Stereotactic Body Radiation Therapy Treatment Research Articles

Treatment plan quality and delivery accuracy assessments on 3 IMRT delivery methods of stereotactic body radiotherapy for spine tumors

Stereotactic body radiotherapy (SBRT) for spine tumors has demonstrated clinical effectiveness. The treatment planning and delivery techniques have evolved from dynamic conformal arc therapy, to fixed gantry angle intensity modulated radiotherapy (IMRT), and most recently to volumetric modulated arc therapy (VMAT). A hybrid-arc (HARC) planning and delivery method combining dynamic conformal arc therapy delivery with a number of equally spaced IMRT beams is proposed. In this study we investigated plan quality, delivery accuracy, and efficiency of 3 delivery techniques: IMRT, HARC, and VMAT. Patients who underwent spine SBRT treatments were randomly selected from an Institutional Review Board-approved registry. For each patient, the prescription dose was 14 to 16 Gy in a single fraction to cover >90% of the tumor (without planning margin) while constraining V10Gy ≤ 10% of the spinal cord and the maximum point dose (MPD) of the spinal cord ≤ 14 Gy. All cases were clinically treated with fixed gantry step-shoot IMRT plans and then re-planned with VMAT using Pinnacle 9.0 and with HARC using Brainlab iPlan 4.5. Student t-test was used to compare the dosimetric end points, including V16Gy to the planning target volume, homogeneity index, MPDPTV, the conformity index, V10Gy of the spinal cord, and MPDcord. To compare the accuracy of delivery, we delivered all plans on a phantom and conducted gamma index (GI) comparisons with 3 mm/3% and 2 mm/2% criteria. All plans met our clinical requirements. Among 3 techniques, there were no differences on dose coverage to the tumor volume, maximum dose to the spinal cord, and plan homogeneity index (p > 0.05). The average V10Gy of the spinal cord was 6.66 ± 0.03%, 5.49 ± 0.03%, and 4.76 ± 0.02% for IMRT, HARC, and VMAT plans, respectively. Accordingly, the conformity indices were 1.30 ± 0.11 and 1.29 ± 0.20, 1.53 ± 0.29, respectively. VMAT plans were significantly (p < 0.05) less conformal but significantly (p < 0.05) lower V10Gy of the spinal cord than those from HARC and IMRT plans. With delivery accuracy measured by GIs, the average GIs of 3%/3 mm were 92.6 ± 1.1%, 96.5 ± 2.7%, 99.0 ± 1.1% for IMRT, HARC, and VMAT plans, respectively. The differences were significant (p < 0.05). Accordingly, the average monitor units were 9238 ± 2242, 9853 ± 2548 and 5091 ± 910. The plan quality created from the 3 planning techniques can meet the clinical requirement. Adding arc beams in delivery such as in HARC and VMAT plans improves the delivery accuracy. VMAT is the most efficient delivery method.

An Evaluation of the Efficacy of Corrections in 6 Degrees of Freedom for Standard-Fractionation Head and Neck IGRT

The HexaPODTM evo RT System allows for corrections in 6 degrees of freedom (DoF) (translations and rotations along each of the x-, y-, and z-axes). It has most commonly been used for stereotactic body radiotherapy (SBRT) treatments in combination with highly rigid immobilization to enhance the quality of image registrations. The purpose of this study is twofold: to determine whether the use of 6-DoF corrections will yield superior image registrations for conventionally-fractionated head and neck IMRT treatments with 0.5-cm PTV margins, and to determine a margin for such H&N treatments at which the use of 6-DoF corrections demonstrates significant registration improvements. Twenty patients retrospectively treated for H&N cancers were selected. A variety of H&N subsites were included, provided that the relevant treatment volumes included the primary tumours and lymph nodal groups. Patients were prescribed 60-70 Gy/30-35 # to the primary tumour, and 54-56 Gy to the nodal volumes; patients being treated with small treatment volumes (e.g., SBRT, early-stage glottic cancers) were excluded. Global cone beam CT (CBCT)-CT image registrations were performed by a single observer for 6 fractions per patient. The same observer produced contours for the clivus, C2 vertebra, C7 vertebra, and mandible for each patient. Uniform expansions (0.5-cm and 0.3-cm) of these sub-volumes were generated, and an acceptable sub-volume match for each margin was defined by the expansion contour's complete encapsulation, observed in all three spatial planes, of the pertinent structure on the secondary CBCT image. Acceptability was evaluated for each sub-volume, for both 0.5-cm and 0.3-cm margins, with 3- and 6-DoF corrections. For the 0.5-cm margin, the percentage of unacceptable registrations across all sub-volumes was 8% using 3-DoF corrections and 2% using 6-DoF corrections. This increases to 32% and 9%, respectively, for the registrations using the 0.3-cm uniform expansion margin. In both cases, the C7 vertebra shows the greatest improvement (43% of improved registrations for 0.3-cm, and 15% for 0.5-cm). C2 demonstrated the least impact of the 6-DoF corrections, with reductions of only 11% and 3% in unacceptable registrations for the 0.3-cm and 0.5-cm margins, respectively. There were no significant correlations seen in registration improvement with respect to treatment fraction. The improvement in using 6-DoF corrections for a 0.5-cm margin are not significant enough to warrant the consideration of implementing such a technique. The use of 6-DoF corrections in the case of a 0.3-cm margin proves to be beneficial, and such a margin has been demonstrated to be adequate for planning target volume coverage. This technique would be worth considering, if it resulted in no increased cost with regards to workflow, or in reduction of patient-related toxicities.

Leveraging Advanced Practice: Building Capacity and Maximizing Impact

The Stereotactic Body Radiation Therapy (SBRT) program at our institution has rapidly grown in both anatomic sites and patient numbers since 2008; treating over 700 patients last year to sites including lung, liver, spine, prostate, kidney, pancreas, head and neck , bone and nodes. With such a rapidly expanding program, a clinical specialist radiation therapist (CSRT) position was created in 2012 to ensure optimal, consistent care across the program. Since inception, the role has demonstrated significant impact in terms of time savings for physicians and improved quality of care for patients. The next logical step was to translate the expertise of the CSRT into programmatic efficiencies. An initial area of focus for the position was to have the CSRT assume responsibility of approval of day 1 cone beam computed tomography (CBCT) registrations in place of the radiation oncologist (RO). The CSRT attained competence through a combination of didactic and practical instruction. Concordance between the CSRT and RO with respect to CBCT registration assessment was established. As the department's experience in certain sites of SBRT matured, specific clinical scenarios were identified where, with appropriate training, treatment therapists could independently review day 1 CBCT images for SBRT treatments. The CSRT implemented a therapist led day 1 CBCT registration review policy and facilitated staff education through creation and delivery of an instructional module. A follow up audit was performed to ensure maintenance of quality standards and to quantify departmental impact. Benefits: Greater autonomy for radiation therapists; Eliminated need for calling a third party for treatment and resultant delays; Freed up CSRT to focus on more complex tasks. Challenges: Maintaining continued clinical competence throughout department; Consistent adherence to new guidelines; Managing challenging cases within sites identified for therapist review. The progression of the CSRT in SBRT role highlights how advanced practice radiation therapy roles should evolve continuously. To maximize impact, it is necessary to be cognizant of the changing needs of the department and to align the role accordingly. This process demonstrated how advanced knowledge, skills and judgment of CSRTs can be leveraged for wider departmental benefit.

Safety and clinical activity of pembrolizumab immunotherapy and multi-organ site ablative stereotactic body radiotherapy (iMOSART) in patients with advanced solid tumors.

20 Background: Clinical responses to PD1 blockade have been linked to IFN-γ associated gene expression in the tumor microenvironment. Stereotactic body radiotherapy (SBRT) can stimulate innate and adaptive immunity to potentially augment immunotherapy. Anti-PD1 treatment outcomes are improved with lower disease burden and multi-site radiation is an emerging paradigm for eradicating metastatic disease. Methods: We conducted a phase I study for patients with metastatic solid tumors who progressed on standard treatment. The primary aim was to evaluate the safety of pembrolizumab Immunotherapy with Multi-Organ Site Ablative stereotactic body Radiation Therapy (iMOSART). Two to four metastases were chosen for each patient and not all sites of disease were targeted with SBRT. Metastases &gt; 65cc were partially irradiated. Pembrolizumab was initiated within 7 days after the final SBRT treatment. Results: 79 patients were enrolled, three patients did not receive any treatment and three patients only received SBRT. The 73 patients included in the analysis were treated with SBRT and at least 1 cycle of pembrolizumab. 94.5% of patients had two lesions treated with SBRT. Median follow-up for toxicity was 5.5 months (IQR 3.3-8.1). Six patients experienced dose-limiting toxicity (DLT) with no radiation dose reductions. RECIST overall objective response rate was 13.5% in the 68 patients with imaging follow-up. Superior control of irradiated lesions was observed compared to non-irradiated target lesions for the 52 patients with paired data (p = 0·0005) with a mean percent tumor burden change -21·7% (SD 24·3%) for irradiated lesions vs. 1·7% (SD 46·3%) for non-irradiated lesions (p = 0·0008). While abscopal response defined by 30% reduction in any single non-irradiated measurable lesion was present in 26·9% of patients, abscopal response was 13·2% when defined by 30% reduction in aggregate diameter of non-irradiated measurable lesions. Conclusions: iMOSART was well tolerated with acceptable toxicity. Further randomized studies are warranted to investigate the potential clinical benefit of this combination approach. Clinical trial information: NCT02608385.

Compton scatter imaging: A promising modality for image guidance in lung stereotactic body radiation therapy.

Lung stereotactic body radiation therapy (SBRT) requires delivering large radiation doses with millimeter accuracy, making image guidance essential. An approach to forming images of patient anatomy from Compton-scattered photons during lung SBRT is presented. To investigate the potential of scatter imaging, a pinhole collimator and flat-panel detector are used for spatial localization and detection of photons scattered during external beam therapy using lung SBRT treatment conditions (6 MV FFF beam). MCNP Monte Carlo software is used to develop a model to simulate scatter images. This model is validated by comparing experimental and simulated phantom images. Patient scatter images are then simulated from 4DCT data. Experimental lung tumor phantom images have sufficient contrast-to-noise to visualize the tumor with as few as 10 MU (0.5 s temporal resolution). The relative signal intensity from objects of different composition as well as lung tumor contrast for simulated phantom images agree quantitatively with experimental images, thus validating the Monte Carlo model. Scatter images are shown to display high contrast between different materials (lung, water, bone). Simulated patient images show superior (~double) tumor contrast compared to MV transmission images. Compton scatter imaging is a promising modality for directly imaging patient anatomy during treatment without additional radiation, and it has the potential to complement existing technologies and aid tumor tracking and lung SBRT image guidance.

Evaluation of a commercial automatic treatment planning system for liver stereotactic body radiation therapy treatments

PurposeAutomated treatment planning is a new frontier in radiotherapy. The Auto-Planning module of the Pinnacle3 treatment planning system (TPS) was evaluated for liver stereotactic body radiation therapy treatments. MethodsTen cases were included in the study. Six plans were generated for each case by four medical physics experts. The first two planned with Pinnacle TPS, both with manual module (MP) and Auto-Planning one (AP). The other two physicists generated two plans with Monaco TPS (VM). Treatment plan comparisons were then carried on the various dosimetric parameters of target and organs at risk, monitor units, number of segments, plan complexity metrics and human resource planning time. The user dependency of Auto-Planning was also tested and the plans were evaluated by a trained physician. ResultsStatistically significant differences (Anova test) were observed for spinal cord doses, plan average beam irregularity, number of segments, monitor units and human planning time. The Fisher-Hayter test applied to these parameters showed significant statistical differences between AP e MP for spinal cord doses and human planning time; between MP and VM for monitor units, number of segments and plan irregularity; for all those between AP and VM. The two plans created by different planners with AP were similar to each other. ConclusionsThe plans created with Auto-Planning were comparable to the manually generated plans. The time saved in planning enables the planner to commit more resources to more complex cases. The independence of the planner enables to standardize plan quality.

Approaches to stereotactic body radiation therapy for large (≥5 centimeter) non-small cell lung cancer.

Although larger (≥5 cm) node-negative non-small cell lung cancer (NSCLC) lesions are altogether uncommon, their incidence may increase following the implementation of lung cancer screening. A rigorous assessment of stereotactic body radiation therapy (SBRT) for these challenging cases is imperative not only owing to concerns of increased risks when delivering ablative doses to large volumes, but also due to lack of prospective data, as these patients were excluded from seminal phase II SBRT trials. In addition to appraising the available institutional or multi-institutional experiences, multiple strategies to reduce toxicities are discussed. These include exploration of several different dose/fractionation schemes and regimens, as well as specialized techniques for SBRT treatment planning and delivery. Because these lesions have a higher rate of occult lymphatic or distant spread, the role of systemic therapies (including chemotherapy and immunotherapy) are also discussed. Altogether, the publication of several key reports, entirely over the last few years, has created a more solid foundation with which to utilize evidence-based management for this unique patient population.

Association of conformality index and post-treatment radiation pneumonitis in early-stage non-small cell lung cancer treated with stereotactic body radiotherapy

Conformality index of the 50% prescription isodose volume (CI50) is an important variable in lung stereotactic body radiotherapy (SBRT) planning but has not been previously correlated to radiation pneumonitis (RP). We hypothesized that adherence to recommended CI50 for patients undergoing lung SBRT would result in decreased incidence and/or severity of RP compared to that for patients with minimal deviations and unacceptable deviations. We retrospectively identified patients treated between 2006 and 2016, with > 3 months follow up from lung SBRT treatment. CTCAE v4.0 toxicity grades were used to classify RP. Clinically significant RP was defined as grade ≥ 2 toxicity. Using Radiation Therapy Oncology Group CI50 planning guidelines, patients were separated into three groups: acceptable, minor deviation, and unacceptable deviation. CI25 and CI75 values in patients with and without clinically significant RP were also reported in this study. One hundred seventy-four patients with a median follow-up time of 26.8 months were included in this analysis. Overall incidence of grade ≥ 2 RP was 12.7%. Thirty-eight (21.8%) patients had acceptable CI50, 100 (57.5%) had minor deviations, and 36 (20.7%) had unacceptable deviations. Incidence of RP did not significantly differ between patients with acceptable, minor deviation, and unacceptable CI50. Additionally, CI25 and CI75 did not significantly differ between patients with and without clinically significant RP. Adhering to recommended CI50 values does not significantly decrease the incidence of clinically significant RP in patients with NSCLC treated with SBRT. To the authors’ knowledge, this observation has not been published previously.

Treatment planning with intensity modulated particle therapy for multiple targets in stage IV non-small cell lung cancer

Intensity modulated particle therapy (IMPT) can produce highly conformal plans, but is limited in advanced lung cancer patients with multiple lesions due to motion and planning complexity. A 4D IMPT optimization including all motion states was expanded to include multiple targets, where each target (isocenter) is designated to specific field(s). Furthermore, to achieve stereotactic treatment planning objectives, target and OAR weights plus objective doses were automatically iteratively adapted. Finally, 4D doses were calculated for different motion scenarios. The results from our algorithm were compared to clinical stereotactic body radiation treatment (SBRT) plans. The study included eight patients with 24 lesions in total. Intended dose regimen for SBRT was 24 Gy in one fraction, but lower fractionated doses had to be delivered in three cases due to OAR constraints or failed plan quality assurance. The resulting IMPT treatment plans had no significant difference in target coverage compared to SBRT treatment plans. Average maximum point dose and dose to specific volume in OARs were on average 65% and 22% smaller with IMPT. IMPT could also deliver 24 Gy in one fraction in a patient where SBRT was limited due to the OAR vicinity. The developed algorithm shows the potential of IMPT in treatment of multiple moving targets in a complex geometry.

Initial clinical observations of intra- and interfractional motion variation in MR-guided lung SBRT.

To evaluate variations in intra- and interfractional tumour motion, and the effect on internal target volume (ITV) contour accuracy, using deformable image registration of real-time two-dimensional-sagittal cine-mode MRI acquired during lung stereotactic bodyradiation therapy (SBRT) treatments. Five lung tumour patients underwent free-breathing SBRT treatments on the ViewRay system, with dose prescribed to a planning target volume (defined as a 3-6 mm expansion of the 4DCT-ITV). Sagittal slice cine-MR images (3.5 × 3.5 mm2 pixels) were acquired through the centre of the tumour at 4 frames per second throughout the treatments (3-4 fractions of 21-32 min). Tumour gross tumour volumes (GTVs) were contoured on the first frame of the MR cine and tracked for the first 20 min of each treatment using offline optical-flow based deformable registration implemented on a GPU cluster. A ground truth ITV (MR-ITV20min) was formed by taking the union of tracked GTV contours. Pseudo-ITVs were generated from unions of the GTV contours tracked over 10 s segments of image data (MR-ITV10s). Differences were observed in the magnitude of median tumour displacement between days of treatments. MR-ITV10s areas were as small as 46% of the MR-ITV20min. An ITV offers a "snapshot" of breathing motion for the brief period of time the tumour is imaged on a specific day. Real-time MRI over prolonged periods of time and over multiple treatment fractions shows that ITV size varies. Further work is required to investigate the dosimetric effect of these results. Advances in knowledge: Five lung tumour patients underwent free-breathing MRI-guided SBRT treatments, and their tumours tracked using deformable registration of cine-mode MRI. The results indicate that variability of both intra- and interfractional breathing amplitude should be taken into account during planning of lung radiotherapy.

Pretreatment 18F-Fluorodeoxyglucose Positron Emission Tomography Standardized Uptake Values and Tumor Size in Medically Inoperable Nonsmall Cell Lung Cancer Is Prognostic of Overall 2-Year Survival After Stereotactic Body Radiation Therapy.

The aim of this study was to determine prognostic value of tumor size and metabolic activity on survival for patients with early stage nonsmall cell lung cancer receiving stereotactic body radiation therapy. We retrospectively evaluated the patients who underwent positron emission tomography-computed tomography scan before stereotactic body radiation therapy treatment. Tumor diameter, tumor volume, maximum standardized uptake value (SUVmax), standardized uptake value (SUV) average, and SUV volume were obtained. Cox regression analyses were performed to determine the associations between tumor characteristics and survival. The patients with large tumors and high SUVmax have worse survival than patients with small tumors and low SUVmax (hazard ratio [HR] = 3.47, P = 0.007). Patients with small tumors and high SUVmax (HR = 1.80; P = 0.24) and large tumors and low SUVmax (HR = 1.55; P = 0.43) had increased risk of death compared with patients with small tumors and low SUVmax. Both increased tumor size and metabolic activity are associated with increased risk of death. Combining size and metabolic activity together is superior for predicting 2-year survival and identifying patients for whom survival is statistically worse.

Application of Variance Component Analysis (ANOVA) in Setup Errors and PTV Margins for Lung Cancer with Stereotactic Body Radiation Therapy (SBRT)

Purpose: To investigate the feasibility of applying ANOVA newly proposed by Yukinori to verify the setup errors, PTV (Planning Target Volume) margins, DVH for lung cancer with SBRT. Methods: 20 patients receiving SBRT to 50 Gy in 5 fractions with a Varian iX linear acceleration were selected. Each patient was scanned with kV-CBCT before the daily treatment to verify the setup position. Two other error calculation methods raised by Van Herk and Remeijer were also compared to discover the statistical difference in systematic errors (Σ), random errors (σ), PTV margins and DVH. Results: Utilizing two PTV margin calculation formulas (Stroom, Van Herk), PTV calculated by Yukinori method in three directions were (5.89 and 3.95), (5.54 and 3.55), (3.24 and 0.78) mm; Van Herk method were (6.10 and 4.25), (5.73 and 3.83), (3.51 and 1.13) mm; Remeijer method were (6.39 and 4.57), (5.98 and 4.10), (3.69 and 1.33) mm. The volumes of PTV using Yukinori method were significantly smaller (P 0.05) among three methods. Conclusions: In lung SBRT treatment, due to fraction reduction and high level of dose per fraction, ANOVA was able to offset the effect of random factors in systematic errors, reducing the PTV margins and volumes. However, no distinct dose distribution improvement was founded in target volume and organs at risk.

Analysis of Motion-dependent Clinical Outcome of Tumor Tracking Stereotactic Body Radiotherapy for Prostate Cancer.

BackgroundTo analyze clinical outcome of CyberKnife (CK) tumor-tracking stereotactic body radiotherapy (SBRT) for prostate cancer (Pca) according to the magnitude of intra-fractional prostate motion.MethodsMedical records and daily treatment logs for 71 patients who received CK tumor-tracking SBRT were retrospectively analyzed. Statistical relationships between prostate motion and various outcome results, including local recurrence (LR), biochemical failure (BF), and treatment-related toxicity, were investigated in order to evaluate motion-dependent efficacy of tumor-tracking SBRT for Pca.ResultsIn a total 71 patients, 3 (4.2%) patients with LR, 12 (16.9%) patients with BF, and 22 (31%) patients with grade-II or worse toxicities to rectal or bladder (22 to rectal, 22 to bladder and 8 patients to both) were observed in a median follow-up of 47 months. Magnitudes of intra-fractional tumor motion along superior-inferior, right-left, and anterior-posterior (AP) axes were 0.15 ± 0.31, 0.12 ± 0.19, and 0.73 ± 0.32 mm, respectively. Radial magnitude was estimated to be 1.0 ± 0.35 mm. Intra-fractional movement was not significantly correlated with tumor control. However, it was significant correlated with the incidence of grade-II or worse toxicity to rectum or bladder particularly when tumor motion was in the AP axis.ConclusionOur quantitative results revealed that toxicity related to SBRT treatment was highly sensitive to intra-fractional prostate movements, although local-tumor control was not affected by such movements. Our results demonstrate that precise motion correction is essential in prostate SBRT, even if it seems to be small.

Stereotactic Body Radiotherapy Treatment for Recurrent, Previously Irradiated Head and Neck Cancer

Purpose:Locally recurrent, previously irradiated primary head and neck tumors have historically been associated with poor outcomes. Stereotactic body radiation therapy has emerged as a feasible and promising treatment option for tumor recurrence, particularly in nonsurgical candidates. This study aimed to assess the associated outcomes of stereotactic body radiation therapy used in this setting.Methods:Retrospective analysis of a prospectively collected database of 25 patients treated with CyberKnife for unresectable, recurrent head and neck cancer in a previously irradiated field. The primary end points evaluated were rates of survival, tumor control, and treatment-related toxicities.Results:Median survival of the study population was 7.5 months (range, 1.5-47.0 months). Median survival of the 20 (80%) patients who were treated with curative purpose was 8.3 months. One-year overall survival rate for the entire population was 32%. The respective 1-year and 2-year survival rates for the curative subcohort were 40% and 20%, respectively. Local and locoregional failure occurred in 8 (32%) and 7 (28%) patients, respectively. Low severe acute (4%) and late (6%) treatment-related toxicity rates were observed. No grade 4 or 5 toxicities were observed.Conclusion:Stereotactic body radiation therapy is a viable treatment option for patients with unresectable, recurrent head and neck cancer. Significant tumor control rates are achievable with minimal severe toxicity. Although perhaps associated with patient selection and a heterogeneous sample, overall survival of stereotactic body radiation therapy outcomes appears unfavorable.

Fine-tuning the normal tissue objective in eclipse for lung stereotactic body radiation therapy

The purpose of this study was to characterize the effects of the normal tissue objective (NTO) on lung stereotactic body radiation therapy (SBRT) dose distributions. The NTO is a spatially varying constraint used in Eclipse to limit dose to normal tissues by steepening the dose gradient. However, the multitude of potential NTO setting combinations challenges optimal NTO tuning. In the present study, a broad range of NTO settings are investigated for lung SBRT treatment planning with volumetric modulated arc therapy(VMAT). Ten prior lung SBRT cases were replanned using NTO priorities of 1, 50, 100, 200, 500, and 999 in combination with fall-off values of 0.01, 0.05, 0.10, 0.15, 0.20, 0.30, 0.50, 1.00, and 5.00 mm−1 and the automatic NTO. NTO distances to planning target volume (PTV), start dose, and end dose were 1 mm, 100%, and 10%, respectively, for all 600 plans. Prescription dose covered 95% of the PTV. The following metrics were recorded: conformity index (CI), ratio of the 50% prescription isodose volume to PTV (R50%), maximum dose 2 cm away from PTV (D2cm), lung volume of ≥20 Gy (V20Gy), maximum PTV dose (PTVmax), and monitor units (MUs). Differences between prior plans and NTO plans were evaluated using the Wilcoxon signed-rank test. Different combinations of NTO settings resulted in wide-ranging plan quality metrics: CI (1.00 to 1.54), R50% (3.95 to 7.57), D2cm (33.4% to 67.9%), V20Gy (1.66% to 2.75%), MU (1.81 cGy−1 to 4.69 cGy−1), and PTVmax (118% to 175%). Although no settings were optimal for all metrics, a fall-off of 0.15 mm−1 and a priority of 500 best satisfied institutional criteria. Compared with prior plans, NTO plans resulted in significantly lower R50% (4.00 vs 4.35, p = 0.002), lower V20Gy (1.22% vs 1.32%, p = 0.006), and higher PTVmax (138% vs 122%, p = 0.002). All of the prior and well-tuned NTO plans met Radiation Therapy Oncology Group (RTOG) 0813 guidelines. Lung SBRT dose distributions were characterized across a range of NTO settings. NTO plans with well-tuned settings compared favorably with prior plans.

Noninvasive Cardiac Radiation for Ablation of Ventricular Tachycardia

BackgroundRecent advances have enabled noninvasive mapping of cardiac arrhythmias with electrocardiographic imaging and noninvasive delivery of precise ablative radiation with stereotactic body radiation therapy (SBRT). We combined these techniques to perform catheter-free, electrophysiology-guided, noninvasive cardiac radioablation for ventricular tachycardia.MethodsWe targeted arrhythmogenic scar regions by combining anatomical imaging with noninvasive electrocardiographic imaging during ventricular tachycardia that was induced by means of an implantable cardioverter–defibrillator (ICD). SBRT simulation, planning, and treatments were performed with the use of standard techniques. Patients were treated with a single fraction of 25 Gy while awake. Efficacy was assessed by counting episodes of ventricular tachycardia, as recorded by ICDs. Safety was assessed by means of serial cardiac and thoracic imaging.ResultsFrom April through November 2015, five patients with high-risk, refractory ventricular tachycardia underwent treatment. The mean noninvasive ablation time was 14 minutes (range, 11 to 18). During the 3 months before treatment, the patients had a combined history of 6577 episodes of ventricular tachycardia. During a 6-week postablation “blanking period” (when arrhythmias may occur owing to postablation inflammation), there were 680 episodes of ventricular tachycardia. After the 6-week blanking period, there were 4 episodes of ventricular tachycardia over the next 46 patient-months, for a reduction from baseline of 99.9%. A reduction in episodes of ventricular tachycardia occurred in all five patients. The mean left ventricular ejection fraction did not decrease with treatment. At 3 months, adjacent lung showed opacities consistent with mild inflammatory changes, which had resolved by 1 year.ConclusionsIn five patients with refractory ventricular tachycardia, noninvasive treatment with electrophysiology-guided cardiac radioablation markedly reduced the burden of ventricular tachycardia. (Funded by Barnes–Jewish Hospital Foundation and others.)

Classification of early stage non-small cell lung cancers on computed tomographic images into histological types using radiomic features: interobserver delineation variability analysis.

Radiomics, which involves the extraction of large numbers of quantitative features from medical images, has attracted attention in cancer research. In radiomics analysis, tumor segmentation is a crucial step. In this study, we evaluated the potential application of radiomics for predicting the histology of early stage non-small cell lung cancer (NSCLC) by analyzing interobserver variability in tumor delineation. Forty patient datasets were included in this study, 21 involving adenocarcinomas and 19 involving squamous cell carcinomas. All patients underwent stereotactic body radiotherapy treatment. In total, 476 features were extracted from each dataset, representing treatment planning, computed tomography images, and gross tumor volume (GTV). The definition of GTV can significantly affect the histology prediction. Therefore, in the present study, the effect of interobserver tumor delineation variability on radiomic features was evaluated by preparing 4 volumes of interest (VOIs) for each patient, as follows: the original GTV (which was delineated at treatment planning); two GTVs delineated retrospectively by radiation oncologists; and a semi-automatic GTV contoured by a medical physicist. Radiomic features extracted from each VOI were then analyzed using a naïve Bayesian model. Area-under-the-curve (AUC) analysis showed that interobserver variability in delineation is a significant factor in radiomics performance. Nevertheless, with 8 selected features, AUC values averaged over the VOIs were high (0.725±0.070). The present study indicated that radiomics has potential for predicting early stage NSCLC histology despite variability in delineation. The high prediction accuracy implies that noninvasive histology evaluation by radiomics is a promising clinical application.

Optimal beam margins in linac-based VMAT stereotactic ablative body radiotherapy: a Pareto front analysis for liver metastases

We explored the Pareto fronts mathematical strategy to determine the optimal block margin and prescription isodose for stereotactic body radiotherapy (SBRT) treatments of liver metastases using the volumetric-modulated arc therapy (VMAT) technique. Three targets (planning target volumes [PTVs] = 20, 55, and 101 cc) were selected. A single fraction dose of 26 Gy was prescribed (prescription dose [PD]). VMAT plans were generated for 3 different beam energies. Pareto fronts based on (1) different multileaf collimator (MLC) block margin around PTV and (2) different prescription isodose lines (IDL) were produced. For each block margin, the greatest IDL fulfilling the criteria (95% of PTV reached 100%) was considered as providing the optimal clinical plan for PTV coverage. Liver Dmean, V7Gy, and V12Gy were used against the PTV coverage to generate the fronts. Gradient indexes (GI and mGI), homogeneity index (HI), and healthy liver irradiation in terms of Dmean, V7Gy, and V12Gy were calculated to compare different plans. In addition, each target was also optimized with a full-inverse planning engine to obtain a direct comparison with anatomy-based treatment planning system (TPS) results. About 900 plans were calculated to generate the fronts. GI and mGI show a U-shaped behavior as a function of beam margin with minimal values obtained with a +1 mm MLC margin. For these plans, the IDL ranges from 74% to 86%. GI and mGI show also a V-shaped behavior with respect to HI index, with minimum values at 1 mm for all metrics, independent of tumor dimensions and beam energy. Full-inversed optimized plans reported worse results with respect to Pareto plans. In conclusion, Pareto fronts provide a rigorous strategy to choose clinical optimal plans in SBRT treatments. We show that a 1-mm MLC block margin provides the best results with regard to healthy liver tissue irradiation and steepness of dose fallout.

Compass model-based quality assurance for stereotactic VMAT treatment plans

PurposeTo use Compass as a model-based quality assurance (QA) tool for stereotactic body radiation therapy (SBRT) and stereotactic radiation therapy (SRT) volumetric modulated arc therapy (VMAT) treatment plans calculated with Eclipse treatment planning system (TPS). Materials and methodsTwenty clinical stereotactic VMAT SBRT and SRT treatment plans were blindly selected for evaluation. Those plans included four different treatment sites: prostate, brain, lung and body. The plans were evaluated against dose-volume histogram (DVH) parameters and 2D and 3D gamma analysis. The dose calculated with Eclipse treatment planning system (TPS) was compared to Compass calculated dose (CCD) and Compass reconstructed dose (CRD). ResultsThe maximum differences in mean dose of planning target volume (PTV) were 2.7 ± 1.0% between AAA and Acuros XB calculation algorithm TPS dose, −7.6 ± 3.5% between Eclipse TPS dose and CCD dose and −5.9 ± 3.7% between Eclipse TPS dose and CRD dose for both Eclipse calculation algorithms, respectively. 2D gamma analysis was not able to identify all the cases that 3D gamma analysis specified for further verification. ConclusionsCompass is suitable for QA of SBRT and SRT treatment plans. However, the QA process should include wide set of DVH-based dose parameters and 3D gamma analysis should be the preferred method when performing clinical patient QA. The results suggest that the Compass should not be used for smaller field sizes than 3 × 3 cm2 or the beam model should be adjusted separately for both small (FS ≤ 3 cm) and large (FS > 3 cm) field sizes.

Effects of magnetic field orientation and strength on the treatment planning of nonsmall cell lung cancer.

Magnetic resonance image-guided radiotherapy (MRgRT) has the potential to increase the accuracy of radiation treatment delivery. Several research groups have developed hybrid MRgRT devices differing by radiation source used and magnetic field orientation and strength. In this work, we investigate the impact of different magnetic field orientations and strengths on the treatment planning of nonsmall cell lung cancer patients (NSCLC). A framework using the in-house developed treatment planning system matRad and the EGSnrc Monte Carlo code system was introduced to perform Monte Carlo-based treatment planning in the presence of a magnetic field. A specialized spectrum-based source model for the beam qualities of 6 MV and cobalt-60 was applied. Optimized plans for stereotactic body radiation therapy (SBRT) and intensity-modulated radiation therapy (IMRT) were generated for four NSCLC patients in the presence of different magnetic field orientations and strengths which are applied in hybrid MRgRT devices currently under development or in clinical use. SBRT and IMRT treatment planning could be performed with consistent plan quality for all magnetic field setups. Only minor effects on the treatment planning outcome were found in the case of magnetic fields orientated perpendicular to the beam direction. Compared to the perpendicular magnetic field orientation, the inline orientation showed the capability to reduce the dose to lung while maintaining equal target coverage. Particularly for tumors with a central position in lung, a distinct dose reduction was obtained which led to a maximum reduction of mean lung dose by 18.5% (0.5 Gy), when applying a 1 T inline magnetic field. All plans generated in this work obtained dose metrics within clinical constraints according to RTOG guidelines. When considering conventional dose metrics, no detrimental effects due to the magnetic fields were observed on the dose to the tumor or to organs at risk. An evaluation of the effects on skin dose was not ascertainable due to the simplified specification of the source model used. By accounting for the magnetic field during treatment planning, a dose reduction in lung could be achieved for inline-oriented magnetic fields. An inline orientation of the magnetic field therefore showed a potential benefit when treating NSCLC with MRgRT.