Does dose rate affect efficacy? The outcomes of 256 Gamma Knife surgery procedures for trigeminal neuralgia and other types of facial pain as they relate to the half-life of cobalt

Wake Forest University, Winston-Salem, North Carolina, United States
Journal of Neurosurgery (Impact Factor: 3.74). 11/2006; 105(5):730-5. DOI: 10.3171/jns.2006.105.5.730
Source: PubMed


Gamma Knife surgery (GKS) is a treatment option for patients with refractory typical trigeminal neuralgia (TN), TN with atypical features, and atypical types of facial pain. The Gamma Knife's 201 60Co sources decay with a half-life of 5.26 years. The authors examined whether the decrease in dose rate over 4.6 years between Co source replacements affected the control rates of facial pain in patients undergoing GKS.
The authors collected complete follow-up data on 239 of 326 GKS procedures performed in patients with facial pain. Patients were classified by their type of pain. The isocenter of a 4-mm collimator helmet was targeted at the proximal trigeminal nerve root, and the dose (80-90 Gy) was prescribed at the 100% isodose line. Patients reported the amount of pain control following radiosurgery by answering a standardized questionnaire. Eighty percent of patients experienced greater than 50% pain relief, and 56% of patients experienced complete pain relief after GKS. Neither dose rate nor treatment time was significantly associated with either the control rate or degree of pain relief. A significant association between the type of facial pain and the pain control rate after GKS was observed (p < 0.001; Pearson chi-square test). In their statistical analysis, the authors accounted for changes in prescription dose over time to prevent the dose rate from being a confounding variable. There was no observable effect of the dose rate or of the treatment duration within the typical period to source replacement.
Patients with facial pain appear to receive consistent treatment with GKS at any time during the first half-life of the Co sources.

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    • "As previously mentioned, the GK machine's primary functional unit is cobalt-60, which is used to emit photon energy through 201 separate 4 to 18 mm collimator openings that converge on a target specified by a treatment planning system. Balamucki et al. [47] performed a study examining if the half life of cobalt (5.26 years) relates to the outcomes for patients being treated for TN with GKRS. The authors collected data on 239 GKRS procedures performed at their institution between 1999 and 2004. "
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    ABSTRACT: Since its introduction by Leksell, Gamma Knife radiosurgery (GKRS) has become increasingly popular as a management approach for patients diagnosed with trigeminal neuralgia (TN). For this reason, we performed a modern review of the literature analyzing the efficacy of GKRS in the treatment of patients who suffer from TN. For patients with medically refractory forms of the condition, GKRS has proven to be an effective initial and repeat treatment option. Cumulative research suggests that patients treated a single time with GKRS exhibit similar levels of facial pain control when compared to patients treated multiple times with GKRS. However, patients treated on multiple occasions with GKRS are more likely to experience facial numbness and other facial sensory changes when compared to patients treated once with GKRS. Although numerous articles have reported MVD to be superior to GKRS in achieving facial pain relief, the findings of these comparison studies are weakened by the vast differences in patient age and comorbidities between the two studied groups and cannot be considered conclusive. Questions remain regarding optimal GKRS dosing and targeting strategies, which warrants further investigation into this controversial matter.
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