19 CyberKnife Radiotherapy for Treatment of Sporadic Vestibular Schwannoma

10.1055/b-0039-169173

19 CyberKnife Radiotherapy for Treatment of Sporadic Vestibular Schwannoma

Navjot Chaudhary and Steven D. Chang

19.1 Introduction

Single-session stereotactic radiosurgery (SRS) and fractionated radiotherapy have emerged as viable alternatives to microsurgical resection for vestibular schwannoma (VS). Radiation delivery methods include SRS using the Gamma Knife (GK SRS), linear accelerator-based (LINAC) systems including CyberKnife (CK) using either single session SRS or hypofractionated and conventionally fractioned regimens, and proton beam therapy. Numerous prior publications have documented the safety and efficacy of SRS, hypofractionated radiotherapy (two to five sessions), or conventionally fractionated radiotherapy for VS (Table 19‑1 and Table 19‑2 ). Single-session SRS has shown excellent rates of tumor control; however, a single higher therapeutic dose theoretically may carry a greater risk of injuring adjacent structures than multiple lower dose sessions. One large series investigated single-session GK or CK SRS to treat 386 patients with VS.s. Literatur Tumor volume was the only predictor of trigeminal neuropathy, and no predictor of facial nerve injury was found. On the House-Brackmann scale, one patient had a permanent one-level drop and seven patients experienced a transient drop of 1 to 3 levels. Serviceable hearing was preserved in 75% of cases. In this study, there were no statistically significant differences found when comparing tumor control and toxicity between GK and CK SRS on multivariate regression.

Table 19.1 Vestibular schwannomas treated with single-session stereotactic radiosurgery (n > 100 cases)
Authors	Year published	No. of pts	Modality	Median tumor volume, cm³	Median radiation dose at IDL, Gy	Local control, %	Median follow-up, mo	Median follow-up, no. pts	Serviceable hearing preservation, %	New trigeminal neuropathy, %	New facial neuropathy, %
Murphy et als. Literatur	2011	103	GK	1.95 ± 2.42	13	95.2 (3-y actuarial)	37.5	NR	NR	1	5
Fukuoka et als. Literatur	2009	152	GK	2	12	94 (5-y actuarial)	>60	59	71 crude	2.6	0
Chopra et als. Literatur	2007	216	GK	1.3	13	98.3 ± 1 (10-y actuarial)	68	106	57–74 crude	4.2 ± 1.6	0
Friedman et als. Literatur	2006	295	LINAC	2.2	12.5	90 (5-y actuarial)	34	NR	NR	3.6 overall, 0.7 for dose <12.5 Gy	4.4 overall, 0.7 for dose <12.5 Gy
Hempel et als. Literatur	2006	116	GK	1.6	13	96.7 crude	Mean: 98	NR	NR	5.8	0
Hasegawa et als. Literatur	2005	301	GK	Mean: 5.6	13	93 (5-y actuarial)	94	19	37 crude, 68 crude for dose < 13 Gy	2	1
Wowra et als. Literatur	2005	111	GK	1.6	13	95 (6-y actuarial)	84	NR	NR	11.7	3
Chung et als. Literatur	2005	187	GK	Mean: 4.1	13	96.8 crude	31	26	60 crude	1.1	1.4
Litvack et als. Literatur	2003	134	GK	NR	12	98 crude	36	47	62 crude	5.8	2.3
Rowe et als. Literatur	2003	212	GK	3.7	15	97 crude	34	49	75 crude	3.5	4.5
Unger et als. Literatur	2002	100	GK	3.4	13	96 crude	76	29	55 crude	5	6
Prasad et als. Literatur	2000	153	GK	Mean: 2.7	13.2	92 crude	38	36	58 crude	5	2.3
Abbreviations: IDL, prescriptions isodose line; GK, Gamma Knife; NR, not reported; pts, patients.

Table 19.2 Vestibular schwannomas treated with conventionally fractionated radiotherapy
Authors	Year	No. of pts	No. of fractions	Median tumor volume, cm³	Median radiation dose, Gy	Local control, %	Median follow-up, mo	Median follow-up, no. pts	Serviceable hearing, %	New trigeminal neuropathy, %	New facial neuropathy, %
Kopp et als. Literatur	2010	47	30	3.95	54	97.9 crude	32	33	79 crude	8.5	4.3
Combs et als. Literatur	2010	165	30	2.8	57.6	96 (5-y actuarial)	75	94	78 (5-y actuarial)	3	4
Horan et als. Literatur	2007	42	30	2 cm diameter	50	96.9 (2.5-y actuarial)	18.6	20	100 crude subjective hearing	0	3.2
Koh et als. Literatur	2007	60	25	4.9	50	96 (5-y actuarial)	31.9	22	77 crude	0	0
Maire et als. Literatur	2006	45	30	3.1 cm diameter	51	86 (15-y actuarial)	80	9	78 crude subjective hearing	0	0
Chan et als. Literatur	2005	68	30	2.4	54	92 (5-y actuarial)	45	NR	NR	4	1
Selch et als. Literatur	2004	48	30	2.5	54	100 crude	36	42	91 (5-y actuarial)	2.2	2.1
Sawamura et als. Literatur	2003	101	23	1.9 cm diameter	48	91 (5-y actuarial)	45	36	71 (5-y actuarial)	4	0
Andrews et als. Literatur	2001	56	25	2.8	50	97 crude	26	27	81 crude	7	2
Abbreviation: pts, patients.

Given excellent tumor control rates reported with SRS, there has been an increasing emphasis on minimizing cranial nerve morbidity. The marginal dose for single-fraction SRS has been reduced from 16 to 20 Gy to the currently accepted dose of 12 to 13 Gy in order to reduce the risk of cranial neuropathy and hearing loss.s. Literatur ^, s. Literatur ^, s. Literatur The likelihood of hearing preservation in earlier studies was 51 to 60%.s. Literatur ^, s. Literatur ^, s. Literatur However, more recent studies utilizing a lower marginal dose demonstrate improved hearing preservation rates of 71 and 73%.s. Literatur Fractionation, administering smaller doses over multiple sessions, may help minimize cranial nerve morbidity.s. Literatur The rationale behind multisession radiotherapy is that it allows adjacent brain tissue to recover in between doses. Also, organs at risk including the cochlea receive significantly lower doses with each treatment using multisession radiotherapy. Given these theoretical advantages, fractionated radiotherapy has become the mainstay at many institutions. The results for the frameless CK system are discussed below.