Non-coplanar Arcs Research Articles

An automated treatment planning strategy for highly noncoplanar radiotherapy arc trajectories

AbstractRadiation therapy is a technology‐driven cancer treatment modality that has experienced significant advances over the last decades, due to multidisciplinary contributions that include engineering and computing. Recent technological developments allow the use of noncoplanar volumetric modulated arc therapy (VMAT), one of the most recent photon treatment techniques, in clinical practice. In this work, an automated noncoplanar arc trajectory optimization framework designed in two modular phases is presented. First, a noncoplanar beam angle optimization algorithm is used to obtain a set of noncoplanar irradiation directions. Then, anchored in these directions, an optimization strategy is proposed to compute an optimal arc trajectory. The computational experiments considered a pool of twelve difficult head‐and‐neck tumor cases. It was possible to observe that, for some of these cases, the optimized noncoplanar arc trajectories led to significant treatment planning quality improvements, when compared with coplanar VMAT treatment plans. Although these experiments were done in a research environment treatment planning software (matRad), the conclusions can be of interest for a clinical setting: automated procedures can simplify the current treatment workflow, produce high‐quality treatment plans, making better use of human resources and allowing for unbiased comparisons between different treatment techniques.

Pituitary adenoma treatment plan quality comparison between linear accelerator volumetric modulated arc therapy and Leksell Gamma Knife® radiosurgery.

The aim of this study was to compare radiosurgical treatment plan quality of a linear accelerator with Leksell Gamma Knife (LGK) for pituitary adenoma irradiation. Thirty pituitary adenoma patients were evaluated in this study. Treatment plans were prepared on LGK and stereotactic linear accelerator Varian TrueBeam STx. Volumetric Modulated Arc Therapy (VMAT) plans (21 plans with 2 coplanar arcs and 9 plans with 4 non-coplanar arcs) were calculated for linear accelerator. All the plans were evaluated in terms of conformity, selectivity, gradient index and organ at risk (OAR) sparing. VMAT produced dosimetrically comparable treatment plans to LGK regarding conformity and selectivity (New Conformity Index (NCI): 1.76 ± 0.65 for 4 arc VMAT, 2.33 ± 1,16 for 2 arc VMAT and 1.96 ± 0.71 for LGK; Selectivity Index (SI): 0.63 ± 0.16 for 4 arc VMAT, 0.51 ± 0.16 for 2 arc VMAT and 0.58 ± 0.17 for LGK). Gradient index (GI) was superior for LGK plans (GI: 2.74 ± 0.20 for LGK and 5.28 ± 2.29 for 4 arc VMAT). OAR sparing for optics, brainstem, and hypophysis was similar for both modalities while target volume coverage was maintained the same. Finally, treatment time resulted in favor of VMAT plans (in this study VMAT plans were almost 5 times faster than LGK treatment regarding beam on time). According to the results of this study stereotactic linear accelerator with VMAT treatment could be used as a reasonable alternative to LGK for pituitary adenoma radiosurgery but only if the same head fixation method accuracy and target volume delineation are maintained for both modalities.

A case study of evaluating bilateral lung dose for VMAT treatment planning using a partial sagittal arc.

Radiation pneumonitis (RP) is a potential toxic side effect of thoracic radiotherapy. Optimal planning techniques must maintain tumor coverage while limiting dose to normal lung tissue to reduce the risk of patients developing RP. The addition of a noncoplanar arc may be beneficial by increasing treatment angles and providing an ideal dose distribution for tumor coverage while decreasing dose to organs at risk (OAR). The purpose of this research was to compare the effects on the normal bilateral lung tissue receiving 20 Gy, 10 Gy and 5 Gy (V20, V10, V5) and the mean lung dose (MLD) values when medial lung tumors are treated with 3 partial coplanar arcs vs 2 partial coplanar arcs combined with a partial sagittal arc. Researchers hypothesized that a beam arrangement of 2 partial coplanar arcs and 1 partial sagittal arc would reduce V20, V10, V5, and MLD values when compared to a 3 partial coplanar arc plan. In a retrospective study of 5 patients with bulky, medial right lung lesions without nodal involvement, cases were planned with both a noncoplanar and a coplanar arc geometry. Results were evaluated using a two-tailed t-test to determine the statistical significance (p < 0.05) of changes to total lung volume analyzation metrics when a noncoplanar sagittal arc was incorporated compared to the standard lung treatment using only coplanar arcs. Although some patient cases showed minor improvement in the V20, V10, V5, and MLD metrics, the study results were not statistically significant and showed no advantage with the introduction of an anterior sagittal arc over a coplanar beam arrangement.

Dosimetric comparison of coplanar intensity-modulated radiotherapy, noncoplanar intensity-modulated radiotherapy, and volumetric arc therapy planning technique in hippocampal-sparing whole-brain radiotherapy

The aim of this study was to compare the dosimetric parameters of Co-planar Intensity modulated radiotherapy (C-IMRT), non-coplanar (NC-IMRT), and volumetric arc therapy (VMAT) planning technique in hippocampal sparing (HS) whole brain radiotherapy (WBRT). Fifteen patients of brain metastasis (BM) treated with hippocampal sparing whole-brain palliative radiation were selected for this study. C-IMRT, NC-IMRT and VMAT plans were generated for the comparison. Generated plans were evaluated based on planning target volume (PTV) coverage, conformity index (CI), homogeneity index (HI), beam-on time (BOT) and dose delivered to organs at risk (OARs) for the prescribed dose (PD) of 30 Gy in 10 fractions. Statistically significant difference was found in PTVD95%, PTVmax, HI, BOT, MU, Dmax of the brainstem, Dmean of eyes, Dmax of lenses and Dmax, Dmean and D2% of the bilateral hippocampus. However, a non-significant difference was observed in CI, D100% of both the hippocampus, Dmax of the optic chiasm, optic nerves, and Dmax of eyes in all the three planning techniques. Considering the superior plan quality, both NC-IMRT and VMAT are better than the C-IMRT planning technique. Based on beam-on time and delivery efficiency VMAT is found to be superior to both the C-IMRT and NC-IMRT technique. Doses to OARs are very well within the limits in all the three planning techniques.

Management of multiple brain metastases via dual-isocenter VMAT stereotactic radiosurgery.

Single-isocenter volumetric modulated arc therapy (VMAT) stereotactic radiosurgery (SRS) techniques to treat multiple brain metastases simultaneously can significantly improve treatment delivery efficiency, patient compliance, and clinic workflow. However, due to large number of brain metastases sharing the same MLC pair causing island blocking, there is higher low- and intermediate-dose spillage to the normal brain and higher dose to organs-at-risk (OAR). To minimize this problem and improve plan quality, this study proposes a dual-isocenter planning strategy that groups lesions based on hemisphere location (left vs right sided) in the brain parenchyma, providing less island blocking reducing the MLC travel distance. This technique offers simplified planning while also increasing patient comfort and compliance by allowing for large number of brain metastases to be treated in 2 groups. Seven complex patients with 5 to 16 metastases (64 total) were planned with a single-isocenter VMAT-SRS technique using a 10MV-FFF beam with a prescription of 20 Gy to each lesion. The isocenter was placed at the approximate geometric center of the targets. Each patient was replanned using the dual-isocenter approach, generating 2 plans and placing each isocenter at the approximate geometric center of the combined targets of each side with corresponding non-coplanar partial arcs. Compared to single-isocenter VMAT, dual-isocenter VMAT plans provided similar target coverage and dose conformity with less spread of intermediate dose to normal brain with reduction of dose to OAR. Reduction in total monitor units and beam on time was observed, but due to the second isocenter setup and verification, overall treatment time was increased. Dual-isocenter VMAT-SRS planning for multiple brain metastases is a simplified approach that provides superior treatment options for patient compliance who may not tolerate longer traditional treatment times as with individual isocenters to each target. This planning technique significantly reduces the amount of low- and intermediate-dose spillage, further sparing OAR and normal brain, potentially improving target accuracy though localization of left vs right-sided tumors for each isocenter set up.

Non-coplanar VMAT plans for postoperative primary brain tumour to reduce dose to hippocampus, temporal lobe and cochlea: a planning study.

Objectives:This study aimed to compare radiotherapy plan quality of coplanar volumetric modulated arc therapy (CO-VMAT) and non-coplanar VMAT (NC-VMAT) for post-operative primary brain tumour.Methods:A total of 16 patients who were treated for primary brain tumours were retrospectively selected for this study. For each patient, identical CT sets with structures were used for both CO-VMAT and NC-VMAT planning. For CO-VMAT, one full arc and two coplanar half arcs were used. For NC-VMAT, one full coplanar and two non-coplanar half arcs with couch rotation of 315° or 45° were used. Dose constraints were adhered to the RTOG 0614, RTOG 0933 and TMH protocol. Dose volumetric parameters were collected for statistical analysis.Results:.NC-VMAT achieved significant dose reduction in contralateral hippocampus, both temporal lobes and cochleae, and other OARs while the plan qualities remained the same. In particular, NC-VMAT decreased contralateral hippocampus mean dose by 1.67Gy. Similarly, the NC-VMAT decreased temporal lobe mean dose by 6.29Gy and 2.8Gy for ipsilateral and contralateral side respectively. Furthermore, it decreased cochlea mean dose by 5.34Gy and 0.97Gy for ipsilateral and contralateral side respectively. Overall, there was a reduction of 5.4% of normal brain tissue volume receiving low dose irradiation.Conclusion:The proposed NC-VMAT showed more favourable plan quality than the CO-VMAT for primary brain tumours, in particular to hippocampus, temporal lobes, cochleae and OARs located to the contralateral side of tumours.Advances in knowledge:For primary brain tumours radiotherapy, NC-VMAT can reduce doses to the hippocampus, both temporal lobes, and cochleae, as well as OARs located to the contralateral side of tumours.

A novel restricted single-isocenter stereotactic body radiotherapy (RESIST) method for synchronous multiple lung lesions to minimize setup uncertainties.

Treating multiple lung lesions synchronously using a single-isocenter volumetric modulated arc therapy (VMAT) stereotactic body radiation therapy (SBRT) plan can improve treatment efficiency and patient compliance. However, due to set up uncertainty, aligning multiple lung tumors on a single daily cone beam CT (CBCT) image has shown clinically unacceptable loss of target(s) coverage. Herein, we propose a Restricted Single-Isocenter Stereotactic Body Radiotherapy (RESIST), an alternative treatment that mitigates patient setup uncertainties. Twenty-one patients with two lung lesions were treated with single-isocenter VMAT-SBRT using a 6MV-FFF beam to 54 Gy in 3 fractions (n = 7) or 50 Gy in 5 fractions (n = 14) prescribed to 70-80% isodose line. To minimize setup uncertainties, each plan was re-planned using the RESIST method, utilizing a single-isocenter placed at the patient's mediastinum. It allows for an individual plan to be created for each tumor, using the first plan as the base-dose for the second plan, while still allowing both tumors to be treated in the same session. The technique uses novel features in Eclipse, including dynamic conformal arc (DCA)-based dose and aperture shape controller before each VMAT optimization. RESIST plans provided better target dose conformity (p < 0.001) and gradient indices (p < 0.001) and lower dose to adjacent critical organs. Using RESIST to treat synchronous lung lesions with VMAT-SBRT significantly reduces plan complexity as demonstrated by smaller beam modulation factors (p < 0.001), without unreasonably increasing treatment time. RESIST reduces the chance of a geometric miss due by allowing CBCT matching of one tumor at a time. Placement of isocenter at the mediastinum avoids potential patient/gantry collisions, provides greater flexibility of noncoplanar arcs and eliminates the need for multiple couch movements during CBCT imaging. Efficacy of RESIST has been demonstrated for two lesions and can potentially be used for more lesions. Clinical implementation of this technique is ongoing.

Test cases for commissioning an add-on micro multi-leaf collimator Apex for stereotactic radiosurgery treatments

Two comprehensive test cases are presented for dosimetric commissioning of a radiosurgery system, in a hospital where dedicated phantoms are not available. The system consisted of an Elekta Precise linear accelerator, an Apex micro multi-leaf collimator, and a Monaco treatment planning system (TPS). The purpose of Test I was to assess the dose accuracy with coplanar arc beams. Test II was an end-to-end type test, a rigid Leksell stereotactic frame was fixed to a watermelon phantom and Ergo++ TPS was used for stereotactic coordinates definition. The purpose of Test II was to assess the dose accuracy with non-coplanar arc beams and the influence of geometrical accuracy in the whole process. Ionization chambers were used for dose measurements. Results of Test I showed that discrepancies below 1% are achievable, while results of Test II allowed detection of geometric shifts &lt; 1 mm with dose discrepancies lower than 1%. To the best of our knowledge, there are not published works reporting test cases for commissioning a stereotactic radiosurgery system like the one tested in this work. The designed test cases showed adequacy for assessment of TPS accuracy in complex treatment configurations, like those used in stereotactic radiosurgery.

Hypofractionated stereotactic radiotherapy for large brain metastases: Optimizing the dosimetric parameters

PurposeStereotactic radiotherapy plays a major role in the treatment of brain metastases (BM). We aimed to compare the dosimetric results of four plans for hypofractionated stereotactic radiotherapy (HFSRT) for large brain metastases. Material and methodsTen patients treated with upfront NovalisTx® non-coplanar multiple dynamic conformal arcs (DCA) HFSRT for≥25mm diameter single BM were included. Three other volumetric modulated arc therapy (VMAT) treatment plans were evaluated: with coplanar arcs (Eclipse®, Varian, VMATcEclipse®), with coplanar and non-coplanar arcs (VMATncEclipse®), and with non-coplanar arcs (Elements Cranial SRS®, Brainlab, VMATncElements®). The marginal dose prescribed for the PTV was 23.1Gy (isodose 70%) in three fractions. The mean GTV was 27mm3. ResultsBetter conformity indices were found with all VMAT techniques compared to DCA (1.05 vs 1.28, P<0.05). Better gradient indices were found with VMATncElements® and DCA (2.43 vs 3.02, P<0.001). High-dose delivery in healthy brain was lower with all VMAT techniques compared to DCA (5.6 to 6.3 cc vs 9.4 cc, P<0.001). Low-dose delivery (V5Gy) was lower with VMATncEclipse® or VMATncElements® than with DCA (81 or 94 cc vs 110 cc, P=0.02). ConclusionsNovalisTx® VMAT HFSRT for≥25mm diameter brain metastases provides the best dosimetric compromise in terms of target coverage, sparing of healthy brain tissue and low-dose delivery compared to DCA.

Towards Real 3D Patient Specific QA for Mono-Isocentric Multi-Target Stereotactic Radiosurgery Involving Non-Coplanar Beams

Patient specific QA based on measurements has thus far involved recalculation of the dose on a phantom where a phantom measured dose is compared with phantom planned dose. Strictly speaking this is plan-specific rather than patient-specific QA. With the advent of 3D printers, it is possible to generate a phantom detector that closely matches in composition and geometry the patient, therefore specific to that patient. In this case, there is no need for a dose recalculation on the phantom and the real patient planned dose distribution can be directly compared to the phantom measured dose. This real 3D patient specific QA was achieved for a complex mono-isocentric case involving multiple targets and non-coplanar beams. The QA was based on a previously treated brain patient with seven (7) metastasis, average planning target volume 7.2cc ± 14.1cc (range 0.2cc to 32.4cc), single isocenter and 5 non-coplanar arcs. The average tumor distance from isocenter was 53.8 ± 15.9mm, range (26.4mm to 73.0mm). An anonymized CT data set of the patient was sent to the 3D printer to generate the phantom. In creating the phantom, the fluid and air-filled areas of the head were filled with gel dosimeter. The phantom was then setup in the treatment room just as one would the patient and a CBCT acquired to correct for setup in all translations and rotations. We underscore that the reference images of the real patients were used for the CBCT registration setup. Upon satisfactory setup, we then proceeded to beam delivery. A specialized T2-weighted MRI pulse sequence was implemented on our Siemens Magnetom Aera 1.5T unit to acquire scans of the phantom pre and post irradiation. An assessment of the CBCT of the phantom with the patient’s reference CT image showed very good match. The setup errors based on auto registration just before beam on were 0.0mm, 0.2mm, and 0.2mm in the anterior/posterior (A/P), superior/inferior (S/I), and left/right (L/R) directions respectively and 0.1, 0.1, and 0.0 degrees in yaw, pitch and roll respectively. A 3D gamma analysis considering all 7 PTVs showed a passing rate of 92.7% and 94.8% for a gamma criterion of 5%/1mm and 3%/2mm respectively. The DVH plots showed good agreement, for example mean PTV dose averaging among all 7 targets was 99.6±0.8% versus 99.4±1.3% for real patient plan and measurements respectively. The corresponding values for PTV D95 were 81.6±4.0% versus 79.9±5.2%. The utility of real 3D patient specific QA was presented on a complex case involving multiple targets and non-coplanar beams. The ability to directly measure dose in 3D and relate to the real patient anatomy means one can evaluate additional aspects of the plan such as DVH. The interest in this QA method is expected to increase as technology continues to evolve and 3D printers become readily available in radiotherapy centers.

Novel Monte-Carlo Based IMPT Technique Utilizing Multi-Leaf Collimators on a Gantry Mounted Synchrocyclotron for Cardiac Radioablation of Ventricular Tachycardia Substrate.

The use of noninvasive cardiac radioablation has been increasing for treating refractory ventricular tachycardia (VT). As the target volume is surrounded by normal heart tissue (NHT), intensity modulated proton therapy (IMPT) can potentially improve sparing of the normal myocardium. This treatment planning study compares IMPT plans against clinical volumetric modulated arc therapy (VMAT) plans in terms of NHT sparing. Thirteen patients who received single-fraction radioablation using 6MV photons and 3-5 non-coplanar arcs on a prospective phase I/II clinical trial were retrospectively re-planned using intensity modulated proton therapy (IMPT) with a Monte-Carlo based TPS for a gantry-mounted synchrocyclotron delivery system with adaptive apertures defined by dynamic multi-leaf collimators. Four non-coplanar beams were selected for each plan to minimize irradiated NHT volume. A single-fraction dose of 25 Gy was planned to the planning target volume (PTV), with up to 35 Gy to the internal target volume (ITV). Robust optimization techniques were used for the ITV while maximizing sparing of surrounding organs-at-risk and achieving physician-specified dose limits. Sixteen cardiac substructures were segmented for dosimetric evaluation but not used in optimization. All IMPT plans showed adequate PTV coverage (median V95%Rx = >98.1%) while meeting OAR constraints. NHT mean dose was reduced in IMPT plans from c-VMAT plans (3.3 ± 0.9 Gy vs 6.4 ± 2.0 Gy). Conformity index was comparable between IMPT and c-VMAT plans (1.23 ± 0.07 vs 1.17±0.15) with better VR50%/VRx ratio for IMPT (4.07 ± 0.75 vs 5.03± 1.05). Target coverage, dose conformity and NHT sparing are summarized in Table 1. Dose to the majority of cardiac substructures were found to be lower in IMPT plans than c-VMAT plans. IMPT plans showed improve NHT sparing while maintaining comparable target coverage. IMPT is promising for this group of patients where cardiac toxicity may play a vital role in long-term survivors. Delivery accuracy in the presence of target and OAR motion needs to be thoroughly tested before implementation of IMPT techniques.Tabled 1Abstract 2798; Table; Target coverage, dose conformity and NHT sparing. Mean ± standard deviation are summarized below.Target VolumeVolume (cc)Plan TypeTargets CoverageConformityMean D (Gy)%V_Rx%V_95%RxConf IndexV_R50PTV138.9 ± 67.8Clin. VMAT33.6 ± 1.198.7 ± 1.399.4 ± 1.01.17 ± 0.155.03 ± 1.05IMPT33.4 ± 1.295.6 ± 3.698.1 ± 1.31.23 ± 0.074.07 ± 0.75Normal Heart Tissue SparingMean D (Gy)%V25Gy%V20Gy%V15Gy%V10Gy%V5Gy%V2GyEQD2 (Gy)140.092.054.026.08.02.0Clin. VMAT6.4 ± 2.01.1 ± 0.95.4 ± 2.712.2 ± 5.722.9 ± 9.041.7 ± 13.067.2 ± 17.4IMPT3.3 ± 0.91.6 ± 0.64.3 ± 1.17.9 ± 1.912.7 ± 3.220.4 ± 5.529.5 ± 8.8NHT Volume spared (cc)IMPT-6 ± 1219 ± 3535 ± 1578 ± 45123 ± 101298 ± 438 Open table in a new tab

Comparison of Treatment Plan Robustness Between Dynamic Trajectory Radiotherapy and VMAT

Dynamic trajectory radiotherapy (DTRT) was recently developed in our institute for a non-coplanar arc delivery technique utilizing additionally to VMAT table and collimator rotations. Recent studies on the dosimetric performance suggest a substantial improvement in organs at risks (OARs) sparing when compared with conventional C-arm VMAT delivery. In this work, the treatment plan robustness for DTRT and VMAT is compared with respect to setup errors. Robustness was assessed by generating DVH bands as well as so-called robustness maps (rMaps) by means of a false/true evaluation of certain dosimetric user-defined limits considered acceptable for selected structures with respect to a range of setup errors considered. The robustness was assessed for a clinically motivated head and neck, a lung and a prostate case. For each case systematic translational (ranging from -6 to 6 mm) and rotational (ranging from -3° to 3°) setup error scenarios were defined and for each scenario Monte Carlo dose calculations for the DTRT and VMAT treatment plans were performed. The resulting dose distributions served as input for the robustness assessment determining DVH bands and rMaps. The acceptance conditions for the OARs were defined such that the mean doses for parallel OARs and near maximum doses for serial OARs do not deteriorate more than 2 Gy. For the CTV V95% a deterioration of 1% was allowed in order to pass the robustness criteria. For the isotropic CTV to PTV margins 4 mm, 5 mm and 10 mm were applied for the head and neck, the prostate and the lung case, respectively, except for the dorsal direction of the prostate case, where 3 mm was used. For the head and neck and the prostate case the percentage of setup error scenarios passing the acceptance criteria were 29% and 63% (VMAT) and 23% and 58% (DTRT) for translations and 60% and 100% (VMAT) and 62% and 100% (DTRT) for rotations, respectively. Depending on the direction of the translation setup error, the VMAT plan is slightly more robust. However, for the lung case the VMAT treatment plan is more robust leading to passing rates of 48% (VMAT) and 20% (DTRT) for translations and 83% (VMAT) and 55% (DTRT) for rotations, respectively. In all cases, the robustness determined by the rMaps is dominated by the acceptance criteria for the OARs and not by the ones for the CTV. The results of this study indicate that DTRT treatment plans using additional dynamic table and collimator rotations leading to complex trajectories result in similar systematic setup error robustness as VMAT treatment plans for the head and neck and the prostate case. For the lung case investigated, the VMAT treatment plans show an improved robustness.

Dosimetric feasibility of brain stereotactic radiosurgery with a 0.35 T MRI-guided linac and comparison vs a C-arm-mounted linac.

MRI is the gold-standard imaging modality for brain tumor diagnosis and delineation. The purpose of this work was to investigate the feasibility of performing brain stereotactic radiosurgery (SRS) with a 0.35T MRI-guided linear accelerator (MRL) equipped with a double-focused multileaf collimator (MLC). Dosimetric comparisons were made vs a conventional C-arm-mounted linac with a high-definition MLC. The quality of MRL single-isocenter brain SRS treatment plans was evaluated as a function of target size for a series of spherical targets with diameters from 0.6cm to 2.5cm in an anthropomorphic head phantom and six brain metastases (max linear dimension=0.7-1.9cm) previously treated at our clinic on a conventional linac. Each target was prescribed 20Gy to 99% of the target volume. Step-and-shoot IMRT plans were generated for the MRL using 11 static coplanar beams equally spaced over 360° about an isocenter placed at the center of the target. Couch and collimator angles are fixed for the MRL. Two MRL planning strategies (VR1 and VR2) were investigated. VR1 minimized the 12Gy isodose volume while constraining the maximum point dose to be within ±1Gy of 25Gy which corresponded to normalization to an 80% isodose volume. VR2 minimized the 12Gy isodose volume without the maximum dose constraint. For the conventional linac, the TB1 method followed the same strategy as VR1 while TB2 used five noncoplanar dynamic conformal arcs. Plan quality was evaluated in terms of conformity index (CI), conformity/gradient index (CGI), homogeneity index (HI), and volume of normal brain receiving ≥12Gy (V12Gy ). Quality assurance measurements were performed with Gafchromic EBT-XD film following an absolute dose calibration protocol. For the phantom study, the CI of MRL plans was not significantly different compared to a conventional linac (P>0.05). The use of dynamic conformal arcs and noncoplanar beams with a conventional linac spared significantly more normal brain (P=0.027) and maximized the CGI, as expected. The mean CGI was 95.9±4.5 for TB2 vs 86.6±3.7 (VR1), 88.2±4.8 (VR2), and 88.5±5.9 (TB1). Each method satisfied a normal brain V12Gy ≤10.0cm3 planning goal for targets with diameter ≤2.25cm. The mean V12Gy was 3.1cm3 for TB2 vs 5.5cm3 , 5.0cm3 and4.3cm3 , for VR1, VR2, and TB1, respectively. For a 2.5-cm diameter target, only TB2 met the V12Gy planning objective. The MRL clinical brain plans were deemed acceptable for patient treatment. The normal brain V12Gy was ≤6.0cm3 for all clinical targets (maximum target volume=3.51cm3 ). CI and CGI ranged from 1.12-1.65 and 81.2-88.3, respectively. Gamma analysis pass rates (3%/1mm criteria) exceeded 97.6% for six clinical targets planned and delivered on the MRL. The mean measured vs computed absolute dose difference was -0.1%. The MRL system can produce clinically acceptable brain SRS plans for spherical lesions with diameter ≤2.25cm. Large lesions (>2.25cm) should be treated with a linac capable of delivering noncoplanar beams.

Noncoplanar volumetric modulated arc therapy for patient with optic nerve sheath meningioma: a case report and literature review

Noncoplanar volumetric modulated arc therapy for patient with optic nerve sheath meningioma: a case report and literature review

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.

Dosimetric comparison of coplanar and non-coplanar volumetric-modulated arc therapy in head and neck cancer treated with radiotherapy.

PurposeTo evaluate the dosimetric variations in patients of head and neck cancer treated with definitive or adjuvant radiotherapy using optimized non-coplanar (ncVMAT) beams with coplanar (cVMAT) beams using volumetric arc therapy.Materials and MethodsTwenty-two patients of head and neck cancer that had received radiotherapy using VMAT in our department were retrospectively analyzed. Each of the patients was planned using coplanar and non-coplanar orientations using an optimized couch angle and fluences. We analyzed the Conformity Index (CIRTOG), Dose Homogeneity Index (DHI), Heterogeneity Index (HIRTOG), low dose volume, target and organs-at-risk coverage in both the plans without changing planning optimization parameters. ResultsThe prescription dose ranged from 60 Gy to 70 Gy. Using ncVMAT, CIRTOG, DHI and HIRTOG, and tumor coverage (ID95%) had improved, low dose spillage volume in the body V5Gy was increased and V10Gy was reduced. Integral dose and intensity-modulated radiation therapy factor had increased in ncVMAT. In the case of non-coplanar beam arrangements, maximum dose (Dmax) of right and left humeral head were reduced significantly whereas apex of the right and left lung mean dose were increased.ConclusionThe use of ncVMAT produced better target coverage and sparing of the shoulder and soft tissue of the neck as well as the critical organ compared with the cVMAT in patients of head and neck malignancy.

A simple, yet novel hybrid-dynamic conformal arc therapy planning via flattening filter-free beam for lung stereotactic body radiotherapy.

PurposeDue to multiple beamlets in the delivery of highly modulated volumetric arc therapy (VMAT) plans, dose delivery uncertainties associated with small‐field dosimetry and interplay effects can be concerns in the treatment of mobile lung lesions using a single‐dose of stereotactic body radiotherapy (SBRT). Herein, we describe and compare a simple, yet clinically useful, hybrid 3D‐dynamic conformal arc (h‐DCA) planning technique using flattening filter‐free (FFF) beams to minimize these effects.Materials and MethodsFifteen consecutive solitary early‐stage I‐II non‐small‐cell lung cancer (NSCLC) patients who underwent a single‐dose of 30 Gy using 3–6 non‐coplanar VMAT arcs with 6X‐FFF beams in our clinic. These patients’ plans were re‐planned using a non‐coplanar hybrid technique with 2–3 differentially‐weighted partial dynamic conformal arcs (DCA) plus 4–6 static beams. About 60–70% of the total beam weight was given to the DCA and the rest was distributed among the static beams to maximize the tumor coverage and spare the organs‐at‐risk (OAR). The clinical VMAT and h‐DCA plans were compared via RTOG‐0915 protocol for conformity and dose to OAR. Additionally, delivery efficiency, accuracy, and overall h‐DCA planning time were recorded.ResultsAll plans met RTOG‐0915 requirements. Comparison with clinical VMAT plans h‐DAC gave better target coverage with a higher dose to the tumor and exhibited statistically insignificance differences in gradient index, D2cm, gradient distance and OAR doses with the exception of maximal dose to skin (P = 0.015). For h‐DCA plans, higher values of tumor heterogeneity and tumor maximum, minimum and mean doses were observed and were 10%, 2.8, 1.0, and 2.0 Gy, on average, respectively, compared to the clinical VMAT plans. Average beam on time was reduced by a factor of 1.51. Overall treatment planning time for h‐DCA was about an hour.ConclusionDue to no beam modulation through the target, h‐DCA plans avoid small‐field dosimetry and MLC interplay effects and resulting in enhanced target coverage by improving tumor dose (characteristic of FFF‐beam). The h‐DCA simplifies treatment planning and beam on time significantly compared to clinical VMAT plans. Additionally, h‐DCA allows for the real time target verification and eliminates patient‐specific VMAT quality assurance; potentially offering cost‐effective, same or next day SBRT treatments. Moreover, this technique can be easily adopted to other disease sites and small clinics with less extensive physics or machine support.

Long-Term Outcomes After Linac Radiosurgery for Benign Meningiomas

AimsAlthough several studies on outcomes following stereotactic radiosurgery (SRS) for benign meningiomas have been reported, Linac-based SRS outcomes have not been as widely evaluated. The aim of this retrospective institutional single-centre study was to determine long-term outcomes of Linac-based SRS for benign intracranial meningiomas. Materials and methodsFrom July 1996 to May 2011, 60 patients with 69 benign meningiomas were included. All patients were treated with single-fraction Linac-based SRS with four to five non-coplanar arcs, dynamic or not. The marginal dose prescribed for the periphery was 16 Gy. Prognostic factors associated with local control, progression-free survival (PFS) and overall survival were tested. ResultsThe median follow-up was 128 months. No patient was lost to follow-up. The values observed at 1, 5 and 10 years were, respectively, 100%, 98.4% and 92.6% for local control, 94.9%, 93.2% and 78% for PFS and 100%, 94.7% and 92.7% for overall survival. In univariate analysis, local control after SRS was significantly higher for skull base and parasagittal meningiomas compared with convexity meningiomas (P = 0.031). Multivariate analyses showed significantly longer PFS when the minimum dose delivered to the tumour was greater than 10 Gy (P = 0.0082). No grade 5 toxicity was reported. ConclusionOur long-term results from a large sample size of benign meningiomas treated with Linac-based SRS confirmed excellent local control (>90%) and good safety, which is in line with published studies on Gamma Knife surgery. Above all, we showed significantly poorer PFS if the minimum dose to the tumour was under 10 Gy.

Dosimetric comparison between single and double isocenters VMAT for SRT with multiple targets

The focal irradiation approach for brain metastasis (BMs) Stereotactic Radiosurgery (SRS) or Stereotactic Radiotherapy (SRT) has emerged as an important modality for multiple BMs. This study aimed to evaluate the dosimetric effects between single isocentre (SI) and double isocentres (DI) VMAT SRT of multiple brain metastases. Eighteen VMAT SRT plans with varying lesions size, number and distance were simulated on patient CT image using Eclipse treatment planning system version 15. The plan consists of 3 techniques in: 2 coplanar arcs SI, 1 coplanar combine with 2 non-coplanar arcs SI and 2 non-coplanar and 1 coplanar arc DI. The VMAT plans were generated with 21Gy prescription dose to all lesions in 3 fractions. The plans were evaluated in terms of Gradient index (Paddick GI), Conformity index (Paddick CI), and Homogeneity index (ICRU HI) for PTV and V12Gy and V6Gy for normal brain. The same dose constraints were used to optimize for all cases. On the average result from 3 techniques, 3 arcs SI plans and DI were better in GI (14.79±5.83, 13.70±4.72) and CI (0.63±0.08, 0.62±0.09) than 2 arcs SI (17.56±6.15, 0.62±0.11), while HI values was comparable for all techniques. For normal brain, V12Gy for 2 arcs and 3 arcs SI plans were comparable with DI and the volumes of normal brain receiving 6 Gy in 3 arcs SI and DI (77.40 ± 34.30 cm3, 68.94 ± 30.50 cm3) were better than 2 arcs SI (108.10 ± 57.20 cm3). Moreover, the number of arcs, monitoring units and treatment time were also increased and inconvenience in practice in DI. In conclusion, 3 arcs non-coplanar SI VMAT technique presents the suitable in dosimetric evaluation in 2-5 lesions metastases SRT.

Assessment of an Elekta Versa HD linear accelerator for stereotactic radiosurgery with circular cone collimators.

Versa HD linear accelerators (linacs) are used for stereotactic radiosurgery treatment. However, the mechanical accuracy of such systems remains a concern. The purpose of this study was to evaluate the accuracy of an Elekta Versa HD linac. We performed measurements with a ball bearing phantom to calculate the rotational isocenter radii of the linac's gantry, collimator, and table, and determine the relative locations of those isocenters. We evaluated the accuracy of the cone-beam computed tomography (CBCT) guidance with a film-embedding head phantom and circular cone-collimated radiation beams. We also performed dosimetric simulations to study the effects of the linac mechanical uncertainties on non-coplanar cone arc delivery. The mechanical uncertainty of the linac gantry rotation was 0.78 mm in radius, whereas that of the collimator and the table was <0.1 mm and 0.33 mm, respectively. The axes of rotation of the collimator and the table were coinciding with and 0.13 mm away from the gantry isocenter, respectively. Experiments with test plans demonstrated the limited dosimetric consequences on the circular arc delivery given the aforementioned mechanical uncertainties. End-to-end measurements determined that the uncertainty of the CBCT guidance was≤1 mm in each direction with respect to the reference CT image. In arc delivery, the mechanical uncertainties associated with the gantry and the table do not require remarkable increases in geometric margins. If large enough, the residual setup errors following CBCT guidance will dominate the overall dosimetric consequence. Therefore, the Versa HD linac is a valid system for stereotactic radiosurgery using non-coplanar arc delivery.