Noncoplanar Volumetric Modulated Arc Therapy Plans Research Articles

Clinical Feasibility of Using Single-isocentre Non-coplanar Volumetric Modulated Arc Therapy Combined with Non-coplanar Cone Beam Computed Tomography in Hypofractionated Stereotactic Radiotherapy for Five or Fewer Multiple Intracranial Metastases

AimsTo evaluate the clinical feasibility of single-isocentre non-coplanar volumetric modulated arc therapy (NC-VMAT) with non-coplanar cone beam computed tomography (NC-CBCT) in hypofractionated stereotactic radiotherapy (HSRT) for five or fewer multiple brain metastases. Materials and methodsTen patients with multiple brain metastases who underwent single-isocentre NC-VMAT HSRT with limited couch rotations (within ±45°) and NC-CBCT with a limited scanning range (150–200°) were included in the current analysis. Conventional single-isocentre coplanar VMAT (C-VMAT) plans were generated and compared with NC-VMAT plans. The intracranial response and toxicities of single-isocentre NC-VMAT HSRT were also evaluated. ResultsCompared with C-VMAT, NC-VMAT generated better target conformity (P < 0.05), a lower gradient index (P < 0.05) and better normal brain tissue sparing, especially for volume ≥12 Gy, with a median reduction of 12.65 cm3. For 45° couch rotation, NC-CBCT produced sufficient image quality to differentiate bony anatomy, even with a 150° scanning range, which could be successfully used for patient set-up correction. After NC-CBCT, 57.1% of the measured non-coplanar set-up errors exceeded the threshold value. The median gamma passing rate of NC-VMAT was higher than that of C-VMAT plans (P < 0.05). The non-coplanar beam of NC-VMAT with NC-CBCT corrections exhibited superior gamma passing rate to that without NC-CBCT corrections. The intracranial objective response rate and disease control rate for all patients were 80% (8/10) and 100% (10/10), respectively, and the most common toxicities were headache (20%) and dizziness (20%). ConclusionNC-VMAT with limited couch rotation (within ±45°) combined with NC-CBCT with a limited scanning range (150–200°) markedly improves the plan quality and set-up accuracy in single-isocentre multiple-target HSRT.

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.

Automated Non-coplanar Volumetric Modulated Arc Therapy Planning for Maxillary Sinus Carcinoma.

Dosimetric parameters in volumetric modulated arc therapy (VMAT), non-coplanar VMAT (NC-VMAT), and automated NC-VMAT (HyperArc, HA) were compared for patients with maxillary sinus carcinoma (MSC). Twenty HA plans were generated to deliver 70.4, 64, and 46 Gy for planning target volumes with high (PTV1), intermediate (PTV2), and low risk (PTV3), respectively. The VMAT and NC-VMAT plans were retrospectively generated using the same optimized parameters as those used in the HA plans. For PTV1, the three treatment plans provided comparable target coverages. For PTV2, the D95%, D99%, and Dmin in the HA plans (64.7±1.2, 62.7±2.1 and 54.6±6.2 Gy, respectively) were significantly higher (p<0.05) than those in the VMAT plans (64.3±1.7, 61.9±2.4 and 52.9±6.4 Gy, respectively). The NC-VMAT and HA plans provided significantly higher (p<0.05) dosimetric parameters for PTV3 than those in the VMAT plans, and D99% in the HA was significantly higher than that in the NC-VMAT plans (52.5±3.0 vs. 51.8±2.7 Gy, p<0.05). The doses to the brain and brainstem were lowest in the HA plans (p<0.05). Moreover, dosimetric parameters of the contralateral organs (lens, optic nerve, retina, and parotid) were lower in the HA plans than in the VMAT and NC-VMAT plans. The HA plans provided the best target coverage and OAR sparing compared with VMAT and NC-VMAT plans for patients with MSC.

Dosimetric Comparision of Coplanar versus Noncoplanar Volumetric Modulated Arc Therapy for Treatment of Bilateral Breast Cancers.

The purpose of this study was to compare the dosimetric parameters of volumetric modulated arc therapy (VMAT) treatment plans using coplanar and noncoplanar beams in patients with bilateral breast cancer/s (BBCs) in terms of organ at risk sparing and target volume coverage. The hypothesis was to test whether VMAT with noncoplanar beams can result in lesser dose delivery to critical organs such as heart and lung, which will result in lesser overall toxicity. Data of nine BBC cases treated at our hospital were retrieved. Computed tomography simulation data of these cases was used to generate noncoplanar VMAT plans and the parameters were compared with standard VMAT coplanar plans. Contouring was done using radiation therapy oncology group guidelines. Forty-five Gray in 25 fractions was planned followed by 10 Gy in five fractions boost in breast conservation cases. No significant difference in planning target volume (PTV) coverage was found for the right breast/chestwall (P = 0.940), left breast/chestwall (P = 0.872), and in the total PTV (P = 0.929). Noncoplanar beams resulted in better cardiac sparing in terms of Dmean heart. The difference in mean dose was >1 Gy (8.80 ± 0.28 - 7.28 ± 0.33, P < 0.001). The Dmean, V20 and V30 values for total lung slightly favor noncoplanar beams, although there was no statistically significant difference. The average monitor units (MUs) were similar for coplanar plans (1515 MU) and noncoplanar plans (1455 MU), but the overall treatment time was higher in noncoplanar plans due to more complex setup and beam arrangement. For noncoplanar VMAT plans, the mean conformity index was slightly better although the homogeneity indices were similar. VMAT plans with noncoplanar beam arrangements had significant dosimetric advantages in terms of sparing of critical organs, that is Dmean of heart doses with almost equivalent lung doses and equally good target coverage. Larger studies with clinical implications need to be considered to validate this data.

Dosimetric Effects of Dynamic Jaw Tracking and Collimator Angle Optimization in Non-Coplanar Cranial Arc Radiotherapy.

The stereotactic treatment of single cranial targets using noncoplanar volumetric modulated arc therapy (VMAT) allows for effective dose delivery to the target, while sparing normal brain tissue. In this study, the dosimetric effect of adding dynamic jaw tracking and automatic collimator angle selection in the optimization of single target cranial VMAT plans was investigated. Twenty-two cranial targets, previously treated with VMAT without dynamic jaw tracking and automatic collimator angle optimization (CAO) were chosen for replanning. Target volumes ranged from 0.441cc to 25.863cc with doses between 18Gy and 30Gy delivered in 1 to 5 fractions. Original plans were reoptimized with automatic CAO, keeping all other objectives the same (CAO plans). Next, original plans were reoptimized with both dynamic jaw tracking and CAO (DJT plans). Original, CAO, and DJT target doses were compared using the Paddick gradient index (GI) and the Paddick inverse conformity index (ICI), while normal tissue dose was compared using the volume of the normal brain receiving 5Gy, 10Gy, and 12Gy. The normal tissue volume was normalized to target size to allow cross comparison between plans. A one-sided t-test was performed to determine whether the changes in the plan metrics were statistically significant. CAO plans had improved GIs compared to the originals (p = 0.03) with insignificant changes in other plan metrics (p > 0.20). The addition of dynamic jaw tracking in DJT plans greatly improved ICIs and normal brain metrics (p < 0.01) compared to the CAO plans with minor improvement in ICIs (p = 0.07). The combined effect of adding dynamic jaw tracking and collimator optimization led to improvements in all metrics of the DJT plans when compared to the original (p < 0.02). The addition of dynamic jaw tracking and CAO led to improvements in both target and normal tissue dose metrics for single-target noncoplanar cranial VMAT plans.

Clinical validation of ring-mounted halcyon linac for lung SBRT: comparison to SBRT-dedicated C-arm linac treatments.

Stereotactic body radiotherapy (SBRT) of lung tumors via the ring‐mounted Halcyon Linac, a fast kilovoltage cone beam CT‐guided treatment with coplanar geometry, a single energy 6MV flattening filter free (FFF) beam and volumetric modulated arc therapy (VMAT) is a fast, safe, and feasible treatment modality for selected lung cancer patients. Four‐dimensional (4D) CT‐based treatment plans were generated using advanced AcurosXB algorithm with heterogeneity corrections using an SBRT board and Halcyon couch insert. Halcyon VMAT‐SBRT plans with stacked and staggered multileaf collimators produced highly conformal radiosurgical dose distribution to the target, lower intermediate dose spillage, and similar dose to adjacent organs at risks (OARs) compared to SBRT‐dedicated highly conformal clinical noncoplanar Truebeam VMAT plans following the RTOG‐0813 requirements. Due to low monitor units per fraction and less multileaf collimator (MLC) modulation, the Halcyon VMAT plan can deliver lung SBRT fractions with an overall treatment time of less than 15 min (for 50 Gy in five fractions), significantly improving patient comfort and clinic workflow. Higher pass rates of quality assurance results demonstrate a more accurate treatment delivery on Halcyon. We have implemented Halcyon for lung SBRT treatment in our clinic. We suggest others use Halcyon for lung SBRT treatments using abdominal compression or 4D CT‐based treatment planning, thus expanding the access of curative ultra‐hypofractionated treatments to other centers with only a Halcyon Linac. Clinical follow‐up results for patients treated on Halcyon Linac with lung SBRT is ongoing.

Risk of target coverage loss for stereotactic body radiotherapy treatment of synchronous lung lesions via single-isocenter volumetric modulated arc therapy.

Treating multiple lung lesions synchronously via single‐isocenter volumetric modulated arc therapy (VMAT) stereotactic body radiation therapy (SBRT) improves treatment efficiency and patient compliance. However, aligning multiple lung tumors accurately on single pretreatment cone beam CTs (CBCTs) can be problematic. Tumors misaligned could lead to target coverage loss. To quantify this potential target coverage loss due to small, clinically realistic setup errors, a novel simulation method was developed. This method was used on 26 previously treated patients with two metastatic lung lesions. Patients were treated with 4D CT‐based, highly conformal noncoplanar VMAT plans (clinical VMAT) with 6MV‐flattening filter free (FFF) beam using AcurosXB dose calculation algorithm with heterogeneity corrections. A single isocenter was placed approximately between the lesions to improve patient convenience and clinic workflow. Average isocenter to tumor distance was 5.9 cm. Prescription dose was 54 Gy/50 Gy in 3/5 fractions. For comparison, a plan summation (simulated VMAT) was executed utilizing randomly simulated, clinically relevant setup errors, obtained from pretreatment setup, per treatment fraction, in Eclipse treatment planning system for each of the six degrees of freedom within ± 5.0 mm and ± 2°. Simulations yielded average deviations of 27.4% (up to 72% loss) (P < 0.001) from planned target coverage when treating multiple lung lesions using a single‐isocenter plan. The largest deviations from planned coverage and desired biological effective dose (BED10, with α/β = 10 Gy) were seen for the smallest targets (<10 cc), some of which received < 100 Gy BED10. Patient misalignment resulted in substantial decrease in conformity and increase in the gradient index, violating major characteristics of SBRT. Statistically insignificant differences were seen for normal tissue dose. Although, clinical follow‐up of these patients is ongoing, the authors recommend an alternative treatment planning strategy to minimize the probability of a geometric miss when treating small lung lesions synchronously with single‐isocenter VMAT SBRT plans.

Novel strategy with the automatic non-coplanar volumetric-modulated arc therapy for angiosarcoma of the scalp

BackgroundTotal scalp irradiation presents technical and dosimetric challenges. While reports suggest that HyperArc, a new stereotactic radiosurgery planning technique applied to non-coplanar volumetric-modulated arc therapy (VMAT) technique, is associated with high conformity and rapid dose fall-off, the performance of HyperArc for total scalp irradiation has not been explored. The current study aimed to compare the dosimetric performance of HyperArc plans with those of non-coplanar VMAT plans in angiosarcoma of the scalp.MethodsTen patients with angiosarcoma of the scalp were included in this study. The performance of three different plans administered using TrueBeam Edge were compared: non-coplanar VMAT using flattening filter (FF) beams (VMAT-FF), HyperArc using FF beams (HyperArc-FF), and HyperArc using flattening filter free (FFF) beams (HyperArc-FFF). The dose distribution, dosimetric parameters, and dosimetric accuracy for each of these plans were evaluated.ResultsThe three plans showed no statistically significant differences in target volume coverage, conformity, and homogeneity. The HyperArc-FF and HyperArc-FFF plans provided significantly lower mean brain doses (12.63 ± 3.31 Gy and 12.71 ± 3.40 Gy) than did the VMAT-FF plans (17.11 ± 5.25 Gy). There were almost no differences in sparing the organs at risk between the HyperArc-FF and HyperArc-FFF plans. The HyperArc-FF and HyperArc-FFF plans provided a shorter beam-on time than did the VMAT-FF plan. The 3%/2 mm gamma test pass rates were above 95% for all three plans.ConclusionsOur results suggest that the HyperArc plan can be potentially used for radiation therapy of target regions with large and complicated shapes, such as the scalp, and that there are no advantages of using FFF beams.

Non-coplanar VMAT plans for lung SABR to reduce dose to the heart: a planning study.

This study aimed to compare the plan quality of non-coplanar partial arc (NPA) volumetric modulated arc therapy (VMAT) to that of coplanar partial arc (CPA) VMAT for stereotactic ablative radiotherapy (SABR) for lung cancer. A total of 20 patients treated for lung cancer with the SABR VMAT technique and whose lung tumors were close to the heart were retrospectively selected for this study. For the CPA VMAT, three coplanar half arcs were used while two coplanar half arcs and one noncoplanar arc rotating 315°-45° with couch rotations of 315° ± 5° were used for the NPA VMAT. For each patient, identical CT image sets and identical structures were used for both the CPA and NPA VMAT plans. Dose-volumetric parameters of each plan were analyzed. For the planning target volume and both lungs, no statistically significant differences between the CPA and NPA VMAT plans were observed in general. For the heart, average values of D0.1cc of the CPA and NPA VMAT plans were 29.42 ± 13.37 and 21.71 ± 9.20 Gy, respectively (p < 0.001). For whole body, the mean dose and the gradient index of the CPA VMAT plans were 1.2 ± 0.5 Gy and 4.356 ± 0.608 while those of the NPA VMAT plans were 1.1 ± 0.5 Gy and 4.111 ± 0.480, respectively (both with p < 0.001). The NPA VMAT proposed in this study showed more favorable plan quality than the CPA VMAT plans for lung SABR with tumors located close to the heart. For lung SABR, NPA VMAT can reduce doses to the heart as well as whole-body irradiation.

Comparison of Plan Quality Between Stereotactic and Volumetric Modulated Arc Therapy Radiosurgery for Many Brain Metastases

The objective of this study was to compare radiation dose distributions created by two radiosurgery modalities for treating a large number (≥7) brain metastases: single-isocenter volumetric modulated arc therapy (VMAT) and GammaKnife Perfexion (GK). We examined 103 brain metastases (range 0.01- 19.95 cc) from twelve patients. The mean number of targets per patient was 9 (range 7-14). Highly-optimized GK plans were compared to highly-optimized single-isocenter, multiple non-coplanar arc VMAT plans using both 6FFF (1400 MU/min) and 10FFF (2400 MU/min) high intensity modes from a Truebeam linear accelerator equipped with a high-definition multileaf collimator. Three layers of ‘tuning rinds’ were used in VMAT planning to control dose-volume constraints corresponding to high (Rx of each target), medium (12 Gy), and low-dose levels (6 Gy) [1-4]. Dosimetric parameters analyzed included RTOG conformity index (CI), 12 Gy (a known predictor of radiation necrosis [5]), 6 Gy, 3 Gy isodose volumes (V12Gy, V6Gy, V3Gy), mean and maximum hippocampus dose, maximum skin dose, and beam-on time. Each lesion had > 99.5% volume covered by the Rx dose. Direct comparison was performed using a Kruskal-Wallis test with Dunn’s post hoc comparisons (significance criteria: p < 0.05). There was a significant CI difference between GK and both 6FFF and 10FFF (2.52 ± 1.64 vs 1.59 ± 0.81 and 1.68 ± 0.87, p < 0.001). For V12Gy, there was a significant difference between GK and both 6FFF and 10FFF (2.79 ± 6.13 cc vs 2.97 ± 5.22 cc and 3.13 ± 5.39 cc, p <0.001). For V6Gy, there was no significant difference between GK and 6FFF, however, GK was significantly smaller compared to 10FFF (81.12 ± 72.86 cc vs 167.55 ± 87.55 cc, p=0.011). For V3Gy, GK was significantly smaller compared to both 6FFF and 10FFF (323 ± 295 cc vs, 880 ± 369 cc and 938 ± vs 362 cc, p < 0.001). For mean hippocampus dose, there was no significant difference between GK and 6 FFF, however, GK was significantly smaller compared to 10FFF (1.88 ± 1.35 Gy vs 3.59 ± 1.36 Gy, p = 0.013). No significant differences existed for maximum hippocampus or skin doses. There was a significant beam-on time difference between GK and both 6FFF and 10 FFF (148 ± 49 min vs 11 ± 2 min and 6 ± 1 min, p < 0.001). This study focused on cases with at least 7 brain metastases. Highly-optimized VMAT produced improved conformity at the expense of a higher V12Gy and V3Gy volume when compared to highly-optimized GK. However, the increased V12Gy with VMAT may not be clinically significant while increased V3Gy is comparable to a single fraction of whole-brain radiotherapy. [1] Liu et al. Front. Oncol. 6:26 (2016) [2] Thomas et al. Neurosurgery. 75(4): 409-418 (2014) [3] McDonald et al. J Neurosurg (Suppl 2) 121: 51-59 (2014) [4] Clark et al. Pract. Radiat. Oncol. 2: 306-313 (2012) [5] Minniti et al. Radiat. Oncol. J. 6: 48 (2011).

SU‐F‐T‐646: SBRT Lung: Moving Beyond the 3D Conformal Paradigm with An Elekta VersaHD Accelerator

Purpose:To develop a volumetric modulated arc therapy (VMAT) planning and delivery methodology for lung stereotactic body radiation therapy (SBRT) that addresses the unique geometric challenges presented when using an Elekta VersaHD linear accelerator.Methods:The Elekta VersaHD imaging panels are fixed at 160cm SID when deployed, limiting the ability to perform non‐coplanar treatments due to collisions with the treatment table. The panels can be folded in a stored position for non‐coplanar treatments, but in this configuration, longitudinal table travel is restricted by the space required for the folded panels. To overcome these design features, a non‐coplanar VMAT technique was designed and evaluated for 6 patients that uses a superiorly placed isocenter near the apex of the lung. A coplanar VMAT technique with isocenter placement within the target was also assessed for each patient. Non‐coplanar plans included three arcs, totalling 340° of arc angle, while coplanar plans included two arcs, totalling 280° of arc angle. Each technique avoided the contralateral lung and major overlap on patient skin. Corresponding 3DCRT plans were used as a baseline for each patient in evaluating VMAT plans.Results:Coplanar and noncoplanar VMAT plans yielded a high dose conformity index (CI) improvement of 6% and low dose CI improvements of 9% and 11%, respectively, over corresponding 3DCRT plans. While both VMAT techniques provided greater skin sparing compared to 3DCRT, the non‐coplanar technique offered an improvement of 20% over the coplanar approach. Treatment time with for VMAT was ∼2.5 minutes compared to ∼10 minutes for 3DCRT.Conclusion:Two VMAT techniques were developed for lung SBRT that account for machine design limitations and provide greater dose conformity and normal tissue sparing than 3DCRT plans. The non‐coplanar VMAT plans showed a marginal improvement over coplanar VMAT plans and may not warrant the additional complexity.

A modular approach to intensity-modulated arc therapy optimization with noncoplanar trajectories

Utilizing noncoplanar beam angles in volumetric modulated arc therapy (VMAT) has the potential to combine the benefits of arc therapy, such as short treatment times, with the benefits of noncoplanar intensity modulated radiotherapy (IMRT) plans, such as improved organ sparing. Recently, vendors introduced treatment machines that allow for simultaneous couch and gantry motion during beam delivery to make noncoplanar VMAT treatments possible. Our aim is to provide a reliable optimization method for noncoplanar isocentric arc therapy plan optimization. The proposed solution is modular in the sense that it can incorporate different existing beam angle selection and coplanar arc therapy optimization methods.Treatment planning is performed in three steps. First, a number of promising noncoplanar beam directions are selected using an iterative beam selection heuristic; these beams serve as anchor points of the arc therapy trajectory. In the second step, continuous gantry/couch angle trajectories are optimized using a simple combinatorial optimization model to define a beam trajectory that efficiently visits each of the anchor points. Treatment time is controlled by limiting the time the beam needs to trace the prescribed trajectory. In the third and final step, an optimal arc therapy plan is found along the prescribed beam trajectory. In principle any existing arc therapy optimization method could be incorporated into this step; for this work we use a sliding window VMAT algorithm.The approach is demonstrated using two particularly challenging cases. The first one is a lung SBRT patient whose planning goals could not be satisfied with fewer than nine noncoplanar IMRT fields when the patient was treated in the clinic. The second one is a brain tumor patient, where the target volume overlaps with the optic nerves and the chiasm and it is directly adjacent to the brainstem.Both cases illustrate that the large number of angles utilized by isocentric noncoplanar VMAT plans can help improve dose conformity, homogeneity, and organ sparing simultaneously using the same beam trajectory length and delivery time as a coplanar VMAT plan.

Volumetric modulated arc planning for lung stereotactic body radiotherapy using conventional and unflattened photon beams: a dosimetric comparison with 3D technique

PurposeFrequently, three-dimensional (3D) conformal beams are used in lung cancer stereotactic body radiotherapy (SBRT). Recently, volumetric modulated arc therapy (VMAT) was introduced as a new treatment modality. VMAT techniques shorten delivery time, reducing the possibility of intrafraction target motion. However dose distributions can be quite different from standard 3D therapy. This study quantifies those differences, with focus on VMAT plans using unflattened photon beams.MethodsA total of 15 lung cancer patients previously treated with 3D or VMAT SBRT were randomly selected. For each patient, non-coplanar 3D, coplanar and non-coplanar VMAT and flattening filter free VMAT (FFF-VMAT) plans were generated to meet the same objectives with 50 Gy covering 95% of the PTV. Two dynamic arcs were used in each VMAT plan. The couch was set at ± 5° to the 0° straight position for the two non-coplanar arcs. Pinnacle version 9.0 (Philips Radiation Oncology, Fitchburg WI) treatment planning system with VMAT capabilities was used. We analyzed the conformity index (CI), which is the ratio of the total volume receiving at least the prescription dose to the target volume receiving at least the prescription dose; the conformity number (CN) which is the ratio of the target coverage to CI; and the gradient index (GI) which is the ratio of the volume of 50% of the prescription isodose to the volume of the prescription isodose; as well as the V20, V5, and mean lung dose (MLD). Paired non-parametric analysis of variance tests with post-tests were performed to examine the statistical significance of the differences of the dosimetric indices.ResultsDosimetric indices CI, CN and MLD all show statistically significant improvement for all studied VMAT techniques compared with 3D plans (p < 0.05). V5 and V20 show statistically significant improvement for the FFF-VMAT plans compared with 3D (p < 0.001). GI is improved for the FFF-VMAT and the non-coplanar VMAT plans (p < 0.01 and p < 0.05 respectively) while the coplanar VMAT plans do not show significant difference compared to 3D plans. Dose to the target is typically more homogeneous in FFF-VMAT plans. FFF-VMAT plans require more monitor units than 3D or non-coplanar VMAT ones.ConclusionBesides the advantage of faster delivery times, VMAT plans demonstrated better conformity to target, sharper dose fall-off in normal tissues and lower dose to normal lung than the 3D plans for lung SBRT. More monitor units are often required for FFF-VMAT plans.