Abstract
IntroductionWith conventional radiation technique alone, it is difficult to deliver radical treatment (≥ 60 Gy) to gliomas that are close to critical structures without incurring the risk of late radiation induced complications. Temozolomide-related improvements in high-grade glioma survival have placed a higher premium on optimal radiation therapy delivery. We investigated the safety and efficacy of utilizing highly conformal and precise CyberKnife radiotherapy to enhance conventional radiotherapy in the treatment of high grade glioma.MethodsBetween January 2002 and January 2009, 24 patients with good performance status and high-grade gliomas in close proximity to critical structures (i.e. eyes, optic nerves, optic chiasm and brainstem) were treated with the CyberKnife. All patients received conventional radiation therapy following tumor resection, with a median dose of 50 Gy (range: 40 - 50.4 Gy). Subsequently, an additional dose of 10 Gy was delivered in 5 successive 2 Gy daily fractions utilizing the CyberKnife® image-guided radiosurgical system. The majority of patients (88%) received concurrent and/or adjuvant Temozolmide.ResultsDuring CyberKnife treatments, the mean number of radiation beams utilized was 173 and the mean number of verification images was 58. Among the 24 patients, the mean clinical treatment volume was 174 cc, the mean prescription isodose line was 73% and the mean percent target coverage was 94%. At a median follow-up of 23 months for the glioblastoma multiforme cohort, the median survival was 18 months and the two-year survival rate was 37%. At a median follow-up of 63 months for the anaplastic glioma cohort, the median survival has not been reached and the 4-year survival rate was 71%. There have been no severe late complications referable to this radiation regimen in these patients.ConclusionWe utilized fractionated CyberKnife radiotherapy as an adjunct to conventional radiation to improve the targeting accuracy of high-grade glioma radiation treatment. This technique was safe, effective and allowed for optimal dose-delivery in our patients. The value of image-guided radiation therapy for the treatment of high-grade gliomas deserves further study.
Highlights
With conventional radiation technique alone, it is difficult to deliver radical treatment (≥ 60 Gy) to gliomas that are close to critical structures without incurring the risk of late radiation induced complications
We report the safety and efficacy of using the highly conformal and accurate CyberKnife radiosurgery system to enhance the final week of conventional radiotherapy in 24 patients with high-grade gliomas in close proximity to critical structures
Treatment plans were composed of hundreds of pencil beams shaped using a single circular collimator to generate highly conformal plans
Summary
With conventional radiation technique alone, it is difficult to deliver radical treatment (≥ 60 Gy) to gliomas that are close to critical structures without incurring the risk of late radiation induced complications. Local control is considered the primary practice guidelines recommend treating high-grade gliomas with conventionally fractionated (1.8 - 2.0 Gy) partial brain irradiation over an approximately 6 week period [7]. It is our clinical practice to treat high-grade glioma patients with maximum safe surgery followed by 6 weeks of chemoradiation (60 Gy partial brain irradiation in 2 Gy fractions with concurrent and adjuvant Temozolomide). It has been generally feasible with conventional radiation technique to deliver such "full dose" treatment while respecting institutional peritumoral critical structure maximum point dose tolerances (Table 1). With recent Temozolomide-related improvements in high-grade glioma survival [4], it is more likely than ever that suboptimal radiation treatment will result in either a decrement in overall survival or an increase in late radiation toxicity
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