displayed using traditional 2-dimensional displays or as an isodose surface composited with underlying anatomy and the target volume. Dose volume histogram analysis is an integral part of the system. This paper gives an overview of volume rendering methods and describes the application of these tools to stereotactic radiosurgery treatment planning.

Monte Carlo and convolution dosimetry for stereotactic radiosurgery.

The dosimetry of small photon beams used for stereotactic radiosurgery was investigated using Monte Carlo simulation, convolution calculations, and measurements. A Monte Carlo code was used to simulate radiation transport through a linear accelerator to produce and score energy spectrum and angular distribution of 6 MV bremsstrahlung photons exiting from the accelerator treatment head. These photons were then transported through a stereotactic collimator system and into a water phantom placed at isocenter. The energy spectrum was also used as input for the convolution method of photon dose calculation. Monte Carlo and convolution results were compared with the measured data obtained using an ionization chamber, a diode, and film.

Minimization of small bowel volume within treatment fields utilizing customized "belly boards".

Thirty consecutive patients with pelvic malignancies were evaluated prospectively for the impact of a novel bowel minimization device ("belly board") on the volume of small bowel included within a four field pelvic radiation plan. A customized polyurethane and styrofoam bowel immobilization mold was created for each patient in the prone position. Using contrast enhanced CT scanning on a dedicated radiation treatment planning scanner, we imaged the location of the small intestine in the supine position and the prone position aided by the "belly board". Custom in-house interactive image analysis software was developed to allow volumetric determination of small bowel within the treatment portals. The mean small bowel volume was reduced by 66% (299 cm3 to 102 cm3), comparing the standard supine position to the prone position assisted by the "belly board". In 13 patients without prior pelvic surgery, the small bowel volume reduction was a more dramatic 74% (334 cm3 to 88 cm3). All patients were found to benefit from this prone "belly board" setup regardless of body habitus, weight, and age. Compliance with the set-up including use of bladder distension was excellent. All patients completed their pelvic radiotherapy without requiring a treatment break. Weight loss at completion averaged less than 5%. Seventy-six percent of patients experienced little or no diarrhea. This technique is comfortable, inexpensive, highly reproducible, and permits maximal bowel displacement from standard pelvic radiotherapy fields.