Mean Target Volume Research Articles

Robotic stereotactic ablative radiotherapy for renal cell carcinoma in patients with impaired renal function

BackgroundRobotic stereotactic ablative radiotherapy (SABR) is currently under investigation as a noninvasive treatment option for patients with renal cell carcinoma (RCC). For radiation therapy of RCC, tumor motion and the need for high ablative doses while preserving the remaining renal parenchyma is a challenge. We aimed to analyze the safety and efficacy of robotic radiosurgery in RCC in a specific difficult subgroup of patients with impaired renal function.MethodsWe retrospectively identified all patients with RCC, treated with robotic SABR and motion compensation in our institution between 2012 and 2017. Either single fraction SABR of 24 or 25 Gy or 3 fractions of 12 Gy prescribed to the 70% isodose line was applied. Local control, overall survival, radiation side effects were evaluated together with renal function and tumor motion.ResultsWe analyzed data of 13 lesions treated in 10 patients with clear cell RCC and a mean age of 70.5 ± 13.6 years (range: 48–87). Prior to SABR, 8 patients underwent previous complete and/or partial nephrectomy, 7 patients presented with chronic kidney disease ≥ stage 3. The median of minimum, mean and maximum planning target volume doses were 23.2, 29.5 and 35.0 Gy for single fraction and 24.4, 42.5 and 51.4 Gy for the three fractions regime. Persistent local control by robotic SABR was achieved in 9 out of 10 patients (92.3% of all lesions) within a median follow-up period of 27 month (range: 15–54). One patient underwent nephrectomy due to progressive disease and sufficient renal function of the contralateral kidney. Renal function remained stable with a mean estimated glomerular filtration rate (eGFR) of 51.3 ± 19.7 ml/min at baseline and 51.6 ± 25.8 ml/min at follow-up. The largest respiratory-induced tumor motion was seen in superior-inferior direction, compensated by the CyberKnife with mean targeting errors of maximal 2.2 mm.ConclusionsRobotic SABR is technically feasible for the treatment of RCC in preexisting kidney disease with good local tumor control at about 2 years follow-up. Robotic SABR with motion tracking offers a valid treatment option for patients, who are at increased risk for progression to end-stage renal disease due to partial nephrectomy or ablative techniques.

Field-in-field breast planning for a jawless, double-stack MLC LINAC using flattening-filter-free beams.

BackgroundThis study intends to develop an efficient field‐in‐field (FiF) planning technique with the Eclipse treatment planning system (TPS) to determine the feasibility of using the Halcyon treatment delivery system for 3D treatment of breast cancer.MethodsTen treatment plans were prepared on the Halcyon treatment planning system and compared to the same patients’ clinically delivered TrueBeam plans which used flattened 6 MV and 10 MV beams. Patients selected for this study were treated via simple, tangential breast irradiation and did not receive radiotherapy of the supraclavicular or internal mammary lymph nodes. Planning target volumes (PTV) volumes ranged from 519 cc to 1211 cc with a mean target volume of 877 cc. Several planning techniques involving collimator, gantry rotation, and number of FiF segments were investigated as well as the use of the dynamically flattened beam (DFB) — a predefined MLC pattern that is designed to provide a flattened beam profile at 10 cm depth on a standard water phantom. For comparison, the clinically delivered TrueBeam plans remained unaltered except for normalization of the target coverage to more readily compare the two treatment delivery techniques.ResultsUsing the physician defined PTV, normalized such that 98% of the volume was covered by 95% of the prescribed dose, the Halcyon plans were deemed clinically acceptable and comparable to the TrueBeam plans by the radiation oncologist. Resulting average global maximum doses in the test patients were identical between the TrueBeam and Halcyon plans (108% of Rx) and a mean PTV dose of 102.5% vs 101.6%, respectively.ConclusionsFrom this study a practical and efficient planning method for delivering 3D conformal breast radiotherapy using the Halcyon linear accelerator has been developed. When normalized to the clinically desired coverage, hot spots were maintained to acceptable levels and overall plan quality was comparable to plans delivered on conventional C‐arm LINACs.

P03.07 Radiosurgical managementof trigeminal schwannomas: A single center experience

Abstract BACKGROUND Trigeminal schwannomas are a rare form of intracranial schwannomas. They can occur anywhere along the track of the trigeminal nerve, including the middle, posterior fossa or both. It can even extend extracranially. The variability of its location and extent, in addition to its close proximity to critical neurovascular structures makes surgical intervention challenging. Taking from the success of treating vestibular schwannomas with stereotactic radiosurgery, it has been used as an alternative to surgery for the treatment of trigeminal schwannomas. Because these tumors are rare more clinical evidence is required to assess the response of these tumors to stereotactic radiosurgery.The aim of this study was to evaluate the efficacy and complications associated with treatment of the trigeminal schwannomas by gamma knife radiosurgery. MATERIAL AND METHODS The study included 51 patients with trigeminal schwannomas not associated with NF2, treated by Leksell gamma knife. There were 25 males and 26 females. The mean age at presentation was 43 years. The patients underwent a total of 58 gamma knife sessions (44 single and 7 volume-staged sessions). Eight patients had previous surgery. The tumor nature was solid in 46, cystic in 3 and mixed in 2 patients. The mean target volume was 8.5 cc (0.6–30.7 cc) with the mean overall tumor volume being 9.6 cc (0.6–31.1 cc). The mean prescription dose was 12 Gy. RESULTS The mean follow up was 57 months (12–152 months). The tumor shrank in 23 (45%) patients and remained stable in 25 (49%). Tumor progressions occurred in 3 (6%) patients. The tumor control rate was 92%. The progression-free survival at 5,7 and 10 years was 95%, 88% and 79%, respectively. Clinical improvement occurred in 27 (53%) patients and was significantly associated with tumor shrinkage (p 0.03). Twenty patients (39%) remained clinically unchanged. Adverse radiation events occurred in 7 patients and were significantly associated with target and overall tumor volume (p 0.028 and 0.004). CONCLUSION Gamma knife radiosurgery appears to be an effective and safe adjuvant and primary treatment modality for trigeminal schwannomas. Large tumors should be debulked first before radiosurgery, when feasible.

Assessment of dosimetric and positioning accuracy of a magnetic resonance imaging-only solution for external beam radiotherapy of pelvic anatomy.

Background and purposeThe clinical feasibility of synthetic computed tomography (sCT) images derived from magnetic resonance imaging (MRI) images for external beam radiation therapy (EBRT) planning have been studied and adopted into clinical use recently. This paper evaluates the dosimetric and positioning performance of a sCT approach for different pelvic cancers.Materials and methodsSeventy-five patients receiving EBRT at Turku University Hospital (Turku, Finland) were enrolled in the study. The sCT images were generated as part of a clinical MRI-simulation procedure. Dose calculation accuracy was assessed by comparing the sCT-based calculation with a CT-based calculation. In addition, we evaluated the patient position verification accuracy for both digitally reconstructed radiograph (DRR) and cone beam computed tomography (CBCT) -based image guidance using a subset of the cohort. Furthermore, the relevance of using continuous Hounsfield unit values was assessed.ResultsThe mean (standard deviation) relative dose difference in the planning target volume mean dose computed over various cancer groups was less than 0.2 (0.4)% between sCT and CT. Among all groups, the average minimum gamma-index pass-rates were better than 95% with a 2%/2mm gamma-criteria. The difference between sCT- and CT-DRR-based patient positioning was less than 0.3 (1.4) mm in all directions. The registrations of sCT to CBCT produced similar results as compared with CT to CBCT registrations.ConclusionsThe use of sCT for clinical EBRT dose calculation and patient positioning in the investigated types of pelvic cancers was dosimetrically and geometrically accurate for clinical use.

Impact of Integral Dose on the Maintenance of Pain Relief in Patients with Idiopathic Trigeminal Neuralgia Treated with Upfront Gamma Knife Radiosurgery

Integral dose (ID) defined as the product of mean dose and target volume, is a measure of the absorbed radiation energy. To evaluate the effect of ID on the duration of pain relief after primary Gamma knife stereotactic radiosurgery (GKSRS) in trigeminal neuralgia. A total of 78 patients who achieved initial pain response of I-III on the Barrow Neurological Institute Pain Scale (BNI-PS) following primary GKSRS for idiopathic trigeminal neuralgia were included in this study. A Cox regression model was used to compute the prognostic factor with respect to the ID within the 50% isodose line. Facial pain relief maintenance interval was defined as time interval between the day of improved BNI-PS grade and pain level back to the BNI-PS IV or V. The median duration of follow-up was 42 months (range 6-108 months). After the initial GKSRS, patients achieved pain relief at a median of 0.5 months (range, 7 days to 6 months); 28 patients developed recurrence of pain. There was a positive correlation between the pain relief maintenance and increasing ID within 50% isodose line (hazard ratio 1.85, P= 0.04) on multivariable Cox-regression analysis. Using logistic regression analysis, we found that ID was not predictive of developing post-stereotactic radiosurgery hypoesthesia (P= 0.64, hazard ratio 1.057). Stereotactic radiosurgery can be individualized based on trigeminal nerve morphology to achieve durable pain relief in patients with trigeminal neuralgia. ID calculation aids in planning an optimal radiation dose based on the nerve morphology to provide durable pain relief of idiopathic trigeminal neuralgia.

Multimodality Imaging for Radiosurgical Management of Arteriovenous Malformations

Background: Cerebral arteriovenous malformations (AVMs) are rarely seen congenital vascular anomalies. AVMs may lead to intracranial hemorrages due to disorganized tangle of vessels. Lifetime risk of bleeding from AVMs may be significant given the diagnosis at typically earlier ages of the lifespan, and complications associated with hemorrhage may lead to substantial morbidity or mortality. Management of AVMs aims at eliminating or reducing the risk of subsequent bleeding. In this context, microvascular surgical resection, endovascular embolization and radiosurgical treatment may be used for management of AVMs.Objective: In this study, we assessed the incorporation of Magnetic Resonance Imaging (MRI) in treatment planning for AVM radiosurgery. Methods: We identified 25 patients receiving radiosurgery for AVMs at our institution. Radiosurgery target volumes generated by using CT-only based imaging and CT-MR fusion based imaging for each patient were evaluated.Results: Twenty five patients undergoing SRS for AVMs were evaluated for target volume determination in this study. Mean target volume was 4.9 cc (range: 1.3-15.9 cc) on CT-only imaging, 5.7 cc (range: 1.4-16.7 cc) on CT-MR fusion based imaging, and 5.9 cc (range: 1.4-16.9 cc) on consensus decision of all treating physicians with colleague peer review. Target definition based on CT-MR fusion based imaging was identical to the consensus decision of all treating physicians in majority of patients.Conclusions: Treatment planning for AVM radiosurgery may be improved by incorporating CT-MR fusion based imaging, which clearly should be supplemented with additional data from angiography. There is need for additional studies to establish a consensus on optimal target definition by multimodality imaging for SRS of AVMs.

Gamma Knife radiosurgery for intravestibular and intracochlear schwannomas.

Schwannomas of the VIIIth cranial nerve are benign tumours, with vast majority occurring in vestibular division. Rarely, they can also arise from distal branches of cochlear, superior or inferior vestibular. We review our experience with Gamma Knife radiosurgery (GKR), as first intention treatment for intracochlear (ICS) and intravestibular (IVS) schwannomas. A total number of five patients were analysed, treated over 8years, between June 2010 and September 2018, with Leksell Gamma Knife Perfexion or Icon (Elekta Instruments, AB, Sweden). The marginal dose prescribed was 12Gy at a mean prescription isodose line of 61.4% (range 50-70). Clinical evaluation included auditory and facial function. The mean age was 49.9 (range 34-63). The mean follow-up period was 52.8months (range 12-84). The mean target volume (TV) was 0.087ml (range 0.014-0.281). The mean maximal dose received by the cochlea was 11.2Gy (range 2.6-20.3). The mean marginal dose received by the vestibule (e.g. utricula) was 14.2Gy (range 3.8-17.5). No patient experienced an acute or subacute clinical adverse radiation effect after GKR. Four cases had overall symptom stability. In one patient (1/5), the vertigo, which was the main clinical complain, disappeared 1year after GKR. However, it reappeared 3years later, with same pretherapeutic characteristics and is currently fluctuating. One patient experienced hearing decrease after GKR, during the first 12months. This case received 11.2Gy to the cochlea. Follow-up MRI course showed a decrease in size in four patients, and stability in one. Gamma Knife radiosurgery is a valuable first intention treatment for ICS or IVS, in selected cases. Special attention should be paid for the dose delivered to the cochlea and the vestibular apparatus. Acute and subacute clinical effects are exceptional, while tumour control was achieved in all cases in our small series.

Dose uncertainty from calculation grid resolution and its alignment with MLC

The aims are (1) to present a clinical brain case where the dose distribution calculated at 2.5-mm grid resolution was significantly different from that of 1.0 mm with Varian HD120 multileaf collimator (MLC; 2.5-mm central leaf width), and (2) to present our analysis results to better understand the influence of dose calculation grid resolution and its spatial alignment with MLC. A simulation using a static MLC pattern with 10 open strips was conducted to demonstrate the possibility that the characteristics of MLC dose profiles can be completely hidden. The effects of the spatial MLC alignment with the dose grid were investigated for grid resolutions from 1.0 mm to 5.0 mm. In the end, 20 recent stereotactic radiotherapy plans (5 brain, 5 lung, 5 spine, and 5 other) were retrospectively selected, and their dose distributions were recalculated at 1.0 mm, 1.5 mm, and 2.5 mm resolutions for comparisons. Film dosimetry results were used as references. At 2.5-mm grid resolution, the MLC open-strip patterns were not visible in the dose distribution when the MLC leaf interspaces were at exact alignment with the dose grid. The effects were smaller at 1.0-mm grid resolution. The dose error at the centers of the open strips varied significantly (7% to 39%) depending on the alignments. Overall, the planning target volume mean dose of 1.5-mm plans was higher than 1.0-mm plans by 1.3 ± 0.3% (mean ± 1SD) with a maximum of 2.6%, while the mean dose of 2.5-mm plans was lower by −0.5 ± 0.5% with a maximum mean dose of −3.7%. In conclusion, the choice of dose calculation grid resolution can affect the plan dose distribution significantly. The dose grid resolution must be smaller than the width of MLC leaf at a minimum. A finder resolution is expected to produce less uncertainty in the calculated dose and influenced less by the MLC-grid spatial alignment.

Long-Term Outcome of Gamma Knife Radiosurgery for Symptomatic Brainstem Cavernous Malformation

We sought to analyze the long-term outcome of Gamma Knife radiosurgery (GKS) for symptomatic brainstem cavernous malformation (s-BSCM). Forty-five patients (14 males, 31 females) were treated with GKS for s-BSCM from January 1998 to December 2011. All patients were followed up for >5 years, and their clinical data were analyzed retrospectively. All patients had a history of symptomatic bleeding once or more before GKS. These hemorrhages caused neurologic deficits including cranial nerve deficits, hemiparesis, hemisensory deficits, spasticity, or chorea. The mean target volume of s-BSCM was 1.82 cm3, and the median prescribed marginal dose of radiation was 13 Gy. The mean clinical and imaging follow-up period was 9.31 years (range 5.1-19.4 years). The 45 patients had 69 hemorrhagic events before GKS. During the follow-up period after GKS, 35 patients had no hemorrhagic event, 6 patients had 1 episode of symptomatic hemorrhage, and 4 patients had 2 episodes. The calculated annual hemorrhage rate was 40.06% at pre-GKS, 3.3% at 2 years after GKS, 1.48% at 5 years after GKS, and 4.64% at >5 years after GKS. In this study of 45 patients, symptomatic radiation-induced complications developed in only 1 patient (2.2%). No patients had died at the last follow-up. GKS for s-BSCM is a safe and effective alternative to surgical resection for reducing the rate of recurrent hemorrhage. Because the annual hemorrhage rate increases >5 years after GKS, clinicians should monitor patients closely to determine their subsequent treatment.

Magnetic resonance guided focused high frequency ultrasound ablation for focal therapy in prostate cancer - phase 1 trial.

To evaluate the feasibility and safety of focal therapy for low-intermediate risk prostate cancer (PCa) with magnetic resonance-guided high frequency focused ultrasound (MRgFUS) METHODS: This IRB-approved phase 1 prospective study enrolled eight patients with prostate specific antigen (PSA) ≤ 10 ng/ml, ≤ cT2a and Gleason score ≤ 7 (4 + 3) disease following informed consent. Under MRI guidance, focused high frequency ultrasound energy was delivered to ablate the target tissue. Treatment-related adverse events were recorded. Oncologic outcomes were evaluated with multiparametric MRI, PSA and TRUS biopsy at 6 months following treatment. Ten target lesions [six Gleason 6 lesions, two Gleason 7 (3 + 4) and two Gleason 7 (4 + 3)] were treated in eight men (prostate volume range, 25-50 cc; mean MRI time, 248 min per patient; mean sonication duration, 65 min). Mean target volume was 2.7 cc and mean post-treatment non-perfused volume was 4.3 cc. Quality of life parameters were similar between baseline and 6 months in 6/8 patients. All treated regions were negative on MRI; 4/8 patients and 6/10 target lesions (60%) were clear of disease on biopsy. One patient with 2-mm Gleason 8 disease in one of five cores from treatment site (4 + 3 disease at baseline) subsequently underwent prostatectomy with negative surgical margins. Three patients with low volume (5-15%) Gleason 6 residual disease were offered active surveillance. Mean PSA decreased from 5.06 at baseline to 3.4 ng/ml at 6 months. MRgFUS is a feasible and safe method of noninvasively ablating low-intermediate risk PCa with acceptable short-term oncologic outcomes. • Focal therapy selectively ablates locally confined, clinically significant index lesion with a margin while sparing rest of gland and adjacent vital structures. • Magnetic resonance-guided focused high frequency ultrasound surgery (MRgFUS) combines MRI with HIFU. • MRgFUS provides ability to monitor treatments in real time and allows a targeted approach for focal ablation. • MRgFUS is a feasible, safe method of noninvasively ablating low-intermediate risk PCa. • MRgFUS providesacceptable oncologic outcomes at 6 months.

Dosimetric comparison of two-dimensional versus three-dimensional intracavitary brachytherapy in locally advanced cervical cancer

Introduction/Objective. The aim of this study was to dosimetric comparison of two-dimensional (2D) with three-dimensional (3D) planning for high-dose-rate intracavitary brachytherapy (HDR-BT) in locally advanced cervical cancer by dose evaluation in given International Commission on Radiation Units and Measurements (ICRU) reference points, as well as in target volume and organs at risk (OAR). Methods. 66 sessions of HDR-BT were performed in 22 patients, with 3D planning, but also virtual 2D plan for dosimetric comparison was made. 2D planning was performed on radiography obtained by C-arm in ICRU points, while 3D planning in volumes delineated on computer tomography. Results. The comparative analysis has indicated a significant mean dose difference of point ?A? left (p=0.00014) and right (p=0.003), through higher doses in 2D and lower doses in 3D reconstructed points "A". According to the dose volume histograms 56.88% and 61.41% mean target volume received 100% and 90% of prescribed dose, respectively. 2D bladder analysis showed a mean dose of 3.487 Gy in ICRU point, while in 3D analysis a maximum mean dose of 8.804 Gy and mean dose of 4.716 Gy in 2ccm volume. 2D analysis showed rectal mean dose of 2.892 Gy in ICRU points, while 3D analysis maximum mean dose of 6.411 Gy and 3.947 Gy mean dose in 2ccm volume. Conclusion. 2D planning showed unreal higher doses in the ICRU points for the target and lower doses for the OAR.

MP70-16 SAFETY AND FEASIBILITY OF REAL-TIME MRI-GUIDED FOCUSED ULTRASOUND FOR FOCAL THERAPY OF LOCALIZED PROSTATE CANCER USING THE EXABLATE 2100 DEVICE: PHASE 1 STUDY

You have accessJournal of UrologyProstate Cancer: Localized: Ablative Therapy I1 Apr 2017MP70-16 SAFETY AND FEASIBILITY OF REAL-TIME MRI-GUIDED FOCUSED ULTRASOUND FOR FOCAL THERAPY OF LOCALIZED PROSTATE CANCER USING THE EXABLATE 2100 DEVICE: PHASE 1 STUDY Nathan Perlis, Eugen Hlasny, Walter Kucharczyk, Masoom Haider, Antonio Finelli, Alexandre Zlotta, Girish Kulkarni, John Trachtenberg, and Sangeet Ghai Nathan PerlisNathan Perlis More articles by this author , Eugen HlasnyEugen Hlasny More articles by this author , Walter KucharczykWalter Kucharczyk More articles by this author , Masoom HaiderMasoom Haider More articles by this author , Antonio FinelliAntonio Finelli More articles by this author , Alexandre ZlottaAlexandre Zlotta More articles by this author , Girish KulkarniGirish Kulkarni More articles by this author , John TrachtenbergJohn Trachtenberg More articles by this author , and Sangeet GhaiSangeet Ghai More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2017.02.2292AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Organ preserving therapy is emerging as an option for localized prostate cancer to minimize the morbidity associated with whole-gland therapy. We examine the short-term oncologic and functional data of the initial phase 1 trial of patients treated with focal transrectal MRI-guided focused ultrasound (MRgFUS) in North America. METHODS This phase 1 prospective study was approved by institutional review board. Eight patients with organ-confined PC visible on multiparametric MRI (mpMRI) and confirmed by the MRI-fusion biopsy (Artemis, Eigen) were enrolled. Patients were eligible with PSA ≤10ng/mL and Gleason score (GS) ≤ 7(4+3). Tumors larger than 1.5 cm in any dimension, too peripheral for a 5mm ablation margin or with concern for extraprostatic extension were excluded. Under MRI-guidance and real-time MR thermography, focal lesions were ablated using high frequency ultrasound energy delivered via an endorectal transducer with 990 elements (ExAblate 2100, InSightec). Incidence and severity of treatment-related adverse events were recorded at 6 months. RESULTS Eight patients with 10 peripheral zone lesions were treated. Prostate volume ranged from 25 to 50 cc with mean target volume of 2.7cc (range 0.4 - 5.7cc). Mean procedure time was 248 minutes. Based on pre-treatment biopsy, six lesions were GS6(3+3), two were GS7(3+4) and two others were GS7(4+3). Treatments were all completed as planned without major technical delays or surgical complications. Mean post treatment non-perfused volume was 4.3cc (range 2.2 - 7.6cc). Quality of life parameters were similar between baseline and 6-months in 6 of 8 patients. One patient with bilateral ablation had significantly worse storage symptoms while a second patient developed self-limiting acute prostatitis with erectile dysfunction. Mean PSA decreased from 5.06 to 3.4 ng/ml at 6 months. All patients were MRI negative in their treated regions. On biopsy, five patients were disease-free in treated regions (7 of 10 lesions). In one patient with a presumed GS7(4+3) tumor, a 2mm MRI-invisible focus of GS8(4+4) PC was seen in 1 of 5 cores from the ablation site. He underwent prostatectomy with negative surgical margins. CONCLUSIONS MRgFUS is a feasible and safe method of ablating localized PC. Further work is required to improve patient selection and address causes of failed ablation. Our study is limited by small sample size and brief follow-up. More meaningful oncologic and functional outcomes for MRgFUS can be assessed with larger trials with longer follow-up. © 2017FiguresReferencesRelatedDetails Volume 197Issue 4SApril 2017Page: e941 Advertisement Copyright & Permissions© 2017MetricsAuthor Information Nathan Perlis More articles by this author Eugen Hlasny More articles by this author Walter Kucharczyk More articles by this author Masoom Haider More articles by this author Antonio Finelli More articles by this author Alexandre Zlotta More articles by this author Girish Kulkarni More articles by this author John Trachtenberg More articles by this author Sangeet Ghai More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Stereotactic radiosurgery and stereotactic fractionated radiotherapy for metastatic tumors of the spine

Objectives: The objectives of this paper are to describe pain control, neurologic improvement, local tumor control, progression-free survival, and overall survival of spine SRS/SFRT patients, and to compare our outcomes with other studies on spine stereotactic radiotherapy for metastatic tumors.Methods: A chart review of patients who underwent spine SRS/SFRT was done. Information was collected on patient age, sex, histology, site treated, pain relief, local control, neurologic function, prescription dose, and complications. Descriptive statistics, median local control rates, progression-free survival, and overall survival were calculated.Results: Twenty eight SRS and 3 SFRT target volumes in 21 patients were studied. Eighteen underwent SRS and 3 underwent SFRT for metastasis from August 2012 to February 2016. Follow-up ranged from 4 to 41 months. Average dose was 16.6 ± 3.9 Gy. Spine SRS mean target volume was 31.1 cc (95% CI, 21.7–40.6 cc). Median overall survival after treatment was 16 months (95% CI, 9.7–22.3 months) and median progression-free survival was 13 months (95% CI, 8.4–17.6 months). Local control was 46%, 30%, and 15% at 6, 8, and 10 months, respectively. Average onset of pain relief is 4.9 days (95% CI, 0.8–8.9 days). One patient (5%) developed post SRS vertebral compression fracture.Conclusion: SRS/SFRT is a safe and effective alternative to EBRT for the treatment of spine metastasis. Improvement in pain control and motor strength and incidence of adverse events are comparable with other studies. Local tumor control was lower in our series due to a lower mean prescribed dose.

First intention radiosurgery and combined approach in trochlear and abducens nerve

Introduction Most intracranial schwannomas arise from the cranial nerve (CN) VIII for whom radiosurgery has proven its safety and efficacy for tumor control and function preservation in small to medium-size tumors. Less common, CN III, IV and VI schwannomas are very disabling due to the associated palsies. We prospectively evaluated the safety and efficacy of Gamma Knife surgery (GKS) in these rare cases. Patients and method Five patients with CN IV (3) and VI (2) schwannomas were treated in Lausanne University Hospital between 2010 and 2015. Four were treated with upfront GKS and one by a combined approach (CN VI, subtotal surgery followed by GKS) due to a large tumor volume (7.9 cc). All cases had neuro-ophthalmological evaluation at baseline and at 6 and 12 months and on annual basis after. In one patient, a type II neurofibromatosis was diagnosed. Results The mean follow-up period was 29 months (range 6–54). The mean target volume was 1.51 cc (range 0.086–5.8). Initial clinical presentation was diplopia (four cases) and cavernous sinus syndrome (one case). The mean marginal dose was 12 Gy (range 12–12). The mean prescription isodose volume was 1.71 cc (range 0.131–6.7). The mean maximal dose to the optic pathways was 1,5 Gy (range 0,1–6,6). Following GKS, all patients presented clinical alleviation, with disappearance of baseline symptoms. However, one of them had an additional surgical intervention (left superior oblique tendon folding). Tumor control was achieved in all (100%, 100% decreased). Conclusion Our data suggests that first intention GKS is a safe and effective treatment option for CN IV and VI schwannomas, with high rates of both clinical alleviation and tumor control. In cases where the initial tumor volume is too large for first intention GKS, combined approaches can be performed, with favorable results.

Gamma Knife Radiosurgery of Brainstem Cavernous Malformations

Background/Aims: Our study aimed to evaluate the efficiency and morbidity of Gamma Knife radiosurgery (GKS) in the treatment of hemorrhagic brainstem cavernous malformations (CMs). Methods: We included in this study all patients who underwent GKS for the treatment of a hemorrhagic brainstem CM(s) in our institution between January 2007 and December 2012. The GKS was privileged when the surgical procedure was evaluated as very risky. The mean dose of radiation was 14.8 Gy, and the mean target volume was 0.282 cm³. All patients participated in a scheduled clinical follow-up. The posttreatment MRI was performed after 6 months and after 1 year, and then all patients had an annual MRI follow-up. Results: There were 19 patients with a mean age of 36.7 years. The mean follow-up period was 51.2 months. The annual hemorrhage rate (AHR) was 27.31% before GKS, 2.46% during the first 2 years following the GKS, and 2.46% after the first 2 years following the GKS. The decrease in AHR after GKS was significant (p < 0.001). Conclusion: GKS should be suggested when the surgical procedure harbors a high risk of neurological morbidity in patients with brainstem CM. Compared to prior literature results, a lower dose than applied in this study could be discussed.

Inherent Functional Dependence Among Cochlear Dose Surrogates for Stereotactic Radiosurgery of Acoustic Schwannomas

Various cochlear dose surrogates such as the mean dose, maximum point dose and central modiolus dose have been reported as associated with hearing outcome in studies of stereotactic radiosurgery (SRS) for vestibular schwannomas. In this study, we investigated whether an inherent functional relationship exists among these dose surrogates and its analytical formalism and expressions. A cohort of 97 serial patient cases treated with single-fraction stereotactic radiosurgery at our institution from 2007-2013 was reviewed and 85 cases were found to be analyzable, excluding cases such as surgically absent cochlea, incomplete visualization of the structure, etc. For all the cases, the mean prescription dose was 12.5 ± 0.3 Gy (range, 12-13 Gy) and mean target volume 1.32 ± 1.51 mL (range, 0.80-8.77 mL). The mean cochlea volume was 0.078 ± 0.016 mL (range, 0.048-0.131 mL; median, 0.076 mL). Correlation analysis among mean cochlear dose, point maximum dose and modiolus dose was performed and also parameterized with new variables such as the Effective Dose Radius (EDR) as derived from a general dose fall-off model (Ma et al., IJROBP, 76(3) 943-8, 2010). Weak correlation via linear regression was found between the point maximum dose and the mean cochlear dose (R2 = 0.719) as well as the modiolus dose (R2 = 0.568). However, when parameterized with EDR, a near perfect correlation via linear regression was found between the EDR for the point maximum dose and the EDR for the mean cochlear dose (R2 = 0.996), and with the EDR for the modiolus dose (R2 = 0.993). Such a result led to a functional formula relating these dose surrogates, yielding dose equivalence results such as 12 Gy point maximum dose is equivalent to mean cochlear dose of 5.6 ± 0.1 Gy (95% CL) or modiolous dose of 6.0 ± 0.2 Gy (95% CL). An inherent functional relationship exists among point maximum, modiolous, and mean cochlear doses for stereotactic radiosurgery of vestibular schwannomas. As such, clinical hearing outcome can be interchangeably analyzed or reported via any of these dose surrogates.

Inherent functional dependence among cochlear dose surrogates for stereotactic radiosurgery of vestibular schwannomas

PurposeVarious cochlear dose surrogates have been reported as associated with hearing outcome in studies of stereotactic radiosurgery (SRS) for vestibular schwannomas. In this study, we investigated whether an inherent functional relationship exists among these reported surrogates. Methods and materialsA cohort of 85 serial patient cases treated with single-fraction stereotactic radiosurgery from 1997 through 2013 at our institution was analyzed. For all the cases, the mean prescription dose was 12.5 ± 0.3 Gy (range, 12-13 Gy) and mean target volume 1.32 ± 1.51 mL (range, 0.80-8.77 mL). The mean cochlea volume was 0.078 ± 0.016 mL (range, 0.048-0.131 mL; median, 0.076 mL). Correlation analysis among mean cochlear dose, point maximum dose and modiolus dose was performed and also parameterized with new variables such as the effective dose radius (EDR) as derived from a general dose fall-off model. ResultsWeak correlation via linear regression was found between the point maximum dose and the mean cochlear dose (R2 = 0.719) as well as the modiolus dose (R2 = 0.568). However, when parameterized with EDR, a near-perfect correlation (P < .0001) via linear regression was found between the EDR for the point maximum dose and the EDR for the mean cochlear dose (R2 = 0.996), and with the EDR for the modiolus dose (R2 = 0.993). Such a result led to a functional formula relating these dose surrogates, yielding dose equivalence results such as: 12-Gy point maximum dose is equivalent to mean cochlear dose of 5.6 ± 0.1 Gy (95% confidence level), or modiolus dose of 6.0 ± 0.2 Gy (95% confidence level). ConclusionsAn inherent functional relationship was found among point maximum, modiolus, and mean cochlear doses for SRS of vestibular schwannomas. As such, clinical hearing outcome can be interchangeably analyzed or reported via any of these dose surrogates.

SU‐F‐T‐626: Intracranial SRS Re‐Treatment Without Acquisition of New CT Images

Purpose:Linear accelerator based stereotactic radiosurgery (SRS) for multiple intracranial lesions with frequent surveillance is becoming a popular treatment option. This strategy leads to retreatment with SRS as new lesions arise. Currently, each course of treatment uses magnetic resonance (MR) and computed tomography (CT) images for treatment planning. We propose that new MR images, with course 1 CT images, may be used for future treatment plans with negligible loss of dosimetric accuracy.Methods:Ten patients that received multiple courses of SRS were retrospectively reviewed. The treatment plans and contours from non‐initial courses were copied to the initial CTs and recalculated. Doses metrics for the plans calculated on the initial CTs and later CTs were compared. All CT scans were acquired on a Philips CT scanner with a 600 mm field of view and 1 mm slice thickness (Philips Healthcare, Andover, MA). All targets were planned to 20 Gy and calculated in Eclipse V. 13.6 (Varian, Palo Alto, CA) using analytic anisotropic algorithm with 1 mm calculation grid.Results:Sixteen lesions were evaluated. The mean time between courses was 250 +/− 215 days (range 103–979). The mean target volume was 2.0 +/− 2.9 cc (range 0.1–10.1). The average difference in mean target dose between the two calculations was 0.2 +/− 0.3 Gy (range 0.0 – 1.0). The mean conformity index (CI) was 1.28 +/− 0.14 (range 1.07 – 1.82). The average difference in CI was 0.03 +/− 0.16 (range 0.00 – 0.44). Targets volumes &lt; 0.5 cc showed the largest changes in both metrics.Conclusion:Continued treatment based on initial CT images is feasible. Dose calculation on the initial CT for future treatments provides reasonable dosimetric accuracy. Changes in dose metrics are largest for small volumes, and are likely dominated by partial volume effects in target definition.

SU-F-T-603: Safe Treatment of the Maximum Tolerable Brain Metastases with Gamma Knife in Single Patient Clinical Findings

Purpose: Safe treatment of the maximum tolerable brain metastases with GK in single patient–clinical findings Methods: A patient diagnosed with stage IV NSCLC has received 6 courses of Gamma Knife radiosurgery (GKRS) treatments. The plans were generated with GammaPlan (version 10.1.1), six courses of treatment were administered in 2.5 years. A total of 53 metastases were treated with retreatment foci (n = 5) and planned on newly identified lesions (n = 48). Individual prescription dose varied from 12 Gy to 24 Gy.The homogeneity index (HI) was evaluated as the ratio of maximum dose to prescription dose (HI = (D2%–D98%) /DRx). The gradient index (GI) was evaluated as the ratio of prescription isodose volume (PIV) at half of the prescription isodose line to PIV (GI = PIV1/2 / PIV). Composite dose of brain from all six courses was generated on Velocity AI (version 3.0.1). All V5, V10, and V12 of brain were estimated. Results: Mean target volume was 0.39 ± 0.96 cm3 (range from 0.047 to 6.55 cm3). The mean volume of half of prescribed dose was 1.08 ± 2.46 cm3. HI and GI were calculated as 1.37 ± 0.32 and 2.98 ± 0.52, respectively. The patient had no new neurologic symptoms. V5, V10, and V12 of brain were 820, 118, and 71.94 cc, respectively.All doses were delivered with focused and sharp dose gradients, with superior indexes compared to LINAC based delivery. Conclusion: With exceptional steep dose gradients, GKRS is ideal to treat multiple metastases in continuous courses. The hot spots were observed in the overlapped area for the given high prescription dose with no side effects.GKRS has advantages of treating multiple brain metastases from NSCLC with low whole brain dose. Our data presented conclusions of excellent local control of large numbers of metastases being treated on GKRS with superior clinical outcome.

SU‐F‐T‐15: Evaluation of 192Ir, 60Co and 169Yb Sources for High Dose Rate Prostate Brachytherapy Inverse Planning Using An Interior Point Constraint Generation Algorithm

Purpose:The effectiveness of using a combination of three sources, 60Co, 192Ir and 169Yb, is analyzed. Different combinations are compared against a single 192Ir source on prostate cancer cases. A novel inverse planning interior point algorithm is developed in‐house to generate the treatment plans.Methods:Thirteen prostate cancer patients are separated into two groups: Group A includes eight patients with the prostate as target volume, while group B consists of four patients with a boost nodule inside the prostate that is assigned 150% of the prescription dose. The mean target volume is 35.7±9.3cc and 30.6±8.5cc for groups A and B, respectively. All patients are treated with each source individually, then with paired sources, and finally with all three sources. To compare the results, boost volume V150 and D90, urethra Dmax and D10, and rectum Dmax and V80 are evaluated. For fair comparison, all plans are normalized to a uniform V100=100.Results:Overall, double‐ and triple‐source plans were better than single‐source plans. The triple‐source plans resulted in an average decrease of 21.7% and 1.5% in urethra Dmax and D10, respectively, and 8.0% and 0.8% in rectum Dmax and V80, respectively, for group A. For group B, boost volume V150 and D90 increased by 4.7% and 3.0%, respectively, while keeping similar dose delivered to the urethra and rectum. 60Co and 192Ir produced better plans than their counterparts in the double‐source category, whereas 60Co produced more favorable results than the remaining individual sources.Conclusion:This study demonstrates the potential advantage of using a combination of two or three sources, reflected in dose reduction to organs‐at‐risk and more conformal dose to the target. three sources, reflected in dose reduction to organs‐at‐risk and more conformal dose to the target. Our results show that 60Co, 192Ir and 169Yb produce the best plans when used simultaneously and can thus be an alternative to 192Ir‐only in high‐dose‐rate prostate brachytherapy.