Patients with low-grade gliomas often have a better prognosis than patients harboring higher-grade tumors [3–10, 12, 18–21]. In fact, the median survival for patients with low-grade gliomas is typically between 5 and 10 years [3–10, 12, 18–21]. Despite this more favorable prognosis, 50–75 % of patients with low-grade gliomas eventually die from their disease because of either tumor progression or degeneration to a higher malignant grade [1, 7, 8]. The optimal treatment for patients who harbor low-grade gliomas, however, remains unclear because many patients are followed radiographically and intervention is only pursued when clinical or radiographic progression becomes evident [35]. Moreover, the role of surgery in delaying recurrence and/or malignant degeneration as well as prolonging survival remains controversial [7, 35].

This lack of understanding of the effectiveness of surgery for patients with low-grade gliomas is because there are no randomized control trials or matched pair analyses. Keles et al. performed a literature review of the role of surgery for patients with low-grade gliomas and found 30 studies evaluating the role of surgery for patients with low-grade gliomas [1]. In this review, all but five studies were excluded because they included patients with grade I gliomas, relied upon intraoperative determination of extent of resection, and had small sample sizes, among others [36–39]. These five studies that met the inclusion criteria were also limited because extent of resection was determined by intraoperative gross visualization rather than neuro-imaging, and a distinction between gross total and near total resection was not made [36–39]. This review and others have found data supporting a role of surgery in delaying recurrence and prolonging survival controversial [1, 40].

Despite this, there are an increasing number of studies demonstrating a benefit for increasing extent of resection for patients with low-grade gliomas [7]. Wisoff et al. evaluated 518 pediatric patients with low-grade glioma, and found that extent of resection was significantly associated with improved progression-free survival [41]. The 5-year survival rate was 99 % with gross total resection, 95 % with 1.5 cm³ residual disease, 94 % with 1.5–2.9 cm³ residual, and 87 % with >3 cm³ residual [41]. The 5-year progression-free survival rate was 90 % with gross total resection and 45–65 % with any volume (1.5–3 cm³) of residual disease [41]. More recently, Smith et al. performed a retrospective volumetric analysis of extent of hemispheric LGG resection in 216 patients and found that patients with at least 90 % resection had 5- and 8-year survival rates of 97 % and 91 %, respectively, while patients with less than 90 % resection had 5- and 8-year survival rates of 76 % and 60 %, respectively [42]. We recently evaluated 170 patients with low-grade gliomas and found that gross-total resection was associated with increased overall survival as compared to patients who underwent subtotal resection [11]. Five-year overall survival after gross total, near total, and subtotal resection was 95 %, 80 %, 70 %, respectively, and 10-year survival was 76 %, 57 %, and 49 %, respectively [11]. Additionally, after gross total, near total, and subtotal resection, median time to tumor progression was 7.0, 4.0, and 3.5 years, respectively [11]. The median time to malignant degeneration after gross total, near total, and subtotal resection was 12.5, 5.8, and 7 years, respectively [11]. In a separate study, we found that gross total resection was independently associated with delayed malignant degeneration [7].

There is a growing body of evidence that surgery is an effective treatment for patients with low-grade gliomas, despite an absence of randomized control trials. For patients who present with large tumors, significant neurological deficits, and medically intractable seizures, immediate surgical intervention is generally the preferred treatment option [7, 43]. Extensive resection without causing an iatrogenic deficit can lead to improvements in overall survival, progression-free survival, and malignant transformation-free survival [7–9, 44]. However, for incidentally discovered small tumors without mass effect or symptoms, observation with surveillance imaging is a viable option given the slow growth and natural history of low-grade gliomas (Table 18.1) [45].

The standard of care for patients with high-grade gliomas is extensive resection, followed by radiation and temozolomide chemotherapy [46]. Regardless of treatment, tumor recurrence typically occurs close to the tumor margins [20]. At the tumor margin, there is an increased tumor cell density [20]. Beyond the periphery, there is a sharp fall-off in cell numbers as the distance from the resection cavity increases [20]. Extensive surgical resection of gliomas can prolong progression-free and overall survival by decreasing tumor burden and possibly increasing adjuvant therapy efficacy as it has with other types of solid tumors [47]. Moreover, the use of adjuvant therapies have been developed to help reduce the tumor burden at the tumor periphery. One of these developments is SBT (Table 18.2).

It is generally considered beneficial to provide radiation to the gliomatous areas around the surgical cavity, especially for high-grade gliomas [14, 48, 49]. The techniques to deliver this radiation include stereotactic radiation therapy and SBT [14, 48, 49]. SBT involves the delivery of radiation by stereotactically implanting radioactive sources near or within tumors [14, 48, 49]. SBT can be applied peri- or postoperatively by either permanent isotope seeds or by temporary catheters containing radioisotopes [14, 48, 49]. There are a variety of different isotopes that can be administered for radiation therapy including Iodine-125, Iodine-131, and Iridium-192, among others [14, 48, 49]. The exposure times of these seeds range from a few days to several months and vary whether temporary implants or permanent seeds are used [14, 48, 49]. In the central nervous system, the most common radioactive source used for SBT are Iodine-125 seeds (¹²⁵I) which emit low-energy radiation of 0.028–0.035 meV and have a steep falloff dose that reduces peripheral normal tissue exposure [14, 15].

SBT has been used as adjuvant treatment following surgical resection for both primary and recurrent low- and high-grade gliomas and has been used for tumors in eloquent regions that are considered unresectable [14, 48, 49]. The theoretical benefit of SBT is that it allows for precise surgical implantation of radioisotopes within the tumor or tumor cavity, thus providing local radiation to adjacent tissue while sparing surrounding tissue [15]. Additionally, SBT avoids the systemic side effects of chemotherapy and the potential neuro-cognitive effects of external beam radiation therapy (EBRT) [50]. However, while numerous retrospective studies have demonstrated SBT to be safe and efficacious in gliomas [15, 51–56], three small single institution prospective randomized trials failed to demonstrate a survival advantage [57–59]. Therefore, the efficacy of this treatment option requires further investigation as well as potential advances in imaging and implant technology before it will be widely used.