Correlation of radiation response with tumor oxygenation in the Dunning prostate R3327-AT1 tumor.

PURPOSE: To investigate the application of pretreatment oxygenation to the AT1 subline of the Dunning R3327 prostate tumor, which is more hypoxic and faster growing than the H1 subline previously studied. METHODS AND MATERIALS: Dunning prostate R3327-AT1 tumors growing on Copenhagen rats were administered 30 Gy of X-ray radiation either with or without oxygen inhalation. Tumor oxygenation was sampled by (19)F nuclear magnetic resonance echo planar imaging relaxometry of the reporter molecule hexafluorobenzene, no more than 24 h before irradiation. RESULTS: Large tumors (>3.0 cm(3)) exhibited significantly greater hypoxic fractions and lower mean partial pressure of oxygen (pO(2)) than their smaller counterparts (<1.5 cm(3)). However, unlike the R3327-HI subline, large AT1 tumors generally did not respond to oxygen inhalation in terms of altered hypoxic fraction or response to irradiation. Although the tumors did not respond to oxygen inhalation, each tumor had a different pO(2), and there was a clear trend between level of oxygenation at time of irradiation and tumor growth delay, with considerably better outcome when mean pO(2) > 10 mm Hg. The comparatively small baseline hypoxic fraction in the group of small tumors was virtually eliminated by breathing oxygen, and the growth rate was significantly reduced for tumors on rats breathing oxygen during irradiation. CONCLUSIONS: These results further validate the usefulness of nuclear magnetic resonance oximetry as a predictor of response to radiation therapy.

Robotically guided radiosurgery for children.

BACKGROUND: A robotically guided linear accelerator has recently been developed which provides frameless radiosurgery with high precision. Potential advantages for the pediatric population include the avoidance of the cognitive decline associated with whole brain radiotherapy, the ability to treat young children with thin skulls unsuitable for frame-based methods, and the possible avoidance of general anesthesia. We report our experience with this system (the "Cyberknife") in the treatment of 21 children. PROCEDURES: Cyberknife radiosurgery was performed on 38 occasions for 21 patients, age ranging from 8 months to 16 years (7.0 +/- 5.1 years), with tumors considered unresectable. Three had pilocytic astrocytomas, two had anaplastic astrocytomas, three had ependymomas (two anaplastic), four had medulloblastomas, three had atypical teratoid/rhabdoid tumors, three had craniopharyngiomas, and three had other pathologies. The mean target volume was 10.7 +/- 20 cm(3), mean marginal dose was 18.8 +/- 8.1 Gy, and mean follow-up is 18 +/- 11 months. Twenty-seven (71%) of the treatments were single-shot and eight (38%) patients did not require general anesthesia. RESULTS: Local control was achieved in the patients with pilocytic and anaplastic astrocytoma, three of the patients with medulloblastoma, and the three with craniopharyngioma, but not for those with ependymoma. Two of the patients with rhabdoid tumors are alive 16 and 35 months after this diagnosis. There have been no procedure related deaths or complications. CONCLUSION: Cyberknife radiosurgery can be used to achieve local control for some children with CNS tumors without the need for rigid head fixation.

Feasibility of radiosurgery for malignant brain tumors in infants by use of image-guided robotic radiosurgery: preliminary report.

OBJECTIVE: The benefits of radiation therapy are generally denied to infants with malignant brain tumors because of the risk of devastating cognitive decline. Efforts to limit this morbidity with radiosurgical techniques have not been feasible for infants because of the dual requirements of rigid head fixation and high precision. We report the radiosurgical treatment of five infants by use of a robotically controlled system without rigid head fixation. METHODS: Five infants with malignant brain tumors received radiosurgical treatment with a robotically driven linear accelerator. Immobilization was aided by general anesthesia, form-fitting head supports, face masks, and body molds. The average marginal dose was 17 +/- 2 Gy, and the average treatment volume was 18 +/- 22 ml. RESULTS: X-rays obtained during treatment revealed acceptable agreement with preoperative computed tomographic scans in all patients. In one patient, the lesion did not progress, but a distant recurrence occurred 15 months after radiosurgery and also was treated with radiosurgery. In another patient, tumor in the treated region did not progress, but recurrence elsewhere led to death 7 months after treatment. Tumor enlargement occurred in Patient 3 at 3 months posttreatment, leading to death 2 months later. Tumor size was smaller in the remaining two patients at 9 and 11 months after treatment. There has been no toxicity attributed to treatment. CONCLUSION: Radiosurgery with minimal toxicity can be delivered to infants by use of a robotically controlled system that does not require rigid fixation. A formal dose-escalation trial is under way to address dose and toxicity for infants more thoroughly.