HyperArc Plans Research Articles

Optimizing normal tissue objectives (NTO) in eclipse treatment planning system (TPS) for stereotactic treatment of multiple brain metastases using non-coplanar RapidArc and comparison with HyperArc techniques.

To optimize NTO parameters in non-coplanar RapidArc (RA) stereotactic radiosurgery (SRS) for multiple brain metastases and compare them with HyperArc (HA) plans. Thirty patients with multiple brain metastases, receiving 21Gy prescriptions, were retrospectively enrolled, with lesions ranging from two to eight and volumes between 0.27 and 10.56 cm3. Non-coplanar RapidArc plans utilized manual NTO (RA-mNTO) with varying dose fall-off values (0.1mm-1, 0.5mm-1, 1.0mm-1, 2.0mm-1, 3.0mm-1) and end doses (50%, 25% & 10%). Additionally, two HyperArc plans were generated: HA-ALDO used Automatic Lower Dose Objectives with SRS NTO, while HA-mNTO used the same beam geometry with manual NTO parameters optimized from RA-mNTO plans. TrueBeam with High-Definition Multi-leaf Collimators (HDMLC), 6 MV Flattening Filter Free (FFF) Beam at a maximum dose rate of 1400 MU/min, and Eclipse version 16.1 TPS were used. Plans were assessed for Paddick Conformity Index (CI), Gradient Index (GI), Homogeneity Index (HI), normal brain doses (V18Gy, V15Gy, and V12Gy), Monitor Units (MUs), and delivery accuracy using aS1200 Digital Megavolt Imager (DMI) with 2%/2mm gamma criteria. Statistical analysis utilized integrated scoring and the Wilcoxon signed-rank test. RA-mNTO plans with 0.5mm⁻1 dose fall-off and 10% end-dose showed superior dosimetric outcomes: CI (0.85 ± 0.08), GI (3.63 ± 0.87), and HI (0.36 ± 0.06) compared to HA-ALDO (CI 0.84 ± 0.09, GI: 3.97 ± 0.85, HI: 0.39 ± 0.07) and HA-mNTO (CI 0.83 ± 0.08, GI: 3.60 ± 0.93, HI: 0.40 ± 0.06). MUs were comparable: RA-mNTO (9679 ± 1882), HA-ALDO (9509 ± 1315), and higher for HA-mNTO (10,457 ± 1980). RA-mNTO plans exhibited significantly lower normal brain doses (V18Gy: 1.78 ± 1.23, V15Gy: 3.54 ± 2.37, V12Gy: 6.21 ± 4.09) compared to HA-ALDO (V18Gy: 2.02 ± 1.34, V15Gy: 4.09 ± 2.66, V12Gy: 7.15 ± 4.56) and HA-mNTO (V18Gy: 1.85 ± 1.20, V15Gy: 3.68 ± 2.33, V12Gy: 6.36 ± 3.97). All techniques achieved > 98% gamma pass rate. Non-coplanar RA plans with optimized mNTO settings outperformed HyperArc plans in all studied dosimetric parameters for SRS treatment of multiple brain metastases.

Dosimetric Comparison between the HyperArc and Conventional VMAT in Cervical Spine Stereotactic Radiosurgery.

Background: This research aims to evaluate the usability of the HyperArc (HA) technique in stereotactic radiosurgery for cervical spine metastasis by comparing the dosimetry of the target and organs at risk, specifically the spinal cord, between HA and VMAT and conventional volumetric modulated arc therapy (VMAT). Methods: A RANDO® phantom and QFix EncompassTM and support system were used to simulate three target types (A, B, and C) based on RTOG0631 guidelines. Treatment plans included one VMAT and two HyperArc techniques with different SRS NTO values (100 and 250). Dosimetric parameters such as conformity index (CI), homogeneity index (HI), R50, and spinal cord sparing were analyzed. Gamma analysis was performed using portal dosimetry to validate the dose delivery accuracy. Results: HyperArc plans demonstrated higher conformity, sharper dose fall-off, and improved quality assurance (QA) results compared to VMAT plans. HA with SRS NTO 250 showed even better results in terms of conformity, dose fall-off, and spinal cord dose reduction (V10 and Dmax) compared to HA with SRS NTO 100. Although the mean gamma passing rates were slightly lower, all plans achieved rates above 95%. Conclusion: The findings suggest that HA provides superior dosimetric benefits over VMAT and could be effectively utilized for cervical spine radiation therapy.

224: Targeting accuracy of image-guided HyperArc plans using resampled planning CT and CBCT images

224: Targeting accuracy of image-guided HyperArc plans using resampled planning CT and CBCT images

Dosimetric comparison of HyperArc and InCise MLC-based CyberKnife plans in treating single and multiple brain metastases.

This study aimed to compare the dosimetric attributes of two multi-leaf collimator based techniques, HyperArc and Incise CyberKnife, in the treatment of brain metastases. 17 cases of brain metastases were selected including 6 patients of single lesion and 11 patients of multiple lesions. Treatment plans of HyperArc and CyberKnife were designed in Eclipse 15.5 and Precision 1.0, respectively, and transferred to Velocity 3.2 for comparison. HyperArc plans provided superior Conformity Index (0.91±0.06vs. 0.77±0.07, p<0.01) with reduced dose distribution in organs at risk (Dmax, p<0.05) and lower normal tissue exposure (V4Gy-V20Gy, p<0.05) in contrast to CyberKnife plans, although the Gradient Indexes were similar. CyberKnife plans showed higher Homogeneity Index (1.54±0.17vs. 1.39±0.09, p<0.05) and increased D2% and D50% in the target (p<0.05). Additionally, HyperArc plans had significantly fewer Monitor Units (MUs) and beam-on time (p<0.01). HyperArc plans demonstrated superior performance compared with MLC-based CyberKnife plans in terms of conformity and the sparing of critical organs and normal tissues, although no significant difference in GI outcomes was noted. Conversely, CyberKnife plans achieved a higher target dose and HI. The study suggests that HyperArc is more efficient and particularly suitable for treating larger lesions in brain metastases.

HyperArc performance in radiotherapy and its correlations with number and volume of multiple brain metastases

ObjectiveTo assess the performance and advantages of HyperArc for radiotherapy of multiple brain metastases with dosimetric parameters with respect to coplanar volumetric modulated arc radiotherapy (c-VMAT), and characterize implicit correlations between tumor features and dosimetric parameters. MethodsThis retrospective study involved 40 patients with multiple brain metastases (4–16 tumors, 12.8–240.8 cm3) who received simultaneous radiotherapy at the Department of Radiation Oncology, Shenzhen People's Hospital from January 2019 to December 2022. Both HyperArc and c-VMAT plans were designed by the same and qualified physicist using the Eclipse system with Truebeam. A single isocenter and a 6 ​MV flattening filter-free (6FFF) photon beam were used for radiotherapy of multiple brain metastases in each plan. Dosimetric parameters of tumors and organs at risk (OARs) were compared between HyperArc and c-VMAT plans. Correlations between tumor features (number and volume) and dosimetric parameters were revealed and analyzed. Furthermore, monitor units (MUs) of both plan types were recorded to assess rays utilization and delivery efficiency. ResultsCompared to c-VMAT plans, HyperArc plans achieved higher maximum dose (Dmax) (5.23%, t ​= ​7.87, P ​< ​0.01), but lower minimum dose (Dmin) (3.94%, t ​= ​−2.12, P ​= ​0.04) and mean dose (Dmean) (1.05%, t ​= ​−3.29, P < ​0.01) for planning gross tumor volumes (PGTVs). The conformity index (CI), homogeneity index (HI), gradient index (GI) and R50% of PGTVs with HyperArc were better than those with c-VMAT, with the improvements of 20.78%, 1.68%, 19.83% and 36.20%, respectively (P ​< ​0.01). The dosimetric parameters of OARs were significantly improved in HyperArc plans compared to c-VMAT plans. Specifically, the Dmax and the Dmean to the brainstem decreased by 16.14% and 11.37%, respectively. The Dmax for eye_L decreased by 16.88%, for eye_R decreased by 11.67%, for optical nerve_L decreased by 12.56 ​%, and for chiasm decreased by 18.12%. Few correlations were observed between the differences of CI/HI/GI/R50% and the number of PGTVs between the two plan types. Whereas, regression analysis indicated that the differences of CI/ GI/ R50% were negatively correlated with the volume of PGTVs, respectively. Moreover, although HyperArc plans reduced the MUs by 4.74 ​% compared to c-VMAT, no significant difference was observed (P ​> ​0.05). ConclusionsThis study demonstrates the promising performance of HyperArc for radiotherapy of multiple brain metastases, including better dose conformity for the tumors, more rapid dose drop and less dose spillage outside the tumors area, effective reduction of dose bridges among close tumors, and sparing OARs. It also reveals the correlations between the number or volume of tumors and dose parameters, which can help optimize the use of HyperArc and predict clinical benefits.

Plan quality assessment of modern radiosurgery technologies in the treatment of multiple brain metastases

Stereotactic radiosurgery (SRS) of multiple brain metastases has evolved over the last 40 years allowing centres to treat an increasing number of brain metastases in a single treatment fraction. HyperArcTM planning optimisation technique is one such development that streamlines the treatment of multiple metastases with a single isocentre. Several studies have investigated the plan quality of HyperArc compared to CyberKnife or Gamma Knife, however there are limited number of studies that include all three modalities. It is the aim of this study to provide an assessment of plan quality between the three SRS platforms across ten patients with multiple brain metastases ranging from three to eight metastases per patient. Strict planning workflows were established to avoid bias towards any particular treatment platform. Plan quality was assessed through dose to organs at risk, Paddick conformity index (PCI), gradient index (GI), global efficiency index (Gη) and dose to normal brain tissue. Results from this study found mean PCI observed across Gamma Knife plans was significantly lower than HyperArc and CyberKnife. HyperArc plans observed significantly shorter beam-on times which were 10 to 20 times faster than CyberKnife and Gamma Knife plans. Gamma Knife and CyberKnife were found to produce plans with significantly superior GI, global efficiency index and the volume of healthy brain receiving greater than 12 Gy (V12Gy) when compared to HyperArc plans. Lesion volume was seen to influence the relative difference in dose metrics between systems. The study revealed that all three treatment modalities produced high quality plans for the SRS treatment of multiple brain metastases, each with respective benefits and limitations.

Dose-Painting Linear Accelerator Radiosurgery of Glomus Jugulare With Dosimetric Comparison to Gamma Knife.

Objectives In this study, we outline our rationale for delivering a dose of ≥15 Gy in stereotactic radiosurgery (SRS) of glomus jugulare tumor (GJT) while ensuring the avoidance of complications associated with doses >13 Gy to the facial nerve. To avoid such complications, we initially utilized the Gamma Knife Perfexion (GK) system (Elekta Instrument AB, Stockholm, Sweden) at our institution but encountered challenges related to lengthy treatment times and difficulty in sculpting doses to minimize doses to spare the facial nerve. As a potential solution, we propose the use of HyperArc (Varian Medical Systems, Palo Alto, CA), a newly developed automated delivery platform for linear accelerator (LINAC)-based SRS. HyperArc offers the potential for faster treatment and more complex shaping of the radiotherapy dose with multiple arcs and multi-leaf collimators. Methods We retrospectively reviewed nine cases of patients with GJT treated with HyperArc. Patients' demographic and treatment data were collected. Additionally, simulated GK treatment plans were created and compared with HyperArc plans to assess time savings, PTV coverage, and plan quality. Results One male and eight female patients, with a mean age of 63.9 years, were included. Treatments were delivered on average in 29 minutes, achieving 95-100% of the tumor while limiting the facial nerve to <13 Gy. Treatments replanned using our GK system could achieve only 92-99% tumor coverage while respecting facial nerve constraints, with average treatment times of 180 minutes. Comparable plan quality parameters were attained with both modalities. Conclusions The HyperArc system provides a qualitatively satisfactory and rapid treatment delivery of a highly sculpted radiotherapy dose to maximize tumor coverage and minimize facial nerve complications.

Stereotactic radiotherapy of intracranial tumor beds on a ring-mounted Halcyon LINAC.

This study sought to evaluate the feasibility and efficacy of the Halcyon Ring Delivery System (RDS) for delivering stereotactic radiotherapy (SRT) treatments for intracranial tumors beds. Ten previously treated brain SRT patients for 30Gy in five fractions with non-coplanar HyperArc plans on TrueBeam (6MV-FFF) were replanned on Halcyon (6MV-FFF) using the same number of arcs and Eclipse's AcurosXB dose engine. Plan quality evaluation metrics per SRT protocol included: PTV coverage, GTV dose (minimum and mean), target conformity indices (CI), heterogeneity index (HI), gradient index (GI), maximum dose 2cm away from the PTV (D2cm), and doses to organs-at-risk (OAR). Additionally, patient-specific quality assurance (QA) results and beam-on-time (BOT) were analyzed. The Halcyon RDS provided highly conformal SRT plans for intracranial tumor beds with similar dose to target. When benchmarked against clinically delivered HyperArc plans, target coverage, CI(s) and HI were statistically similar. The Halcyon plans saw no statistical difference in maximum OAR doses to the brainstem, spinal cord, and cochlea. Due to the machine's coplanar geometry, the Halcyon plans showed a decrease in optic pathway dose (0.75Gy vs. 2.08Gy, p=0.029). Overall, Halcyon's coplanar geometry resulted in a larger GI (3.33vs. 2.72, p=0.008) and a larger D2cm (39.59%vs. 29.07%, p<0.001). In this cohort, multiple cases had the PTV and the optic pathway in the same axial plane. In one such instance, the PTV was<2cm away from the optic pathway but even at this close proximity OAR, Halcyon still adequately spared the optic pathway. Additionally, the Halcyon's geometry provided slightly larger amount of normal brain dose receiving 24.4Gy (8.99 cc vs. 7.36 cc) and 28.8Gy (2.9 cc vs. 2.5 cc), although statistically insignificant. The Halcyon plans achieved similar delivery accuracy, quantified by patient-specific QA results evaluated with a 2%/2mm gamma criteria (99.42%vs. 99.70%). For both plans, independent Monte Carlo second checks calculation agreed within 1%. Average Halcyon BOT was slightly higher by 0.35min (p=0.045), however, due to the one-step patient set-up and verification overall estimated treatment times on Halcyon were lower compared to HyperArc treatments (7.61min vs. 10.26min, p<0.001). When benchmarked against clinically delivered HyperArc treatments, the Halcyon brain SRT plans provided similar plan quality and delivery accuracy but achieved faster overall treatment times. We have started treating select brain SRT patients on the Halcyon RDS for patients having tumor beds greater than 1cm in diameter with the closest OAR distance of greater than 2cm away from the target. We recommend other clinics to consider commissioning SRT treatments on their Halcyon systems-allowing including remote Halcyon-only clinics to provide exceptionally high-quality therapeutic brain SRT treatments to an otherwise underserved patient cohort.

Dosimetric effects of rotational errors for single isocenter multiple targets in HyperArc plans: A phantom and retrospective imaging analysis study.

This study uses a phantom to investigate the dosimetric impact of rotational setup errors for Single Isocenter Multiple Targets (SIMT) HyperArc plans. Additionally, it evaluates intra-fractional rotational setup errors in patients treated with Encompass immobilization system. The Varian HyperArc system (Varian Medical systems) was used to create plans targeting spherical PTVs with diameters of 5, 10, and 15mm and with offsets of 1.3-5.3cm from the isocenter. Dosimetric parameters, including mean and maximum dose, D99% and D95% were evaluated for various rotational setup errors ranging from 0.5° to 2° for the PTVs and certain CTVs created within PTVs. These rotational errors were applied in an order and direction that resulted in the maximum displacement of targets. The rotation was applied both uniformly around all three axes and individually around each axis. Furthermore, to link the findings to actual treatment scenarios, the intra-fractional rotational setup errors were obtained for stereotactic cranial patients treated with the Encompass system using CBCT images acquired during treatments. The maximum displacement of 2.7mm was observed for targets located at 4.4 and 4.5cm from the isocenter with rotational setup errors of 2°. The dose reduction for D99% values corresponding to this displacement were about 50%, 40%, and 30% for PTVs with diameters of 5, 10, and 15mm, respectively. Both D99% and D95% showed a consistent trend of dose reduction across various rotational errors and PTV volumes. While the maximum dose remained consistent for different targets with various rotational errors, the mean dose decreased by approximately 25%, 12%, and 6% for PTVs with diameters of 5, 10, and 15cm, respectively, with rotational errors of 2°. In addition, by analyzing CBCT images, the absolute mean rotational setup errors obtained during treatment with Encompass for pitch, roll, and yaw were 0.17°±0.13°, 0.11°±0.10°, and 0.12°±0.10° respectively. This data, combined with existing studies, suggest that a 0.5° rotational setup error is a safe choice to consider for calculating additional PTV margin to ensure adequate CTV coverage. Therefore, the assessment of maximum displacement and dosimetric parameters in this study, for a 0.5° rotational error, highlights the need for an additional 0.7mm PTV margin for targets positioned at distances of 4.4cm or greater from the isocenter. For SIMT Plans, a 0.5° rotational setup error is recommended as a basis for calculating additional PTV margins to ensure adequate CTV coverage when using the Encompass system.

Whole-brain radiotherapy with hippocampus sparing and simultaneous integrated boost to metastases: A plan quality comparison study between Ethos, HyperArc, VMAT and Tomotherapy

This study provides a concise and structured overview of a dosimetric comparison study conducted to assess the feasibility and effectiveness of 4 advanced radiotherapy techniques in treating brain metastases with hippocampus sparing and simultaneous integrated boost (HS-WBRT+SIB). Eleven patients with brain metastases previously treated with radiotherapy were included in the study. Planning CT scans with 2 mm slice thickness and MR imaging were used for contouring and dose prescription. The bilateral hippocampus and other organs at risk (OARs) were automatically contoured, and hippocampal avoidance regions (HAR) were defined as a 7 mm 3D expansion around the hippocampus. Gross tumor volume for each metastasis (GTVmet) and planning target volume for metastases (PTVmet) were delineated. The whole-brain CTV (CTVWB) and planning target volume for whole brain (PTVWB) were defined accordingly. Treatment planning and optimization were conducted using state-of-the-art radiotherapy techniques: Ethos, HyperArc, VMAT, and Tomotherapy. Tomotherapy achieved the highest D98% for PTVmet, indicating the best metastasis coverage. HyperArc plans showed the highest D98% for PTVWB, suggesting superior whole-brain coverage. Tomotherapy demonstrated significantly lower D98%, D2%, and Dmean values for the hippocampus, indicating its superiority in sparing the hippocampus. VMAT resulted in the lowest D2% values for the eyes, optic nerves, brainstem, and hypophysis, showing the best sparing of these critical structures. Tomotherapy consistently achieved lower Dmean values for parotids, oral cavity, and lips compared to the other techniques. The dosimetric comparison revealed distinct strengths and weaknesses for each radiotherapy technique. Tomotherapy excelled in sparing the hippocampus, while VMAT showed promise in sparing OARs. HyperArc plans demonstrated the best overall whole-brain coverage. These findings should guide clinicians in selecting the most suitable technique based on patient characteristics and institutional resources.

Two novel stereotactic radiotherapy methods for locally advanced, previously irradiated head and neck cancers patients

To determine the feasibility and utility of conebeam CT-guided stereotactic radiotherapy for locally recurrent, previously irradiated head and neck cancer (HNC) patients on the Halcyon, a ring delivery system (RDS). This research aims to quantify plan quality, treatment delivery accuracy, and overall efficacy by comparing against novel clinical TrueBeam HyperArc method. Ten recurrent HNC patients who were treated at our institution on TrueBeam (6MV-FFF) for 30 to 40 Gy in 3 to 5 fractions with noncoplanar HyperArc plans were re-planned on Halcyon (6MV-FFF). These plans were re-planned with the same Acuros-based dose engine. Additionally, we used site-specific full/partial coplanar VMAT arcs. PTV coverage, mean dose to GTV, maximum dose to organs-at-risk (OAR), beam-on time (BOT), and quality assurance (QA) results were investigated and compared. Halcyon provided highly conformal HNC SRT plans with slightly superior mean PTVD99 coverage (96.7% vs 95.5%, p = 0.071), and slightly lower mean GTV dose (37.8 Gy vs 38.2 Gy, p = 0.241) when compared to the HyperArc plans. Differences in plan conformality and maximum dose to OARs were statistically insignificant. Due to Halcyon's coplanar geometry, D2cm was significantly higher (p = 0.001) but Halcyon did result in a reduced normal brain dose by 1 Gy on average and up to 5.2 Gy in some cases. Halcyon provided similar patient-specific QA pass rates with a 2%/2mm gamma criteria (98.2% vs 98.5%) and independent in-house Monte Carlo second check results (97.7% vs 98.2%), suggesting identical treatment delivery accuracy. Halcyon plans resulted in slightly longer beam-on time (3.16 vs 2.30 minutes, p = 0.010), however door-to-door patient time is expected to be <10 minutes. Compared to clinical TrueBeam HyperArc, Halcyon SRT plans provided similar plan quality and treatment delivery accuracy with a potentially faster overall treatment using fully automated patient setup and verification. Rapid delivery of recurrent HNC SRT may reduce intrafraction motion errors while also improving patient compliance and comfort. To provide high-quality of HNC SRT similar to HyperArc, we recommend Halcyon users consider commissioning this novel method. This method will be useful for remote and underserved patient cohorts including Halcyon-only clinics as well.

Feasibility and Safety of Single-Isocenter/Multi-Lesion (SIML) HyperArc Brain SRT: Clinical Implementation and Early Outcomes

Patients with multiple brain metastases may not tolerate relatively longer treatment times for traditional stereotactic radiation therapy (SRT) with individual isocenter plans for each lesion due to discomfort or co-morbidities. SRT using a single-isocenter/multi-lesion (SIML) HyperArc volumetric modulated arc therapy (VMAT) plan with flattening filter free (FFF) beam could significantly shorten overall treatment time, and improve patient comfort, compliance, and clinic efficiency. We report early clinical results of treating multiple brain metastases with SIML HyperArc SRT. Twenty-three patients with multiple brain metastatic tumors (range, 2-9 lesions; total treated lesions, n = 96) were simulated using Encompass support and Q-fix mask, and treated with a highly-conformal SIML VMAT SRT plans via non-coplanar HyperArc geometry. Mean tumor distance to isocenter was 5.3 cm, maximum up to 7 cm. Common prescriptions were 25-30 Gy/5 fractions, 24-27 Gy/3 fractions, and 20 Gy/1 fraction prescribed to each planning target volume (PTV) using 2 mm margin around standard gross tumor volume (GTV) delineated on contrasted enhanced MP-RAGE MRI fusion. Acuros dose calculation for 6MV-FFF beam was used for tissue heterogeneity corrections. Alliance A071801 criteria was used for dose constraints to organs at risk (OAR) and target conformality. Treatment was delivered every other day with CBCT-guidance, adjustments made with 6DOF couch corrections on a medical linear accelerator, and treatment delivery time within 15 minutes. Local control rates were reported, and toxicity profile rated based on CTCAE v5.0 for brain radionecrosis, optic neuropathy, and brainstem dysfunction. All plans met Alliance A071801 requirements for each tumor coverage, dose to OAR including optic apparatus, brainstem, and spinal cord. Mean GTV and PTV volume were 9.4 cc (range, 0.3-54.8 cc) and 16.13 cc (range, 1.0-80.2 cc). Patient-specific quality assurance results were 98.3% for gamma passing criteria of 2%/2mm. Independent in-house Monte Carlo physics second check agreed with HyperArc plans by ±3.0%. Mean follow up was 6 months (range, 0.0-18.6 months). Of the 23 patients treated, 17 (74%) had post-treatment MRI imaging to assess local control and toxicity. Local control was achieved in 69/73 (95%) of treated and followed lesions. CTCAE grade 2 radionecrosis occurred in 2 patients and were managed with dexamethasone. No CTCAE grade 3+ events of radionecrosis, optic pathway dysfunction, or brainstem toxicity were observed. SIML HyperArc Brain SRT for multiple brain metastases has excellent local control and low toxicity profile in our patients. It can significantly reduce treatment delivery time as compared to traditional multiple-isocenter brain SRT or chronologically separate treatment courses and thus, help to improve patient comfort, compliance, ease of care, and clinic workflow. Longer median follow up of SIML brain SRT on larger patient cohort is warranted.

Dosimetric comparison between RapidArc and HyperArc in hippocampal-sparing whole-brain radiotherapy with a simultaneous integrated boost

The HyperArc technique is known for generating high-quality radiosurgical treatment plans for intracranial lesions or hippocampal-sparing whole-brain radiotherapy (WBRT). However, there is no reported feasibility of using the HyperArc technique in hippocampal-sparing WBRT with a simultaneous integrated boost (SIB). This study aimed to compare dosimetric parameters of 2 commercially-available volumetric-modulated arc radiotherapy techniques, HyperArc and RapidArc, when using hippocampal-sparing WBRT with a SIB to treat brain metastases.Treatment plans using HyperArc and RapidArc techniques were generated retrospectively for 19 previously treated patients (1 to 3 brain metastases). The planning target volumes for the whole brain (excluding the hippocampal avoidance region; PTVWB) and metastases (PTVmet) were prescribed 25 and 45 Gy, respectively, in 10 fractions. Each plan included homogeneous and inhomogeneous delivery to the PTVmet. Dosimetric parameters for the target (conformity index [CI], homogeneity index [HI], target coverage [D95%]), and nontarget organs at risk were compared for the HyperArc and RapidArc plans.For homogeneous delivery, dosimetric parameters, including mean CI, HI, and target coverage in PTVWB and PTVmet, were superior for HyperArc than RapidArc plans (all p < 0.01). The PTVWB and PTVmet target coverage for HyperArc plans was significantly greater than for RapidArc plans (96.17% vs 93.38%, p < 0.01; 94.02% vs 92.21%, p < 0.01, respectively). HyperArc plans had significantly lower mean hippocampal Dmax and Dmin values than RapidArc plans (Dmax: 15.53 Gy vs, 16.71 Gy, p < 0.01; Dmin: 8.33 Gy vs 8.93 Gy, p < 0.01, respectively). Similarly, inhomogeneous delivery of hyperArc produced a superior target and lower hippocampal dosimetric parameters than RapidArc, except for the HI of PTVmet (all p < 0.01).HyperArc generated superior conformity and target coverage with lower hippocampal doses than RapidArc. HyperArc could be an attractive technique for hippocampal-sparing WBRT with an SIB.

Comparison between the HyperArc™ technique and the CyberKnife® technique for stereotactic treatment of brain metastases

PurposeThe purpose of this study was to compare the planimetric capacities between HyperArc™-based stereotactic radiosurgery and robotic radiosurgery system-based planning using CyberKnife® M6 for single and multiple cranial metastases. Materials and methodsWe evaluated 51 treatment plans for cranial metastases, including 30 patients with a single lesion and 21 patients with multiple lesions, treated with the CyberKnife® M6. These treatment plans were optimized using the HyperArc™ (HA) system with the TrueBeam. The comparison of the quality of the treatment plans between the two treatment techniques (CyberKnife and HyperArc) was performed using the Eclipse treatment planning system. Dosimetric parameters were compared for target volumes and organs at risk. ResultsCoverage of the target volumes was equivalent between the two techniques, whereas median Paddick conformity index and median gradient index for all target volumes were 0.9 and 3.4, respectively for HyperArc plans, and 0.8 and 4.5 for CyberKnife plans (P<0.001). The median dose of gross tumor volume (GTV) for HyperArc and CyberKnife plans were 28.4 and 28.8, respectively. Total brain V18Gy and V12Gy-GTVs were 11cm3 and 20.2cm3 for HyperArc plans versus 18cm3 and 34.1cm3 for CyberKnife plans (P<0.001). ConclusionThe HyperArc provided better brain sparing, with a significant reduction in V12Gy and V18Gy, associated with a lower gradient index, whereas the CyberKnife gave a higher median GTV dose. The HyperArc technique seems to be more appropriate for multiple cranial metastases and for large single metastatic lesions.

Dose reduction of hippocampus using HyperArc planning in postoperative radiotherapy for primary brain tumors.

To compare dosimetric parameters for the hippocampus, organs at risk (OARs), and targets of volumetric modulated arc therapy (VMAT), noncoplanar VMAT (NC-VMAT), and HyperArc (HA) plans in patients undergoing postoperative radiotherapy for primary brain tumors. For 20 patients, HA plans were generated to deliver 40.05 to 60 Gy for the planning target volume (PTV). In addition, doses for the hippocampus and OARs were minimized. The VMAT and NC-VMAT plans were retrospectively generated using the same optimization parameters as those in the HA plans. For the hippocampus, the equivalent dose to be administered in 2 Gy fractions (EQD2) was calculated assuming α/β = 2. Dosimetric parameters for the PTV, hippocampus, and OARs in the VMAT, NC-VMAT, and HA plans were compared. For PTV, the HA plans provided significantly lower Dmax and D1% than the VMAT and NC-VMAT plans (p < 0.05), whereas the D99% and Dmin were significantly higher (p < 0.05). For the contralateral hippocampus, the dosimetric parameters in the HA plans (8.1 ± 9.6, 6.5 ± 7.2, 5.6 ± 5.8, and 4.8 ± 4.7 Gy for D20%, D40%, D60% and D80%, respectively) were significantly smaller (p < 0.05) than those in the VMAT and NC-VMAT plans. Except for the optic chiasm, the Dmax in the HA plans (brainstem, lens, optic nerves, and retinas) was the smallest (p < 0.05). In addition, the doses in the HA plans for the brain and skin were the smallest (p < 0.05) among the 3 plans. HA planning, instead of coplanar and noncoplanar VMAT, significantly reduces the dosage to which the contralateral hippocampus as well as other OARs are exposed without compromising on target coverage.

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.

Two Novel Irradiation Methods for Angiosarcoma of Total Scalp Irradiation

<h3>Purpose/Objective(s)</h3> Due to large, irregular and superficial spread of the complex target, conventional radiotherapy via photon and electron beams matching technique for angiosarcoma of total scalp irradiation (TSI) presents major technical and dosimetric challenges. To increase superficial target coverage, reduce normal brain dose, and eliminate the difficulty of patient set up and fields matching, we propose two novel irradiation methods: fully-automated non-coplanar HyperArc VMAT and co-planar Halcyon delivery platform utilizing a 3D-printed 1 cm scalp bolus. <h3>Materials/Methods</h3> The technical and dosimetric performance of the proposed two novel methods was simulated using nine previously treated TSI patients in our institution. HyperArc plans utilized 6MV-FFF beam (800 MU/min) on SBRT-dedicated Linac with fully-automated HyperArc module and 1 cm 3D-printed scalp bolus for dose build up to the superficial target to deliver a prescription dose of 70 Gy in 35 fractions. For comparison, these plans were re-planned via 4 full-arcs on recently installed fast rotating co-planar Halcyon Linac equipped with 6MV-FFF (800 MU/min) with lower mean energy of 1.3 MeV and nominal depth of maximum dose at 1.3 cm. Identical isocenter location and similar planning parameters and objectives, were used on both Linac platforms. Plan quality, including BED10 and treatment delivery accuracy and efficacy, was compared. <h3>Results</h3> Both platforms generated highly conformal, homogenous TSI plans and showed statistically insignificant differences on target coverage, mean target dose, conformity, and dose homogeneity. The average BED10 of the mean target dose was 92.0 ± 1.4 Gy (HyperArc) vs 93.4 ± 0.9 Gy (Halcyon) (p = 0.06). HyperArc provided mean brain dose and V60Gy of 8.1 ± 1.5 Gy and 0.8 ± 0.9 cc respectively, compared to 8.5 ± 1.4 Gy (p > 0.05) and 1.4 ± 0.7 cc (p = 0.04), on Halcyon. For both platforms, significantly lower maximal dose of < 5 Gy was observed in organs at risk (OARs), including spinal cord, brainstem, optic pathway, hippocampi, eyes and lenses, and cochlea (p > 0.05 for all OARs). Halcyon plan complexity slightly decreased as seen in the average decreases of total monitor units, modulation factor and beam-on time by 119, 0.6, and 0.6 min respectively, and the estimated overall treatment time was reduced by an average of 2.4 min. Treatment time for both platforms was less than 15 minutes. Portal dosimetry quality assurance results of HyperArc and the corresponding Halcyon plans were 99.8% and 100%, demonstrating comparable treatment delivery accuracy. <h3>Conclusion</h3> We demonstrated that both Halcyon and HyperArc platforms can deliver an accurate and efficient treatment of greater than 90 Gy BED10 to large, complex and superficial angiosarcoma of the scalp and face with significantly lower mean brain dose of less than 10 Gy. Clinical use of these platforms is underway in our center and highly recommended to other centers, including community centers, expanding the use of Halcyon Linac to underserved patient cohort.

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.

PO-1523 Comparison of two MLCs for SRS HyperArc plans

PO-1523 Comparison of two MLCs for SRS HyperArc plans

Clinical implementation of HyperArc.

The aim of this study was to present our experience on clinical implementation of HyperArc including dosimetric comparison between VMAT and HyperArc plans and dosimetric verification of HyperArc. In this study, eleven previously treated cases of brain metastasis were selected from our brain stereotactic radiotherapy program. The cases were retrospectively planned using HyperArc technique and the plan quality was evaluated. In addition, dosimetric effects of HyperArc plan with different energies and using jaw tracking technique were evaluated. Furthermore, dosimetric verification of HyperArc plans was performed using ion chamber and radiochromic film. Our results of dosimetric comparison shows that HyperArc technique improved both conformity index and gradient index compared to VMAT plans. We also found that using 6MV flattening filter free (6MV-FFF) beam improves gradient index in HyperArc plans compared to using 6MV flattening filter beam. Furthermore, our results show that jaw tracking technique reduces the size of low dose volume while maintaining similar target coverage, conformity index, and gradient index. In our dosimetric verification study, results of ion chamber and film measurement indicate no significant difference between VMAT and HyperArc plans. In conclusion, HyperArc simplifies planning of stereotactic treatment for brain and improves the dosimetry in treatment plans. Additionally, HyperArc provides for a safe and efficient treatment delivery system for stereotactic treatments to brain.