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Available treatment geometries for coplanar and non-coplanar radiotherapy. An upper limit on treatment plan quality can be determined by distributing a large number of beams over the full (a) non-coplanar or (b) coplanar space. Other techniques shown are: (c) coplanar VMAT, (d) coplanar IMRT, (e) coplanar IMRT with optimized beam orientations, (f) non-coplanar IMRT with optimized beam orientations, (g) static couch non-coplanar VMAT, (h) non-coplanar trajectory VMAT tracing the great circles around the patient, and (i), non-coplanar trajectory VMAT visiting nine optimized beam orientations. BAO, beam angle optimized, equivalent to BOO in this review; IMRT, intensity modulated radiotherapy; SnS, step and shoot, a type of IMRT delivery; VMAT, volumetric arc therapy. Reprinted from Wild et al 32 with permission from John Wiley and Sons, © American Association of Physicists in Medicine.
Source publication
This paper gives an overview of recent developments in non-coplanar intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). Modern linear accelerators are capable of automating motion around multiple axes, allowing efficient delivery of highly non-coplanar radiotherapy techniques. Novel techniques developed for C-arm an...
Context in source publication
Context 1
... break down into three areas: (1) VMAT with multiple static couch rotations, (2) a coronal VMAT technique that combines dynamic couch rotation with fixed gantry positions, and (3) a trajectory VMAT technique that combines dynamic couch rotation with dynamic gantry rotation. Feasible orientations for non-coplanar VMAT, as well as a range of other techniques, are shown in Figure 2. ...
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Aim:
To assess the precision of dose calculations for Volumetric Modulated Arc Therapy (VMAT) using megavoltage (MV) photon beams, we validated the accuracy of two algorithms: AUROS XB and Analytical Anisotropic Algorithm (AAA). This validation will encompass both flattening filter (FF) and flattening filter-free beam (FFF) modes, using AAPM Medic...
Objective: Performing pre-treatment patient-specific quality assurance (prePSQA) is considered an essential, time-consuming, and resource-intensive task for volumetric modulated arc radiotherapy (VMAT) which confirms the dose accuracy and ensure patient safety. Most current machine learning and deep learning approaches stack excessive convolutional...
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Stereotactic body radiotherapy (SBRT) is an emerging cancer treatment due to its logistical and potential therapeutic benefits as compared to conventional radiotherapy. However, its mechanism of action is yet to be fully understood, likely involving the ablation of tumour microvasculature by higher doses per fraction used in SBRT. In this study, we...
Purpose
To dosimetrically compare Volumetric Modulated Arc Therapy (VMAT) Lattice Radiation Therapy (LRT), brass, and proton grid therapy planning techniques and suggest potential clinical applications for each.
Methods and Materials
Four plans delivering 20 Gray in one fraction were created for each of 22 patients. Brass and proton grid plans use...
Most commonly in radiation therapy, treatments are delivered in a co-planar geometry. Numerous advantages have been reported of adding non-coplanar beams to the treatment plan. The aim of this study was to compare current state-of-the-art VMAT and CyberKnife treatment plans to that of a novel linac design developed at Stanford which utilizes a stat...
Citations
... Noncoplanar optimization methodologies are a subset of trajectory optimization techniques that aim to leverage additional degrees of freedom in radiotherapy (RT) treatment settings. 1 C-arm linear accelerators have great potential for trajectory optimization due to the many axes available for manipulation. Advances in the last decade of research have progressed from beam angle optimization (BAO) that automatically selects ports for intensity-modulated radiotherapy (IMRT), [2][3][4][5] to efficiently choreographed nonisocentric dynamic couch translation and rotation techniques, where almost all possible axes are optimized. ...
... [11][12][13][14] According to a recent review of noncoplanar radiotherapy optimization, there have been few efforts to perform comparisons between coplanar VMAT arcs with noncoplanar VMAT arcs in sites outside of the cranium. 1 This is supported by earlier work finding noncoplanar VMAT arcs chosen by a human were more efficient to deliver than static noncoplanar IMRT ports for liver stereotactic body radiation therapy (SBRT). 15 However, it is impractical to ensure a human operator consistently and optimally selects noncoplanar arcs due to the vast degrees of freedom that must be considered. ...
Noncoplanar arc optimization has been shown to reduce OAR doses in SRS/SRT and has the potential to reduce doses to OARs in SBRT. Extracranial targets have additional considerations, including large OARs and, in the case of the liver, volume constraints on the healthy liver. Considering pathlengths through OARs that encompass target volumes may lead to specific dose reductions as in the encompassing healthy liver tissue. These optimizations must also leverage delivery efficiency and trajectory sampling to ensure ease of clinical translation. The purpose of this research is to generate optimized static‐couch arcs that separately consider serial and parallel OARs and arc delivery efficiency, with a trajectory sampling metric, towards the aim of reducing dose to OARs and the surrounding healthy liver tissue. Separate BEV cost maps were created for parallel, and serial OARs by means of a fast ray‐triangle intersection algorithm. An additional BEV cost map was created for the liver which, by definition, encompasses the liver tumors. The individual costs of these maps were summed and combined with the sampling metric for 100 000 random combinations of arc trajectories. A search algorithm was applied to find an arc trajectory solution that satisfied BEV cost and sampling optimization, while also ensuring an efficient delivery was possible with a low number of arcs. This method of arc selection was evaluated for 16 liver SBRT patients characterized by small and large target volumes. Comparisons were made with a clinical arc template of coplanar arcs. Dosimetric plan quality was evaluated using published guidelines and metrics from RTOG1112. Four of five plan quality metrics for the liver were significantly reduced when planned with optimized noncoplanar arcs. Median (range) reductions of the volumes receiving 10, 18, and 21 Gy were found of 140.4 (295.8) cc (p = 0.001), 28.2 (230.6) cc (p = 0.002) and 18.5 (155.5) cc (p = 0.04). A significant increase in median (range) dose to the right kidney of 0.2 ± 0.9 Gy (p = 0.03) was also found using optimized noncoplanar arcs, which was below the tolerance of 10 Gy for all cases. The average number of arcs chosen was 4 ± 1. Optimizing serial and parallel OARs separately during static couch noncoplanar arc selection significantly reduced the dose to the liver during SBRT using a moderate number of arcs.
... IMRT and VMAT are today's state-of-the-art techniques for H&N cancer [6]. Recent developments extended these techniques by incorporating additional degrees-of-freedom: The research technique dynamic trajectory radiotherapy (DTRT) [7,8] includes dynamic table and collimator rotation during beam-on. Compared to VMAT, DTRT has been shown to improve OAR sparing, while maintaining similar target coverage [9]. ...
Background and purpose
Dynamic trajectory radiotherapy (DTRT) has been shown to improve healthy tissue sparing compared to volumetric arc therapy (VMAT). This study aimed to assess and compare the robustness of DTRT and VMAT treatment-plans for head and neck (H&N) cancer to patient-setup (PS) and machine-positioning uncertainties.
Materials and methods
The robustness of DTRT and VMAT plans previously created for 46 H&N cases, prescribed 50–70 Gy to 95 % of the planning-target-volume, was assessed. For this purpose, dose distributions were recalculated using Monte Carlo, including uncertainties in PS (translation and rotation) and machine-positioning (gantry-, table-, collimator-rotation and multi-leaf collimator (MLC)). Plan robustness was evaluated by the uncertainties’ impact on normal tissue complication probabilities (NTCP) for xerostomia and dysphagia and on dose-volume endpoints. Differences between DTRT and VMAT plan robustness were compared using Wilcoxon matched-pair signed-rank test (α = 5 %).
Results
Average NTCP for moderate-to-severe xerostomia and grade ≥ II dysphagia was lower for DTRT than VMAT in the nominal scenario (0.5 %, p = 0.01; 2.1 %, p < 0.01) and for all investigated uncertainties, except MLC positioning, where the difference was not significant. Average differences compared to the nominal scenario were ≤ 3.5 Gy for rotational PS (≤ 3°) and machine-positioning (≤ 2°) uncertainties, <7 Gy for translational PS uncertainties (≤ 5 mm) and < 20 Gy for MLC-positioning uncertainties (≤ 5 mm).
Conclusions
DTRT and VMAT plan robustness to the investigated uncertainties depended on uncertainty direction and location of the structure-of-interest to the target. NTCP remained on average lower for DTRT than VMAT even when considering uncertainties.
... Beam angle optimization (BAO) in radiation therapy has been the subject of extensive investigation for many years. 1 Nevertheless, current state-of -the-art techniques like coplanar intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) rely on treatment site-specific class-solutions and planner experience rather than BAO for beam/arc setup. 2 On the other hand, there has been a renewed interest for non-coplanar radiotherapy because planning studies have shown improved dosimetric plan quality for multiple treatment sites compared to standard coplanar techniques. [3][4][5][6][7][8][9] Non-coplanar beam arrangements exploit a greater number of possible beam directions which also increase the complexity of the BAO problem. ...
Background
Non‐coplanar techniques have shown to improve the achievable dose distribution compared to standard coplanar techniques for multiple treatment sites but finding optimal beam directions is challenging. Dynamic collimator trajectory radiotherapy (colli‐DTRT) is a new intensity modulated radiotherapy technique that uses non‐coplanar partial arcs and dynamic collimator rotation.
Purpose
To solve the beam angle optimization (BAO) problem for colli‐DTRT and non‐coplanar VMAT (NC‐VMAT) by determining the table‐angle and the gantry‐angle ranges of the partial arcs through iterative 4π fluence map optimization (FMO) and beam direction elimination.
Methods
BAO considers all available beam directions sampled on a gantry‐table map with the collimator angle aligned to the superior‐inferior axis (colli‐DTRT) or static (NC‐VMAT). First, FMO is performed, and beam directions are scored based on their contributions to the objective function. The map is thresholded to remove the least contributing beam directions, and arc candidates are formed by adjacent beam directions with the same table angle. Next, FMO and arc candidate trimming, based on objective function penalty score, is performed iteratively until a desired total gantry angle range is reached. Direct aperture optimization on the final set of colli‐DTRT or NC‐VMAT arcs generates deliverable plans. colli‐DTRT and NC‐VMAT plans were created for seven clinically‐motivated cases with targets in the head and neck (two cases), brain, esophagus, lung, breast, and prostate. colli‐DTRT and NC‐VMAT were compared to coplanar VMAT plans as well as to class‐solution non‐coplanar VMAT plans for the brain and head and neck cases. Dosimetric validation was performed for one colli‐DTRT (head and neck) and one NC‐VMAT (breast) plan using film measurements.
Results
Target coverage and conformity was similar for all techniques. colli‐DTRT and NC‐VMAT plans had improved dosimetric performance compared to coplanar VMAT for all treatment sites except prostate where all techniques were equivalent. For the head and neck and brain cases, mean dose reduction—in percentage of the prescription dose—to parallel organs was on average 0.7% (colli‐DTRT), 0.8% (NC‐VMAT) and 0.4% (class‐solution) compared to VMAT. The reduction in D2% for the serial organs was on average 1.7% (colli‐DTRT), 2.0% (NC‐VMAT) and 0.9% (class‐solution). For the esophagus, lung, and breast cases, mean dose reduction to parallel organs was on average 0.2% (colli‐DTRT) and 0.3% (NC‐VMAT) compared to VMAT. The reduction in D2% for the serial organs was on average 1.3% (colli‐DTRT) and 0.9% (NC‐VMAT). Estimated delivery times for colli‐DTRT and NC‐VMAT were below 4 min for a full gantry angle range of 720°, including transitions between arcs, except for the brain case where multiple arcs covered the whole table angle range. These times are in the same order as the class‐solution for the head and neck and brain cases. Total optimization times were 25%–107% longer for colli‐DTRT, including BAO, compared to VMAT.
Conclusions
We successfully developed dosimetrically motivated BAO for colli‐DTRT and NC‐VMAT treatment planning. colli‐DTRT and NC‐VMAT are applicable to multiple treatment sites, including body sites, with beneficial or equivalent dosimetric performances compared to coplanar VMAT and reasonable delivery times.
... This work consists of evaluation of clinical patient data for determination of the positioning accuracy in cranial SRT. One major distinction between SRT and other RT treatments is the widely used application of non-coplanar couch angles, which are indispensable for optimal dose distribution [27][28][29][30]. As a result of the couch rotation, it must be expected that the patient will also move and change their original position. ...
Purpose
The objective of this work is to estimate the patient positioning accuracy of a surface-guided radiation therapy (SGRT) system using an optical surface scanner compared to an X‑ray-based imaging system (IGRT) with respect to their impact on intracranial stereotactic radiotherapy (SRT) and intracranial stereotactic radiosurgery (SRS).
Methods
Patient positioning data, both acquired with SGRT and IGRT systems at the same linacs, serve as a basis for determination of positioning accuracy. A total of 35 patients with two different open face masks (578 datasets) were positioned using X‑ray stereoscopic imaging and the patient position inside the open face mask was recorded using SGRT. The measurement accuracy of the SGRT system (in a “standard” and an SRS mode with higher resolution) was evaluated using both IGRT and SGRT patient positioning datasets taking into account the measurement errors of the X‑ray system. Based on these clinically measured datasets, the positioning accuracy was estimated using Monte Carlo (MC) simulations. The relevant evaluation criterion, as standard of practice in cranial SRT, was the 95th percentile.
Results
The interfractional measurement displacement vector of the SGRT system, σSGRT, in high resolution mode was estimated at 2.5 mm (68th percentile) and 5 mm (95th percentile). If the standard resolution was used, σSGRT increased by about 20%. The standard deviation of the axis-related σSGRT of the SGRT system ranged between 1.5 and 1.8 mm interfractionally and 0.5 and 1.0 mm intrafractionally. The magnitude of σSGRT is mainly due to the principle of patient surface scanning and not due to technical limitations or vendor-specific issues in software or hardware. Based on the resulting σSGRT, MC simulations served as a measure for the positioning accuracy for non-coplanar couch rotations. If an SGRT system is used as the only patient positioning device in non-coplanar fields, interfractional positioning errors of up to 6 mm and intrafractional errors of up to 5 mm cannot be ruled out. In contrast, MC simulations resulted in a positioning error of 1.6 mm (95th percentile) using the IGRT system. The cause of positioning errors in the SGRT system is mainly a change in the facial surface relative to a defined point in the brain.
Conclusion
In order to achieve the necessary geometric accuracy in cranial stereotactic radiotherapy, use of an X‑ray-based IGRT system, especially when treating with non-coplanar couch angles, is highly recommended.
... Furthermore, diverging from the coplanar plane is usually connected with increased delivery times, especially for 4 -IMRT, 11,15,16 which can negatively impact patient comfort. Hence, more efficient delivery is desired and can be achieved by combining dynamic gantry and table rotation with intensity modulation 17,18 : Dynamic trajectory radiotherapy (DTRT) 19,20 is an extension of VMAT that involves dynamic table and collimator rotations during delivery, allowing for treatment times similar to VMAT. ...
... • Dosimetric plan quality • Plan complexity • Dosimetric robustness • Deliverability • Delivery time Dosimetric treatment plan comparisons considering different treatment sites already indicated substantially improved sparing of OARs for DTRT as compared to VMAT. 18,19 With the added DoF and the associated increased complexity, the dosimetric robustness of DTRT plans could be compromised. The number of robustness studies including DTRT are limited, and usually focus on patient setup uncertainties. ...
Background
To improve organ at risk (OAR) sparing, dynamic trajectory radiotherapy (DTRT) extends VMAT by dynamic table and collimator rotation during beam‐on. However, comprehensive investigations regarding the impact of the gantry‐table (GT) rotation gradient on the DTRT plan quality have not been conducted.
Purpose
To investigate the impact of a user‐defined GT rotation gradient on plan quality of DTRT plans in terms of dosimetric plan quality, dosimetric robustness, deliverability, and delivery time.
Methods
The dynamic trajectories of DTRT are described by GT and gantry‐collimator paths. The GT path is determined by minimizing the overlap of OARs with planning target volume (PTV). This approach is extended to consider a GT rotation gradient by means of a maximum gradient of the path (Gmax${G}_{max}$) between two adjacent control points (G=|Δtableangle/Δgantryangle|$G = | \Delta {{\mathrm{table\ angle}}/\Delta {\mathrm{gantry\ angle}}} |$) and maximum absolute change of G (ΔGmax${{\Delta}}{G}_{max}$). Four DTRT plans are created with different maximum G&∆G: Gmax${G}_{max}$&ΔGmax${{\Delta}}{G}_{max}$ = 0.5&0.125 (DTRT‐1), 1&0.125 (DTRT‐2), 3&0.125 (DTRT‐3) and 3&1(DTRT‐4), including 3–4 dynamic trajectories, for three clinically motivated cases in the head and neck and brain region (A, B, and C). A reference VMAT plan for each case is created. For all plans, plan quality is assessed and compared. Dosimetric plan quality is evaluated by target coverage, conformity, and OAR sparing. Dosimetric robustness is evaluated against systematic and random patient‐setup uncertainties between ±3mm$ \pm 3\ {\mathrm{mm}}$ in the lateral, longitudinal, and vertical directions, and machine uncertainties between ±4∘$ \pm 4^\circ \ $in the dynamically rotating machine components (gantry, table, collimator rotation). Delivery time is recorded. Deliverability and delivery accuracy on a TrueBeam are assessed by logfile analysis for all plans and additionally verified by film measurements for one case. All dose calculations are Monte Carlo based.
Results
The extension of the DTRT planning process with user‐defined Gmax&ΔGmax${G}_{max}\& {{\Delta}}{G}_{max}$ to investigate the impact of the GT rotation gradient on plan quality is successfully demonstrated. With increasing Gmax&ΔGmax${G}_{max}\& {{\Delta}}{G}_{max}$, slight (case C, Dmean,parotidl.${D}_{mean,\ parotid\ l.}$: up to−1Gy) and substantial (case A, D0.03cm3,opticnerver.${D}_{0.03c{m}^3,\ optic\ nerve\ r.}$: up to −9.3 Gy, caseB,Dmean,brain$\ {D}_{mean,\ brain}$: up to −4.7Gy) improvements in OAR sparing are observed compared to VMAT, while maintaining similar target coverage. All plans are delivered on the TrueBeam. Expected and actual machine position values recorded in the logfiles deviated by <0.2° for gantry, table and collimator rotation. The film measurements agreed by >96% (2%global/2 mm Gamma passing rate) with the dose calculation. With increasing Gmax&ΔGmax${G}_{max}\& {{\Delta}}{G}_{max}$, delivery time is prolonged by <2 min/trajectory (DTRT‐4) compared to VMAT and DTRT‐1. The DTRT plans for case A and B and the VMAT plan for case C plan reveal the best dosimetric robustness for the considered uncertainties.
Conclusion
The impact of the GT rotation gradient on DTRT plan quality is comprehensively investigated for three cases in the head and neck and brain region. Increasing freedom in this gradient improves dosimetric plan quality at the cost of increased delivery time for the investigated cases. No clear dependency of GT rotation gradient on dosimetric robustness is observed.
... In the past several studies have tried to evaluate the dosimetric differences in the usage of noncoplanar and coplanar plans in treatment of carcinoma breast. [10,11] However, none of the studies have used the technique for the treatment of BBCs. Hence, we designed a study aimed at analyzing the possible dosimetric advantages and disadvantages of using noncoplanar plans in the treatment of BBCs. ...
... The literature gives us various examples of noncoplanar RT plans from different sites. Various methods [10] have been followed like (i) VMAT static couch mode at different couch orientation, (ii) a coronal VMAT technique that combines dynamic couch rotation with fixed gantry positions, and (iii) A trajectory VMAT technique that combines dynamic couch rotation with dynamic gantry rotation. The authors have also tried fixed gantry and dynamic couch rotation for accelerated partial breast irradiation (APBI). ...
Introduction
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.
Materials and Methods
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.
Results
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.
Conclusion
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.
... With its a long successful history in cancer treatment, since the use of treatments based on ionizing radiation, several techniques have been developed in radiotherapy, like the Intensity-Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) based on X-ray beams with kilovolt (kV) to megavolt (MV) photons, to be an effective alternative or complementary method in oncology (Teoh et al., 2011;Hussein et al., 2018;Smyth et al., 2019). ...
Background
The purpose of this research was to establish the primary electron beam characteristics for an Elekta Synergy linear accelerator. In this task, we take advantage of the PRIMO Monte Carlo software, where the model developed contains the majority of the component materials of the Linac.
Materials and methods
For all energies, the Elekta Linac electron mode and 14 × 14 cm² applicator were chosen. To obtain percentage depth dose (PDD) curves, a homogeneous water phantom was voxelized in a 1 × 1 × 0.1 cm³ grid along the central axis. At the reference depth, the dose profile was recorded in 0.1 × 1 × 1 cm³ voxels. Iterative changes were made to the initial beams mean energy and full width at half maximum (FWHM) of energy in order to keep the conformity of the simulated and measured dose curves within. To confirm simulation results, the Gamma analysis was performed with acceptance criteria of 2 mm — 2%. From the validated calculation, the parameters of the PDD and profile curve (R100, R50, Rp, and field size) were collected.
Results
Initial mean energies of 7.3, 9.85, 12.9, and 15.7 MeV were obtained for nominal energies of 6, 9, 12, and 15, respectively. The PRIMO Monte Carlo model for Elekta Synergy was precisely validated.
Conclusions
PRIMO is an easy-to-use software program that can calculate dose distribution in water phantoms.
... [2][3][4][5][6] Efficient non-coplanar delivery, such as in dynamic trajectory radiotherapy (DTRT 2 ), can be obtained by combination of dynamic gantry and table rotation with intensity modulation, with or without dynamic collimator rotation. 7,8 Regardless of the chosen treatment technique, respiratory motion in the thorax [9][10][11][12][13] and abdomen requires motion management to mitigate the degradation of the delivered dose distribution. 14 Motion management techniques include breath-hold, free-breathing gating, or MLC or couch tracking. ...
Background
Dynamic trajectory radiotherapy (DTRT) extends state‐of‐the‐art volumetric modulated arc therapy (VMAT) by dynamic table and collimator rotations during beam‐on. The effects of intrafraction motion during DTRT delivery are unknown, especially regarding the possible interplay between patient and machine motion with additional dynamic axes.
Purpose
To experimentally assess the technical feasibility and quantify the mechanical and dosimetric accuracy of respiratory gating during DTRT delivery.
Methods
A DTRT and VMAT plan are created for a clinically motivated lung cancer case and delivered to a dosimetric motion phantom (MP) placed on the table of a TrueBeam system using Developer Mode. The MP reproduces four different 3D motion traces. Gating is triggered using an external marker block, placed on the MP. Mechanical accuracy and delivery time of the VMAT and DTRT deliveries with and without gating are extracted from the logfiles. Dosimetric performance is assessed by means of gamma evaluation (3% global/2 mm, 10% threshold).
Results
The DTRT and VMAT plans are successfully delivered with and without gating for all motion traces. Mechanical accuracy is similar for all experiments with deviations <0.14° (gantry angle), <0.15° (table angle), <0.09° (collimator angle) and <0.08 mm (MLC leaf positions). For DTRT (VMAT), delivery times are 1.6–2.3 (1.6– 2.5) times longer with than without gating for all motion traces except one, where DTRT (VMAT) delivery is 5.0 (3.6) times longer due to a substantial uncorrected baseline drift affecting only DTRT delivery. Gamma passing rates with (without) gating for DTRT/VMAT were ≥96.7%/98.5% (≤88.3%/84.8%). For one VMAT arc without gating it was 99.6%.
Conclusion
Gating is successfully applied during DTRT delivery on a TrueBeam system for the first time. Mechanical accuracy is similar for VMAT and DTRT deliveries with and without gating. Gating substantially improved dosimetric performance for DTRT and VMAT.
... 3,5 Intensity-modulated radiotherapy (IMRT) has the ability to generate complicated spatial dose distributions for HCC patients that conform more closely to the target volume while sparing critical organs by employing an inverse planning algorithm. [6][7][8][9][10][11] Volumetric modulated arc therapy (VMAT), the newest form of IMRT, can improve the time efficiency of dose delivery and deliver more conformal dose distributions to HCC patients by changing treatment apertures (dynamic multiple leaf collimators) as well as providing a modulated dose rate. [12][13][14] Recently, the incorporation of noncoplanar beam arrangements has been proposed in liver radiotherapy modalities, which can reduce the dose in normal tissues compared to coplanar techniques. ...
Background:
The incorporation of noncoplanar beam arrangements has been proposed in liver radiotherapy modalities, which can reduce the dose in normal tissues compared to coplanar techniques. Noncoplanar radiotherapy techniques for hepatocellular carcinoma treatment based on the Linac design have a limited effective arc angle to avoid collisions.
Purpose:
To propose a novel noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system and investigate its performance in hepatocellular carcinoma patients.
Methods:
The computed tomography was deflected 90° to meet the structure of a cage-like radiotherapy system and design the noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system plan in the Pinnacle3 planning system. An noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system plan was customized for each of 10 included hepatocellular carcinoma patients, with 6 dual arcs ranging from -30° to 30°. Six couch angles were set with an interval of 36° and distributed along with the longest diameter of planning target volume. The dosimetric parameters of noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system plan were compared with the noncoplanar volumetric modulated arc therapy and volumetric modulated arc therapy plan.
Results:
The 3 radiotherapy techniques regarding planning target volume were statistically different for D98%, D2%, conformity index, and homogeneity index with χ2 = 9.692, 14.600, 8.600, and 12.600, and P = .008, .001, .014, and .002, respectively. Further multiple comparisons revealed that noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system significantly reduced the mean dose (P = .005) and V5 (P = .005) of the normal liver, the mean dose (P = .005) of the stomach, and V30 (P = .028) of the lung compared to noncoplanar volumetric modulated arc therapy. Noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system significantly reduced the mean dose (P = .005) and V5 (P = .005) of the normal liver, the mean dose (P = .017) of the spinal cord, V50 (P = .043) of the duodenum, the maximum dose (P = .007) of the esophagus, and V30 (P = .047) of the whole lung compared to volumetric modulated arc therapy. The results indicate that noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system protects the normal liver, stomach, and lung better than noncoplanar volumetric modulated arc therapy and protects the normal liver, spinal cord, duodenum, esophagus, and lung better than volumetric modulated arc therapy.
Conclusions:
The noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system technique with the arrangement of noncoplanar arcs provided optimal dosimetric gains compared with noncoplanar volumetric modulated arc therapy and volumetric modulated arc therapy, except for the heart. Noncoplanar volumetric modulated arc therapy technique based on a cage-like radiotherapy system should be considered in more clinically challenging cases.
... Despite improvements achieved from using non-coplanar IMRT, they are still not adopted for use at most treatment centers. The use of a non-coplanar treatment trajectory significantly enhances the degree of freedom and flexibility but increases drastically the complexity of the optimization (Smyth et al. 2019). ...
Non-coplanar Intensity-Modulated Radiation Therapy (IMRT) goes a step further by orienting the gantry carrying the radiation beam and the patient couch in a non-coplanar manner to accurately target the cancer region and better avoid organs-at-risk. The use of a non-coplanar treatment trajectory significantly enhances the degree of freedom and flexibility but increases drastically the complexity of the optimization. In inverse planning optimization the dose contribution for all potential beam directions is usually pre-calculates and pre-loads into the Treatment Planning System (TPS). The size the dose matrix becomes more critical when moving from coplanar IMRT to non-coplanar IMRT since the number of beams increases drastically. A solution would be to calculate "on-the-fly" the dose contribution to each new candidate beam during optimization. This is only possible if a dose calculation engine is fast enough to be used online during optimization iterations, which is not the case in standard method. Therefore, in this work we propose an IMRT optimization scheme using deep learning based dose engine to compute the dose matrix on-line. The proposed deep learning approach will be combined into a simulated-annealing-based optimization method for non-coplanar IMRT. Since the dose engine will compute the dose contribution on-line during the optimization, the final main optimization method requires to keep in memory a very lightweight dose matrix. The proposed method was compared with clinical data showing a good agreement considering dosimetry of the treatment plans. The main advantage of the proposed method was the reduction of the memory storage from 9GB to 10MB during the optimization process.
