Dosimetric comparison of sector-blocked and non-sector-blocked Gamma Knife Perfexion treatment plans for trigeminal neuralgia.

The purpose of this study is to compare the quality of trigeminal neuralgia (TN) treatment plans with and without utilizing sector blocking. Twelve patients with 13 cases of TN were evaluated in this retrospective study. Identical magnetic resonance imaging (MRI) contour sets and prescription doses used in treatments were reused for all plans. Treatment plans were compared on the basis of the amount of dose received by critical structures (i.e., brainstem, ipsilateral temporal lobe, optic chiasm, optic nerves, cochlea) and the estimated total treatment time. The use of sector blocking resulted in a statistically significant decrease in the radiation dose to the brainstem but increased doses to the cerebellum and temporal lobe regions. The magnitude of these differences was small and individual patient anatomy specific. The use of sector blocking also resulted in a statistically significant increase in the treatment time. The magnitude of the change in treatment time was dependent on the number of sectors blocked. Our study suggests some potential benefits, as well as disadvantages, to the use of sector blocking in the treatment of TN. Treatment decision needs to be individualized based on the patient's anatomy and overall condition.

Kendall E ，Ahmad S ，Algan O 《-》

Hybrid isocenter technique for Gamma-Knife Perfexion treatment of trigeminal neuralgia.

Gamma-Knife (GK), Perfexion (PFX) has 8 sectors that can be blocked compared with the older model 4C, which has 201 independent source blocking options using plugs. This limits the ability of PFX to shape a single isocenter plan, such as trigeminal neuralgia. In this retrospective review and prospective re-planning comparison study of trigeminal neuralgia radiosurgery plans, a hybrid isocenter technique (HIT) is compared with single isocenter GK radiosurgery plans on 2 models (4C and PFX) dosimetric parameters. With ethics approval, patients treated on 4C (n = 100) and PFX (n = 50) between 2005 and 2014 for trigeminal neuralgia were reviewed. All clinical plans were produced using 1 isocenter with a 4-mm collimator and a prescription dose of 80Gy at 100% while limiting brainstem dose to < 15Gy ( [Formula: see text] ). Dose shaping was performed using plugs in 4C and sector blocking in PFX to optimize the plan, if required. Re-planning using HIT was retrospectively attempted for PFX plans with brainstem dose > 15Gy. In the implementation of HIT, we used 2 shots at the same isocenter, but with different sector block configuration and weights, to further reduce brainstem dose while optimizing dose coverage of the nerve. Planning parameters such as dose to the treated nerve, brainstem, and surrounding tissue were compared between the clinical plans and the new plans with HIT. Source blocking was applied in 66/100 4C plans with mean blocked sources of 40.2/201 (ranging 1 to 99) and in 36/50 PFX plans with mean blocked sectors of 2.2/8 (1 to 4). There is no significant differences in mean dose, integral dose, irradiated volume of the treated nerve between 4C, and PFX plans. The 4C plans had smaller irradiated volume of tissue (90.6mm3) than PFX plans (103.5mm3) (p < 0.001). The irradiated volume of tissue increases by 17% when half of the sources are blocked for both 4C and PFX plans. In 9/50 PFX plans, brainstem [Formula: see text] was 15.8Gy on average (15.2 to 16.5Gy) and [Formula: see text] was 12.2Gy (11.4 to 13.2Gy). Re-plans of these 9 cases using HIT resulted in a significant reduction in [Formula: see text] to 13.5Gy (12.2 to 15.1) and [Formula: see text] to 10.5Gy (8.1 to 12.2) (p < 0.001). There was < 1% difference between the original PFX and re-planned HIT plans in dose to the nerve, and treatment time (p = 0.186). It is noted that the increase in the irradiated volume of tissue is proportional to the use of source blocking. Larger irradiated volume may be a reason that higher pain control rate and complication rate at the same time. Hybrid isocenter technique results in greater sparing of the brainstem without compromise in the dose to the nerve or treatment time on GK PFX planning for the treatment of trigeminal neuralgia.

Cho YB ，Laperriere N ，Hodaie M ，Chung C ... -  《-》

Selective source blocking for Gamma Knife radiosurgery of trigeminal neuralgia based on analytical dose modelling.

Li K ，Ma L 《PHYSICS IN MEDICINE AND BIOLOGY》

Gamma Knife Radiosurgery for Trigeminal Neuralgia: Role of Trigeminal Length and Pontotrigeminal Angle on Target Definition and on Clinical Effects.

Gamma Knife radiosurgery (GKRS) is a well-defined treatment for trigeminal neuralgia. The aim of this study was to determine how the GKRS planning might change on the basis of the patient's own anatomy and how to best choose the target location. Trigeminal cisternal length, pontotrigeminal angle, and distance between middle of the shot and emergence were evaluated in 112 consecutive GKRS plans for trigeminal neuralgia. Correlations with pain outcomes and facial hypoesthesia were analyzed. The mean angle was 29° ± 4.4° and 37° ± 0.9°, respectively, in patients developing and not developing severe hypoesthesia (P = 0.045), despite no significant difference on brainstem dose (11.9 ± 0.8 and 10.5 ± 0.3 Gy; P = 0.22). The length of the nerve was not relevant on clinical outcomes but the shot-emergence distance (mean 8.1 ± 0.2 mm) depended on both trigeminal length and angle (P = 0.01). At constant prescription dose, 6-month cumulative rates of pain relief and control without therapy were 52.9% when the shot-emergence distance was ≤8 mm, whereas 25% when this distance was >8 mm (P = 0.017). The maintenance of good pain control was more long lasting in the first group (49.5 ± 6.6 vs. 25.4 ± 5 months; P = 0.006) with a 5-year cumulative rate of 70% and 26%, respectively (P < 0.001). The pontotrigeminal angle and the shot-emergence distance should be considered during GKRS planning: the first as a potential risk factor for hypoesthesia, and the second should not exceed 8 mm.

Barzaghi LR ，Albano L ，Scudieri C ，Gigliotti CR ，Nadin F ，Del Vecchio A ，Mortini P ... -  《-》

Linac-based stereotactic radiosurgery for treatment of trigeminal neuralgia.

Gerbi BJ ，Higgins PD ，Cho KH ，Hall WA ... -  《Journal of Applied Clinical Medical Physics》