Stereotactic Radiosurgery Plans Research Articles

Impact of MRI resolution for Linac-based stereotactic radiosurgery.

Magnetic resonance imaging (MRI) is a standard imaging modality in intracranial stereotactic radiosurgery (SRS) for defining target volumes. However, wide disparities in MRI resolution exist, which could directly impact accuracy of target delineation. Here, sequences with various MRI resolution were acquired on phantoms to evaluate the effect on volume definition and dosimetric consequence for cranial SRS. Four T1-weighted MR sequences with increasing 3D resolution were compared, including two Spin Echo (SE) 2D acquisitions with 5mm and 3mm slice thickness (SE5mm, SE3mm) and two gradient echo 3D acquisitions (TFE, BRAVO). The voxel sizes were 0.4×0.4×5.0, 0.5×0.5×3.0, 0.9×0.9×1.25, and 0.4×0.4×0.5 mm3, respectively. Four phantoms with simulated lesions of different shape and volume (range, 0.53-25.0 cm3) were imaged, resulting in 16 total sets of MRIs. Four radiation oncologists provided contours on individual MR image set. All observer contours were compared with ground truth, defined on CT image according to the absolute dimensions of the target structure, using Dice similarity coefficient (DSC), Hausdorff distance (HD), mean distance-to-agreement (MDA), and the ratio between reconstructed and true volume (Ratiovol ). For dosimetric consequence, SRS plans targeting observer volumes were created. The true Paddick conformity index ( ), calculated with true target volume, was correlated with quality of observer volume. All measures of observer contours improved as increasingly higher MRI resolution was provided from SE5mm to BRAVO. The improvement in DSC, HD and MDA was statistically significant (p<0.01). Dosimetrically, strongly correlated with DSC of the planning observer volume (Pearson's r=0.94, p<0.00001). Significant improvement in target definition and reduced inter-observer variation was observed as the MRI resolution improved, which also improved the quality of SRS plans. Results imply that high resolution 3D MR sequences should be used to minimize potential errors in target definition, and multi-slice 2D sequences should be avoided.

Improvement in plan quality after Implementation of clinical goals in a large network of cancer centers.

Clinical Goals (CG) is a tool available in the Varian Eclipse planning system to objectively and visually evaluate the quality of treatment plans based upon user-defined dose-volume parameters. We defined a set of CG for Stereotactic Radiosurgery (SRS) and Intensity-Modulated Radiotherapy (IMRT) based on published data and guidelines and implemented this in a network of cancer centers in India (American Institute of Oncology). A dosimetric study was performed to compare brain SRS and breast IMRT plan quality before and after CG implementation.The CG defined for SRS plans were target V100% ≥ 98%, dose gradient measure (GM) ≤ 0.5 cm, conformity index (CI) 1.0 to 1.2. For breast IMRT plans, CG defined target V100% ≥ 97%, V95% ≥ 95%, V107% ≤ 2%, V105% ≤ 10%, and Dmax ≤ 2.4 Gy. Dose limits to organs-at-risk (OAR) were summarize in supplemental materials. Twenty brain SRS and 10 breast IMRT treatment plans that were previously delivered on patients were selected and re-planned using CG. The pre and postoptimized plan parameters were compared using student t-tests.For brain SRS plans, the V100, GM, and CI for the pre- and post-Clinical-Goals plans were 93.22% ± 7.2% vs 97.96% ± 0.29% (p = 0.009), 0.63 ± 0.16 vs 0.42 ± 0.05 (p < 0.001) and 1.07 ± 0.18 vs 1.06 ± 0.06 (p = 0.79), respectively. There were no differences in max dose to OARs. In breast IMRT plans, the target V107% for pre and postimplemented plans were 16.50% ± 10.98% vs 0.32% ± 0.32%, respectively (p = 0.001). The average target V105% were 44.00% ± 15.72% and 8.69% ± 4.53%, respectively (p < 0.001). No differences were found in the average target V100% (p = 0.128) and V95% (p = 0.205). The average target Dmax were 112.28% ± 1.59% and 109.14% ± 0.73%, respectively (p < 0.001). There were only minor differences in doses to OARs.The implementation of CG in Varian Eclipse significantly improved SRS and IMRT plan quality with enhanced coverage, dose GM, and CI without increased dose to OARs.

Validation of the Fabricated Cast Nylon Head Phantom for Stereotactic Radiosurgery End-to-End Test using Alanine Dosimeter.

Stereotactic radiosurgery (SRS) is an alternative to surgery as it precisely delivers single-large doses to small tumors. Cast nylon is used in phantom due to its computed tomography (CT) number of about 56-95 HU, which is close to that of the soft tissue. Moreover, cast nylon is also more budget-friendly than the commercial phantoms. The aim of this study is to design and validate the fabricated cast nylon head phantom for SRS end-to-end test using an alanine dosimeter. The phantom was designed using cast nylon. It was initially created by a computer numerical control three-axis vertical machining center. Then, the cast nylon phantom was scanned using a CT simulator. Finally, the validation of the fabricated phantom using alanine dosimeter proficiency with four Varian LINAC machines was performed. The fabricated phantom presented a CT number of 85-90 HU. The outcomes of VMAT SRS plans showed percentage dose differences from 0.24 to 1.55, whereas the percentage dose differences in organ at risk (OAR) were 0.09-10.80 due to the low-dose region. The distance between the target (position 2) and the brainstem (position 3) was 0.88 cm. Variation in dose for OAR is higher, which might be due to a high-dose gradient in the area where measurement was being conducted. The fabricated cast nylon end-to-end test head phantom had been suitably designed to image and irradiate during an end-to-end test for SRS using an alanine dosimeter.

A hybrid method to improve efficiency of patient specific SRS and SBRT QA using 3D secondary dose verification.

Patient Specific QA (PSQA) by direct phantom measurement for all intensity modulated radiation therapy (IMRT) cases is labor intensive and an inefficient use of the Medical Physicist's time. The purpose of this work was to develop a hybrid quality assurance (QA) technique utilizing 3D dose verification as a screening tool to determine if a measurement is necessary. This study utilized Sun Nuclear DoseCHECK (DC), a 3D secondary verification software, and Fraction 0, a trajectory log IMRT QA software. Twenty-two Lung stereotactic body radiation therapy (SBRT) and thirty single isocentre multi-lesion SRS (MLSRS) plans were retrospectively analysed in DC. Agreement of DC and the TPS dose for selected dosimetric criteria was recorded. Calculated 95% confidence limits (CL) were used to establish action limits. All cases were delivered and measured using the Sun Nuclear stereotactic radiosurgery (SRS) MapCheck. Trajectory logs of the delivery were used to calculate Fraction 0 results for the same criteria calculated by DC. Correlation of DC and Fraction 0 results were calculated. Phantom measured QA was compared to Fraction 0 QA results for the cases which had DC criteria action limits exceeded. Correlation of DC and Fraction 0 results were excellent, demonstrating the same action limits could be used for both and DC can predict Fraction 0 results. Based on the calculated action limits, zero lung SBRT cases and six MLSRS cases were identified as requiring a measurement. All plans that passed the DC screening had a passing measurement based PSQA and agreed with Fraction 0 results. Using 95% CL action limits of dosimetric criteria, a 3D secondary dose verification can be used to determine if a measurement is required for PSQA. This method is efficient for it is part of the normal clinical workflow when verifying any clinical treatment. In addition, it can drastically reduce the number of measurements needed for PSQA.

Step-by-Step Stereotactic Radiotherapy Planning of Brain Metastasis: A Guide to Radiation Oncologists—the ROSE Case (Radiation Oncology from Simulation to Execution)

Brain metastasis is seen in 10% to 20% of all adult cancer patients. One of the main modalities of treatment is stereotactic radiosurgery (SRS). Here, we describe the step by step procedure for stereotactic planning of brain metastasis by using a clinical scenario. The management of brain metastasis starts with the clinical evaluation of the patient followed by imaging and SRS treatment in the present case. The paper highlights the sequential process of radiation planning for SRS—starting from simulation, planning, evaluation of plan, and treatment.

Step-by-Step Stereotactic Radiotherapy Planning of Glomus Jugulare: A Guide to Radiation Oncologists—Dr Kanhu’s ROSE (Radiation Oncology from Simulation to Execution)

Background Glomus jugulare is a rare, slow-growing tumor that arise within the jugular foramen of the temporal bone. In the past, surgery was the primary modality of treatment for glomus Jugulare, but it leads to many complications and increased mortality. Radiotherapy was indicated in adjuvant setting in post-operative residual disease. But, with the advent of highly conformal radiation planning, stereotactic radiosurgery (SRS), is now one of the main modalities of radiation treatment in glomus jugulare. Objective To describe the procedural steps for radiation planning of SRS of glomus jugulare. Methods The step-by-step procedure for stereotactic planning of glomus jugulare has been described using a clinical scenario of glomus jugulare. Results The stereotactic radiation planning of glomus jugulare starts with the basic history and relevant clinical evaluation, that is, visual testing. Computed tomography (CT) scan and magnetic resonance imaging (MRI) of the brain is the imaging modality of choice. The radiation planning of glomus jugulare starts with CT simulation. MRI of brain should be done in the prescribed format to achieve uniformity in radiation planning. After CT and MRI image fusion, contouring of target, organs at risk (OAR) and radiation planning should be done. The plan evaluation includes target and OAR coverage index, conformity, homogeneity and gradient index, and beam arrangement. After radiation plan evaluation, treatment is delivered after quality assurance and dry run. Conclusion The paper highlights the sequential process of radiation planning for SRS in glomus jugulare—starting from simulation, planning, evaluation of plan, and treatment.

Dosimetric potential of knowledge-based planning model trained with HyperArc plans for brain metastases.

Dosimetric potential of knowledge-based RapidPlan planning model trained with HyperArc plans (Model-HA) for brain metastases has not been reported. We developed a Model-HA and compared its performance with that of clinical volumetric modulated arc therapy (VMAT) plans. From 67 clinical stereotactic radiosurgery (SRS) HyperArc plans for brain metastases, 47 plans were used to build and train a Model-HA. The other 20 clinical HyperArc plans were recalculated in RapidPlan system with Model-HA. The model performance was validated with the 20 plans by comparing dosimetric parameters for normal brain tissue between clinical plans and model-generated plans. The 20 clinical conventional VMAT-based SRS or stereotactic radiotherapy plans (CL-VMAT) were reoptimized with Model-HA (RP) and HyperArc system (HA), respectively. The dosimetric parameters were compared among three plans (CL-VMAT vs. RP vs. HA) in terms of planning target volume (PTV), normal brain excluding PTVs (Brain-PTV), brainstem, chiasm, and both optic nerves. In model validation, the optimization performance of Model-HA was comparable to that of HyperArc system. In comparison to CL-VMAT, there were no significant differences among three plans with respect to PTV coverage (p>0.17) and maximum dose for brainstem, chiasm, and optic nerves (p>0.40). RP provided significantly lower V20Gy , V12Gy , and V4Gy for Brain-PTV than CL-VMAT (p<0.01). The Model-HA has the potential to significantly reduce the normal brain dose of the original VMAT plans for brain metastases.

A Radiomics-Integrated Deep Learning Model for Identifying Radionecrosis Following Brain Metastasis Stereotactic Radiosurgery (SRS)

<h3>Purpose/Objective(s)</h3> To develop a radiomics-integrated deep learning (RIDL) model for identifying radionecrosis in brain metastasis patients with post-SRS radiographic progression. Such a novel model is hypothesized to outperform classic radiomics and deep learning approaches in radionecrosis/recurrence differentiation. <h3>Materials/Methods</h3> The model was developed based on a 51-patient cohort at our institution with post-SRS radiographic progression and known biopsy outcome (37 radionecrosis, 14 recurrence) from Laser Interstitial Thermal Therapy (LITT). Utilizing the 3-month post-SRS high resolution T1+c volume, the RIDL model comprises three key steps: 1) 184 radiomics features (RFs) are extracted from within the SRS planning target volume (PTV) and 60% isodose volume (V₆₀) followed with Z-score normalization; 2) a deep neural network (DNN) mimicking the encoding path of U-net is trained for radionecrosis/recurrence prediction using the 3D volume. Prior to the binary prediction output, latent variables in the DNN are extracted as 512 deep features (DFs); and 3) all extracted features are synthesized as an input of support vector machine (SVM) execution. Key features with higher linear kernel weighting factor values are identified by clustering analysis, and these key features are utilized by SVM to generate the final radionecrosis/recurrence prediction result. During the model training, a 7:3 training/test data sample ratio was adopted, and 50 model versions were acquired with random validation sample assignments. Sensitivity, specificity, accuracy, and ROC of the model were evaluated, and these results were compared with 1) classic radiomics-based prediction (i.e., radiomics features-only for SVM input) and 2) DNN prediction results. Potential associations between the identified key radiomics/deep features and patients' genetic profiles were studied. <h3>Results</h3> As seen in the table, while radiomics-based prediction achieved acceptable accuracy but very low sensitivity, DNN prediction achieved similar accuracy with an improved sensitivity; in contrast, the RIDL achieved the best prediction accuracy and sensitivity results with 32 identified key features (3 RFs+29 DFs), and it also demonstrated superior ROC results. For patients with NSCLC primary disease, 2 RFs extracted in SRS V₆₀ exhibited significant correlation with ALK mutation (R>0.6), and 1 DF exhibited significant correlation with EGFR mutation (R>0.7). <h3>Conclusion</h3> The developed RIDL can accurately differentiate brain metastasis radionecrosis/recurrence using a single post-SRS MR scan. Future work that investigates its integration with genomics as a comprehensive radiogenomic tool is indicated.

A Method to Simplify Patient-Specific QA of Single Isocenter Multiple Met SRS Plans

<h3>Purpose/Objective(s)</h3> Pre-treatment quality assurance of single isocenter multi-met stereotactic radiosurgery (SRS) plans is standardly performed by acquiring a dose measurement using a detector array or ion chamber and film. The major efficiency issue with QA of these plans is how many, and which of the multiple metastases (mets) should be measured. The purpose of this study was to develop a workflow using an independent 3D dose calculation (DC) and trajectory log (TL) QA software to efficiently determine which of the brain mets should be further evaluated by measurement. <h3>Materials/Methods</h3> 30 single isocenter multiple metastasis patient SRS plans with a total of 82 mets were retrospectively studied. The clinical SRS plans were generated with an automated dynamic conformal arc SRS planning system (TPS). All plans were sent to the DC software for calculation. The gamma analysis (3%, 1 mm), percent difference between TPS and DC calculated mean and max dose to PTV, and the dose difference of the centroid point of each PTV was recorded. All plans were delivered to a high-resolution diode array designed for SRS and measurements were used to perform a gamma analysis (3%, 1 mm). In addition, the trajectory logs of the QA delivery were used to calculate 3D dose distributions and the same metrics acquired from the DC software were calculated and recorded. Pearson correlation between DC and TL calculated metrics was calculated. <h3>Results</h3> The results of the dosimetric metrics calculated by the DC and TL software are presented in Table 1. Overall agreement between DC and TPS was excellent, with all mean percent differences within 1.1% and mean gamma pass rates greater than 99%. Furthermore, dosimetric metrics calculated by DC and TL were highly correlated, with the correlation coefficients for all metrics at least 0.96, which suggests DC results can be used to predict TL QA results. To use DC to screen which PTVs should be further evaluated, an action level was set such that if any metric fell outside the 95% confidence interval (mean + 1.96 × SD), a QA measurement would be performed. For all metrics, a ±5% action level was calculated to cover the 95% confidence interval. DC results for 6 PTVs exceeded the action level. Of these plans, the measured patient specific QA passed for all plans. While all measured QA passed, DC and TL QA appeared to be more sensitive than the diode array measurement in identifying potential plan quality issues. <h3>Conclusion</h3> An efficient workflow for patient specific QA of single isocenter multiple met SRS plans was developed. An independent 3D dose calculation is used to calculate agreement of dosimetry metrics compared to the TPS. If the percent difference of a metric for a PTV exceeds a 5% action level, it is selected for further QA using a dose measurement.

Automated Brain Metastasis Detection and Segmentation Using Deep-Learning Method

<h3>Purpose/Objective(s)</h3> Brain metastases (BM) detection and segmentation can be difficult and time-consuming during stereotactic radiosurgery (SRS) planning. This work aims to develop deep learning models to automatically detect and segment BM on MRI. <h3>Materials/Methods</h3> Two volumetric deep convolutional neural network (V-net) models, general (GM) and small lesion models (SM), were developed using T1-weighted gadolinium contrast enhanced and T2-weighted FLAIR MRIs along with ground truth contours of all BMs collected for 53 patients from our own institution. The GM was developed by transfer learning based on a model previously trained with multi-institutional datasets. The SM was a new model presently trained using images slices with small lesions (volumes < 1 cc). The training sets for both models were the data from 43 patients, a total of 5,204 image sets extracted with three different patch sizes (16 × 16 × 16, 32 × 32 × 32, and 64 × 64 × 64). The obtained models were evaluated using a test set of 10 patients in terms of the Dice similarity coefficient (DSC), sensitivity, specificity, and area under the receiver operating characteristic curve (AUC). <h3>Results</h3> For the GM, the voxel-level segmentation AUCs were 0.90 +/- 0.10, 0.88 +/- 0.10, and 0.87 +/- 0.11 for patch sizes of 16 × 16 × 16, 32 × 32 × 32, and 64 × 64 × 64, respectively, and the detection sensitivity and specificity were 0.86 and 0.94, respectively, for all test datasets (all lesions). For the test data excluding small lesions, the sensitivity and specificity became 0.93 and 0.95, respectively. For SM, a sensitivity of 0.76 and a specificity of 0.91 were achieved for all small lesions in the test datasets. The DSC was 0.92 for GM for all lesions and was 0.82 for SM for all the small BMs. <h3>Conclusion</h3> The two deep learning models, SM and GM, can automatically detect and segment brain metastases with reasonable accuracy, sensitivity, and specificity on the MRIs commonly used for SRS planning. For BMs with volumes > 1 cc, the GM achieved clinically relevant results. With further development using larger datasets, the models can be implemented to improve the clinical practice of SRS planning.

Analysis and Comparison of Treatment Planning Software for Normal Tissue Dose for Large and Small brain Tumors Treated with a Non-Invasive Stereotactic Radiosurgery Instrument

<h3>Purpose/Objective(s)</h3> Patients with metastatic brain tumors may be treated with a stereotactic radiosurgery (SRS) platform or a linear accelerator (LINAC)-based platform. Recently, Leksell GammaPlan (LGP) received an update that made an optimization algorithm. Our objective was to review and compare older, completed plans with the newer "optimized" plans to establish if there were improvements on plan parameters, namely, Gradient Index (GI), Selectivity Index (SI), and Paddick Conformity Index (PCI). <h3>Materials/Methods</h3> We reviewed our institutional database in order to identify and gather patients with brain metastases treated by SRS. We chose patients with varying lesion sizes to see if there were any significant differences in how the optimization algorithm would treat large lesions (>5 cc), what we defined as very small (<2 cc), small (2-3 cc) and medium-sized lesions (3-4 cc). All lesions were originally treated with a 900 cGy x3 fractionation scheme. Optimization within the LGP software was performed on these plans while maintaining at least 99.51% coverage of the lesion volume as well as normalizing each plan to prescribe to the 50% isodose line in order to preserve the integrity of the original SRS plans. Because PCI is SI * coverage, and coverage was considered to be unity, only values of SI were directly observed. <h3>Results</h3> The cohorts had improvements overall in both GI and SI. 30 patients with metastases were identified that were treated using SRS. 15 of which had large lesions, 5 of which had medium-sized lesions, 5 of which had small lesions, and 5 of which had very small lesions. The GI improved for the very small on average by 0.492 (14.88%), for the small on average by 0.482 (16.27%), for the medium on average by 0.37 (12.66%), and for the large by 0.176 (6.63%). The SI improved for the very small on average by 0.144 (25.71%), for the small on average by 0.096 (12.83%), for the medium on average by 0.132 (22.92%). For the large tumors, SI on average lowered by 0.017 (2.05%). It is important to note that SI for only large tumors has appeared to marginally decrease. <h3>Conclusion</h3> From the advent of the new LGP optimization algorithm, utilizing this new update may be associated with improvement in dose falloff and local control of the tumor volume. Our data suggests that for lesions of all sizes, the optimization significantly improves all parameters in question for Gamma Knife treatment planning.

An Optimal Solution Study on a Non-Invasive Stereotactic Radiosurgery Instrument Optimizer for Stereotactic Radiosurgery of Single Brain Metastasis

<h3>Purpose/Objective(s)</h3> This study looks at a fast inverse planning (FIP) optimizer that enables more efficient and less planner dependent stereotactic radiosurgery (SRS) treatment planning. FIP generates a plan using multiple user-inputted variables that affect plan quality metrics, such as target coverage (TC), maximum dose to the target and organs-at-risk, low dose (LD), and beam-on time (BOT). The objective of this study is to systematically characterize each of these variables and determine which combination leads to the best SRS plan quality metrics. <h3>Materials/Methods</h3> Thirty patients with a single brain metastasis who were previously treated with SRS were evaluated. Each lesion was planned using FIP by varying the LD and BOT variables in 0.1 increments from 0.0 to 1.0 (i.e., plan #1 [0.0, 0.0], plan #2 [0.0, 0.1], ..., plan #120 [1.0, 0.9] and plan #121 [1.0, 1.0]). All plans were generated with the same prescription dose (24 Gy/1 fraction), TC (100%), maximum allowed dose (43.2 Gy), and Gamma angle (90°). The following metrics were recorded for each plan to evaluate plan quality: Paddick conformity index (PCI), gradient index (GI), and BOT. Heat maps for each of the above metrics as a function of LD and BOT penalties were analyzed. An objective score matrix was calculated for each plan using a linear weighted combination of scaled and normalized GI, PCI, and BOT. An optimal solution space containing the 5 lowest values of the score matrix per patient was extracted. A frequency histogram was subsequently created in the LD-BOT coordinate space. <h3>Results</h3> The target volumes in the study ranged from 1.0 cc to 2.5 cc. For every patient, 121 plans were generated across the range of LD and BOT penalties, resulting in 3630 plans included in this analysis. The range of PCI, GI, and BOT across all plans were 0.71 to 0.95, 2.5 to 2.9, and 17.2 to 221 minutes, respectively. The variation of the LD/BOT penalties had a much larger impact resulting in a higher deviation about the mean for BOT (169%), followed by PCI (28%). Heat map analysis revealed that the plans that maximized PCI and minimized GI values occupied the upper triangular matrix of the LD/BOT penalty space, while plans that minimized BOT occupied the lower triangular space. The optimal solutions frequently occupied the diagonal space in between these zones. Specifically, the histogram analysis showed that 4 highest frequencies occurred at the user-inputted settings (LD, BOT) of (0.6, 0.5), (0.8, 0.6), (0.7, 0.5), and (0.7, 0.6), in order of plan quality. <h3>Conclusion</h3> In this study, the user-inputted variables (LD and BOT) were systematically varied to determine the optimal solutions to simultaneously maximize PCI while minimizing GI and BOT. The results of this study may permit SRS planners to generate single brain metastasis plans more efficiently using the study-defined optimal settings of LD and BOT.

A Novel Lightning Dose Optimizer for Radiosurgery of Irregular-Shaped Arteriovenous Malformations and Pituitary Adenomas

<h3>Purpose/Objective(s)</h3> To demonstrate the clinical feasibility of a novel inverse planning algorithm via dose optimizer (DO) on a treatment planning system (TPS)for generating high-quality treatment plans with significantly faster planning times for Stereotactic Radiosurgery (SRS) of the complex and difficult cases of arteriovenous malformation (AVM) and pituitary adenomas. <h3>Materials/Methods</h3> After completing the in-house end-to-end phantom testing and independent dose verification of recently upgraded DO on TPS using one institution's IROC anthropomorphic SRS head phantom irradiation credentialing, twenty previously treated SRS patients (10 AVM, average volume 3.61 cc) and (10 pituitary adenomas, average volume 0.86 cc) who underwent manual forward planning on TPS were retrospectively re-planned via DO under IRB protocol. DO finds the target curvature boundary by well formulated linear programming objectives, and inversely optimize SRS plan by isocenter placement, optimization, and sequencing. For identical tumor dose, the DO and original manual plans were compared for target conformity, gradient index, dose to critical organs, and surrounding normal brain. Additionally, various treatment delivery parameters including beam on time were recorded. <h3>Results</h3> For both patient cohorts, DO provided similar target coverage with better dose conformity, tighter radiosurgical dose distribution with lower value of gradient indices (all p < 0.001), and lower dose to critical organs. For AVM, significant reduction of normal brain V10, V12 and V14 by 4.74 cc, 3.67 cc, and 2.67 cc (all p < 0.001), on average via DO was observed at the cost of as many as twice the numbers of shots (p < 0.001), and relatively longer beam on time (p = 0.012) by a factor of 1.44, compared to the clinical manual plans. For pituitary adenoma, DO provided systematically lower values of V10, V12 and V14 by 1.08 cc, 0.86 cc and 0.68 cc (all p < 0.001), on average and lower maximal dose to optic pathway by 0.7 Gy (p = 0.005), but had almost twice the numbers of shots (p < 0.001) and increased beam on time (p = 0.005) by a factor of 1.2, compared to the original manual plans. However, for both patient groups, average planning time for the DO was < 5 minutes, compared to estimated 30-60 min of manual planning times. <h3>Conclusion</h3> SRS treatment via new inverse DO provided highly conformal target coverage, steep dose gradient, spared critical organs, and significantly reduced normal brain dose for complex targets who presented with very irregular nidus or pituitary adenoma. DO generated high quality treatment plans and could yield significant time saving in planning the treatment, particularly for inexperienced SRS users–improving patient compliance, and clinic workflow. If available, DO algorithm is suggested for validation and clinical use for irregular, complex and difficult SRS cases in the future.

A Comprehensive Evaluation of Single Isocenter Multiple Target SRS Plans and the Analytical Relationship between Plan Quality Indices with the Number and Volume of Targets.

To study the relationship of plan quality indices with the number and volume of target for 5 to 10 brain metastases treated with LINAC-based Single Isocenter Multiple Target (SIMT) Stereotactic radiosurgery (SRS) planning and to determine the maximum volume of spherical targets treated without exceeding the normal tissue tolerances. Spherical targets of 5 to 10 numbers per plan, with individual target volumes ranging from 0.025 cc to 11.5 cc, were simulated with randomly drawn planning target volumes (PTVs) within the brain. SIMT SRS plans were generated for the 21 Gy prescription dose with a 6 MV Flattening Filter Free photon beam. Target coverage, organ at risk sparing, plan quality indices, R50%, and gradient measure were studied. Mean brain dose, V12 for Brain minus PTV (BmP), V10, V12, V15, V18, V20, and V24 for brain volume were evaluated. Equations relating the gradient index, mean brain dose, and V12 (BmP) to the given number and volume of the targets were constructed. PTV coverage D98 was 98.77 ± 1.37 %. The mean CIRTOG, QRTOG, HIRTOG, CIP, GI, and R50% of the individual targets were 1.02 ± 0.08, 0.94 ± 0.02, 1.49 ± 0.11, 0.91 ± 0.06, 4.74 ± 2.3, and 4.95 ± 2.67, respectively. The gradient measure achieved was in the range of 0.49 to 1.35 cm. The mean brain dose was in the range of 1.62 to 6.69 Gy. The mean V12 (BmP) per target obtained was 3.85 ± 2.83 cc. Equations relating the number and volume of targets to the gradient measure, mean brain dose, V12 (BmP), and V10-24 can serve as a baseline for multiple brain metastases SIMT planning. The target volume for 5, 6, 7, 8, 9, and 10 targets that can be treated without exceeding V12 (BmP) is 6, 5, 4.7, 4, 3.7, and 3.4 cc, respectively, for the 21 Gy prescription dose.

Monte Carlo-based independent dose verification of radiosurgery HyperArc plans

PurposeTo investigate the feasibility of using the free PRIMO Monte Carlo software for independent dose check of cranial SRS plans designed with the Varian HyperArc (HA) technique. Materials and methodsIn this study, the PRIMO Monte Carlo software v. 0.3.64.1800 was used with the phase-space files (v. 2, Feb. 27, 2013) provided by Varian for 6 MV flattening-filter-free (FFF) photon beams from a Varian TrueBeam linear accelerator (linac), equipped with a Millennium 120 multileaf collimator (MLC). This configuration was validated by comparing the percentage depth doses (PDDs), lateral profiles and relative output factors (OFs) simulated in a water phantom against measurements for field sizes from 1 × 1 to 40 × 40 cm2. The agreement between simulated and experimental relative dose curves was evaluated using a global (G) gamma index analysis. In addition, the accuracy of PRIMO to model the MLC was investigated (dosimetric leaf gap, tongue and groove, leaf transmission and interleaf leakage).Thirty-five HA SRS plans computed in the Eclipse treatment planning system (TPS) were simulated in PRIMO. The Acuros XB algorithm v. 16.10 (dose to medium) was used in Eclipse. Sixty targets with diameters ranging from 6 to 33 mm were included. Agreement between the dose distributions given by Eclipse and PRIMO was evaluated in terms of 3D global gamma passing rates (GPRs) for the 2 %/2 mm criteria. ResultsAverage GPR greater than 95 % with the 2 %(G)/1 mm criteria were obtained over the PDD and profiles of each field size. Differences between PRIMO calculated and measured OFs were within 0.5 % in all fields, except for the 1 × 1 cm2 with a discrepancy of 1.5 %. Regarding the MLC modeling in PRIMO, an agreement within 3 % was achieved between calculated and experimental doses. Excellent agreement between PRIMO and Eclipse was found for the 35 HA plans. The 3D global GPRs (2 %/2 mm) for the targets and external patient contour were 99.6 % ± 1.1 % and 99.8 % ± 0.5 %, respectively. ConclusionsAccording to the results described in this study, the PRIMO Monte Carlo software, in conjunction with the 6X FFF Varian phase-space files, can be used as secondary dose calculation software to check stereotactic radiosurgery plans from Eclipse using the HyperArc technique.

Stereotactic radiotherapy of brain metastases: clinical impact of three-dimensional SPACE imaging for 3T-MRI-based treatment planning

PurposeFor planning CyberKnife stereotactic radiosurgery (CK SRS) of brain metastases (BM), it is essential to precisely determine the exact number and location of BM in MRI. Recent MR studies suggest the superiority of contrast-enhanced 3D fast spin echo SPACE (sampling perfection with application-optimized contrast by using different flip angle evolutions) images over 3D gradient echo (GE) T1-weighted MPRAGE (magnetization-prepared rapid gradient echo) images for detecting small BM. The aim of this study is to test the usability of the SPACE sequence for MRI-based radiation treatment planning and its impact on changing treatment.MethodsFor MRI-based radiation treatment planning using 3T MRI in 199 patients with cerebral oligometastases, we compared the detectability of BM in post-gadolinium SPACE images, post-gadolinium MPRAGE images, and post-gadolinium late-phase MPRAGE images.ResultsWhen SPACE images were used for MRI-based radiation treatment planning, 29.8% and 16.9% more BM, respectively, were detected and included in treatment planning than in the post-gadolinium MPRAGE images and the post-gadolinium late-phase MPRAGE images (post-gadolinium MPRAGE imaging: ntotal = 681, mean ± SD 3.4 ± 4.2; post-gadolinium SPACE imaging: ntotal = 884, mean ± SD 4.4 ± 6.0; post-gadolinium late-phase MPRAGE imaging: ntotal = 796, mean ± SD 4.0 ± 5.3; Ppost-gadolinium SPACE imaging versus post-gadolinium MPRAGE imaging < 0.0001, Ppost-gadolinium SPACE imaging versus post-gadolinium late-phase MPRAGE imaging< 0.0001).ConclusionFor 3T MRI-based treatment planning of stereotactic radiosurgery of BM, we recommend the use of post-gadolinium SPACE imaging rather than post-gadolinium MPRAGE imaging.

Frameless Co-Registration of Biplane 2D Digital Subtraction Angiography Whole Frames and 3D Rotational Angiography-Based Cone-Beam Computed Tomography Angiogram on Dedicated Software for Stereotactic Radiosurgery of Cranial Vascular Malformations.

Purpose: Given its high spatial resolution and vasculature selectivity, the cone-beam computed tomography (CT) angiography (CBCTA) image acquired by selective 3D rotational angiography (3DRA) is the most suitable 3D image for the target definition of stereotactic radiosurgery (SRS) for intracranial arteriovenous malformations (AVMs) and dural arteriovenous fistulas (DAVFs). Furthermore, the relatively low temporal resolution of 3DRA-based CBCTA can be complemented by the stereotactic co-registration of orthogonally paired 2D dynamic digital subtraction angiography (2D-DSA). The integration of 2D-DSA, which is usually limited to one or a few frames for each projection, into CBCTA and/or planning CT can be achieved only by catheter-directed angiography on the day of SRS via a dedicated image localizer under rigid frame fixation to the skull, which imposes substantial burdens on patients. This study aimed to demonstrate a novel, convenient, and significantly less invasive method for the frameless co-registration of biplane 2D-DSA whole frames and CBCTA on commercially available dedicated software, namely, Brainlab® Elements (Brainlab AG, Munich, Germany), and present its prerequisite for successful image fusion.Technical Report: Elements have afforded the following functionality: A 3D vasculature image is automatically extracted as a floating image from any 3D image series containing vascular details and then subsequently co-registered manually and automatically to a selected frame pair of 2D-DSA with a six-degree-of-freedom rigid registration. As a preclinical feasibility study, two anonymous image datasets from patients harboring cerebral AVM and transverse-sigmoid (TS) DAVF were used to verify the accuracy and practicality of Elements for the frameless co-registration of 2D/3D vascular images, particularly on the assumption of clinical workflow for the target delineation of SRS planning. The use of ordinary unsubtracted CBCTA resulted in the insufficient extraction of abutting vessels or vessels that are in close proximity to bony structures, particularly in the case of TS-DAVF, where the fistulous pouch and the affected venous sinuses were adjacent to the cranial bone. By contrast, the amount and selectivity of vasculatures and the accuracy of subsequent image fusion were significantly improved from the subtracted CBCTA. The integration of CBCTA into dynamic 2D-DSA allowed the simultaneous review of both image information by sharing any concerning point and 2D or 3D structures under a common 3D coordinate.Conclusions: Elements enable the clinically useful frameless co-registration of biplane 2D-DSA whole frames into CBCTA, for which the routine acquisition of both subtracted and unsubtracted CBCTA axial images for ordinary diagnostic purposes is an indispensable prerequisite for successful image fusion and further widespread application. This frameless integration of the 2D/3D angiogram would dramatically enhance both the frame-based and frameless SRS workflow and circumstances by allowing users to forward SRS planning well in advance before SRS, along with the omission of invasive angiography on the day of SRS, and would broaden the implementation of frameless SRS. Furthermore, the comprehensive alternating interactive review of the 2D/3D integrated angiogram leads to a more in-depth quasi-4D understanding of the affected angioarchitectures compared with the separate viewing of each image.

NEIM-05 FEASIBILITY OF NAVIGATED TRANSCRANIAL MAGNETIC STIMULATION (NTMS) BASED DIFFUSION TENSOR IMAGING (DTI) TRACTOGRAPHY OF MOTOR PATHWAYS IN PATIENTS UNDERGOING STEREOTACTIC RADIOSURGERY: A CROSS-SECTIONAL DOSIMETRIC AND PATIENT OUTCOMES ANALYSIS

BACKGROUNDNo current dose limitations exist for the motor tracts during stereotactic radiosurgery (SRS) planning due to challenges in localizing this region of interest by conventional imaging. Navigated Transcranial Magnetic Stimulation (nTMS) is a non-invasive tool that utilizes electromyographic signal combined with magnetic resonance diffusion tensor imaging (DTI) to functionally map cortical motor tracts. Although nTMS is utilized for functional mapping prior to brain tumor resection, it has not been implemented in SRS planning. OBJECTIVESTo determine the feasibility of performing nTMS-based DTI in patients treated with SRS and examine the relationship between dose to functionally-defined motor tracts and patient outcomes measured by objective hand function testing and patient reported outcomes (PROs). METHODS16 patients treated with SRS to a brain metastasis located near anatomically-defined motor tracts were enrolled on an IRB-approved clinical trial. At median follow-up of 5.4m after SRS, patients underwent nTMS testing, brain MRI with DTI, functional outcomes testing (Pinch Dynamometer,9-Hole Peg Test), and quality-of-life (QOL) PROs (EQ-5D-5L, MDASI-BT). nTMS-seeded DTI tractography was generated (Brainlab iPlan) and imported into GammaPlan for dosimetric evaluation. RESULTSTractography reconstitution was attempted for 8/16 patients and successful in 7/8 (87.5%). One patient who had prior resection of a lesion in the right pre-central gyrus failed to map in the right cortex and was unable to complete functional testing for the affected extremity. Median Dmax to the treated motor tracts was 4.6Gy [0.5-13.4Gy]. Median Dmean was 0.9Gy [0-1.2Gy]. Increased Dmax correlated with deficits in lateral pinch strength (R2=0.76) and 9-Hole Peg testing time (R2=0.61). Increased Dmean correlated with increased MDASI-BT interference scores (R2=0.93) and EQ5D5L score (R2=0.94) indicating worsened QOL. CONCLUSIONSnTMS testing was feasible and dose to nTMS-defined motor tracts correlated with subjective and objective patient outcomes. Future steps will include characterization of motor tract dose tolerance for SRS.

The Influence of the Technical Parameters of the SRS Plans on the Dosimetric and Radiobiologic Evaluation

Background: The purpose of this study was to evaluate influence of technical parameters on Stereotactic Radiosurgery (SRS) plans on dosimetric evaluation. Materials and methods: There were considered and selected two patients who had brain tumors and had been treating in Tomsk Regional Oncology Center. All treatment plans were simulated using the Monaco treatment planning system v 5.11 (Elekta Instrument AB, Stockholm) on the Elekta Synergy linac with photon beam nominal energy 6 MV. For study there were created several plans with different technical parameters (number of arcs, increment, gantry angle, collimator angle, couch angle, minimum segment width). Each plan was evaluated by metrics such as Conformal, Homogeneity and Gradient indexes. Results: If we use a large increment value it may create few sectors and which can produce low quality plans, and increase treatment time, otherwise if we use a too small increment value it will give us more sectors and they can increase the quality of the plan. The dose which was measured with higher MSW showed to us better agreement with the calculated dose. Conclusion: It is valuable to carefully select technical parameters. The use of rigid increment value, segment width or increasing number of arcs can make plans have lower quality and to rise time of treatment.

Single-isocenter multiple-target stereotactic radiosurgery for multiple brain metastases: dosimetric evaluation of two automated treatment planning systems

PurposeAutomated treatment planning systems are available for linear accelerator (linac)-based single-isocenter multi-target (SIMT) stereotactic radiosurgery (SRS) of brain metastases. In this study, we compared plan quality between Brainlab Elements Multiple Brain Metastases (Elements MBM) software which utilizes dynamic conformal arc therapy (DCAT) and Varian HyperArc (HA) software using a volumetric modulated arc therapy (VMAT) technique.Patients and methodsBetween July 2018 and April 2021, 36 consecutive patients ≥ 18 years old with 367 metastases who received SIMT SRS at UPMC Hillman Cancer San Pietro Hospital, Rome, were retrospectively evaluated. SRS plans were created using the commercial software Elements MBM SRS (Version 1.5 and 2.0). Median cumulative gross tumor volume (GTV) and planning tumor volume (PTV) were 1.33 cm3 and 3.42 cm3, respectively. All patients were replanned using HA automated software. Extracted dosimetric parameters included mean dose (Dmean) to the healthy brain, volumes of the healthy brain receiving more than 5, 8,10, and 12 Gy (V5Gy, V8Gy, V10Gy and V12Gy), and doses to hippocampi.ResultsBoth techniques resulted in high-quality treatment plans, although Element MBM DCAT plans performed significantly better than HA VMAT plans, especially in cases of more than 10 lesions). Median V12Gy was 13.6 (range, 1.87–45.9) cm3 for DCAT plans and 18.5 (2.2–62,3) cm3 for VMAT plans (p < 0.0001), respectively. Similarly, V10Gy, V8Gy, V5Gy (p < 0.0001) and median dose to the normal brain (p = 0.0001) were favorable for DCAT plans.ConclusionsBoth Elements MBM and HA systems were able to generate high-quality plans in patients with up to 25 brain metastases. DCAT plans performed better in terms of normal brain sparing, especially in patients with more than ten lesions and limited total tumor volume.