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Dose-Response and Dose-Complications Relationships in Stereotactic Radiosurgery for

Trigeminal Neuralgia

Sandra Vermeulen MD, Robert Meier MD, Vivek Mehta MD, Ron Young MD, Francisco Li MS

Northwest Gamma Knife Center, Seattle, WA, USA


Trigeminal Neuralgia: Overview• Definition: brief episodic, unilateral face pain,

confined to one or more divisions of the 5th nerve.

• Cause: tumors, vascular compression of the root entry zone, multiple sclerosis and idiopathic causes

• Pharmacotherapy is the initial treatment modality of choice

• Annual incidence in the United States: 15,000


Purpose/Objective

In Patients treated with Gamma Knife Radiosurgery for Trigeminal Neuralgia, to

determine if a relationship exists between dose delivered, and the incidence of response, or the

incidence of complications


Material and Methods

• 382 patients with either typical or atypical TN were treated between August 1993 and January 2005

• None had tumor or Multiple Sclerosis

• All were treated with a single 4-mm isocenter targeting the ipsilateral trigeminal nerve at the dorsal root entry zone

• Dose was prescribed at the Dmax


Treatment Iso-Center


Dose Protocols

Three dose protocols were employed using an output factor or 0.87:

76 patients received 76 Gy




Patient CharacteristicsGroup

Dose

Group 1

76 Gy

Group 2

87 Gy

Group 3

98 Gy

Patient No. 76 179 127

Mean F/U 4.16 yrs 2.74 yrs 3.76 yrs

Sex (M/F) 26/50 68/111 50/77

Mean Age 63 yrs 62 yrs 60 yrs

Location R/L 48/28 99/80 61/66

Division No. >1: 48 >1: 109 >1:70

Pre-GK Procedures

None/1/>1

41/16/19

None/1/>1

119/25/35

None/1/>1

89/17/21


Treatment Characteristic

Isodose 20% 30% 40% 50%

Group 1

76 Gy11% 1% 63% 25%

Group 2

87 Gy40% 28% 0% 32%

Group 3

98 Gy63% 0% 0% 37%


ResultsTreatment outcomes were measured at 6 months,

at last follow-up and actuarially

“Favorable” responders were patients rendered free of pain, either with or without medication

Complications were defined as lasting neurologic deficits attributable to treatment and included

numbness or paresthesias


Pain Relief

• At 6 months post-treatment, “favorable” outcomes occurred with similar rates in all 3 groups

• Log-rank test showed no significant difference in the Kaplan-Meier curves for these three groups (p=0.835)

0

10

20

30

40

50

60

70

80

90

100

76Gy

87Gy

98Gy

ResponseRate toGammaKnife RS


Complications

• The only lasting complication was new numbness or paresthesia

• At 6 months, patients treated with higher doses more often developed sensory deficits (p<0.05)

0

10

20

30

40

50

60

70

80

90

100

76Gy

87Gy

98Gy

Rates OfSensoryDeficits


Severity of Numbness

0

10

20

30

40

50

60

70

80

90

100

76Gy 87 Gy 98 Gy

Not Bothersome

Bothersome

Painful


Conclusion

In stereotactic radiosurgery for TN, escalation of maximum nerve dose from

76 Gy to 87 Gy to 98 Gy does not significantly improve pain relief, but is associated with a higher incidence of

complications

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