Volumetric-modulated arc therapy (VMAT) may have the highest overall performance for stereotactic body radiotherapy (SBRT) treatment of inoperable early-stage NSCLC. However, in centers lacking the VMAT technique, the dynamic conformal arc therapy (DCAT) technique is potentially the best option for small and rounded NSCLC-SBRT. Therefore, we will comprehensively analyze the advantages of the DCAT versus the other techniques except VMAT in terms of dosimetry, plan complexity, delivery time, γ-passing rates and the interplay effect.

36 patients with early-stage centrally located NSCLC with PTV volumes < 65 cc were enrolled. All patients were redesigned with 50Gy/5f, and 100% of the prescribed dose was normalized to cover 95% of the PTV. The other two delivery techniques compared to the DCAT technique include 3-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT), which use the same parameters for all three techniques.

The dosimetric parameters of the 3-group plans all met the RTOG 0813 protocol. Unsurprisingly, plan complexity parameters such as segments and MUs were significantly reduced in the DCAT plans by 159.56 and 925.90 compared to the IMRT plans, respectively (all P < 0.001). The delivery time of the DCAT plans was the least of 164.51 s (all P < 0.05). Compared to the IMRT plans, the γ-passing rates were higher in the DCAT plans (P < 0.001), with the most significant difference of 6.01% in the (2%, 1 mm) criteria. As for the interplay effect, the mean dose difference (MDD) in the DCAT plans was as good as the 3DCRT plans at different respiratory amplitudes but better than the IMRT plans (all P < 0.05), and the MDD of DCAT plans did not exceed 3% in all respiratory amplitude.

In centers lacking the VMAT technique, implementing SBRT treatment based on the DCAT technique for inoperable early-stage centrally-located NSCLC patients with PTV volumes < 65 cc achieves better treatment efficiency and delivery accuracy while maintaining the plan quality.

Cardiac stereotactic body radiotherapy (CSBRT) is an emerging and promising noninvasive technique for treating refractory arrhythmias utilizing highly precise, single or limited-fraction high-dose irradiations. This method promises to revolutionize the treatment of cardiac conditions by delivering targeted therapy with minimal exposure to surrounding healthy tissues. However, the dynamic nature of cardiorespiratory motion poses significant challenges to the precise delivery of dose in CSBRT, introducing potential variabilities that can impact treatment efficacy. The complexities of the influence of cardiorespiratory motion on dose distribution are compounded by interplay and blurring effects, introducing additional layers of dose uncertainty. These effects, critical to the understanding and improvement of the accuracy of CSBRT, remain unexplored, presenting a gap in current clinical literature.

To investigate the cardiorespiratory motion characteristics in arrhythmia patients and the dosimetric impact of interplay and blurring effects induced by cardiorespiratory motion on CSBRT plan quality.

The position and volume variations in the substrate target and cardiac substructures were evaluated in 12 arrhythmia patients using displacement maximum (DMX) and volume metrics. Moreover, a four-dimensional (4D) dose reconstruction approach was employed to examine the dose uncertainty of the cardiorespiratory motion.

Cardiac pulsation induced lower DMX than respiratory motion but increased the coefficient of variation and relative range in cardiac substructure volumes. The mean DMX of the substrate target was 0.52 cm (range: 0.26-0.80 cm) for cardiac pulsation and 0.82 cm (range: 0.32-2.05 cm) for respiratory motion. The mean DMX of the cardiac structure ranged from 0.15 to 1.56 cm during cardiac pulsation and from 0.35 to 1.89 cm during respiratory motion. Cardiac pulsation resulted in an average deviation of -0.73% (range: -4.01%-4.47%) in V25 between the 3D and 4D doses. The mean deviations in the homogeneity index (HI) and gradient index (GI) were 1.70% (range: -3.10%-4.36%) and 0.03 (range: -0.14-0.11), respectively. For cardiac substructures, the deviations in D50 due to cardiac pulsation ranged from -1.88% to 1.44%, whereas the deviations in Dmax ranged from -2.96% to 0.88% of the prescription dose. By contrast, the respiratory motion led to a mean deviation of -1.50% (range: -10.73%-4.23%) in V25. The mean deviations in HI and GI due to respiratory motion were 4.43% (range: -3.89%-13.98%) and 0.18 (range: -0.01-0.47) (p < 0.05), respectively. Furthermore, the deviations in D50 and Dmax in cardiac substructures for the respiratory motion ranged from -0.28% to 4.24% and -4.12% to 1.16%, respectively.

Cardiorespiratory motion characteristics vary among patients, with the respiratory motion being more significant. The intricate cardiorespiratory motion characteristics and CSBRT plan complexity can induce substantial dose uncertainty. Therefore, assessing individual motion characteristics and 4D dose reconstruction techniques is critical for implementing CSBRT without compromising efficacy and safety.

Biology-guided radiotherapy (BgRT) is a novel radiotherapy delivery technique that utilizes the tumor itself to guide dynamic delivery of treatment dose to the tumor. The RefleXion X1 system is the first radiotherapy system developed to deliver SCINTIX® BgRT. The X1 is characterized by its split arc design, employing two 90-degree positron emission tomography (PET) arcs to guide therapeutic radiation beams in real time, currently cleared by FDA to treat bone and lung tumors.

This study aims to comprehensively evaluate the capabilities of the SCINTIX radiotherapy delivery system by evaluating its sensitivity to changes in PET contrast, its adaptability in the context of patient motion, and its performance across a spectrum of prescription doses.

A series of experimental scenarios, both static and dynamic, were designed to assess the SCINTIX BgRT system's performance, including an end-to-end test. These experiments involved a range of factors, including changes in PET contrast, motion, and prescription doses. Measurements were performed using a custom-made ArcCHECK insert which included a 2.2 cm spherical target and a c-shape structure that can be filled with a PET tracer with varying concentrations. Sinusoidal and cosine4 motion patterns, simulating patient breathing, was used to test the SCINTIX system's ability to deliver BgRT during motion-induced challenges. Each experiment was evaluated against specific metrics, including Activity Concentration (AC), Normalized Target Signal (NTS), and Biology Tracking Zone (BTZ) bounded dose-volume histogram (bDVH) pass rates. The accuracy of the delivered BgRT doses on ArcCHECK and EBT-XD film were evaluated using gamma 3%/2 mm and 3%/3 mm analysis.

In static scenarios, the X1 system consistently demonstrated precision and robustness in SCINTIX dose delivery. The end-to-end delivery to the spherical target yielded good results, with AC and NTS values surpassing the critical thresholds of 5 kBq/mL and 2, respectively. Furthermore, bDVH analysis consistently confirmed 100% pass rates. These results were reaffirmed in scenarios involving changes in PET contrast, emphasizing the system's ability to adapt to varying PET avidities. Gamma analysis with 3%/2 mm (10% dose threshold) criteria consistently achieved pass rates > 91.5% for the static tests. In dynamic SCINTIX delivery scenarios, the X1 system exhibited adaptability under conditions of motion. Sinusoidal and cosine4 motion patterns resulted in 3%/3 mm gamma pass rates > 87%. Moreover, the comparison with gated stereotactic body radiotherapy (SBRT) delivery on a conventional c-arm Linac resulted in 93.9% gamma pass rates and used as comparison to evaluate the interplay effect. The 1 cm step shift tests showed low overall gamma pass rates of 60.3% in ArcCHECK measurements, while the doses in the PTV agreed with the plan with 99.9% for 3%/3 mm measured with film.

The comprehensive evaluation of the X1 radiotherapy delivery system for SCINTIX BgRT demonstrated good agreement for the static tests. The system consistently achieved critical metrics and delivered the BgRT doses per plan. The motion tests demonstrated its ability to co-localize the dose where the PET signal is and deliver acceptable BgRT dose distributions.

For many thoracic tumors, patient respiration can introduce a significant amount of variability in tumor position that must be accounted for during radiotherapy. Of all existing techniques, real-time dynamic tumor tracking (DTT) represents the most ideal motion management strategy but can be limited by the treatment delivery technique. Our objective was to analyze the dosimetric performance of a dynamic conformal arc (DCA) approach to tumor tracking on standard linear accelerators that may offer similar dosimetric benefit, but with less complexity compared to intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT).

Ten patients who previously received free-breathing VMAT for lung cancer were retrospectively analyzed. Patient 4D-CT and respiratory traces were simultaneously acquired prior to treatment and re-planned with DCA and VMAT using the Eclipse v15.6 Treatment Planning System with gated, deep inspiration breath hold (DIBH), and motion encompassment techniques taken into consideration, generating seven new plans per patient. DTT with DCA was simulated using an in-house MATLAB script to parse the radiation dose into each phase of the 4D-CT based on the patient's respiratory trace. Dose distributions were normalized to the same prescription and analyzed using dose volume histograms (DVHs). DVH metrics were assessed using ANOVA with subsequent paired t-tests.

The DCA-based DTT plans outperformed or showed comparable performance in their DVH metrics compared to all other combinations of treatment techniques while using motion management in normal lung sparing (p < 0.05). Normal lung sparing was not significantly different when comparing DCA-based DTT to gated and DIBH VMAT (p > 0.05), while both outperformed the corresponding DCA plans (p < 0.05). Simulated treatment times using DCA-based DTT were significantly shorter than both gating and DIBH plans (p < 0.05).

A DCA-based DTT technique showed significant advantages over conventional motion encompassment treatments in lung cancer radiotherapy, with comparable performance to stricter techniques like gating and DIBH while conferring greater time-saving benefits.

This study exposed the implementation of a novel technique (VMATLSL) for the planning of moving targets in lung stereotactic body radiation therapy (SBRT). This new technique has been compared to static conformal radiotherapy (3D-CRT), volumetric-modulated arc therapy (VMAT), and dynamic conformal arc (DCA). The rationale of this study was to lower geometric complexity (54.9% lower than full VMAT) and hence ensure the reproducibility of the treatment delivery by reducing the risk for interplay errors induced by respiratory motion. Dosimetry metrics were studied with a cohort of 30 patients. Our results showed that leaf speed limitation provided conformal number (CN) close to the VMAT (median CN of VMATLSL is 0.78 vs 0.82 for full VMAT) and was a significant improvement on 3D-CRT and DCA with segment-weight optimized (respectively 0.55 and 0.57). This novel technique is an alternative to VMAT or DCA for lung SBRT treatments, combining independence from the patient's breathing pattern, from the size and amplitude of the lesion, free from interplay effect, and with dosimetry metrics close to the best that could be achieved with full VMAT.

With the advancement of radiotherapy equipment, stereotactic radiotherapy (SRT) has been increasingly used. Among the many radiotherapy devices, Halcyon shows promising applications. This article reviews the dosimetric performance such as plan quality, plan complexity, and gamma passing rates of SRT plans with Halcyon to determine the effectiveness and safety of Halcyon SRT plans. This article retrieved the last 5 years of PubMed studies on the effectiveness and safety of the Halcyon SRT plans. Two authors independently reviewed the titles and abstracts to decide whether to include the studies. A search was conducted to identify publications relevant to evaluating the dosimetric performance of SRT plans on Halcyon using the key strings Halcyon, stereotactic radiosurgery, SRT, stereotactic body radiotherapy, and stereotactic ablative radiotherapy. A total of 18 eligible publications were retrieved. Compared to SRT plans on the TrueBeam, the Halcyon has advantages in terms of plan quality, plan complexity, and gamma passing rates. The high treatment speed of SRT plans on the Halcyon is impressive, while the results of its plan evaluation are also encouraging. As a result, Halcyon offers a new option for busy radiotherapy units while significantly improving patient comfort in treatment. For more accurate results, additional relevant publications will need to be followed up in subsequent studies.

Purpose.This dosimetric study is intended to lower the modulation factor in lung SBRT plans generated in the Eclipse TPS that could replace highly modulated plans that are prone to the interplay effect.Materials and methods.Twenty clinical lung SBRT plans with high modulation factors (≥4) were replanned in Varian Eclipse TPS version 15.5 utilizing 2 mm craniocaudal and 1 mm axial block margins followed by light optimization in order to reduce modulation. A unique plan optimization methodology, which utilizes a novel shell structure (OptiForR₅₀) for R_50%optimization in addition to five consecutive concentric 5 mm shells, was utilized to control dose falloff according to RTOG 0813 and 0915 recommendations. The prescription varied from 34-54 Gy in 1-4 fractions, and the dose objectives were PTV D_95%= Rx, PTV D_max< 140% of Rx, and minimizing the modulation factor. Plan evaluation metrics included modulation factor, CI_RTOG, homogeneity index (HI), R_50%, D_2cm, V_105%, and lung V_8-12.8Gy(Timmerman Constraint). A random-intercept linear mixed effects model was used with a p ≤ 0.05 threshold to test for statistical significance.Results.The retrospectively generated plans had significantly lower modulation factors (3.65 ± 0.35 versus 4.59 ± 0.54; p < 0.001), lower CI_RTOG(0.97 ± 0.02 versus 1.02 ± 0.06; p = 0.001), higher HI (1.35 ± 0.06 versus 1.14 ± 0.04; p < 0.001), lower R_50%(4.09 ± 0.45 versus 4.56 ± 0.56; p < 0.001), and lower lungs V_8-12.8Gy(Timmerman) (4.61% ± 3.18% versus 4.92% ± 3.37%; p < 0.001). The high dose spillage V_105%was borderline significantly lower (0.44% ± 0.49% versus 1.10% ± 1.64%; p = 0.051). The D_2cmwas not statistically different (46.06% ± 4.01% versus 46.19% ± 2.80%; p = 0.835).Conclusion.Lung SBRT plans with significantly lower modulation factors can be generated that meet the RTOG constraints, using our planning strategy.

To elucidate the important factors and their interplay that drive performance on IMRT phantoms from the Imaging and Radiation Oncology Core (IROC).

IROC's IMRT head and neck phantom contains two targets and an organ at risk. Point and 2D dose are measured by TLDs and film, respectively. 1,542 irradiations between 2012-2020 were retrospectively analyzed based on output parameters, complexity metrics, and treatment parameters. Univariate analysis compared parameters based on pass/fail, and random forest modeling was used to predict output parameters and determine the underlying importance of the variables.

The average phantom pass rate was 92% and has not significantly improved over time. The step-and-shoot irradiation technique had significantly lower pass rates that significantly affected other treatment parameters' pass rates. The complexity of plans has significantly increased with time, and all aperture-based complexity metrics (except MCS) were associated with the probability of failure. Random forest-based prediction of failure had an accuracy of 98% on held-out test data not used in model training. While complexity metrics were the most important contributors, the specific metric depended on the set of treatment parameters used during the irradiation.

With the prevalence of errors in radiotherapy, understanding which parameters affect treatment delivery is vital to improve patient treatment. Complexity metrics were strongly predictive of irradiation failure; however, they are dependent on the specific treatment parameters. In addition, the use of one complexity metric is insufficient to monitor all aspects of the treatment plan.

Tumor motion and delivery efficiency are two main challenges of lung stereotactic body radiotherapy (SBRT). The present work implemented the deep inspiration breath hold technique (DIBH) with surface guided radiation therapy (SGRT) on closed-bore linacs and investigated the correlation between SGRT data and internal target position.

Thirteen lung SBRT patients treated in DIBH using a closed-bore gantry linac and a ring-mounted SGRT system were retrospectively analysed. Visual coaching was used to achieve DIBH with a ± 1 mm threshold window in the anterior-posterior direction. Three kV-CBCTs were added to the treatment workflow and examined offline to verify intra-fraction tumor position. Surface-based DIBH was analysed using SGRT treatment reports and an in-house python script. Data from 73 treatment sessions and 175 kV-CBCTs were studied. Correlations between target and surface positions were studied with Linear Mixed Models.

Median intra-fraction tumor motion was 0.8 mm (range: 0.7-1.3 mm) in the anterior-posterior direction, 1.2 mm (range: 1-1.7 mm) in the superior-inferior direction, and 1 mm (range: 0.7-1.1 mm) in the left-right direction, with rotations of <1° (range: 0.6°-1.1°) degree in all three directions. Planned target volumes and healthy lung volumes receiving 12.5 Gy and 13.5 Gy were reduced on average by 67% and 54%, respectively.

Lung SBRT in DIBH with the ring-mounted SGRT system proved reproducible. The surface monitoring provided by SGRT was found to be a reliable surrogate for internal target motion. Moreover, the implementation of DIBH technique helped reduce target volumes and lung doses.

We measure the dose distribution of gated delivery for different target motions and estimate the gating latency in a magnetic resonance-guided radiotherapy (MRgRT) system.

The dose distribution accuracy of the gated MRgRT system (MRIdian, Viewray) was investigated using an in-house-developed phantom that was compatible with the magnetic field and gating method. This phantom contains a simulated tumor and a radiochromic film (EBT3, Ashland, Inc.). To investigate the effect of the number of beam switching and target velocity on the dose distribution, two types of target motions were applied. One is that the target was periodically moved at a constant velocity of 5 mm/s with different pause times (0, 1, 3, 10, and 20 s) between the motions. During different pause times, different numbers of beams were switched on/off. The other one is that the target was moved at velocities of 3, 5, 8, and 10 mm/s without any pause (i.e., continuous motion). The gated method was applied to these motions at MRIdian, and the dose distributions in each condition were measured using films. To investigate the relation between target motion and dose distribution in the gating method, we compared the results of the gamma analysis of the calculated and measured dose distributions. Moreover, we analytically estimated the gating latencies from the dose distributions measured using films and the gamma analysis results.

The gamma pass rate linearly decreased with increasing beam switching and target velocity. The overall gating latencies of beam-hold and beam-on were 0.51 ± 0.17 and 0.35 ± 0.05 s, respectively.

Film measurements highlighted the factors affecting the treatment accuracy of the gated MRgRT system. Our analytical approach, employing gamma analysis on films, can be used to estimate the overall latency of the gated MRgRT system.

The aim of this study is to perform patient quality controls and end-to-end tests for stereotactic VMAT lung treatment plans and to investigate the influence of various parameters on the results.

18 plans were defined by an experimental design methodology to cover a large variety of stereotactic VMAT lung treatments including different doses per fraction, target diameters, target movements and respiratory parameters. Plans were first controlled using portal dosimetry and a homogeneous static cylindrical phantom. End-to-end tests were then performed in a dynamic respiratory thorax phantom. Measurements were conducted with ionization chamber and films. Calculations were performed with the AcurosXB and AAA algorithms in 6 FFF.

Portal dosimetry gave excellent gamma pass rates (greater than 97.1 %) and dose deviations between measurement and calculations in a homogeneous static phantom were smaller than 2 %. The methodology followed for comparing calculated and measured doses in a moving target was validated in static fields (largest deviation smaller than  2 %). End-to-end tests showed mean deviations of 1.9 %, 3.3 % and 6.6 % for the 3, 2 and 1 cm diameter's target respectively. Deviations increased for larger movements for the 1 cm lesion.

End-to-end tests revealed that stereotactic VMAT lung treatment plans for moving targets can be delivered within 5 % for 3 and 2 cm diameter targets and amplitudes up to 1.5 cm. The AcurosXB and AAA algorithms however tend to underestimate the dose to the target. Even with satisfactory patient quality controls like portal dosimetry, extra care should be taken for GTV lesions smaller than 2 cm.

The use of volumetric modulated arc therapy (VMAT) with flattening-filter-free (FFF) beams is becoming more prevalent in lung cancer stereotactic body radiotherapy (SBRT). The aim in this study was to assess the impact of dosimetric and radiobiological differences between FFF and flattening filter (FF) beams for lung SBRT based on the target volume.

A total of 198 lung stereotactic body radiation therapy treatment plans with FFF beams and FF beams were retrospectively selected for this study. For all plans, the prescribed dose was 50 Gy/5 fractions, and the dose volume histogram (DVH) for the target and organs at risk (OAR) and the normal tissue complication probability (NTCP) of the lung were recorded and compared. Moreover, monitor units (MUs), the beam on-time and the treatment time were evaluated.

The study was performed following the Radiation Therapy Oncology Group (RTOG) 0813 and 0915 protocols. No significant differences in D90, coverage rate (CR) or conformity index (CI) of the target were observed between FFF beams and FF beams (p>0.05). The D2, R50% and gradient index (GI) for the target improved with FFF beams compared with FF beams (p<0.05). FFF beams also significantly reduced the dose for the lung, heart, spinal cord, esophagus and NTCP of the lung (p<0.05), compared with FF beams. However, there was no significant difference in sparing of the trachea (p>0.05). The mean MUs, beam on-time and treatment time were 1871 ± 278 MUs, 3.2 ± 0.2 min and 3.9 ± 0.3 min for FFF beams, and 1890 ± 260 MUs, 4.2 ± 0.3 min and 4.8 ± 0.4 min for FF beams, respectively.

The FFF beam technique for lung SBRT with VMAT results in a better dose fall-off, better dose-sparing of OAR, lower NTCP of the lung and a shorter beam on-time compared with the FF beam technique. Additionally, the improvement in target and OAR-sparing for FFF beams was increased with increasing target volume.

The purpose of this study is to investigate the effect of plan complexity on the dosimetry, delivery accuracy, and interplay effect in lung stereotactic body radiation therapy (SBRT) using volumetric modulated arc therapy (VMAT) with 6 MV flattening-filter-free (FFF) beam.

Twenty patients with early stage non-small cell lung cancer were included. For each patient, high-complexity (HC) and low-complexity (LC) three-partial-arc VMAT plans were optimized by adjusting the normal tissue objectives and the maximum monitoring units (MUs) for a Varian TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, CA, USA) using 6 MV FFF beam. The effect of plan complexity was comprehensively evaluated in three aspects: (1) The dosimetric parameters, including CI, D_2cm, R₅₀, and dose-volume parameters of organs at risk were compared. (2) The delivery accuracy was assessed by pretreatment quality assurance for two groups of plans. (3) The motion-induced dose deviation was evaluated based on point dose measurements near the tumor center by using a programmable phantom. The standard deviation (SD) and maximum dose difference of five measurements were used to quantify the interplay effect.

The dosimetry of HC and LC plans were similar except the CI (1.003 ± 0.032 and 1.026 ± 0.043, p = 0.030) and D_max to the spinal cord (10.6 ± 3.2 and 9.9 ± 3.0, p = 0.012). The gamma passing rates were significantly higher in LC plans for all arcs (p < 0.001). The SDs of HC and LC plans ranged from 0.5-16.6% and 0.03-2.9%, respectively, under the conditions of one-field, two-field, and three-field delivery for each plan with 0.5, 1, 2, and 3 cm motion amplitudes. The maximum dose differences of HC and LC plans were 34.5% and 9.1%, respectively.

For lung VMAT SBRT, LC plans have a higher delivery accuracy and a lower motion-induced dose deviation with similar dosimetry compared with HC plans.

We evaluated the probabilistic randomness of predictions by using individual numerical data based on general data for treatment planning computed tomography (CT) and evaluated the importance of patient-specific management through statistical analysis of our facility's data in lung stereotactic body radiotherapy (SBRT) and prostate volumetric modulated arc therapy (VMAT). The subjects were 30 patients who underwent lung SBRT with fiducial markers and 24 patients who underwent prostate VMAT. The average 3-dimensional (3D) displacement error between the fiducial marker and lung mass in 4DCT of lung SBRT was calculated and then compared with the 3D displacement error between the upper-lobe group (UG) and middle- or lower-lobe group (LG). The duty cycles between the lung tumor and fiducial marker at the <2-mm³ ambush area were compared between the UG and LG. In the prostate VMAT, the Shewhart control chart was analyzed by comparing multiple acquisition planning CT (MPCT) and cone-beam CT (CBCT) during the treatment period. The average 3D displacement errors in 4DCT for the lung tumor and fiducial marker were significantly different between the UG and middle- or lower-lobe group, but there was no correlation with the duty cycle. The Shewhart control chart for 3D displacement errors of the prostate for MPCT and CBCT showed that errors of >8 mm exceeded the control limit. In lung SBRT and prostate VMAT, overall statistical data from planning CT showed probabilistic randomness in predictions during the treatment period, and patient-specific motion management was needed to increase accuracy. A radiotherapy planning CT report showing a statistical analysis graph would be useful to objective share with staff.