Robotic radiosurgery versus micro-multileaf collimator: a dosimetric comparison for large or critically located arteriovenous malformations

Abstract

BackgroundStereotactic irradiation of large or critically located arteriovenous malformations (AVMs) is a special challenge for clinicians and radiation physicists. To date, no comprehensive comparison of two linac-based radiosurgery systems used for hypofractionated radiotherapy of large AVMs was published. The aim of the study was to compare dose distributions between CyberKnife (CK) system and linac with a micro-multileaf collimator (L-mMLC) in high-grade or critically located cerebral AVMs.MethodsTwo sets of plans made for 15 different patients with at least 95% target coverage were selected for comparisons. Conformity (CI), homogeneity (HI) and gradient score (GSI) indices, conformity index proposed by Lomax (CIL), conformation number (CN), quality of coverage (Q), volumes of brain receiving 12,10,8,6,4, and 2 Gy, minimum and maximum doses for critical structures in both treatment planning systems (TPS) were compared. Finally, the number of monitor units needed to deliver the prescribed dose was compared.ResultsThe mean minimum doses in the target volume were 93.3% (CK) and 90.7% (L-mMLC),p=n.s, maximum: 119.7 and 110%, respectively (p=0.004). The mean CI was 1.46 and 1.86, HI: 1.2, and 1.11, CIL 0.7, and 0.6, CN: 0.68 and 0.58 for CK and mMLC, respectively (p<0.05). The values of GSI and Q were not significantly different. The volumes of the brain receiving low doses (4 Gy and 2 Gy) were significantly lower in the CK system. The number of monitor units necessary to deliver the prescribed dose was significantly greater in case of the CK system.ConclusionsBetter conformity can favor the CK system for treatment of large AVMs at the cost of higher maximum doses and worse homogeneity. L-mMLC is superior when shorter treatment time is required. Neither system can assure satisfying dose gradients outside large targets surrounded by numerous critical structures.

Characteristics and performance of the first commercial multileaf collimator for a robotic radiosurgery system

“…The specific features of CyberKnife have been demonstrated to yield excellent accuracy for static and moving targets, 1,2 at the expense of prolonged treatment times in comparison to other delivery techniques. 1,3,4 It has been suggested that a non-coplanar arrangement of irregular-shaped fields can yield improvements in sparing of organs at risk over a coplanar geometry 5,6 and reduce treatment times compared to non-coplanar circular beams, 7,8 thus promoting the addition of a multileaf-collimator (MLC) to the CK platform.…”

Gamma Knife, CyberKnife or micro-multileaf collimator LINAC for intracranial radiosurgery?

“…Treatment plans of various equipment using photon beams have been compared directly for radiosurgery of arteriovenous malformations [1,4,5], acoustic neuromas [3,5], brain metastases [8], trigeminal neuralgia [2], various pathologies [7] and a simulated ellipsoidal target [9]. Since protonbeam therapy is not applied as a single-session radiosurgery, it is not discussed.…”

Dosimetric comparison of robotic and linear accelerator multi-leaf collimator-based stereotactic radiosurgery for arteriovenous malformation

“…Blamek et al . [ 11 ] studied the dosimetric comparison for large or critically located AVM plans, which were generated by CK and LINAC mMLC with a mean volume of 21.7cc (1.02cc to 146.45cc) for 15 patients. The mean CI Paddick (it was denoted as conformation number-CN[ 19 ]) was 0.68, 0.58 for CK based and L-mMLC plans, respectively.…”

“…[ 10 ] An earlier study, which compared CK and LINAC plans, was performed with a large volume AVM. [ 11 ] The present study evaluated the dosimetric impact of three different collimators used in SRS. A comparison was made between FIXED cone (FIXED) and IRIS® collimator in CK and multi-leaf collimator (MLC) beam modulator in Elekta LINAC.…”