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

Abstract

The number of publications comparing the various technologies for intracranial radiosurgery is increasing slowly but steadily. 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. The authors of this issue's contribution, "Dosimetric comparison of different treatment modalities for stereotactic radiosurgery of meningioma" (Kaul et al. [6]), undertake an interesting and important further step in the comparison of three different radiosurgical technologies. They compare radiosurgical plans generated on the three different platforms for the treatment of meningiomas. Radiosurgical treatment plans for ten meningiomas are investigated using Gamma Knife (GK) technology, CyberKnife (CK) technology, and the micro-multileaf collimator system of the Novalis linear accelerator (MML). All ten patients have been treated with the CK. In that sense, the CK plans are real life plans and the GK and MML plans are sham plans. Unfortunately, the tumour volumes are rather large and the prescription dose (PD) seems rather high. In that sense, the study may not necessarily reflect typical cases. The nature of the study leads to an investigation which remains on a technical level and it does not take radiosurgical issues into account such as differences in: dose rates, radiation source, radiation spectrum, planning paradigms, isodose lines to which the PD is typically applied in the various systems, etc. In this setting with an identical PD, the authors find no differences in tumour coverage for the three technologies and no differences in conformity index between GK and CK technologies. The gradient index which indicates the steepness of the dose fall-off outside the target is best for the GK technology; on the other hand, beamon-time is longest for the GK technology. Personally, I find it rather unlikely that as in this issue's study by Kaul et al. [6], identical meningiomas would be treated with identical treatment parameters such as PD or treatment plans with the three various systems in question. The experienced neurosurgeon who uses one or another technology is aware of inherent diverging factors of the various technologies such as dose rate, which is at least 5 times higher in CK technology than in GK technology and adjusts his or her decisions accordingly. In my view, an excellent or good GK plan is not necessarily an excellent or good CK plan and vice versa. It is important that the radiosurgeon is aware of that. Ideally, the radiosurgeon is familiar with more than just one technology which allows him or her to adjust for the necessary clinical decisions.Since the present and most of the former trials focus on dosimetry, the nature of dosimetry needs to be looked into more closely. What is dosimetry? Dosimetry is ...