VMAT Radiosurgery Research Articles

Evaluation of Plan Quality and Complexity for Automated Intracranial SBRT VMAT Treatment Plans

The purpose of this study was to evaluate the dosimetric quality and plan complexity of intracranial SBRT VMAT plans generated with an automated treatment planning system (TPS) compared to the standard conventional manually optimized VMAT plans. Ten clinical intracranial conventional SBRT VMAT plans manually generated using our standard TPS, (SE), were replanned using an automated VMAT radiosurgery TPS, Elements Cranial (EC). The plan target volume (PTV), OARs, prescription dose, fractionation, and beam arrangement remained constant between the corresponding plans from both systems. The PTV volume varied from 0.861cc to 40.022cc with prescription doses of 25Gy or 30Gy in 5 fractions. For each plan, PTV mean and max dose were recorded, as well as inverse Paddick conformity index (CI), gradient index (GI), and OAR mean and max doses. A Python script was used to calculate plan complexity metrics, including total MU, complexity metric, aperture irregularity metric, and modulation index total. Statistical significance of the comparisons was determined by performing a paired t-Test with α = 0.05. The results of plan quality and complexity metrics for each planning system are presented in Table 1. Dose conformality of the PTV showed no differences between plans generated with either planning system, with no statistical differences in the CI. The GI showed improvement for the automated plans, which appeared to be due to the system allowing higher PTV mean and max doses to achieve a sharper dose gradient from the target. There was a decrease in MU for the automated plans, which also correlated to statistically lower Complexity, Aperture Irregularity, and Modulation Index metrics. Differences in OAR mean and max doses between both systems were statistically insignificant. Clinically acceptable intracranial SBRT VMAT plans can be generated using an Automated TPS. Plan dosimetric quality with respect to PTV coverage and dose conformality, as well as OAR doses, were equivalent to manual plans. The automated plans were found to be less complex than manual plans, which may be related to the automated system allowing larger target dose inhomogeneity. While statistically significant differences were found between both systems, they may not be clinically relevant, and the differences could be related to the different planning techniques between systems.

HyperArc Planning for Benign Intracranial Pathologies: A Prospective Analysis on Plan Quality, Delivery, Control and Toxicity

<h3>Purpose/Objective(s)</h3> This study reviews a treatment planning system (TPS) that automates both treatment planning and delivery of single-isocenter VMAT radiosurgery (SRS). The TPS was intended for complex multi-metastasis cases, for which it generates high quality, rapidly-deliverable plans. The effectiveness of treating benign intracranial pathologies (BIP) with TPS was unknown. Under an IRB-approved prospective registry, we collected data on the treatment planning and delivery as well as clinical outcomes of BIP managed with SRS since deployment of TPS. <h3>Materials/Methods</h3> Patients included received SRS between October 2017 and November 2021 using TPS. Patients with less than 3 months follow-up (FU) were censored. For all targets, full prescription dose was normalized to ≥ 99% of target volume without additional PTV expansion. All treatments were delivered on a linear accelerator with 10MV flattening-filter free beam at 2400 MU/min with high-definition (2.5mm) multi-leaf collimator. Descriptive statistics related to SRS treatment, pathology, and prior therapy determined at the time of or prior to treatment were analyzed. Post-treatment imaging, toxicities, and standard pathology-specific outcomes were assessed during FU visits. Significant toxicity was defined as ≥ Grade 3 by CTCAE. <h3>Results</h3> 245 targets (min=0.1cc, max=58.9cc) in 235 patients (53.5% female, median age=59) were treated with TPS. The most common pathologies were meningiomas (134), AVMs (43), pituitary adenomas (30), and acoustic schwannomas (23). 45% of patients were treated due to recurrent, residual, or persistent disease after prior treatment with 15% having prior radiation. A majority (53.5%) were treated in a single fraction (12-22Gy), and 46.5% were treated with fractionated SRS (24-35Gy). A majority (74%) were treated with 3 arcs with median (MED) total treatment and beam-on time lasting 10.4 and 2.3 minutes, respectively. MED RTOG CI and Paddick GI were 1.12 and 3.28, respectively. MED FU was 1.1 years. Excluding AVMs, 11 of 202 (5.4%) benign tumors progressed on FU imaging. Among those that progressed, MED time to failure was 1.14 years. Of those, 9 were WHO grade 2+ meningiomas with prior surgery. Of all patients, significant CNS toxicity was reported in 13 (5.6%, G3=9, G4=4), most of whom had persistent cerebral edema after steroids. Of those with BIP near cochlea (> 3 Gy dose max) without severe hearing loss prior to SRS (n=65), 14% subjectively reported decreased hearing after SRS and 3.5% did not preserve hearing. Of those with BIP near the optics (> 3 Gy dose max, n=81), visual preservation was 100%. <h3>Conclusion</h3> Although developed for multi-metastasis SRS, TPS is capable of generating and efficiently delivering high quality plans characterized by excellent conformality and rapid fall-off. Early clinical outcomes appear congruent with historical controls.

PD-0942 Intrafraction error analysis of homemade mouth-bite masks in linac-based SRS for brain metastasis

Purpose or Objective To assess the intrafraction accuracy of a frameless stereotactic linac-based radiosurgery (SRS) for brain metastases (BM) using a homemade mouth-bite thermoplastic mask in combination with cone-beam computed tomography (CBCT) and six-degrees of freedom (6-DOF) couchtop. Materials and Methods Covid-19 restrictions resulted in significant delays in the supply of the dedicated devices for BM SRS. A frameless approach using a homemade mouth-bite thermoplastic mask was implemented to offer BM SRS in a period of limited mobility (figure 1). All patients were immobilized and treated at the same institution with 6 MV FFF VMAT radiosurgery, with a 2 mm isotropic expansion from the GTV to the PTV. Before treatment delivery, patients underwent a low-dose CBCT to check position accuracy. Through image co-registration, translational (x, y, z) and rotational errors (roll, pitch, and yaw) were determined. The 6-DOF couchtop was used to automatically relocate the patient with sub-millimetric precision. Immediately after irradiation, patients underwent a second CBCT to verify any translational or rotational errors occurring during therapy (intrafraction motion). $Φg Results From February 2020 to January 2021 sixteen patients (29 lesions) received BM SRS (14-21 Gy). The whole procedure, from the first CBCT scan to the end of irradiation and subsequent CBCT, required a median time of 9 minutes [6-13]. Mean translational error was 0.0 ± 0.3 mm [-0.7;0.9] in lateral direction, and -0.1 ± 0.5 mm [-1.4;1.0] in longitudinal direction. A 2.2 mm maximum shift was recorded on the vertical axis, nevertheless the mean translation error was 0.1 ± 0.6 mm. Roll, pitch and yaw registered a mean value of -0.1 ± 0.3° [-0.8;0.2], 0.0 ± 0.2° [-0.8;0.2], and -0.1 ± 0.3° [-0.8;0.4], respectively. The results are summarized in figure 2. Conclusion This study demonstrated that homemade mouth-bite thermoplastic masks combined with CBCT, 6-DOF couchtop, and fast FFF treatment delivery allow minimal intra-fraction uncertainties in BM SRS, confirming the accuracy of PTV margin definition. The results are comparable to the declared specifics of SRS dedicated commercial frameless mask, while improving patient's comfort compared to the invasive fixed frame. However, the moulding procedure requires improved RTT skills and expertise. Our findings show that SRS can be safely delivered in radiotherapy units without dedicated expensive installations, such as CyberKnife and Gamma Knife, thus reducing patient mobility according to Covid-19 restrictions.

Single isocenter SRS using CAVMAT offers improved robustness to commissioning and treatment delivery uncertainty compared to VMAT.

PurposeIn this study, we evaluate and compare single isocenter multiple target VMAT (SIMT) and Conformal Arc Informed VMAT (CAVMAT) radiosurgery's sensitivity to uncertainties in dosimetric leaf gap (DLG) and treatment delivery. CAVMAT is a novel planning technique that uses multiple target conformal arcs as the starting point for limited inverse VMAT optimization.MethodsAll VMAT and CAVMAT plans were recalculated with DLG values of 0.4, 0.8, and 1.2 mm. DLG effect on V6Gy[cc], V12Gy[cc], and V16Gy[cc], and target dose was evaluated. Plans were delivered to a Delta4 (ScandiDos, Madison, WI) phantom and gamma analysis performed with varying criteria. Log file analysis was performed to evaluate MLC positional error. Sixteen targets were delivered to a SRS MapCHECK (Sun Nuclear Corp., Melbourne, FL) to evaluate VMAT and CAVMAT's dose difference (DD) as a function of DLG.ResultsVMAT's average maximum and minimum target dose sensitivity to DLG was 9.08 ±3.50%/mm and 9.50 ± 3.30%/mm, compared to 3.20 ± 1.60%/mm and 4.72 ± 1.60%/mm for CAVMAT. For VMAT, V6Gy[cc], V12Gy[cc], and V16Gy[cc] sensitivity was 35.83 ± 9.50%/mm, 34.12 ± 6.60%/mm, and 39.23 ± 8.40%/mm. In comparison, CAVMAT's sensitivity was 23.19 ± 4.50%/mm, 22.45 ± 4.40%/mm, and 24.88 ± 4.90%/mm, respectively. Upon delivery to the Delta4, CAVMAT offered superior dose agreement compared to VMAT. For a 1%/1 mm gamma analysis, VMAT and CAVMAT had a passing rate of 94.53 ± 4.40% and 99.28 ± 1.70%, respectively. CAVMAT was more robust to DLG variation, with the SRS MapCHECK plans yielding an absolute average DD sensitivity of 2.99 ± 1.30%/mm compared to 5.07 ± 1.10%/mm for VMAT. Log files demonstrated minimal differences in MLC positional error for both techniques.ConclusionsCAVMAT remains robust to delivery uncertainties while offering a target dose sensitivity to DLG less than half that of VMAT, and 65% of that of VMAT for V6Gy[cc], V12Gy[cc], and V16Gy[cc]. The superior dose agreement and reduced sensitivity of CAVMAT to DLG uncertainties indicate promise as a robust alternative to VMAT for SIMT SRS.

RADT-36. PROSPECTIVELY ASSESSED TUMOR CONTROL AND TOXICITY OF BENIGN INTRACRANIAL PATHOLOGIES TREATED WITH AUTOMATED VMAT RADIOSURGERY – INITIAL 2 YEAR EXPERIENCE WITH FIRST 100 PATIENTS

Abstract BACKGROUND HyperArc is a treatment planning technology that automates treatment planning and delivery of single-isocenter VMAT radiosurgery (SRS). The technique generates high quality, rapidly deliverable plans. It is unknown whether HyperArc is effective for commonly-encountered, benign, intracranial conditions managed with SRS. Under IRB-approved prospective registry, we collected data on treatment planning/delivery, and clinical outcomes of non-malignant conditions managed with single-fraction or fractionated SRS since deployment in October 2017. METHODS Patients received either single-fraction or fractionated SRS with HyperArc™ (Varian Medical Systems) between October 2017 &amp; October 2019. Patients with &amp;lt; 3 months follow-up were censored. All patients treated received prescription dose to ≥ 99% of gross tumor volume without PTV expansion. All treatments were delivered on Varian Edge linac with 10MV flattening-filter free beam at 2400 MU/min with high-definition (2.5mm) multi-leaf collimator. Standard pathology-specific outcomes and toxicities were assessed. Significant CNS toxicity was defined as Grade 3 or higher event by CTCAE. RESULTS Total of 100 targets (min=0.13cc, max=58.9cc) were treated. 55 received single-fraction SRS (12-22Gy), two received 2-fraction fSRS boost (12Gy) following fractionated treatment, and 43 received 5-fraction fSRS (25-30Gy). The most common pathology was meningioma (n=55), followed by AVM (n=18), non-secretory pituitary adenoma (n=12), acoustic schwannoma (n=9), secretory pituitary adenoma (n=3), glomus tumor (n=2), pineocytoma (n=1), and paraganglioma (n=1). Follow-up ranged from 1.2 to 19.5 months (median 7.2). There were three local failures, all in atypical meningiomas. One patient in the cohort experienced ≥Gr3 toxicity. Each radiosurgery session used median of 3 arcs, with median treatment and beam-on time of 12.03 and 2.3 minutes. Plan quality was excellent; median RTOG conformity was 1.15, and median Paddick GI was 3.52. CONCLUSION Although HyperArc was developed for automated multiple-metastasis radiosurgery, we found it effective and efficient for benign intracranial indications too. Early clinical outcomes appear congruent with historical controls.

Use of a plastic scintillator detector for patient-specific quality assurance of VMAT SRS.

PurposeTo evaluate a scintillator detector for patient‐specific quality assurance of VMAT radiosurgery plans.MethodsThe detector was comprised of a 1 mm diameter, 1 mm high scintillator coupled to an acrylic optical fiber. Sixty VMAT SRS plans for treatment of single targets having sizes ranging from 3 mm to 30.2 mm equivalent diameter (median 16.3 mm) were selected. The plans were delivered to a 20 cm × 20 cm x 15 cm water equivalent plastic phantom having either the scintillator detector or radiochromic film at the center. Calibration films were obtained for each measurement session. The films were scanned and converted to dose using a 3‐channel technique.ResultsThe mean difference between scintillator and film was ‒0.45% (95% confidence interval ‒0.1% to 0.8%). For target equivalent diameter smaller than the median, the mean difference was 1.1% (95% confidence interval 0.5% to 1.7%). For targets larger than the median, the mean difference was ‒0.2% (95% confidence interval ‒0.7% to 0.1%). ConclusionsThe scintillator detector response is independent of target size for targets as small as 3 mm and is well‐suited for patient‐specific quality assurance of VMAT SRS plans. Further work is needed to evaluate the accuracy for VMAT plans that treat multiple targets using a single isocenter.

Feasibility of radiosurgery dosimetry using NIPAM 3D dosimeters and x-ray CT

We investigated the feasibility of using N-isopropylacrylamide (NIPAM) dosimeters with x-ray CT to verify radiosurgery dose. Dosimeters were prepared at one facility and shipped to a second facility for irradiation. A simulation CT was acquired and plans prepared for a 4 field box, and a 4 arc VMAT radiosurgery plan to 6 targets with 1cm diameter. Each dosimeter was aligned via CBCT and irradiated, followed by 5 diagnostic CTs acquired after >24 hours, which were averaged for analysis. Absolute dose calibration was applied and dose evaluated for both plans. Hounsfield Units were proportional to dose above 10-12Gy. For the 4-field box, mean difference between measured and predicted dose >10Gy was -0.13Gy ±1.69Gy and gamma index was <1 for 72% and 65% of voxels using a 5% / 1mm and 3% / 2mm criteria, respectively (threshold = 15Gy, global dose criteria). For the multifocal SRS case, mean dose within each target was within -0.14Gy± 0.55Gy of the expected value, and gamma index was < 1 for 94.0% and 99.5% of voxels, respectively (threshold = 15Gy). NIPAM based 3D dosimetry with x-ray CT is well suited for validating radiosurgery spatial alignment, as well as dose distributions when dose is above 10-12Gy.

EP-1209 First clinical results using HyperArcTM and Linac-based VMAT radiosurgery in brain metastases.

EP-1209 First clinical results using HyperArcTM and Linac-based VMAT radiosurgery in brain metastases.

32. Linac based VMAT radiosurgery for multiple brain lesions: comparison between a conventional multi-isocenter approach and a new dedicated mono-isocenter 4π technique (HyperArc™)

Purpose Linac based VMAT radiosurgery (SRS) of multiple brain lesions (MBL) is typically performed by a multiple-isocenter approach, i.e.one isocenter per lesion.Here we present the worldwide first experience with a new mono-isocenter technique with multiple non-coplanar arcs (HyperArc, Varian Inc.)in terms of a plan comparison with a multiple-isocenter approach. Methods From August to October 2017, 20 patients with MBL (mean 5, range 2–10) have been treated by HyperArc: prescribed doses ( D p ) were 18–25 Gy in single-fraction, and 21–27 Gy in three-fractions.Total PTV, defined by a 2 mm isotropic margin from each lesion, had mean size of 9.6 cm3 (range 0.5–27.9 cm3).HyperArc VMAT plans (HA), with 5 non-coplanar 180°-arcs (couch at 0°, ±45°, ±90°), and multiple-isocenter VMAT plans (RA), with 2 coplanar 360°-arcs per isocenter, were generated.100% D p at 98%PTV was prescribed, and D 2 % (PTV) D p was accepted.Constraints for 1(3) -fraction to the brainstem, D 0.5cc D 0.5cc V 12 and mean dose to the brain-minus-PTV, MU and overall treatment time (OTT) per fraction.OTT was measured for HA treatments, whereas estimated (3 min.for patient setup plus 5 min.for each CBCT per isocenter) for RA plans. Results As detailed in Table 1 , HA plans resulted in significantly improved CI ( p V 12 to the brain-minus-PTV (p = .023), MU (p D p isodose shells around the targets for the HA plans is depicted for an example patient.By contrast, no significant difference in terms of mean doses to the brain-minus-PTV resulted (p = .31). Conclusions For linac based VMAT-SRS of MBL, HyperArc plans assured a higher CI and a lower GI, a lower V 12 to the brain-minus-PTV, and a lower OTT than standard multiple-isocenter VMAT plans. Finally, all HyperArc treatments were completed within a typical 20 min. time slot.

PV-0469: Preliminary results of a phase i trial on VMAT radiosurgery in primary or oligometastatic cancer

PV-0469: Preliminary results of a phase i trial on VMAT radiosurgery in primary or oligometastatic cancer

EP-1695: VMAT radiosurgery boost after EBRT in oligometastatic patient with vertebral metastases

EP-1695: VMAT radiosurgery boost after EBRT in oligometastatic patient with vertebral metastases

SU‐G‐TeP4‐01: A High Resolution Pre‐Treatment VMAT QA Technique Based On EPID for Single Isocenter Multiple Mets Stereotactic Radiosurgery

Purpose:For multiple mets radiosurgery, it is advantageous to use VMAT with a single isocenter for the ease in planning and efficiency in delivery. Insightful pre‐treatment QA for these cases is difficult to obtain because (1) target size is often small and the same order of magnitude as the detector size for commercial array based VMAT pre‐treatment QA devices; and furthermore (2) targets are located away from central axis where the array detectors are located. In this study, we present and validate an in‐house developed VMAT QA technique that is capable of addressing these challenges.Methods:The VMAT plan is delivered on a Varian Truebeam STX with HDMLC. The MV cine images are converted to portal dose (PD) after calibration. The gantry and MU index encoded in each image are used to extract a sub‐arc from the plan to compute corresponding PD. A 3D matrix is constructed with the 3rd axis representing gantry angle for subsequent γ‐analysis. The EPID has a resolution of 0.8×0.8 mm2 and field size up to 40×30 cm2. Measurements were performed for 21 arcs from 4 patients. Average(range) number of mets is 7(4–9), with volume of 0.36(0.01–1.39)cc. Varian's integrated PD was compared.Results:In PD analysis with 3%, 3mm, and 5% in threshold, pass rate of γ&gt;1.0 is (99.6±0.3)%. Our EPID 3D analysis has the pass rate of (98.8±0.9)%, with additional criteria of 3° in angle‐to‐agreement. Projecting the 3D matrix along each axis, our analysis is reduced to 3 2D analyses, with one mimicking PD analysis at (99.0±0.9)%. Results on other planes are (99.5±0.4)% and (99.5±0.4)%, respectively. Additional criteria can be chosen to diagnose potential treatment abnormalities.Conclusion:We have developed an efficient EPID‐based QA technique for VMAT that has sufficient spatial and gantry angular resolution for use with single isocenter VMAT radiosurgery of multiple mets.

SU‐E‐T‐453: Image‐Guided Patient‐Specific Quality Assurance for Multi‐Target Single Isocenter Intracranial VMAT Radiosurgery

Purpose:To demonstrate a patient specific, image‐guided quality assurance method that tests both dosimetric and geometric accuracy for single‐isocenter multiple‐target VMAT radiosurgery (SIMT‐VMAT‐SRS)Method:We used a new film type, EBT‐XD (optimal range 0.4–40Gy), and an in‐house PMMA phantom having a coronal plane for film and a 0.125 cm3 ionization chamber (IC). The phantom contained fiducial features for kV image guided setup and for accurate film marking. Five patient plans with multiple targets sizes ranging from 3 to 21mm in diameter and prescribed doses from 14 to 18 Gy were selected. Two verification plans were generated for each case with the film plane passing through the center of the largest and smallest targets. For the four largest targets we obtained an IC measurement. For each case, a calibration film was irradiated using a custom designed step pattern. The films were scanned using a flatbed color scanner and converted to dose using the calibration film and the three channel calibration method. Image registration was performed between film and treatment planning system calculations to evaluate the geometric accuracy.Results:The mean registration vector had an average magnitude of 0.47 mm (range from 0.13mm to 0.64 mm). For the four largest targets, the mean ratio of the IC and film measurement to expected dose was 0.990 (range 0.968 to 1.009) and 1.032 (1.021 to 1.046), respectively. The fraction of pixels having gamma index &lt; 1 for criteria of 3%/3mm, 3%/2mm, 3%/1mm was 98.8%, 97.5% and 87.2% before geometric registration and 99.1%, 98.3% and 94.8% after registration.Conclusion:We have demonstrated an image‐guided QA method can assess both geometric and dosimetric accuracy. The phantom was positioned with sub‐millimeter accuracy. Absolute film dosimetry using EBT‐XD film was sufficiently accurate for assessment of dose to multi‐targets too small for IC measurement in SRS VMAT plans.

SU-E-T-291: Dosimetric Accuracy of Multitarget Single Isocenter Radiosurgery

Purpose: To evaluate the accuracy of single-isocenter multiple-target VMAT radiosurgery (SIMT-VMAT-SRS) by analysis of pre-treatment verification measurements. Methods: Our QA procedure used a phantom having a coronal plane for EDR2 film and a 0.125 cm3 ionization chamber. Film measurements were obtained for the largest and smallest targets for each plan. An ionization chamber measurement (ICM) was obtained for sufficiently large targets. Films were converted to dose using a patient-specific calibration curve and compared to treatment planning system calculations. Alignment error was estimated using image registration. The gamma index was calculated for 3%/3 and 3%/1 mm criteria. The median dose in the target region and, for plans having an ICM, the average dose in the central 5 mm was calculated. Results: The average equivalent target diameter of the 48 targets was 15 mm (3–43 mm). Twenty of the 24 plans had an ICM for the plan corresponding to the largest target (diameter 11–43 mm) with a mean ratio of chamber reading to expected dose (ED) and the mean ratio of film to ED (averaged over the central 5 mm) was 1.001 (0.025 SD) and 1.000 (0.029 SD), respectively. For all plans, the mean film to ED (from the median dose in the target region) was 0.997 (0.027 SD). The mean registration vector was (0.15,0.29) mm, with an average magnitude of 0.96 mm. Before (after) registration, the average fraction of pixels having gamma < 1 was 99.3% (99.6%) and 89.1% (97.6%) for 3%/3mm and 3%/1mm, respectively. Conclusion: Our results demonstrate dosimetric accuracy of SIMT-VMAT-SRS for targets as small as 3 mm. Film dosimetry provides accurate assessment of the absolute dose delivered to targets too small for an ionization chamber measurement; however, the relatively large registration vector indicates that image-guidance should replace laser-based setup for patient-specific evaluation of geometric accuracy.

Tumor Volume Threshold for Achieving Improved Conformity Index in VMAT and Gamma Knife Stereotactic Radiosurgery for Vestibular Schwannoma

Tumor Volume Threshold for Achieving Improved Conformity Index in VMAT and Gamma Knife Stereotactic Radiosurgery for Vestibular Schwannoma

EP-1571: VMAT radiosurgery: A planning study to reduce healthy brain dose

EP-1571: VMAT radiosurgery: A planning study to reduce healthy brain dose

PO-0841: VMAT radiosurgery with flattening filter free photon beams for benign brain lesions in comparison to GammaKnife

PO-0841: VMAT radiosurgery with flattening filter free photon beams for benign brain lesions in comparison to GammaKnife

Plan quality and treatment planning technique for single isocenter cranial radiosurgery with volumetric modulated arc therapy

PurposeTo demonstrate plan quality and provide a practical, systematic approach to the treatment planning technique for single isocenter cranial radiosurgery with volumetric modulated arc therapy (VMAT; RapidArc, Varian Medical systems, Palo Alto, CA). Methods and materialsFifteen patients with 1 or more brain metastases underwent single isocenter VMAT radiosurgery. All plans were normalized to deliver 100% of the prescription dose to 99%-100% of the target volume. All targets per plan were treated to the same dose. Plans were created with dose control tuning structures surrounding targets to maximize conformity and dose gradient. Plan quality was evaluated by calculation of conformity index (CI = 100% isodose volume/target volume) and homogeneity index (HI = maximum dose/prescription dose) scores for each target and a Paddick gradient index (GI = 50% isodose volume/100% isodose volume) score for each plan. ResultsThe median number of targets per patient was 2 (range, 1-5). The median number of non-coplanar arcs utilized per plan was 2 (range, 1- 4). Single target plans were created with 1 or 2 non-coplanar arcs while multitarget plans utilized 2 to 4 non-coplanar arcs. Prescription doses ranged from 5-16 Gy in 1-5 fractions. The mean conformity index was 1.12 (± SD, 0.13) and the mean HI was 1.44 (± SD, 0.11) for all targets. The mean GI per plan was 3.34 (± SD, 0.42). ConclusionsWe have outlined a practical approach to cranial radiosurgery treatment planning using the single isocenter VMAT platform. One or 2 arc single isocenter plans are often adequate for treatment of single targets, while 2-4 arcs may be more advantageous for multiple targets. Given the high plan quality and extreme clinical efficiency, this single isocenter VMAT approach will continue to become more prevalent for linac-based radiosurgical treatment of 1 or more intracranial targets and will likely replace multiple isocenter techniques.