**5.3 Treatment selection**

Since radiosurgery/therapy equipment is scarce and extremely expensive, many centers and physicians have adopted particular patient selection and treatment protocols. The availability of different systems per hospital/clinic has further contributed to this diversity. The result has been that there are many controversies regarding patient and modality selection in general, and with respect to radiosurgery/therapy in particular [85]. During the last two decades, this trend has been changing as more physicians and researchers are attempting to standardize scorebased radiotherapy grading and patient selection systems (see Section 4.3) [59]. A treatment selection scheme established at Pittsburgh University is presented in **Figure 7** [81]. Selection relies on AVM volume and location as well as the existence of post-treatment (residual) lesions.

Unlike SM grading in surgery, to date, there has been no distinct established treatment selection criterion for radiosurgery/therapy. Even recent advanced grading systems are not widely considered a sufficiently standardized basis for designating a patient for radiation modality. Common factors are bleeding history, patient age, existing comorbidities, anatomical location, and clinical history [81].

#### **5.4 Outcomes and complications**

Standard protocol for AVM obliteration typically involves clinical diagnostics and a half-yearly MRI, followed by annual MRI imaging. Final validation (classically at 3 years) is DSA-based, as the latter constitutes the gold standard [81]. A meta-analysis, performed by Badra et al. in 2018 [79], found that: obliteration rates are ~70–80% at 2–4 years post-treatment; annual bleeding rates are 1.1–8%; AREs are 12–38%; and overall morbidity is 4–12%. Another study showed [81]: the obliteration rates of 78% at 3-year follow-up, repeated radiosurgery needed in 12.5% of cases, post-surgery annual bleeding rates in 4.1% of cases, and AREs in 16.3%. Thus, while radiation treatment is relatively effective, it is not risk- and complication-free. Several categories merit particular attention: **acute complications** are typically related to the post-procedural presentation of neurological deficits after 2 years or more. Yen et al. studied 1426 Gamma Knife Surgeries (GKS) and found radiationinduced imaging changes (RICs, visualized as increased T2 signal surrounding the

*Advocating Intraluminal Radiation Therapy in Cerebral Arteriovenous Malformation Treatment DOI: http://dx.doi.org/10.5772/intechopen.89662*

**Figure 7.** *AVM treatment selection scheme (following [81]).*

treated nidi on MRI) that are the most common adverse effects following GKS—in 33.8% of lesions [86]. Patients with a relatively healthy brain and large nidi or with a single draining vein were more susceptible to RICs. Few RICs were symptomatic (8.6%), and most symptoms were reversible (only 1.8% had permanent deficit). About 7.7% of RICs were acute—causing a midline shift of the brain. **Late AREs** typically occur many years following SRS (6.9% of patients after a median of 8.7 years. The 5-, 10-, and 15-year incidence is 0.4, 7.7, and 12.5%, respectively). They are characterized by perilesional edema or cyst formation and are distinct from short-term (1–2 years post-surgery) AREs, often labeled as RICs [87]. About 3.4% of Late AREs are symptomatic at detection. Many that are asymptomatic later present with cyst progression. The overall symptomatic rate of late AREs is 4.7% [87]. Another study included radiation necrosis and cystic vessel formations in late ARE diagnosis and found the incidence at 2–6% [79]. Finally, since radiotherapy for AVM is based on ionizing radiation, the concern for carcinogenicity arises. However, little evidence has been found to support **radiation induced tumors** (RITs). A late retrospective analysis performed by Pollock et al. found no RITs in 471 patients observed between 1990 and 2009 (with very few others out of the total 1837 patients presenting malignant transformation) [88]. The authors concluded that the risk of RITs or malignant transformation after SRS is very low and should not be used as a justification for choosing alternative treatments. Lunsford et al. corroborate these findings [81].
