Comparative analysis between 5 mm and 7.5 mm collimators in CyberKnife radiosurgery for trigeminal neuralgia

Abstract

Trigeminal neuralgia (TN) is treated in CyberKnife (Accuray Inc, Sunnyvale, USA) with the 5 mm collimator whose dosimetric inaccuracy is higher than the other available collimators. The 7.5 mm collimator which is having less dosimetric uncertainty can be an alternative for 5 mm collimator provided the dose distribution with 7.5 mm collimator is acceptable. Aim of this study is to analyze the role of 7.5 mm collimator in CyberKnife treatment plans of TN. The treatment plans with 5 mm collimators were re-optimized with 7.5 mm collimator and a bi-collimator system (5 mm and 7.5 mm). The treatment plans were compared for target coverage, brainstem doses, and the dose to normal tissues. The target and brainstem doses were comparable. However, the conformity indices were 2.31 ± 0.52, 2.40 ± 0.87 and 2.82 ± 0.51 for 5 mm, bi-collimator (5mm and 7.5 mm), 7.5 mm collimator plans respectively. This shows the level of dose spillage in 7.5 mm collimator plans. The 6 Gy dose volumes in 7.5 mm plans were 1.53 and 1.34 times higher than the 5 mm plan and the bi-collimator plans respectively. The treatment time parameters were lesser for 7.5 mm collimators. Since, the normal tissue dose is pretty high in 7.5 mm collimator plans, the use of it in TN plans can be ruled out though the treatment time is lesser for these 7.5 mm collimator plans.

Dosimetric and radiobiological comparison of CyberKnife M6TM InCise multileaf collimator over IRISTM variable collimator in prostate stereotactic body radiation therapy

“…Previous studies have suggested that small collimator scan achieves high dose conformity and steep dose gradient, while large collimators tend to minimize the total monitor units (MUs) and treatment beams. [ 16 17 ] With a combination of two collimators, the total MUs in the treatment plan can also be reduced by an average of 31% compared to the single collimator. [ 18 ] Such improvements in prostate plan dosimetry and treatment efficiency are immediately realized by using the more advanced IRIS variable collimator which was introduced in 2008.…”

Effectiveness and Safety of Microvascular Decompression Surgery for Treatment of Trigeminal Neuralgia

“…17 Thought to relieve the symptoms of some patients in the early stage, those antiepileptic drugs have many side effects and the patient would resist against it with time. The other choices are those ablative procedures, such as glycerol injections, 18 radiosurgery (gamma knife), 19-23 radiofrequency rhizotomy, [24][25][26][27][28] and so on. Partial sensory rhizotomy has now rarely been performed for TN because of its higher recurrence and intolerable dysesthesia due to nerve damage.…”

Intra‐arc binary collimation with dynamic axes trajectory optimization for the SRS treatment of multiple metastases with multiple prescriptions

“…20 However, large dose heterogeneity inside a target is often acceptable in SRS/SRT, such as in CyberKnife and Gamma Knife radiosurgery in which the normalization of dose distributions to low isodoses can often be seen in trigeminal neuralgia treatments to improve target conformity and OAR dose sparing. 21,22 F I G U R E 1 3 Absolute dose difference in (a) average maximum dose and (b) average mean dose to each OAR between VMAT and 3-arc CODA-iABC techniques (N = 7). Positive values indicate that 3-arc CODA-iABC plans achieve better dose sparing to an OAR when comparing to VMAT plans.…”

“…Decreased MLC aperture margins have been shown to have a sharper dose gradient outside the target volume and a narrower shoulder of target DVHs, but with a cost in target dose homogeneity 20 . However, large dose heterogeneity inside a target is often acceptable in SRS/SRT, such as in CyberKnife and Gamma Knife radiosurgery in which the normalization of dose distributions to low isodoses can often be seen in trigeminal neuralgia treatments to improve target conformity and OAR dose sparing 21,22 …”