A proposed plan for personalized radiosurgery in patients with trigeminal neuralgia

Abstract

OBJECTIVE During the last 25 years, more than 100,000 patients worldwide with trigeminal neuralgia (TN) have undergone stereotactic radiosurgery (SRS) with a standard dose of radiation. However, the radiobiological effect of radiation is determined by the amount of energy delivered to the tissue (integral dose [ID] = mean dose × target volume) and is directly associated with the nerve volume. Although the trigeminal nerve volume varies among patients with TN, the clinical impact of this variation in delivered energy is unknown. The objective of this study was to evaluate the effect of delivered ID on the outcome of TN radiosurgery. METHODS The authors evaluated 155 patients with unilateral TN who had undergone SRS as their initial surgical management over a 13-year period. The authors measured the postganglionic ID within the SRS target and retrospectively stratified patients into 3 groups: low (< 1.4 mJ), medium (1.4-2.7 mJ), and high (> 2.7 mJ) ID. Clinical outcomes, which included pain status (scored using the Barrow Neurological Institute Pain Scale) and sensory dysfunction (scored using the Barrow Neurological Institute Numbness Scale), were evaluated at a median follow-up of 71 months. RESULTS Patients who were treated with a medium ID had superior pain relief either with or without medications (p = 0.006). In the medium ID group, the rates of complete pain relief without medications at 1, 3, and 6 years after SRS were 67%, 54%, and 33%, respectively, while the rates in the rest of the cohort were 55%, 36%, and 19%, respectively. Patients given a high ID had a higher rate of post-SRS trigeminal sensory deterioration (p < 0.0001). At 1, 3, and 6 years after SRS, the high ID group had an estimated rate for developing sensory dysfunction of 35%, 45%, and 50%, respectively, while the rates in patients receiving low and medium IDs were 3%, 4%, and 9%, respectively. The optimal clinical outcome (maximum pain relief and minimal trigeminal sensory dysfunction) was obtained in patients who had received a medium ID. CONCLUSIONS With current dose selection methods, nerve volume affects long-term clinical outcomes in patients with TN who have undergone SRS. This study suggests that the prescribed SRS dose should be customized for each TN patient based on the nerve volume.

Factors affecting outcome in frameless non-isocentric stereotactic radiosurgery for trigeminal neuralgia: a multicentric cohort study

“…The ID is the product of the mean dose and the target nerve volume and therefore represents an ideal parameter for non-isocentric treatments in which not only the dose, but also the target volume can be modulated to fit individual anatomy and clinical objectives. Mousavi et al [23] investigated 155 patients treated by GKS and reported that the optimal treatment outcome could be achieved by medium IDs (1.4-2.7 mJ). To be able to compare our cohort with the study by Mousavi et al [23], we categorized the ID in the same way and observed that the patients with lower IDs (i.e.…”

“…Mousavi et al [23] investigated 155 patients treated by GKS and reported that the optimal treatment outcome could be achieved by medium IDs (1.4-2.7 mJ). To be able to compare our cohort with the study by Mousavi et al [23], we categorized the ID in the same way and observed that the patients with lower IDs (i.e. < 1.4 mJ) were more likely to suffer pain relapse.…”

“…As with the GKS series, pain relapse is the major pitfall of the radiosurgical treatments, with pain control decreasing over time [7]. The ratio of dose to nerve volume, smaller nerve volume, and low prescribed dose have been claimed as potential predictors for treatment failure after SRS [7,23,24]; however, large cohort studies analyzing radiation metric factors interfering with the outcome in non-isocentric SRS for TN are yet to be reported. Thus, there is a lack of evidence for standardized therapy algorithms that include the selection of relevant radiosurgical treatment parameters such as dose to the target, target nerve volume, and prescription isodose.…”

Evaluation of CyberKnife Radiosurgery for Recurrent Trigeminal Neuralgia

“…The dose exposure of the adjacent brainstem is a critical factor in repeat SRS and related to post procedure facial numbness [ 45 ]. The total cumulative dose to the brainstem and cumulative doses to adjacent structures such as the temporal lobe must be carefully calculated [ 46 , 47 ]. Normally, the initial SRS dose with either GK or SRS varies between 70 to 90 Gy with most centers using a dose of 75 Gy [ 1 , 5 ].…”

“…The higher dose, both for initial and repeat treatment, is associated with a higher incidence of residual facial numbness varying from 12 to 30% [ 1 , 5 , 13 , 14 ]. There are reports of even third SRS treatments and a more individualized plan, especially targeting sections of the trigeminal nerve not in the original radiation plan in cases with recurrent pain [ 42 , 47 , 48 ]. Experience with treating multiple brain metastatic disease clearly demonstrates the feasibility of multiple repeat SRS treatments [ 49 ].…”