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
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Clinical validation of novel lightning dose optimizer for gamma knife radiosurgery of irregular-shaped arteriovenous malformations and pituitary adenomas.
To demonstrate the clinical feasibility of a novel treatment planning algorithm via lightning dose optimizer (LDO) on Leksell Gamma Knife (LGK) GammaPlan with significantly faster planning times for stereotactic radiosurgery (SRS) of the complex and difficult arteriovenous malformations (AVMs) and pituitary adenomas.
After completing the in-house end-to-end phantom testing and independent dose verification of the recently upgraded LDO algorithm on GammaPlan using the MD Anderson's IROC anthropomorphic SRS head phantom irradiation credentialing, 20 previously treated GK-SRS patients (10 AVM, average volume 3.61 cm3 and 10 pituitary adenomas, average volume 0.86 cm3 ) who underwent manual forward planning on GammaPlan were retrospectively replanned via LDO. These pathologies were included because of the need for adequate dose delivery with organs at risk in very close proximity. LDO finds the target curvature boundary by well-formulated linear programing objectives and inversely optimizes the GK-SRS plan by isocenter placement, optimization, and sequencing. For identical target coverage, the LDO and original manual plans were compared for target conformity, gradient index, dose to critical organs, and surrounding normal brain. Additionally, various treatment delivery parameters, including beam-on time were recorded.
For both patient cohorts, LDO provided similar target coverage with better dose conformity, tighter radiosurgical dose distribution with a lower value of gradient indices (all p < 0.001), and lower dose to critical organs. For AVMs, there was a significant reduction of normal brain V10Gy , V12Gy , and V14Gy by 4.74, 3.67, and 2.67 cm3 (all p < 0.001). LDO had twice the number of shots (p < 0.001), and longer beam-on time (p = 0.012) by a factor of 1.44. For pituitary adenomas, LDO provided systematically lower values of V10Gy , V12Gy , and V14Gy by 1.08, 0.86, and 0.68 cm3 (all p < 0.001), and lower maximum dose to optic pathway by 0.7 Gy (p = 0.005), but had almost twice the numbers of shots (p < 0.001) and increased beam-on time (p = 0.005) by a factor of 1.2. However, for both patient groups, the average planning time for the LDO was <5 min, compared to the estimated 30-90 min of manual planning times.
GK-SRS treatment on Leksell Perfexion GammaPlan using the LDO provided highly conformal target coverage with a steep dose gradient, spared critical organs, and significantly reduced normal brain dose for complex targets at the cost of slightly higher treatment times. LDO generated high-quality treatment plans and could significantly reduce planning time. If available, the LDO algorithm is suggested for validation and clinical use for complex and difficult GK cases.
Pokhrel D
，Bernard ME
，Knight J 2nd
，St Clair W
，Fraser JF
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《Journal of Applied Clinical Medical Physics》
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