198 Radiation Oncology, Biology, Physics October 1987, Volume 13, Supplement 1

205

DEFINITIVE IRRADIATION FOR LOCALIZED NON-HODGKINS LYMPHOMA OF BREAST

Daniel DeBlasio, M.D., Beryl McCormick, M.D., Mitchell Smith, M.D., Ph.D., Sheryl Brunstein, M.D., David Straus, M.D., and Lourdes Nisce, M.D.

Memorial Sloan-Kettering Cancer Center, New York, New York 10021

A diagnosis of primary non-Hodgkins lymphoma of the breast was biopsy-proven in 20 patients who presented to our institution between 1970 and 1984. Four patients were treated with a modified mastectomy, one with chemotherapy only, and one developed wide-spread metastatic disease before local-regional treatment could be instituted. The remaining 14 patients comprise the basis of this study.

All patients were clinically staged. There were 13 patients with lA-E disease, and one with stage IIA-E disease. None had "B" symptoms. Review of the pathology revealed the following histo- logical subtypes, using the Rappaport classifications: DHL-7, DPDL-4, DML-2, and NML-1.

All patients with stage lA-E disease were treated with breast radiation. The axillary nodes as well were included in half of the patients, and one, in addition, received mantle irradiation. The majority of the patients received 3500-4500 cGy, but three received lower doses. One patient, with stage IIA-E disease, received 6 months of systemic chemotherapy, followed by 3500 cGy to the breast and axilla.

Three of the 14 patients relapsed within the treated area, for a crude local control rate of 78%. One of the three local failures was salvaged with a mastectomy and remains alive and well 15 years after diagnosis. Six of the 14 patients relapsed distantly, but only three have died of disease. An additional 3 patients died, NED, of other causes. Thus, with a medium followup time of 6% years, the crude survival rate is 57% (8/14) for localized breast lymphomas treated with radiation therapy.

206 THE VALUE OF THREE-DIMENSIONAL DISPLAY TECHNIQUES IN RADIATION THERAPY TREATMENT PLANNING

Julian Rosenman Ph.D. M.D., Edward Chaney Ph.D., Stephen Pizer Ph.D., George Sherouse M.S., Henry Fuchs, Ph.D.

Departments of Radiation Oncology and Computer Science, University of North Carolina, Chapel Hill

Three-dimensional (3D) dose calculation software provides the radiation therapist with the opportunity to develop high quality radiation therapy treatment plans. However, the conventional display of isodose contours on two-dimensional CT slices imposes important limitations on the treatment planning process. For example, this format makes it difficult to choose the best of several competing 3D treatment plans, because each plan must be evaluated on a slice-by-slice basis. This display format also makes it difficult to visualize the path of any radiation beam not perpendicular to the z-axis of the CT slices, discouraging consideration of all treatment plans that utilize non-transverse planar beams. We believe that these limitations of the conventional CT format can be overcome by the concomitant use of appropriate 3D displays.

There are two general types of 3D displays. In the first, the slice-based reflective display a surface is determined from each object of interest within the original image, and displayed with simulated light reflections. In the second approach (voxel display), the image is produced directly from the original recorded intensities. Slice-based reflective methods require the user to explicitly define the objects to be displayed which can include normal anatomy, tumor, radiation target volumes, implants, beams and isodose contours. High contrast objects can be automatically outlined but low contrast objects, at present, must be hand-contoured. We have found the best approach to deriving surfaces from these contours is the Fuchs-Kedem-Uselton method which computes the surface as that collection of polygons which minimizes the surface area.

Rendering is the process of computing and displaying the intensity and color of each screen pixel so as to give the impression of a solid object. The intensity of the contributing surface at each pixel is determined by calculating the appropriate depth-shading (decreasing the intensity as depth from the viewer increases). Sophisticated renderers allow the intensities of the multiple contributing surfaces to be combined so as to give the effect of transparency. Two methods of shading 3D images are now in common use. The simpler, Gouraud shading, involves linearly interpolating the shading across each polygon from shadings computed at the vertices. A more sophisticated rendering, Phong shading, allows for the inclusion of specular reflections.

We have been studying the value of these images in radiation therapy planning for more than three years. We have learned that high quality static shaded graphics images can be used effectively to display the spatial relationships between anatomy, and radiation beams. They may also be useful as a permanent record of the treatment given. Transparency appears to be of great importance in making these display effective. On the other hand, these techniques appear not to be adequate for the display of isodose surfaces. Current software approaches to this problem include successive display of images rendered at viewpoints separated by a few degrees. The object appears to rotate in space giving the viewer a kinetic depth effect. Even more effective is the polarizing plate which allows the viewer to see a true three-dimensional image while wearing inexpensive spectacles with polarized lenses.

A new massively parallel graphics engine, Pixel-Planes, has been implemented at our institution that allows real-time manipulation of high quality images. Preliminary work on this machine indicates that it may overcome most of the shortcomings of conventional 2D displays.