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Objectives: We conducted a phase I/II prospective trial to determine whether stereotactic dose escalation to the dominant intra-prostatic nodule (DIN) up to 50 Gy incorporating a rectal balloon spacer is safe, does not affect patient quality of life, and preserves local control in patients with intermediate-high risk PCa. Methods: Eligible patients included males with stage ≤T3b localized disease, a prostate-specific antigen (PSA) level ≤50 , International Prostate Symptom Score (IPSS) ≤14, and a gland volume ≤70 cm3. Patients underwent perirectal spacer placement, followed by a planning MRI and were subsequently treated with SBRT doses of 36.25 Gy in five fractions to the whole prostate while simultaneously escalating doses to the magnetic resonance image visible DIN up to 50 Gy. Primary endpoint: safety. Secondary endpoints: biochemical control, quality of life (QofL), and dosimetry outcome. Results: Nine patients were treated in the Phase I part of the study. Dose limiting toxicities (DLTs) were not observed. Further characterization of tolerability and efficacy was conducted in the subsequent 24 patients irradiated at the recommended Phase II dose (50 Gy, RP2D). At a median follow-up of 61 months, biochemical control is 69%. Grade 1 and 2 acute GU and GI toxicity was 57.5 and 15%, and 24.2 and 6.1%, respectively. Grade 1 and 2 late GU and GI toxicity was 66.6 and 12.1%, and 15.1 and 3%, respectively. No Grade 3 or higher toxicity was reported. QofL data confirmed physician’s reported side effects. Dosimetry analysis showed adherence to the doses prescribed in the protocol. Conclusions SBRT of the whole prostate with 36.25 Gy in 5 fractions and dose escalation to 50 Gy to the DIN, when combined with a peri-rectal balloon spacer, was tolerable and established the RP2D. QofL analysis showed minimal negative impact in GU, GI, and sexual domains. Advances in knowledge: Extreme hypofractionated prostate radiation therapy with focal dose escalation to the DIN is well tolerated with efficacy comparable to normal fractionated radiation therapy.

Background and purpose Early-stage Hodgkin lymphoma (HL) is a highly curable disease but the treatment can induce late complications many years later. Irradiation of the healthy heart is inevitable during radiation treatment of mediastinal sites. We developed a novel method to induce a prolonged apnea-like state that can help decrease the dose to organs at risk during radiation therapy. We present the results of the first 8 HL patients treated routinely with percussion assisted radiation therapy (PART) in our clinic. Material and methods We used a newly developed high-frequency non-invasive ventilation system to suppress respiratory motion for prolonged periods and push the heart away from the treated volume. Results All 8 patients were able to rapidly learn the technique and had an advantage to be treated by PART. We lowered the mean heart dose by an average of 3 Gy with similar target coverage compared to a classical free breathing treatment plan. They were all treated for 15 radiotherapy sessions by PART without any notable side effects. Conclusions Percussion assisted radiation therapy can be used routinely to reduce the dose to the heart in Hodgkin lymphoma.

The Gamma Knife ® planning software (TMR 10, Elekta Instruments, AB, Sweden) affords two ways of defining the skull volume, the "historical" one using manual measurements (still perform in some centers) and the new one using image-based skull contours. Our objective was to assess the potential variation of the dose delivery calculation using consecutively in the same patients the two above-mentioned techniques. We included in this self-case-control study, 50 patients, treated with GKRS between July 2016 and January 2017 in Lausanne University Hospital, Switzerland, distributed among four groups: convexity targets (n = 18), deep-seated targets (n = 13), vestibular schwannomas (n = 11), and trigeminal neuralgias (n = 8). Each planning was performed consecutively with the 2 skull definition techniques. For each treatment, we recorded the beam-on time (min), target volume coverage (%), prescription isodose volume (cm 3 ), and maximal dose (Gy) to the nearest organ at risk if relevant, according to each of the 2 skull definition techniques. The image-based contours were performed using CT scan segmentation, based upon a standardized windowing for all patients. The median difference in beam-on time between manual measures and image-based contouring was + 0.45 min (IQR; 0.2-0.6) and was statistically significant (p < 0.0001), corresponding to an increase of 1.28% beam-on time per treatment, when using image-based contouring. The target location was not associated with beam-on time variation (p = 0.15). Regarding target volume coverage (p = 0.13), prescription isodose volume (p = 0.2), and maximal dose to organs at risk (p = 0.85), no statistical difference was reported between the two skull contour definition techniques. The beam-on time significantly increased using image-based contouring, resulting in an increase of the total dose delivery per treatment with the new TMR 10 algorithm. Other dosimetric parameters did not differ significantly. This raises the question of other potential impacts. One is potential dose modulation that should be performed as an adjustment to new techniques developments. The second is how this changes the biologically equivalent dose per case, as related to an increased beam on time, delivered dose, etc., and how this potentially changes the radiobiological effects of GKRS in an individual patient.

Highlights • The first curative management of symptomatic cardiac metastasis of a lung cancer using SBRT. • A CR was obtained and no further specific treatment was needed., Although cardiac metastases (CM) are more common than primary cardiac malignant tumors, they remain a rare localization of metastatic cancer. Until recently, CM were surgically treated as a palliative approach because of a lack of ablative solutions even for oligometastatic patients. Technological advances in radiation therapy (RT) in thoracic oncology have led to high precision delivery that enlarged the indications for stereotactic body radiotherapy (SBRT). To date, there are limited reports of cardiac SBRT for CM. Herein, we report a cardiac SBRT performed in curative intent for a lung cancer patient metastatic to the heart.

Purpose A novel optimization algorithm (VOLO™) for robotic radiosurgery in the Precision™ treatment planning system was evaluated for different SRS/SBRT treatments and compared with the previous Sequential Optimization (SO) algorithm. Materials and methods Fifty cases of brain, spine, prostate and lung tumors previously optimized with SO, were re-planned with VOLO™ algorithm keeping the same prescription, collimator type and size, optimization shells, and blocking structures. The dosimetric comparison involved target coverage, conformity (CI), gradient (GI) and homogeneity indexes, specific indicators of dose to OARs and number of nodes, beams, MU and delivery time. For brain only, plans were IRIS- and MLC-based (10 each). The remaining 30 plans were all IRIS-based. Results VOLO™ optimization was significantly superior for target coverage for prostate and spine, CI for brain, and for brain and urethra dose sparing. SO gave significantly better results for GI for prostate. VOLO™ showed a significantly steeper dose fall-off for brain MLC-based, while for prostate and spine SO was superior. For IRIS-based plans, VOLO™ significantly reduced the nodes (36%), beams (14%), and MU (31%). This led to an average reduction of delivery time of 20% (from 8% for brain to 30% for prostate). For MLC-based plans, VOLO™ significantly increased the nodes and beams (42%) keeping the same number of MU. The averaged delivery time increased by 18%. Conclusions With respect to SO, VOLO™ optimization algorithm provided better results in terms of delivery time for IRIS-based and of quality of dose distribution for MLC-based plans, respectively.

Purpose Helical tomotherapy (HT) has been recently introduced in the neoadjuvant treatment of locally advanced rectal cancer. Aim of this study is to report the toxicity and local control rates of a large series of locally advanced rectal cancer patients treated with neoadjuvant chemotherapy and HT under daily image guidance followed by surgery. Methods Data from 117 locally advanced rectal cancer patients treated at two Swiss Radiotherapy departments were collected and analyzed. Radiotherapy consisted of 45 Gy (1.8 Gy/fraction, 5 fractions/week delivered in 5 weeks) to the regional pelvic lymph nodes. Seventy patients also received a simultaneous integrated boost (SIB) up to 50 Gy to the tumor and involved nodes (2 Gy/fraction, 5 fractions/week delivered in 5 weeks). Chemotherapy consisted of capecitabine 825 mg/m2, twice daily, during the irradiation days. After a median interval of 59 days [95% confidence interval (CI) 53–65 days), all patients underwent surgery. Results Median follow-up was 45 months (range 4–90 months). The overall rate of acute grade 2–4 toxicity was 18.8% (n = 22). Four patients (3.4%) presented a grade 3 dermatitis (n = 1) or diarrhea (n = 3), and 1 (0.8%) demonstrated grade 4 rectal toxicity. No patients presented with grade ≥ 3 hematologic toxicity. Six patients (5.1%) had late grade 3 gastrointestinal toxicity. The 4-year local control rate was 88.4% (95% CI 87.5–88.5%). Conclusions Neoadjuvant chemoradiotherapy delivered with HT under daily image guidance is well tolerated and shows a high 4-year local control rates.

Purpose To assess the interplay effect amplitude between different planned MU distributions and respiratory patterns in the CyberKnife system when treating moving targets with static tracking technique. Methods Small- and Large-Respiratory Motions (SRM and LRM) differing in amplitude and frequency were simulated in a semi-anthropomorphic dynamic thorax phantom. The interplay effect was evaluated for both respiration motions in terms of GTV coverage and conformity for three plans designed with an increasing range of MU per beam (small, medium and large). Each plan was delivered three times changing the initial beam-on phase to assess the inter-fraction variation. Dose distributions were measured using radiochromic films placed in the GTV axial and sagittal planes. Results Generally, SRM plans gave higher GTV coverage and were less dependent on beam-on phases than LRM plans. For SRM (LRM) plans, the GTV coverage ranged from 95.2% to 99.7% (85.9% to 99.8%). Maximum GTV coverage was found for large MU plans in SRM and for small MU plans in LRM. Minimum GTV coverage was found for medium MU plans for both SRM and LRM. For SRM plans, dose conformity decreased with increasing MU range while the variation was reduced for LRM plans. Large MU plans reduced the inter-fraction variation for SRM and LRM. Conclusions We confirmed the interplay effect between target motion and beam irradiation time for CyberKnife static tracking. Plans with large MU per beam improved the GTV coverage for small motion amplitude and the inter-fraction dose variation for large motion amplitude.

Purpose This paper analyzes Tomotherapy-based intracranial stereotactic radiosurgery (HTSRS) of brain metastasis targeting two end-points: 1) evaluation of dose homogeneity, conformity and gradient scores for single and multiple lesions and 2) assay of dosimetric criticality of completion of HTSRS procedures. Methods 42 treatment plans of 33 patients (53 brain lesions) treated with HTSRS were analyzed. Dose to healthy brain, homogeneity, conformity and gradient indexes were evaluated for each lesion. Influence of Field Length and multiple lesions cross-talk effect were assessed. Treatment interruption and completion was investigated using radiochromic films in order to examine the delivered dose and its robustness to patient intrafraction movement. Results The average dose homogeneity index was 1.04 ± 0.02 (SD). Average dose conformity and gradient score indexes were 1.4 ± 0.2 and 50 ± 14 respectively. We found a strong correlation of the dose to healthy brain and conformity and gradient indexes with target(s) volume for which analytical functions were obtained. Field Length and cross-talk effect were significantly correlated with poor gradient scores, but were found not to affect dose conformity. Conclusions Homogeneity and conformity of HTSRS plans achieved excellent scores, while dose falloff and dose to healthy brain were slightly larger when compared with non-coplanar SRS techniques. Care should be given if treating large (>3 cc) or multiple near in-plane lesions in order to reduce dose to healthy brain. Analysis of interrupted treatments suggests splitting HTSRS treatments in two consecutive fractions in order to prevent target miss and overdosage due to patient intrafraction movement.

Background and purpose: Adjuvant radiation therapy (RT) of the whole breast (WB) is still the standard treatment for early breast cancer. A variety of radiation techniques is currently available according to different delivery strategies. This study aims to provide a comparison of six treatment planning strategies commonly adopted for breast-conserving adjuvant RT and to use the Pareto concept in an attempt to assess the degree of plan optimization. Materials and methods: Two groups of six left- and five right-sided cases with different dose prescriptions were involved (22 patients in total). Field-in-Field (FiF), two and four Fields static-IMRT (sIMRT-2f and sIMRT-4f), Volumetric-Modulated-Arc-Therapy (VMAT), Helical Tomotherapy (HT) and Static-Angles Tomotherapy (TomoDirect™ – TD) were planned. Dose volume constraints were taken from the RTOG protocol 1005. Pareto fronts were built for a selected case to evaluate the reliability of the plan optimization process. Results: The best target dose coverage was observed for TD able to improve significantly (p

Purpose The dosimetric differences between four radiation therapy techniques for left sided whole breast irradiation were evaluated side by side in the same patient population. Methods Radiotherapy treatment plans were retrospectively created with Accuray TomoDirect (TD), Elekta Volumetric Modulated Arc Therapy (E-VMAT), Varian RapidArc (RA) and Field-in-field (FinF) technique for 20 patients, who had received left breast irradiation during deep-inspiration breath-hold. Dose characteristics of planning target volume and organs at risk were compared. Results The E-VMAT, TD and RA treatment plans had higher target coverage (V95%) than FinF plans (97.7–98.3% vs. 96.6%). The low-dose spillage to contralateral breast and lung was smaller with FinF and TD (mean 0.1 and 0.3 Gy) compared to E-VMAT and RA (mean 0.6 and 0.9 Gy). E-VMAT, RA and TD techniques were more effective than FinF in sparing left anterior descending artery (mean 4.0, 4.2 and 4.7 Gy vs. 6.1 Gy, respectively). Conclusions In whole breast irradiation TD, E-VMAT and RA plans generated in this study achieved higher dose coverage and sparing of organs from the high dose in the vicinity of the PTV. The advantage of calculated FinF plans is the lowest dose on contralateral organs. The choice of the technique used should be weighted by each institution taking into account the dose characteristics of each technique and its fit with patient anatomy bearing in mind the increased workload of using modulated techniques and the increased beam on time.

Schwannomas involving the occulomotor cranial nerves (CNs; III, IV and VI), can be disabling, due to the associated diplopia and decreased quality of life and are extremely rare. We evaluated the role of Gamma Knife surgery (GKS) in these cases. Five patients with CN IV and VI schwannomas (three and two, respectively) were treated in Lausanne University Hospital between 2010 and 2015. Four benefitted from upfront GKS and one from a combined approach (planned subtotal resection followed by GKS), due to a large preoperative tumour volume (size, 3 × 2 × 2.5 cm; volume, 7.9 ml), with symptomatic mass effect and oedema, as well as an entrapement cyst at the brainstem interface, in a young patient. Neuro-ophtalmological evaluation was performed at baseline and during each follow-up time-point. A systematic literature review is presented and compared to the present report. The mean follow-up was 44.4 months (12–54). Initial clinical presentation was diplopia in four cases and cavernous sinus syndrome in one. The marginal dose was 12 Gy in all cases. The mean target volume was 1.51 cm3 (0.086–5.8). The mean prescription isodose volume (PIV) was 1.71 cm3 (0.131–6.7). At last follow-up, all patients presented with disappearance of the baseline symptoms. Tumour control was achieved in 100%, with decrease in volume in all cases. The systematic review analysed 11 peer-reviewed studies, with a total of 35 patients. For uniformly reported CN VI, the mean marginal radiation dose ranged between 12 and 12.5 Gy, with disappearance of symptoms in 12.5%, improvement in 31.25%, stabilisation in 6.25%, worsening in 12.5%. Tumour volume decreased in all cases. Our data suggest that first intention GKS is a safe and effective option for patients with small to medium size oculomotor schwannomas, providing a high rate of clinical alleviation and tumour control. When the initial tumour volume is too large for first intention GKS, a combined approach with planned subtotal resection followed by GKS can be performed, with favourable and comparable outcomes as in upfront GKS.

Objective Glossopharyngeal neuralgia (GPN) is a very rare condition, affecting the patient’s quality of life. We report our experience in drug-resistant, idiopathic GPN, treated with Gamma Knife radiosurgery (GKRS), in terms of safety and efficiency, on a very long-term basis. Methods The study was opened, self-controlled, non-comparative and bicentric (Marseille and Lausanne University Hospitals). Patients treated with GKRS between 2003 and 2015 (models C, 4C and Perfexion) were included. A single 4-mm isocentre was positioned in the cisternal portion of the glossopharyngeal nerve, with a targeting based both on magnetic resonance imaging (MRI) and computed tomography (CT). The mean maximal dose delivered was 81.4 ± 6.7 Gy (median = 85 Gy, range = 60–90 Gy at the 100% isodose line). Results Twenty-one patients (11 women, 10 men) benefited from 25 procedures. The mean follow-up period was 5.2 ± 3 years (range = 0.9–12.1 years). Seventeen (81%) were initially pain-free after GKRS. At three months, six months and one year after radiosurgery, the percentage of patients with good outcome (BNI classes I to IIIA) was 87.6%, 100% and 81.8%, respectively. Ten cases (58.8%) from the initial pain-free ones had a recurrence, after a mean period of 13.6 ± 10.4 months (range = 3.1–36.6 months). Only three patients (14.2%) had recurrences (two for each one of them) requiring further surgeries. Three patients underwent a second GKRS procedure; one case needed a third GKRS. The former procedures were performed at 7, 17, 19 and 30 months after the first one, respectively. Furthermore, two patients needed additional interventions. At last follow-up, 17 cases (80.9%) were still pain-free without medication. The actuarial pain relief without new surgery was 83%. A transient complication (paraesthesia of the edge of the tongue) was seen in one case (4.8%). Conclusion GKRS is a valuable, minimally invasive, surgical alternative for idiopathic GPN, with a very high short- and long-term efficacy and without permanent complications. A quality imaging, including T2 CISS/Fiesta MRI and bone CT acquisitions for good visualisation of the nerve and the other bony anatomic landmarks, is essential for targeting accuracy and successful therapy.

Stereotactic body radiotherapy (SBRT) is an emerging non-invasive treatment in the management of ventricular tachycardia (VT). We report here an intensive care patient suffering from an electrical storm due to incessant VT, unresponsive to catheter ablation and anti-arrhythmic drugs, showing an immediate and durable response to electrophysiology-guided cardiac SBRT.

Stereotactic body radiotherapy (SBRT) is routinely used in oncology to treat non-invasively solid tumors with high precision and efficacy. Recently, this technology has been evaluated in the treatment of ventricular tachycardia (VT). This article presents the basic underlying principles, proofs of concept and main results of clinical studies that used SBRT for the treatment of VT.La radiothérapie stéréotaxique (SBRT) est une technologie couramment utilisée en oncologie pour traiter de façon non invasive les tumeurs solides avec précision et efficacité. Récemment, cette technologie a été évaluée dans le traitement des tachycardies ventriculaires (TV). Cet article présente les principes de base sous-jacents, le concept ainsi que les résultats des premières études cliniques ayant traité avec succès des patients souffrant de TV avec la SBRT.

Purpose The Leksell Gamma Knife (LGK) Icon has been recently introduced to provide Gamma Knife technology with frameless stereotactic treatments which use an additional cone-beam CT (CBCT) imaging system and a motion tracking system (IFMM, Intra-Fraction Motion Management). The system was commissioned for the treatment unit itself as well as the imaging system. Methods The LGK Icon was calibrated using an A1SL ionization chamber. EBT3 radiochromic films were employed to independently check the machine calibration, to measure the relative output factors (ROFs) and to collect dose distributions. Coincidence between CBCT isocenter and radiological focus was evaluated by means of EBT3 films. CBCT image quality was investigated in terms of spatial resolution, contrast-to-noise ratio (CNR), and uniformity for the two presets available (low dose and high dose). Computed Tomography Dose Index (CTDI) was also measured for both presets. Results The absolute dose rate of the LGK Icon was 3.86 ± 0.09 Gy/min. This result was confirmed by EBT3 readings. ROF were found to be 0.887 ± 0.035 and 0.797 ± 0.032 for the 8 mm and 4 mm collimators, respectively, which are within 2% of the Monte Carlo-derived ROF values. Excellent agreement was found between calculated and measured dose distribution with the gamma pass rate >95% of points for the nine dose distributions analyzed with 3%/1 mm criteria. CBCT isocenter was found to be within 0.2 mm with respect to radiological focus. Image quality parameters were found to be well within the manufacturer's specifications with the high-dose preset being superior in terms of CNR and uniformity. CTDI values were 2.41 mGy and 6.32 mGy, i.e. −3.6% and 0.3% different from the nominal values for the low-dose and high-dose presets, respectively. Conclusions The LGK Icon was successfully commissioned for clinical use. The use of the EBT3 to characterize the treatment unit was demonstrated to be feasible. The CBCT imaging system operates well within the manufacturer's specifications and provides good geometrical accuracy.

OBJECTIVEVestibular schwannomas (VSs) represent a common indication of Gamma Knife surgery (GKS). While most studies focus on the long-term morbidity and adverse radiation effects (AREs), none describe the acute clinical AREs that might appear on a short-term basis. These types of events are investigated, and their incidence, type, and outcomes are reported in the present paper.METHODSThe included patients were treated between July 2010 and March 2016, underwent at least 6 months of follow-up, and presented with a disabling symptom during the first 6 months after GKS that affected their quality of life. The timing of appearance, as well as the type of main symptom and outcome, were noted. The prescribed dose was 12 Gy at the margin.RESULTSThirty-five (22%) of 159 patients who fulfilled the inclusion criteria had acute clinical AREs. The mean followup period was 30 months (range 6–49.2 months). The mean time of appearance was 37.9 days (median 31 days; range 3–110 days). In patients with de novo symptoms, the more frequent symptoms were vertigo (n = 4; 11.4%) and gait disturbance (n = 3; 8.6%). The exacerbation of a preexisting symptom was more frequently related to hearing loss (n = 10; 28.6%), followed by gait disturbance (n = 7; 20%) and vertigo (n = 3, 8.6%). In the univariate logistic regression analysis, the following factors were statistically significant: age (p = 0.002; odds ratio [OR] 0.96), hearing at baseline by Gardner-Robertson (GR) class (p = 0.006; OR 0.21), pure tone average at baseline (p = 0.006; OR 0.97), and Koos grade at baseline (with Koos Grade I used as a reference) (for Koos Grade II, OR 0.17 and p = 0.002; for Koos Grade III, OR 0.42 and p = 0.05). The following were not statistically significant but showed a tendency toward significance: the number of isocenters (p = 0.06; OR 0.94) and the maximal dose received by the cochlea (p = 0.07; OR 0.74). Fractional polynomial regression analysis showed a nonlinear relationship between the outcome and the radiation dose rate (minimum reached at a cutoff of 2.5 Gy/minute) and the maximal vestibular dose (maximum reached at a cutoff of 8 Gy), but the small sample size precludes a detailed analysis of the former. The clinical acute AREs disappeared in 32 (91.4%) patients during the first 6 months after appearance. Permanent and somewhat disabling morbidity was found in 3 cases (1.9% from the whole series): 1 each with complete hearing loss (GR Class I before and V after), hemifacial spasm (persistent but alleviated), and dysgeusia.CONCLUSIONSAcute effects after radiosurgery for VS are not rare. They concern predominantly de novo vertigo and gait disturbance and the exacerbation of preexistent hearing loss. In de novo vestibular symptoms, a vestibular dose of more than 8 Gy is thought to play a role. In most cases, none of these effects are permanent, and they will ultimately improve or disappear with steroid therapy. Permanent AREs remain very rare.

Background and purpose Compensation for respiratory motion is needed while administering radiotherapy (RT) to tumors that are moving with respiration to reduce the amount of irradiated normal tissues and potentially decrease radiation-induced collateral damages. The purpose of this study was to test a new ventilation system designed to induce apnea-like suppression of respiratory motion and allow long enough breath hold durations to deliver complex RT. Material and methods The High Frequency Percussive Ventilation system was initially tested in a series of 10 volunteers and found to be well tolerated, allowing a median breath hold duration of 11.6min (range 3.9–16.5min). An evaluation of this system was subsequently performed in 4 patients eligible for adjuvant breast 3D conformal RT, for lung stereotactic body RT (SBRT), lung volumetric modulated arc therapy (VMAT), and VMAT for palliative pleural metastases. Results When compared to free breathing (FB) and maximal inspiration (MI) gating, this Percussion Assisted RT (PART) offered favorable dose distribution profiles in 3 out of the 4 patients tested. PART was applied in these 3 patients with good tolerance, without breaks during the "beam on time period" throughout the overall courses of RT. The mean duration of the apnea-like breath hold that was necessary for delivering all the RT fractions was 7.61min (SD=2.3). Conclusions This first clinical implementation of PART was found to be feasible, tolerable and offers new opportunities in the field of RT for suppressing respiratory motion.

International audience; INTRODUCTION : Stereotactic radiosurgery (SRS) is increasingly used as a minimally invasive alternative in many neurosurgical conditions, including benign and malignant tumors, vascular malformations, and functional procedures. As for any surgical procedure, strict safety guidelines and checklists are necessary to avoid errors and the inherent unnecessary complications. With regard to the former, other groups have already reported human and/or technical errors. We describe our safety checklist for Gamma Knife radiosurgical procedures.METHODS : We describe our checklist protocol after an experience gained over 1500 radiosurgical procedures, using Gamma Knife radiosurgery, performed over a period of 8 years, while employing the same list of items. Minor implementation has been performed over time to address some safety issues that could be improved.RESULTS : Two types of checklist are displayed. One is related to the indications when a specific tissue volume is irradiated, including tumors or vascular disorders. The second corresponds to functional disorders, such as when the dose is prescribed to one specific point. Using these checklists, no human error had been reported during the past 8 years of practice in our institution.CONCLUSION : The use of a safety checklist for SRS procedures promotes a zero-tolerance attitude for errors. This can lower the complications and is of major help in promoting multidisciplinary cooperation. We highly recommend the use of such tool, especially in the context of the increased use of SRS in the neurosurgical field.

Purpose To study the potential of (99m)Tc-Mebrofenin hepatobiliary scintigraphy (HBS) in identifying the short-term variations of liver function after stereotactic body radiotherapy (SBRT) for liver cancers. Material and methods We treated with SBRT 3 patients (pts) affected by a cholangiocarcinoma and 3 patient presenting liver metastases (3x15 Gy, 4 pts; 5x8 Gy, 1 pt; 6x5 Gy, 1 pt). All patients received HBS before and 3 months after SBRT, which were co-registered with the simulation CT-scan. Structures corresponding to isodoses from 10–90 Gy were created, with intervals of 10 Gy. Finally, the variations of the mean activity (MBq) in each isodose structure have been calculated. Then, a linear regression analysis was performed. Results We showed a linear reduction of the activity, significantly related to the delivered dose (p

Objectif de l’etude Nous presentons l’analyse retrospective d’une cohorte de patients atteints d’un cancer du rectum localement evolue pris en charge par chimioradiotherapie delivree avec la tomotherapie helicoidale, par une technique de simultaneous integrated boost (SIB) et un controle quotidien de la position du patient, suivie par une chirurgie. Materiel et methode Quatre-vingt-six patients ont recu 45 Gy (1,8 Gy par fraction) au niveau du rectum, du mesorectum et des ganglions de drainage pelviens (presacres, iliaques internes et obturateurs jusqu’a L5-S1), delivres avec un SIB jusqu’a la dose totale de 50 Gy (2 Gy par fraction) dans le volume tumoral macroscopique (GTV) rectal et ganglionnaire, et avec une chimiotherapie concomitante (capecitabine, 825 mg/m2, deux fois par jour). La marge entre les volumes cibles anatomoclinique et previsionnel (CTV-PTV) a ete de 5 mm pour les deux volumes. Tous les patients ont ete operes apres la chimioradiotherapie (resection R0 : 84/86 patients). Quarante-cinq patients ont recu une chimiotherapie adjuvante. Le degre de regression tumorale (TRG) a ete evalue avec le score de Mandard. Resultats Le temps de suivi median etait de 54 mois (extremes : 4–91 mois). Trois et six patients ont souffert, respectivement, d’une toxicite de grade 3 ou plus aigue ou tardive. Vingt et un pour cent et 30 % des patients etaient, respectivement, en situation de reponse pathologique complete (TRG = 1) ou quasi complete. Les taux de controle local, de survie globale, et de survie sans rechute a 5 ans etaient, respectivement, de 78 %, 84 % et 66 %. Les patients avec un TRG 1–2 avaient des meilleurs taux de controle local (94 % contre 78 %, p = 0,01) et de survie globale (94 % contre 33 %, p Conclusion Un SIB delivre avec une tomotherapie et un controle quotidien de la position du patient est bien tolere et efficace. Un TRG 1–2 apres la chimioradiotherapie est un facteur pronostique de controle local et de survie globale.

Objective To perform planned subtotal resection followed by gamma knife surgery (GKRS) in a series of patients with large vestibular schwannoma (VS), aiming at an optimal functional outcome for facial and cochlear nerves. Methods Patient characteristics, surgical and dosimetric features, and outcome were collected prospectively at the time of treatment and during the follow-up. Results A consecutive series of 32 patients was treated between July 2010 and June 2016. Mean follow-up after surgery was 29 months (median 24, range 4–78). Mean presurgical tumor volume was 12.5 cm3 (range 1.47–34.9). Postoperative status showed normal facial nerve function (House–Brackmann I) in all patients. In a subgroup of 17 patients with serviceable hearing before surgery and in which cochlear nerve preservation was attempted at surgery, 16 (94.1%) retained serviceable hearing. Among them, 13 had normal hearing (Gardner–Robertson class 1) before surgery, and 10 (76.9%) retained normal hearing after surgery. Mean duration between surgery and GKRS was 6.3 months (range 3.8–13.9). Mean tumor volume at GKRS was 3.5 cm3 (range 0.5–12.8), corresponding to mean residual volume of 29.4% (range 6–46.7) of the preoperative volume. Mean marginal dose was 12 Gy (range 11–12). Mean follow-up after GKRS was 24 months (range 3–60). Following GKRS, there were no new neurological deficits, with facial and hearing functions remaining identical to those after surgery in all patients. Three patients presented with continuous growth after GKRS, were considered failures, and benefited from the same combined approach a second time. Conclusion Our data suggest that large VS management, with planned subtotal resection followed by GKRS, might yield an excellent clinical outcome, allowing the normal facial nerve and a high level of cochlear nerve functions to be retained. Our functional results with this approach in large VS are comparable with those obtained with GKRS alone in small- and medium-sized VS. Longer term follow-up is necessary to fully evaluate this approach, especially regarding tumor control.

The Leksell Gamma Knife (LGK) Icon has been recently introduced to provide Gamma Knife technology with frameless stereotactic treatments which use an additional cone-beam CT (CBCT) imaging system and a motion tracking system (IFMM, Intra-Fraction Motion Management). The system was commissioned for the treatment unit itself as well as the imaging system.The LGK Icon was calibrated using an A1SL ionization chamber. EBT3 radiochromic films were employed to independently check the machine calibration, to measure the relative output factors (ROFs) and to collect dose distributions. Coincidence between CBCT isocenter and radiological focus was evaluated by means of EBT3 films. CBCT image quality was investigated in terms of spatial resolution, contrast-to-noise ratio (CNR), and uniformity for the two presets available (low dose and high dose). Computed Tomography Dose Index (CTDI) was also measured for both presets.The absolute dose rate of the LGK Icon was 3.86 ± 0.09 Gy/min. This result was confirmed by EBT3 readings. ROF were found to be 0.887 ± 0.035 and 0.797 ± 0.032 for the 8 mm and 4 mm collimators, respectively, which are within 2% of the Monte Carlo-derived ROF values. Excellent agreement was found between calculated and measured dose distribution with the gamma pass rate95% of points for the nine dose distributions analyzed with 3%/1 mm criteria. CBCT isocenter was found to be within 0.2 mm with respect to radiological focus. Image quality parameters were found to be well within the manufacturer's specifications with the high-dose preset being superior in terms of CNR and uniformity. CTDI values were 2.41 mGy and 6.32 mGy, i.e. -3.6% and 0.3% different from the nominal values for the low-dose and high-dose presets, respectively.The LGK Icon was successfully commissioned for clinical use. The use of the EBT3 to characterize the treatment unit was demonstrated to be feasible. The CBCT imaging system operates well within the manufacturer's specifications and provides good geometrical accuracy.

Background: The purpose of our report is to describe an innovative system used for mandibular immobilization during Gamma Knife surgery (GKS) procedures. It is based on an approach originally developed in Marseille in extracranial lesions, close to or involving the mandible, which may imply a certain degree of movement during the therapeutic image acquisitions and/or GKS treatment. Methods: The maxillofacial surgeon applied bone titanium self-tapping monocortical screws (4; 2 mm diameter, 10 mm length) between roots of the teeth in the fixed gingiva (upper and lower maxillae) the day before GKS (local anesthesia, 5-10 min time). Two rubber bands were sufficient for the desired tension required to undergo GKS. We further proceeded with application of the Leksell stereotactic G frame and carried out the usual GKS procedure. Results: The mean follow-up period was 2.3 years (range 0.6-3). Three patients have been treated with this approach: 2 cases with extracranial trigeminal schwannomas involving the mandibular branch, with decrease in tumor size on MR follow-up; 1 case with residual paracondylian mandibular arteriovenous malformation following partial embolization, completely obliterated at 7 months (digital subtraction angiography programmed 1 year after treatment). Conclusions: Jaw immobilization appears to be a quick, minimally invasive, safe and accurate adjunctive technique to enhance GKS targeting precision.

We report the first known instance of the clinical use of 99mTc-mebrofenin hepatobiliary scintigraphy (HBS) for the optimization of radiotherapy treatment planning and for the follow-up of acute toxicity in a patient undergoing stereotactic body radiation therapy for hepatocellular carcinoma. In our experience, HBS allowed the identification and the sparing of more functioning liver areas, thus potentially reducing the risk of radiation-induced liver toxicity.

416 Objectives Gastrin releasing peptide receptors (GRPr) are specifically overexpressed in human prostate cancer. High affinity radiolabeled GRPr-antagonists are in clinical trials for PET imaging and have also shown promise for radionuclide treatment of prostate cancer. There currently exists no imaging modality that can accurately measure prostate cancer treatment response after radiation therapy (RT). The goal of this study is to examine a novel dual-label GRPr-antagonist to monitor prostate cancer treatment response to RT and androgen deprivation therapy (ADT). Methods We used an IRDye650 (LI-COR; Absorption Max 648nm, Emission Max 665nm) and DOTA-conjugated GRPr antagonist, HZ220 (DOTA-Lys(IRDye650)-PEG4-[D-Phe6, Sta13]-BN(6-14)NH2) developed by our group to study the expression of GRPr during radiotherapy. Experiments were performed in three cell lines: PC3 (strong GRPr expression, androgen receptor [AR] negative), VCAP (strong GRPr, AR positive), and LNCAP (weak GRPr, AR positive). Cells were exposed to 3Gy or 10Gy of external beam RT (Shepherd Mark I Irradiator, source Cs137, 1.67Gy/min), and uptake of HZ220 measured via flow cytometry at 0-48 hours after RT. For combined RT and ADT, cells were pre-treated for 48 hours with 10-80uM of bicalutamide and then treated with RT. GRPr expression was assessed by the mean fluorescence of the cells on flow cytometry after incubation with 100uM HZ220 in 2% fetal bovine serum in Ca++/Mg++ free PBS for 20 minutes at 37C. GRPr specificity of staining was confirmed by incubation with HZ220 in the presence of an excess of another GRPr antagonist, PETASIN. Cell viability was assessed by DAPI staining. Results In PC3, VCAP, and LNCAP cells, there was no significant alteration of GRPr expression in DAPI-negative cells at 0, 1, 6, 12, 24, 36, and 48 hours after exposure to 3Gy or 10Gy of external beam radiation treatment. These findings were confirmed with Western blots of whole cell protein lysates. Additionally, analysis of non-viable cells showed no significant altered GRPr expression at the same time points. In AR positive cell lines LNCAP and VCAP, there was no significant alteration of GRPr expression after pretreatment with 10-80uM bicalutamide, a nonsteroidal antiandrogen. Radiotherapy reduced percent of maximum mean cell viability to 97.3% (LNCAP), 93.9% (PC3), and 90.9% (VCAP) in the studied cell lines. In the AR positive cell lines VCAP and LNCAP, addition of bicalutamide decreased cell viability by an additional 5.5% and 4.1%, respectively. Conclusions Our data suggest a remarkable stability in expression of GRPR after exposure to high and low dose RT, with or without ADT. This is in contrast to other prostate cancer molecular imaging agents that have either specific or nonspecific change in expression after RT or ADT exposure. This makes GRPR a highly attractive target for prostate cancer imaging as its expression is proportional to cell viability after RT or radionuclide treatment. Further steps include confirming results in murine prostate xenograft models after labeling HZ220 with 68Ga.

Given the limitations in the travel ability of the helical tomotherapy (HT) couch, total marrow irradiation (TMI) has to be split in 2 segments, with the lower limbs treated with feet first orientation. The aim of this work is to present a planning technique useful to reduce the dose inhomogeneity resulting from the matching of the 2 helical dose distributions. Three HT plans were generated for each of the 18 patients enrolled. Upper TMI (UTMI) and lower TMI (LTMI) were planned onto the whole-body computed tomography (CT) and on the lower-limb CT, respectively. A twin lower TMI plan (tLTMI) was designed on the whole-body CT. Agreement between LTMI and tLTMI plans was assessed by computing for each dose-volume histogram (DVH) structure the γ index scored with 1% of dose and volume difference thresholds. UTMI and tLTMI plans were summed together on the whole-body CT, enabling the evaluation of dose inhomogeneity. Moreover, a couple of transition volumes were used to improve the dose uniformity in the abutment region. For every DVH, a number of points >99% passed the γ analysis, validating the method used to generate the twin plan. The planned dose inhomogeneity at the junction level resulted within ±10% of the prescribed dose. Median dose reduction to organs at risk ranged from 30-80% of the prescribed dose. Mean conformity index was 1.41 (range 1.36-1.44) for the whole-body target. The technique provided a "full helical" dose distribution for TMI treatments, which can be considered effective only if the dose agreement between LTMI and tLTMI plans is met. The planning of TMI with HT for the whole body with adequate dose homogeneity and conformity was shown to be feasible.

Aims and background The study focused on the evaluation of the accuracy of intracranial stereotactic radiosurgery treatments delivered with helical tomotherapy by means of the InterFix™ Radiosurgery kit. Methods and study design Twenty-two patients received stereotactic radiosurgery treatments with single fraction dose ranging from 13 to 20 Gy depending on diagnosis. Megavoltage computed tomography scans performed prior the treatments were analyzed in order to determine the position accuracy. For 8 selected cases, they were also performed at the end of the treatment to evaluate the intra-fraction motion. Results Mean setup errors and standard deviations were −1.6 ± 2.2 mm, −0.2 ± 1.2 mm, 0.4 ± 1.3 mm, 0.2 ± 0.5° for the lateral (IEC-x), longitudinal (IEC-y), vertical (IEC-z) directions and rotational variation (roll), respectively. Setup error was found to be greater than 3 mm-PTV expansion in 36% of the cases. Mean intra-fraction motion was 0.5 ± 0.7 mm, −0.3 ± 0.4 mm, 0.1 ± 0.5 mm and 0.1 ± 0.2° for the IEC-x, IEC-y, IEC-z and roll, respectively. Conclusions Observed intra-fraction movements of less than 1 mm suggested the use of the tested fixation device for stereotactic radiosurgery treatment on helical tomotherapy providing that the image-guidance procedure is always performed prior to treatment.

Purpose To optimize the dose delivery to the breast lumpectomy target treated with intraoperative electron beam radiotherapy (IOERT). Materials and methods Two tools have been developed in our MU calculation software NEMO X to improve the dose homogeneity and the in-vivo dosimetry effectiveness for IOERT treatments. Given the target (tumor bed) thickness measured by the surgeon, NEMO X can provide auto dose normalization to cover 95% of the target volume with 95% of the prescription dose (PD) and a "best guess" of the expected dosimeter dose (EDD) for a deep seated in-vivo dosimeter. The tools have been validated with the data of 91 patients treated with IOERT on a LIAC mobile accelerator. In-vivo dosimetry has been performed with microMOSFETs positioned on the shielding disk inserted between the tumor bed and the chest wall. Results On average the auto normalization showed to provide better results if compared to conventional normalization rules in terms of mean target dose (|MTD–PD|/PD⩽5% in 95% vs. 53% of pts) and V107 percentage (〈V107〉=19% vs. 32%). In-vivo dosimetry MOSFET dose (MD) showed a better correlation with the EDD guessed by our tool than just by assuming that EDD=PD (|MD–EDD|/EDD⩽5% in 57 vs. 26% of pts). Conclusions NEMO X provides two useful tools for the on-line optimization of the dose delivery in IOERT. This optimization can help to reduce unnecessary large over-dosage regions and allows introducing reliable action levels for in-vivo dosimetry.

Objectif de l’etude La radiotherapie stereotaxique d’ablation est une technique emergente dans la prise en charge des tachycardies ventriculaires refractaires aux traitements medicamenteux et a l’ablation par catheter. Nous rapportons ici les resultats des premiers patients traites dans notre centre. Materiel et methode Les patients inclus souffraient de tachycardies ventriculaires ou d’une tempete rythmique refractaires aux traitements classiques. Avant chaque traitement, afin de localiser le substrat de la tachycardie ventriculaire, une cartographie tridimensionnelle a ete realisee durant une exploration electrophysiologique endocavitaire. Pour chaque patient, le cardiologue a delimite le substrat de la tachycardie ventriculaire sur la scanographie de radiotherapie grâce aux informations de la cartographie. L’electrode de defibrillation du defibrillateur automatique implantable a servi de fiduciel pour assurer le suivi en temps reel (tracking). Une dose de 25 Gy a ete delivree sur le substrat de la tachycardie ventriculaire grâce a un accelerateur lineaire robotise Cyberknife® M6. Resultats Depuis septembre 2017, trois patients ont ete pris en charge : deux patients electifs et un patient hospitalise en reanimation en raison d’une tempete rythmique a l’origine de nombreux chocs electriques delivres par le defibrillateur automatique implantable, et necessitant une anesthesie generale. Le tracking de l’electrode du defibrillateur automatique implantable a permis de delivrer avec succes la radiotherapie stereotaxique chez tous les patients. Le volume des substrats de la tachycardie ventriculaire etait pour chaque patient de 19 cm3, 21 cm3 et 35 cm3. Apres un suivi median de cinq mois, les patients electifs n’ont pas souffert de recidive rythmique. Le patient en reanimation a ete extube trois jours apres la radiotherapie stereotaxique et sans recidive de tempete rythmique pendant quatre mois, avant de presenter un nouvel episode a 19 semaines. Cet episode a ete impute a un nouveau substrat de la tachycardie ventriculaire, distant du premier, confirme par cartographie tridimensionnelle et traite par ablation par catheter. Il n’y a eu aucune complication imputable a la radiotherapie stereotaxique. Conclusion La radiotherapie stereotaxique apparait comme un traitement prometteur des tachycardies ventriculaires et tempete rythmiques refractaires aux traitements classiques. Un suivi des effets secondaires a long terme reste indispensable.

Aims and Background To report the dosimetric data and clinical outcomes of patients with advanced neoplasm of the paranasal sinuses and nasal cavity, treated by three-dimensional conformal radiotherapy. Methods Between 2000 and 2005, 31 consecutive patients were treated for locally advanced tumors of paranasal sinuses and nasal cavity. The primary tumor was located as follows: maxillary sinus 15 (48.4%); ethmoid sinus 10 (32.3%); nasal cavity 6 (19.3%). The patients were separated in two groups according to the modality of treatment: group Aincluded 21 patients treated with postoperative three-dimensional conformal radiotherapy with or without chemotherapy; group B included 10 patients treated with radical three-dimensional conformal radiotherapy with or without chemotherapy. The median radiation dose to the planning target volume was 60 Gy (range, 56–63) for patients who underwent complete surgical resection and 68 Gy (range, 64–70) for those who did not have tumor resection or patients with residual disease. Results The median follow-up was 42 months. Five-year local tumor control and overall survival actuarial rates were 74% and 72%, respectively, in the postoperative setting, 20% and 25%, respectively, with the primary radiotherapy. Local recurrence was the most common site of failure. No patient developed radio-induced blindness; 4 patients underwent enucleation as part of radical surgery. Dosimetric data are reported. Conclusions The local control rate for these tumors remains low. The prognosis depends on localization, tumor stage and treatment modality. Three-dimensional conformal radiotherapy reduces the risk on optical pathways but does not modify outcome.

Background: Gamma Knife surgery (GKS) for vestibular schwannomas (VS) has a long-term clinical and scientific track record. After a period of de-escalation of dose prescription, results show a high rate of tumor control with improvement of clinical outcome (less than 1% facial palsy, 50-70% hearing preservation). Currently, there is controversial data about the active early treatment of intracanalicular (Koos I) VS. Methods: We prospectively analyzed 208 VS, focusing on 42 Koos I patients treated with GKS as first intention in Lausanne University Hospital, between July 2010 and February 2015. We concentrated on patient, tumor, and dosimetric characteristics. Special attention was given on the dose to the cochlea and its impact in maintaining serviceable hearing. Results: The mean follow-up period was 1.7 years (range 0.6-4.2). Twenty-six (61.9%) were females and 16 (38.1%) males. Preoperative serviceable hearing was present in 33 (78.57%) patients. The mean maximal diameter was 7.7 (5-10). The median target volume at the moment of GKS was 90 mm3 (range 17-317). The median prescription isodose volume was 118 mm3 (range 37-603). The median marginal dose administrated was 12 Gy (range 11-12). The median number of shots was 2 (range 1-9). The median isodose prescription was 50% (range 45-80%). The median maximal dose received by the cochlea in patients in GR class 1 and 2 was 4.2 Gy (mean 4.4 Gy, range 1.8-7.6). Our preliminary results showed 98% tumor control, with 30% shrinkage on MRI. The actuarial probability of keeping the same audition class for those with functional hearing at GKS was 80% at 3 years; the probability of keeping a functional hearing was more than 90%. A paraclinical evolution (on MRI and/or audiometry) at the time diagnosis, before GKS, was associated with a less good prognosis (p

Introduction Le traitement actuel des fistules arterio-veineuses durales (FAVD) comprend l’embolisation endovasculaire, la microchirurgie, la radiochirurgie ou des approches combinees. La radiochirurgie permet une amelioration symptomatique avec des taux d’obliteration raisonnablement eleves. Nous analysons de maniere prospective la securite et l’efficacite de la radiochirurgie par gamma knife (GK) dans le traitement FAVD, utilise seule ou combinee avec d’autres modalites. Materiel et methodes Sept patients avec FAVD Lariboisiere grade I (3), IIA (1), IIA + B (1) et IV (2) ont ete traites au centre hospitalier universitaire de Vaudois (CHUV, Lausanne) entre 2011 et 2015. La localisation la plus frequente etait le sinus transversal/sigmoide (5), le sinus droit (1) et l’ethmoide anterieur (1), respectivement. Deux patients ont beneficie de traitements anterieurs avec obliteration incomplete, par approche endovasculaire (1) et clipping microchirurgical (1). Cinq ont beneficie d’une GK d’emblee. Tous les patients ont ete suivis a 6, a 12 mois et annuellement par avec IRM et par DSA apres que l’IRM a montre une obliteration complete. Resultats L’âge moyen etait de 67,5 ans (49–76). Le suivi moyen a ete de 22,3 mois (6–48). La presentation clinique initiale etait un acouphene pulsatile (5), une crise d’epilepsie (1) et un cas asymptomatique. Le volume–cible moyenne etait 1,026 cc (0,167 a 2,31). Le volume moyen de l’isodose de prescription etait de 1,89 cc (0,895 a 3,46). La dose moyenne marginale etait de 24 Gy. L’evaluation radiologique au dernier suivi a montre une obliteration partielle dans 100 % des cas et complete chez 3 patients (confirmation DSA dans 2 ; IRM dans un cas, due a une atheromatose importante ; notons un suivi total de 6 mois pour 2 cas et de 12 mois dans 2 autres des cas). Quatre des patients se presentant avec acouphenes pulsatifs ont note la disparition des symptomes a 6 mois post-traitement. Aucun patient n’a necessite un traitement supplementaire apres GK. Aucune complication n’a ete observee au cours du suivi, y compris l’absence d’hemorragie. Conclusion La radiochirurgie est un traitement efficace pour les FAVD, offrant des taux d’obliteration favorables et une amelioration symptomatologique. Dans les cas complexes, la radiochirurgie par GK peut etre combinee avec succes avec les approches chirurgicales et/ou endovasculaires, pour une gestion combinee optimale.

Introduction Le traitement actuel des malformations arterio-veineuses (MAV) de haut grade implique souvent une gestion combinee (observation, microchirurgie, approche endovasculaire, et radiochirurgie). En cas de MAV de grand volume, la radiochirurgie peut etre realisee en plusieurs etapes volumetriques pour diminuer les risques d’effets secondaires de l’irradiation. Materiel et methodes Nous avons analyse de maniere prospective la securite et l’efficacite de la radiochirurgie par Gamma Knife (GK) en 2 etapes volumetriques dans 6 cas de MAV complexes : Spetzler-Martin grade III (1), grade IV (3), ou grade V (2), traites au centre hospitalier universitaire Vaudois (CHUV, Lausanne) entre 2010 et 2016. Un patient avait beneficie d’une chirurgie anterieure pour drainage d’un hematome tandis que 2 autres ont ete partiellement embolises. Trois cas ont ete traites par GK d’emblee. Tous les patients ont ete suivis a 6, 12, 24, 36, 48 mois avec une IRM cerebrale, et par DSA apres obliteration complete a l’IRM. Resultats L’âge moyen etait de 36,5 ans (13–60). Le suivi moyen etait de 38,4 mois (12–48). La presentation initiale etait hemorragique (3) et comitiale (3). Pour la 1re etape, le volume-cible moyen de la cible etait de 5,7 cc (1,17 a 11,4), le volume moyen de l’isodose de prescription (VIP) etait de 7,53 cc (2,06 a 14,6), le volume de l’isodose 12 Gy etait de 16,35 cc (5,75 a 27) et la dose marginale moyenne etait de 19,6 Gy (18–20). La periode moyenne entre la phase 1 et la phase 2 etait de 8,5 mois (6–18). Pour la 2e etape, le volume-cible etait de 5,25 cc (2,2 a 10,2), le VIP moyen etait de 6,2 cc (3,3 a 11,7), la dose marginale moyenne etait de 19,6 Gy (18–20) et le volume de l’isodose 12 Gy etait de 13,3 cc (6,7 a 21). Les petits volumes etaient lies aux residus post-embolisation, imposant un traitement par etapes soit du a des considerations anatomiques (compartiment carotidien versus vertebral) et/ou au chevauchement des doses eventuelles sur des zones eloquentes. Le dernier suivi radiologique a montre une obliteration partielle dans 100 % des cas (obliteration complete sur DSA dans 1 seul cas). Un cas a necessite une prise en charge supplementaire par embolisation et microchirurgie pour un residu important. Un cas a presente une hemorragie entre les 2 etapes du traitement GK. Conclusion La radiochirurgie en plusieurs etapes volumetriques represente une alternative interessante pour le traitement des MAV de haut grade. Dans ces cas complexes, le traitement par GK peut etre combine avec succes avec des approches chirurgicales ou endovasculaires, pour un traitement multimodal optimal.