Yuzou Onogi

Real-time beam monitoring in dynamic conformation therapy

PURPOSE Although portal imaging is a promising method of verification during static multiport irradiation, it cannot be applied directly to dynamic irradiation such as rotational conformation with multileaf collimator movement. A real-time beam monitoring system based on megavoltage computed tomography scanning has been developed to establish a verification method for the rotational conformation technique. METHODS AND MATERIALS Exit beam through the patient is extracted by the same detector unit as used for megavoltage scanning during the actual treatment. Beam edge is defined as the 50% level of the maximum dose of the detector array. Megavoltage computed tomography is done after patient setup and just prior to the actual irradiation. Detected beam pathways are overlaid on this image approximately every 1 s. Therapists can monitor correlation between the target and actual beam pathways on a real-time computer display. RESULTS The accuracy of field edge detection has been proven to be less than 2 mm from various measurements. Real-time monitoring is more useful in rotational conformation than in static multiport irradiation due to dynamic movement of the collimator. Field errors were identified in two of 54 sessions using this method. CONCLUSIONS Although several limitations remain to be solved, the method presented is a useful tool for treatment verification of high accuracy radiation therapy, particularly rotational conformation irradiation.

Technological features and clinical feasibility of megavoltage CT scanning

Megavoltage CT scanning using 4-MV and 6-MV radiotherapy beams has been developed and applied to verify errors in patient positioning. A detect or system composed of 120 pairs of cadmium tungstate scintillators with photodiodes is mounted to the treatment unit at a distance of 160 cm from the beam source. Image reconstruction is performed with a standard filtered back-projection algorithm. Scanning time and reconstruction time for a slice is approximately 35 s and 60 s respectively. Although spatial resolution is as large as 4 mm, it has sufficient image quality to be applied for treatment planning and verification. The delivered dose with 4 MV and 6 MV is about 1.4 cGy and 28. cGY respectively. When a megavoltage CT image is taken in treatment position, the positioning errors are easily detected by comparing it with diagnostic CT sections for treatment planning. Several clinical examples are presented.

Radiotherapy of bone metastases of a spinal meningeal hemangiopericytoma

Hemangiopericytoma is a rate tumor arising from pericapillary cells or pericytes of Zimmerman, and can occur anywhere capillaries are found. We describe a patient with a meningeal hemangiopericytoma who was treated with primary surgical resection and experienced multiple bone metastases 20 years after the first treatment. This patient with multiple bone metastases was treated with multiple courses of irradiation and good palliation was achieved.ZusammenfassungDas Hämangioperizytom ist ein seltener Tumor, der seinen Ausgang von perikapillären Zellen oder Zimmermannschen Perizyten nimmt. Er kann überall dort entstehen, wo sich Kapillaren befinden. Wir berichten über einen Patienten mit meningealem Hämangioperizytom, der zunächst radikal operiert wurde und 20 Jahre nach der Primärbehandlung multiple Knochenmetastasen entwickelte. Der Patient wurde mit gutem palliativen Ergebnis mehrfach bestrahlt.