A non-contacting intraoperative electron cone apparatus.

Aluminum tubes, 20 cm long, of various diameter and face angle have been used to collimate electron beams for intraoperative radiotherapy. The tubes placed in a body cavity are clamped to the treatment couch. A thin rod is fixed coaxially to a disc which is placed on the entrance face of the tube. A stepwise procedure involving couch translation, rotation, and gantry rotation is used to align the central axis of the beam with the axis of the cone. Further collimation is provided by an aperture mounted in an assembly which slides into the standard accessory holder of the machine and is separated by a 10 cm air gap from the tube in the patient. Careful adjustment of this aperture diameter results in a relatively uniform dose across the treated area. The use of 3 mm wall thickness aluminum tube provides for minimal leakage outside of the cone. A camera has been mounted to a plate that also mounts in the standard accessory holder and is used to document the area treated.

A frameless method for stereotactic radiotherapy.

A frameless method for stereotactic multiple arc radiotherapy (SMART) is described. Three short gold wires are implanted in the scalp approximately 100 mm apart. These are localized in a computed tomographic or angiographic study along with the target. Subsequently the gold markers are localized on beam films and the target position calculated using a computer program ISOLOC. This program provides the couch movements required to move the target to the isocentre and a micropositioner attached to the couch is used to make the adjustment. Beam films are repeated until the movements required are less than 1 mm in any direction. It is shown that the simple procedures of implanting the markers subcutaneously do not provide a stable reference system in about 25% of patients and the markers are now screwed into the cranium. The precision of the method is evaluated by phantom studies and measurements taken during several hundred treatments.

Localizing the spinal cord in oblique off-cord lung boosts.

We present a method to accurately localize the spinal cord in oblique projections on plain radiographs. Utilizing a CT scan done with the patient in the treatment position, a template is generated to localize the spinal cord. The technique involves analyzing successive axial CT slices and locating cord position relative to the beam central axis. The template is then placed on the simulator fiducial plate at the time of verification simulation. Cord position is documented in the "beam's eye view" on the radiograph. Utilizing this technique, our radiation oncologists are more comfortable defining the medial field border in oblique setups. In most cases, this technique will minimize the perceived need to add superfluous spinal cord blocks that compromise tumor dose.

Practical 3-D radiotherapy planning of brain tumors.

In postoperative radiotherapy of brain tumors it is usually the case that preoperative imaging studies, either CT or MRI, were performed outside of the purview of the radiation therapy department. Thus the target volume is defined in an imaging study that does not lend itself readily for entry to a 3-D treatment planning system. A method is described that adjusts the patient structure defined by scan data to an appropriate position for radiotherapy. Software tools that are simple to use have been incorporated in a 3-D treatment planning program that allows oblique treatment planes to be defined. The program provides beam's-eye-view plots of the fields that are used to overlay simulation films and will automatically describe a field blocking outline that provides a prescribed margin on the target volume or other structures that have been defined. Finally, dose calculations in arbitrary planes through the head are made and isodose plots produced.

Perianal Paget's disease: successful treatment with combined chemoradiotherapy. Report of a case.

A case of locally extensive perianal Paget's disease is presented. Initial wide local excision, guided by frozen sections, was inadequate. Multiple punch biopsies subsequently revealed extensive circumferential involvement of the anoderm by Paget's disease, making wide local excision difficult. Therefore, the patient was treated with combined chemoradiotherapy (5000 cGy, 5-fluorouracil, and mitomycin C). Fourteen months after treatment, the patient had a complete response.