Denis Porcheron

HEARING PRESERVATION AFTER GAMMA KNIFE RADIOSURGERY FOR VESTIBULAR SCHWANNOMAS PRESENTING WITH HIGH-LEVEL HEARING

OBJECTIVEThe aim of this study was to evaluate long-term hearing preservation after gamma knife radiosurgery (GKS) for vestibular schwannomas in patients with initially normal or subnormal hearing (Gardner-Robertson Class 1) and to determine the predictive factors for functional hearing preservation. METHODSSince July 1992, more than 2053 vestibular schwannomas have been treated by GKS and followed at the Timone University Hospital, Marseille. A minimum of 3 years of follow-up (range, 3–11 years; median, 48 months) is available for 74 patients (without neurofibromatosis Type 2 or previous surgery) with Gardner-Robertson Class 1 hearing. RESULTSThe average age of the patients was 47.5 years (range, 17–76 years). The number of tumors in Koos Stage I was 8, the average number in Stage II was 21, the average number in Stage III was 43, and the average number in Stage IV was 2. The median number of isocenters was 8 (range, 2–45), and the median marginal dose was 12 Gy (range, 9–13 Gy). At the time of the last follow-up evaluation, 78.4% of the patients had preserved functional hearing. Tumor control was achieved in 93% of the cases. The probability of preserving functional hearing was higher in patients who had an initial symptom other than hearing decrease (91.1%), in patients younger than 50 years (83.7%), and in those treated with a dose to the cochlea of less than 4 Gy (90.9%). CONCLUSIONThis study shows that the probability of preserving functional hearing in the long term after GKS for patients presenting with unilateral vestibular schwannomas is very high. The positive predictive factors appear to be young age, an initial symptom other than hearing decrease, and a low dose to the cochlea.

Radiosurgery with the world's first fully robotized leksell gamma knife perfeXion in clinical use: A 200-patient prospective, randomized, controlled comparison with the gamma knife 4C

OBJECTIVEThe worlds first Leksell Gamma Knife PerfeXion (Elekta Instrument AB, Stockholm, Sweden) for radiosurgery of the head and neck became operational at Timone University Hospital in Marseille on July 10, 2006. To allow strict evaluation of the capabilities, advantages, disadvantages, and limitations of this new technology, patients were enrolled in a prospective, randomized trial. METHODSIn 66 working days, between July 10 and December 20, 2006, 363 patients were treated by gamma knife surgery at Timone University Hospital, Marseille. Of these patients, 200 were eligible for the comparative prospective study (inclusion criteria were informed consent obtained, tumor or vascular indication, and no previous radiosurgery or radiotherapy). In accordance with the blinded randomization process, 100 patients were treated with the Leksell Gamma Knife 4C (Elekta Instrument AB) and Gamma Knife 100 (Elekta Instrument AB) with the Leksell Gamma Knife PerfeXion. Dose planning parameters, dosimetry measurements on the patients body, workflow, patient comfort, quality assurance procedure, and a series of other treatment-related parameters were systematically and prospectively evaluated in both arms of the trial. RESULTSNo technical failure of the treatment procedure was encountered. The new dose-planning system led to the use of composite shots in 39.4% of the patients. The median number of different collimator sizes used was larger with the PerfeXion than with the 4C (2 and 1, respectively). The mean number of isocenters used was lower (10.67 and 13.08, respectively). The median total treatment time was significantly shorter with the PerfeXion (40 and 60 minutes, respectively), but there was no significant difference in the median radiation time (34.02 and 33.40 minutes, respectively). The procedure was performed using only a single run in 98.99% of the PerfeXion cases and in 42% of the 4C cases. Collision risk on the 4C forced us to change the frame gamma angle for at least 1 shot in 24% of the patients and led to treatment in manual mode for at least 1 shot in 21% of the patients. Collision risk requiring technical adaptation did not occur with the PerfeXion. In 1 patient treated with the PerfeXion, the system required a direct collision check. In terms of dose to structures outside the target area, the PerfeXion delivers 8.2 times less to the vertex, 10 times less to the thyroid, 12.9 times less to the sternum, and 15 times less to the gonads. CONCLUSIONOur prospective study indicates that procedures with the PerfeXion were collision-free, even with very eccentric lesions (e.g., multiple metastases). The duration of the surgical procedure, the amount of time required for nurse, physicist, and physician intervention on the machine, and the duration of the quality assurance procedure were all shown to be dramatically reduced with the PerfeXion gamma knife. Patient protection is greatly improved with the PerfeXion. In our experience, the technological advances of the Leksell Gamma Knife PerfeXion will make a very significant contribution to future progress in head and neck radiosurgery.

Radiosurgery: Operative Technique, Pitfalls and Tips

RATIONALE From frame placement to dose administration, each step of the procedure must be optimized in every detail for better preservation of global precision, accuracy, safety and efficacy. METHODS Quality control for resolution, accuracy and acquisition parameter optimization of both computed tomography (CT) scanners and magnetic resonance imaging (MRI) must be performed. Inaccuracies should then be quantified through systematic combination of MRI and CT in the radiosurgery planning system. Topography of petrous structures such as cochlea, vestibulum and facial nerve canal should be visible on the CT scan. T1-weighted volumetric MRI pulse sequences (3DT1) show a contrast-enhanced signal that is useful for both the pons interface delineation in Koos III cases, and the canal ending. High-resolution CISS T2-weighted volumetric pulse sequences (3DT2) allow direct nerve visualization and give superior stereotactic definition attributable to their better resolution minimizing partial volume effects and to their lower magnetic susceptibility minimizing distortions. The 3DT2 pulse sequences with contrast injection, show improved distinction between the pons and the nerves due to signal differences within the schwannomas. Fat saturation pulse sequences are of interest in postmicrosurgery conditions. The previous technical requirements and the dose planning elaboration will be balanced depending on the lesion volume staging (Koos), treatment history (microsurgery), clinical condition (hearing quality), pathological context (NF2) or age of the patient. The recommended marginal dose is 11-12 Gy. Tumor volume delineation allows the calculation of conformity, selectivity and gradient indexes. These global indexes must be weighted according to the relationship to critical structures and functional status of the patient. CONCLUSIONS As an exclusively image-guided surgical method, radiosurgery requires special attention in the choice of imaging modalities and their acquisition parameters need extreme care. Technical nuances during the elaboration of the dose planning itself will directly influence both the toxicity risk and the chance of cure.

Lateral positioning technique for the treatment of far-lateral targets with the Leksell gamma knife: technical note.

OBJECTIVE To describe a procedure for Leksell gamma knife (LGK) radiosurgery in a lateral position, for treatment of far-lateral intracranial lesions. METHODS Positioning of the patient in the lateral decubitus position during LGK treatment switches the x and y axis coordinates. This increases the range of the x axis from 52 to 148 mm to 40 to 160 mm (i.e., 12 mm in each direction). RESULTS Conversion of the coordinates of the isocenters is easily performed with simple mathematical algorithms and does not impair the precision of target positioning at the isocenters during LGK radiosurgery. CONCLUSION LGK treatment in the lateral decubitus position is a simple accurate procedure for the treatment of far-lateral lesions that cannot be reached with normal supine positioning.