Current Landscape and Future Prospects of Radiation Sensitizers for Malignant Brain Tumors: A Systematic Review

BACKGROUND

Radiation therapy (RT) is the cornerstone of management of malignant brain tumors, but its efficacy is limited in hypoxic tumors. Although numerous radiosensitizer compounds have been developed to enhance the effect of RT, progress has been stagnant. Through this systematic review, we provide an overview of radiosensitizers developed for malignant brain tumors, summarize their safety and efficacy, and evaluate areas for possible improvement.

METHODS

Following PRISMA guidelines, PubMed, EMBASE, Cochrane, and Web of Science were searched using terminology pertaining to radiosensitizers for brain tumor RT. Articles reporting clinical evidence of nonantineoplastic radiosensitizers with RT for malignant central nervous system tumors were included. Data of interest were presumed mechanism of action, median overall survival (OS), progression-free survival (PFS), and adverse events.

RESULTS

Twenty-two unique radiosensitizers were identified. Only 2/22 agents (fluosol with oxygen, and efaproxiral) showed improvement in OS in patients with glioblastoma and brain metastasis, respectively. A larger study was not able to confirm the latter. Improved PFS was reported with use of metronidazole, sodium glycididazole, and chloroquine. There was a wide range of toxicities, which prompted change of schedule or complete discontinuation of 9 agents.

CONCLUSIONS

Progress in radiosensitizers for malignant CNS tumors has been limited. Only 2 radiosensitizers have shown limited improvement in survival. Alternative strategies such as synthetic drug design, based on a mechanism of action that is independent of crossing the blood-brain barrier, may be necessary. Use of drug development strategies using new technologies to overcome past challenges is necessary.

Stage I intraoperative adjustment of eye muscle surgery under general anesthesia: consideration of graduated adjustment

The eyes diverge under general anesthesia. The amount of divergence is predictable; there is a linear relationship between the preoperative and the anesthetized eye position. We have confirmed Apt and Isenberg's regression formula for this relationship (A = 0.8 P + 30). We have previously also reported that adjusting the amount of surgery to be done (stage I adjustment) in cases deviating from this correlation by one standard deviation or more (anomalous) significantly improved our surgical success rate to 85%. Since a fixed arbitrary adjustment of 1 mm more or less surgery had improved our surgical success rate significantly, but still left room for higher success rates, we reviewed our anomalous cases to determine whether a graduated adjustment might be expected to produce even higher success rates. A review of cases including additional ones since our last report failed to support this hypothesis. Satisfactory results in these most recent cases have, however, almost doubled the surgical success rate (in anomalous cases) for our stage I fixed arbitrary 1 mm intraoperative adjustment, from 47% to 90%.