Journal of radiosurgery and SBRT最新文献

Gamma angle plays a major role in Gamma Knife Radiosurgery (GKRS) treatment planning. Selecting an appropriate gamma angle may help in mitigating unnecessary radiation exposure to organs at risk (OARs). The aims in GKRS of vestibular schwannoma (VS) is to deliver sufficient radiation to the tumor extending into internal auditory canal (IAC) while keeping basal turn of cochlea and brain stem away from 4 and 12 Gy radiation exposure, respectively. This study analyses the optimal gamma angle in GKRS for VS treatment planning. The study was performed using old MRI datasets of 16 patients of VS in Leksell GammaPlan version 10.1.1. T2 weighted contrast MRIs were used for the planning purposes. Three different plans were made for each patient at gamma angles 90°, 110° and 70° using hybrid inverse planning technique. Dynamic shaping was used to achieve as low as reasonably achievable (ALARA) doses to the cochlea without compromising target coverage (i.e. coverage of more than 97% of tumor volume). This comparative analysis shows minimal radiation exposure to cochlea for plans made at gamma angle 110° compared to 90° and 70°. Average percentage volume of cochlea receiving 4 Gy were 9.63 ± 12.32%, 6.19 ± 8.24%, and 25.25 ± 31.82% at gamma angles 90°, 110° and 70°, respectively (one-way ANOVA p = 0.0247). The average selectivity indices were 83.44 ± 7.13, 84.06 ± 7.84 and 83.56 ± 7.22 at gamma angles 90°, 110° and 70° respectively. Similarly, the gradient indices and beam on time were 2.80 ± 0.23, 2.81 ± 0.23 and 2.80 ± 0.25 and 120.65 ± 59.63, 117.95 ± 58.06 and 123.99 ± 61.61 min, respectively, at 90°, 110° and 70°. The selectivity index, gradient index and beam on time were minimal at gamma angle 110° compared to the other two angles, but not statistically significant (one-way ANOVA p-values were 0.9686, 0.9942 and 0.9598, respectively). The gamma angle of 110° is a good choice for treatment planning of VS patient in Gamma Knife as it gives better treatment plans (minimal cochlea doses).

Purpose/objective: Linear accelerator (LINAC) based stereotactic radiosurgery (SRS) for arteriovenous malformations (AVMs) is delivered with cone or multileaf collimators (MLCs), and favorable dosimetry is associated with reduced radionecrosis in normal brain tissue. This study aims to determine whether cones or MLCs has better dosimetric characteristics, to predict differences in toxicity.

Methods: All patients treated for AVMs using LINAC SRS from 2003-2017 were examined retrospectively. Demographic data, volumes of normal tissue exposed to 12Gy (V12Gy[cc]) and 4Gy (V4Gy[cc]), maximal dose, and dose gradient were analyzed. Univariate and multivariate analyses were used to evaluate relationships between collimator type, dosimetric parameters, and toxicity. Propensity score matching was used to adjust for AVM size.

Results: Compared to MLC, cones were independently associated with reduced V12Gy[cc] after propensity score matching (p=0.008) and reduced neurotoxicity (p=0.016). Higher V12Gy[cc] (p=0.0008) and V4Gy[cc] (p=0.002) were associated with increased neurotoxicity.

Conclusions: Treating AVMs with cone-based SRS over MLC-based SRS may improve dosimetry and reduce toxicities.

Purpose/methods: This retrospective study evaluated local recurrence (LR) and fracture risk in non-spine bone metastases treated with SBRT.

Results: 181 lesions in 116 patients are reported. The median dose was 27 Gy (range 15-40) in 3 fractions (range 1-6). The cumulative incidence of LR was 2.8%, 7.2% and 12.5% at 6 mo, 1 yr and 2 yrs. Fractures occurred in 11 lesions (6%). Radioresistant histology and increasing PTV predicted for LR on univariate analysis, while rib location was associated with control. Increasing PTV remained a significant predictor for LR on multivariate analysis. Univariate predictors of fracture risk included female gender, lytic lesions and poorer KPS. Average CT-approximated L1 trabecular attenuation in patients with fracture was significantly lower than in patients without fracture (112.2 vs. 142.6 Hounsfield units).

Conclusion: In the largest series to date, we report excellent local control for SBRT to non-spine bone metastases and a novel relationship between CT-based bone quality assessment and fracture risk.

For patients treated with SBRT for spinal metastases in the cervical area, a thermoplastic mask is the usual immobilization technique. This project investigates the impact of shoulder position variability on target coverage for such cases. Eight HN patients treated in a suite equipped with a CT-on-rails system (CTOR) were randomly chosen. Of these, three were treated with shoulder depressors. For each patient, their planning CT was used to contour spine targets at the C5, C6 and C7 levels for which two VMAT plans were developed to deliver 18 Gy to each target per the RTOG 0631 protocol. One plan used full arcs while the other used avoidance sectors around the lateral positions. For each patient, IGRT CTOR images were used to recalculate doses that would have been delivered from these plans. Target coverage and dose to the spinal cord were compared for four scenarios: full and partial arcs, with or without depressors. A Dunn test showed significant differences between groups with and without shoulder depressors, but not between those with full versus partial arcs. For most of the investigated cases, the coverage ended up being higher than planned due to the shoulder position being inferior at treatment compared to simulation. In some cases, this led to higher spinal cord doses than allowed per protocol. The results of this study confirm that, when treating lower cervical spine lesions with SBRT, special care should be taken to ensure that the shoulders are positioned as they were during planning CT acquisition.

Background: In the context of the largest democracy of the world (India) with wide variations in the demographic and socio-economic parameters, there is an immense need for a wide reach of advanced radiotherapy facilities. We aim to study the patterns and socio-economic aspects of stereotactic radiosurgery in India.

Methods: The study is based on an online survey consisting of 20 questions. The participants were all radiation oncology professionals in India.

Results: An online questionnaire was prepared and sent to nearly 400 radiation oncologists across the country and we received responses from 78 members. The majority of the participants were practicing Stereotactic radiotherapy. 76% of the participants were located in urban regions. All centers are equipped with Linear accelerators. 89% of centers have facilities to practice SRS. 65% of them have less than 3 years of experience. There were wide variations in the cost of treatment with an average cost of between 1-3lakhs INR (1350-4100$). The majority of people with medical insurance reside in urban locations and those patients who go to small and medium private hospitals and government colleges have state-run health schemes. Participants gave various suggestions for the wider accessibility of SRS facilities across the nation.

Conclusions: Initiatives are to be taken at multiple levels to make stereotactic radiotherapy easily and widely available across the country.

Purpose: To investigate whether there is a volume threshold in target volume of brain metastases below which a small cone size and sharp penumbra in Gamma Knife (GK) may provide improved plan quality when compared to Volumetric Modulated Arc Therapy (VMAT)-based stereotactic radiosurgery (SRS).

Methods: For patients treated on GK SRS for brain metastases in 2018-2019 in our institution, 121 patients with two and three targets were identified. Twenty-six patients with two or three brain metastases (total of 76 lesions) were selected for this study. Two VMAT plans, SmartArc (Pinnacle) and HyperArc (Eclipse), were generated retrospectively for each patient. Plan quality was evaluated based on RTOG conformity index (CI), Paddick gradient index (GI), normal tissue (NT) V12Gy and V4.5Gy. By using the receiver operating characteristic (ROC) curve for both VMAT plans (SmartArc and HyperArc) and metrics of RTOG CI and NT V12Gy, we compared GK plans to SmartArc and HyperArc plans separately to determine the threshold volume.

Results: For SmartArc plans, both ROC curve analyses showed a threshold volume of 0.4 cc for both CI and NT V12Gy. For HyperArc plans, the threshold volumes were 0.2 cc for the CI and 0.5 cc for NT V12Gy. GK plans produced improved dose distribution compared to VMAT for targets ≤0.4 cc, but HyperArc was found to have competing results with GK in terms of CI and NT V12Gy. For targets > 0.4 cc, both SmartArc and HyperArc showed better plan quality when compared to the GK plans.

Conclusions: Target volumes ≤0.4 cc may require a small cone size and sharp penumbra in GK while for target volumes >0.4 cc, VMAT-based SRS can provide improved overall plan quality and faster treatment delivery.

The study was to find the optimal values of priority in the inverse planning module of Leksell GammaPlan which would give better treatment plan indices in GammaKnife SRS. The study showed that the best optimised setting of the weighting or priority in the inverse planning module of Leksell GammaPlan were 0.6 for coverage, 0.3 for gradient index and 0.5 for beam on time. Inverse plans (Hybrid Inverse Plan, HIP) which were made using this optimal priority setting were compared with forward plans (FP) with all 95% coverage. The results showed that the average selectivity index (SI) was 83.05±9.68 for FP and 85.35±8.03 for HIP. So, SI improved in the HIP technique by about 2.3% compare to FP. Similarly, average gradient index (GI) for FP and HIP were respectively 2.82±0.23 and 2.76±0.33. And the average beam on time (BT) of FP and HIP were, respectively, 48.15±23.14 min and 48.35±18.09 min. So, all plan indices show improvement in the hybrid inverse planning technique over forward plans. Consequently, this will improve the quality of patient treatment in GammaKnife.

Treatments for melanoma have significantly advanced with the approval of targeted treatments against the BRAF/MEK pathway and immunotherapy in the form of checkpoint inhibitors. Studies have shown the effectiveness of these treatments against brain metastases. However, the optimum treatment strategy utilising CNS-directed treatments such as stereotactic radiosurgery (SRS) and neurosurgical resection is less clear. Over six years, 70 patients with metastatic melanoma were treated for brain metastases at a tertiary treatment centre. The median overall survival (OS) for all patients was 10.2 months. 51 patients received localised treatment; 7 resection (median OS 10 months), 11 resection and SRS (median OS 17.3 months) and 33 SRS alone (median OS 17.4 months). For patients treated with SRS those who had <2 cm³ treated had a better median OS (20.5 months) compared to those who had >2 cm³ treated (12 months). 69 Patients received systemic treatment. The median OS of patients who did not have CNS-directed treatment was poor (median OS 1.2 months). Patients treated with first line dual immunotherapy had the best median OS (26.7 months), compared to anti-PD-1 (14.1 months), ipilimumab (14.3 months) and kinase inhibitors (10.9 months). Despite advancements in treatment, the development of brain metastases in melanoma is associated with worse outcomes. A combination of CNS-directed and systemic treatment is important to improve survival. Dual immunotherapy appears to be the most effective systemic treatment and the use of SRS improved outcomes. As metastatic melanoma treatments evolve there need to be an ongoing focus to ensure these strategies adequately treat intracranial disease.

The purpose of this study is to compare patient-specific quality assurance (PSQA) results between two dimensional (2D) diode (SRS MapCHECK^®) and 3D diode (ArcCHECK^®) arrays. Twenty-eight intracranial stereotactic radiosurgery (SRS) and 26 lung stereotactic body radiation therapy (SBRT) clinical plans with a single lesion were selected and categorized into 4 groups: 20 SRS dynamic conformal arc therapy (DCAT) plans (Group A), 8 SRS volumetric modulated arc therapy (VMAT) plans (Group B), 6 SBRT DCAT plans (Group C) and 20 SBRT VMAT plans (Group D). An individual field of each plan was delivered on SRS MapCHECK and ArcCHECK and QA analysis was performed using 4 gamma criteria of dose difference/distance-to-agreement of 3%/3 mm, 3%/2 mm, 2%/2 mm and 2%/1 mm. Statistical analysis was performed to compare PSQA results between the 2 QA devices. For all 4 groups and all 4 gamma criteria, average gamma passing rates were higher with SRS MapCHECK.