Benign Intracranial Lesions - Radiotherapy: An Overview of Treatment Options, Indications and Therapeutic Results

A mini review of plan quality and secondary cancer risk in CyberKnife M6 radiosurgery for benign intracranial tumors

With advancements in medical technology, stereotactic radiosurgery (SRS) has become an essential option for treating benign intracranial tumors. Due to its minimal side effects and high local control rate, SRS is widely applied. This paper evaluates the plan quality and secondary cancer risk (SCR) in patients with benign intracranial tumors treated with the CyberKnife M6 system. The CyberKnife M6 robotic radiosurgery system features both multileaf collimator (MLC) and IRIS variable aperture collimator systems, providing different treatment options. The study included 15 patients treated with the CyberKnife M6 system, examining the differences in plan quality and SCR between MLC and IRIS systems. Results showed that MLC and IRIS plans had equal PTV (planning target volume) coverage (98.57% vs. 98.75%). However, MLC plans demonstrated better dose falloff and conformity index (CI: 1.81 ± 0.26 vs. 1.92 ± 0.27, P = 0.025). SCR assessment indicated that MLC plans had lower cancer risk estimates, with IRIS plans having average LAR (lifetime attributable risk) and EAR (excess absolute risk) values approximately 25% higher for cancer induction and 15% higher for sarcoma induction compared to MLC plans. The study showed that increasing tumor volume increases SCR probability, but there was no significant difference between different plans in PTV and brainstem analyses.

Clinical outcomes of benign brain tumors treated with single fraction LINAC-based stereotactic radiosurgery: Experience of a single institute

Objectives

Accelerator-based stereotactic radiosurgery (SRS) is a noninvasive and effective treatment modality widely used for benign brain tumors. This study aims to report 20-year treatment outcomes in our institute.

Materials and Methods

From May 2001 to December 2020, 127 patients treated with LINAC-based single-fraction SRS for their benign brain lesions were included. A neurosurgeon and two radiation oncologists retrospectively reviewed all data. Computed tomography (CT) simulation was performed after head-frame fixation under local anesthesia. All planning CT images were co-registered and fused with gadolinium-enhanced magnetic resonance imaging taken within 3 months for lesions targeting and critical organs delineation. The marginal dose was prescribed at 60%-90% isodose lines, respectively, to cover ≥95% planning target volume. Outcome evaluations included clinical tumor control rate (TCR), defined as the need for salvage therapy, and radiological response, defined as no enlargement of >2 cm in the maximal diameter. Overall survival (OS) and adverse reaction (defined according to CTCAE 5.0) were also analyzed.

Results

The present study included 76 female and 51 male patients for analysis. The median age was 59 years (range, 20-88 years). Their diagnoses were vestibular schwannoma (VS, n = 54), nonvestibular cranial nerve schwannoma (n = 6), meningioma (n = 50), and pituitary adenoma (n = 17). Totally 136 lesions were treated in a single fraction, predominantly skull base tumors, accounting for 69.1%. Median and mean follow-up duration was 49 and 61 months (range, 1-214 months), Overall TCR was 92.9%. The 5-year disease-specific TCR for VS, nonvestibular schwannoma, meningioma, and pituitary adenoma were 97.4%, 91.7%, 93.8%, and 83.3%. Salvage therapy was indicated for eight patients at 4-110 months after SRS. Among symptomatic patients, post-SRS symptom(s) was improved, stable, and worse in 68.2%, 24.3%, and 3.6%, respectively. Radiological response rate for 111 evaluable patients was 94.6% (shrinkage, 28.8%; stable, 65.8%). OS was 96.1% without treatment-related mortality. One patient with post-SRS cranial nerve injury (0.8%, involving the trigeminal nerve, grade 2 toxicities). No grade 3-4 acute or late toxicity was found.

Conclusion

Our results suggested that LINAC-based SRS effectively controls tumor growth and tumor-related neurological symptoms for patients with benign brain tumors. SRS is less aggressive, associated with low neurological morbidity and no mortality. Continuous follow-up is indicated to conclude longer outcomes.

Assessing the long-term safety and efficacy of gamma knife and linear accelerator radiosurgery for vestibular schwannoma: A systematic review and meta-analysis

Background

Differences in long-term outcomes of single-fraction stereotactic radiosurgery (SRS) between gamma knife (GK) and linear accelerator (LINAC) systems for vestibular schwannoma (VS) management remain unclear. To investigate differences in safety and efficacy between modalities, we conducted a meta-analysis of studies over the past decade.

Methods

MEDLINE, EMBASE, and Cochrane databases were queried for studies with the following inclusion criteria: English language, published between January 2010 and April 2020, cohort size ≥30, and mean/median follow-up ≥5 years. Odds ratios (OR) compared rates of tumor control, hearing preservation, and cranial nerve toxicities before and after SRS.

Results

Thirty-nine studies were included (29 GK, 10 LINAC) with 6516 total patients. Tumor control rates were 93% (95% CI 91-94%) and 94% (95% CI 91-97%) for GK and LINAC, respectively. Both GK (OR 0.06, 95% CI 0.02-0.13) and LINAC (OR 0.47, 95% CI 0.29-0.76) reduced odds of serviceable hearing. Neither GK (OR 0.71, 95% CI 0.41-1.22) nor LINAC (OR 1.13, 95% CI 0.64-2.00) impacted facial nerve function. GK decreased odds of trigeminal nerve (TN) impairment (OR 0.55, 95% CI 0.32-0.94) while LINAC did not impact TN function (OR 1.45, 95% CI 0.81-2.61). Lastly, LINAC offered decreased odds of tinnitus (OR 0.15, 95% CI 0.03-0.87) not observed with GK (OR 0.70, 95% CI 0.48-1.01).

Conclusions

VS tumor control and hearing preservation rates are comparable between GK and LINAC SRS. GK may better preserve TN function, while LINAC decreases tinnitus rates. Future studies are warranted to investigate the efficacy of GK and LINAC SRS more directly.