Stereotactic Body Radiation Therapy Treatment Research Articles

Prolonged overall treatment time negatively affects the outcomes of stereotactic body radiotherapy for early-stage non-small-cell lung cancer: A propensity score-weighted, single-center analysis.

Previous studies have reported conflicting results for the effect of overall treatment time with stereotactic body radiotherapy on tumor control in early-stage non-small-cell lung cancer. To examine this effect, we conducted a propensity score-weighted, retrospective, observational study at a single institution. We analyzed the data of 200 patients with early-stage non-small-cell lung cancer who underwent stereotactic body radiotherapy (48 Gy in 4 fractions) at our institution between January 2007 and October 2013. Patients were grouped into consecutive (overall treatment time = 4–5 days, n = 116) or non-consecutive treatment groups (overall treatment time = 6–10 days, n = 84). The outcomes of interest were local control and overall survival. The Cox regression model was used with propensity score and inverse probability of treatment weighting. The median overall treatment times in the consecutive and non-consecutive groups were 4 and 6 days, respectively. The 5-year local control and overall survival rates in the consecutive vs. the non-consecutive group were 86.3 vs. 77.2% and 55.5 vs. 51.8%, respectively. After propensity score weighting, consecutive stereotactic body radiotherapy was associated with positive local control (adjusted hazard ratio 0.30, 95% confidence interval 0.14–0.65; p = 0.002) and overall survival (adjusted hazard ratio 0.56, 95% confidence interval 0.34–0.91; p = 0.019) benefits. The prolonged overall treatment time of stereotactic body radiotherapy treatment negatively affected the outcomes of patients with early-stage non-small-cell lung cancer. To our knowledge, this is the first study to show that in patients with early-stage non-small-cell lung cancer treated with the same dose-fractionation regimen, consecutive stereotactic body radiotherapy has a more beneficial effect on tumor control than non-consecutive stereotactic body radiotherapy.

On the evaluation of mobile target trajectory between four-dimensional computer tomography and four-dimensional cone-beam computer tomography.

PurposeFor mobile lung tumors, four‐dimensional computer tomography (4D CT) is often used for simulation and treatment planning. Localization accuracy remains a challenge in lung stereotactic body radiation therapy (SBRT) treatments. An attractive image guidance method to increase localization accuracy is 4D cone‐beam CT (CBCT) as it allows for visualization of tumor motion with reduced motion artifacts. However, acquisition and reconstruction of 4D CBCT differ from that of 4D CT. This study evaluates the discrepancies between the reconstructed motion of 4D CBCT and 4D CT imaging over a wide range of sine target motion parameters and patient waveforms.MethodsA thorax motion phantom was used to examine 24 sine motions with varying amplitudes and cycle times and seven patient waveforms. Each programmed motion was imaged using 4D CT and 4D CBCT. The images were processed to auto segment the target. For sine motion, the target centroid at each phase was fitted to a sinusoidal curve to evaluate equivalence in amplitude between the two imaging modalities. The patient waveform motion was evaluated based on the average 4D data sets.ResultsThe mean difference and root‐mean‐square‐error between the two modalities for sine motion were −0.35 ± 0.22 and 0.60 mm, respectively, with 4D CBCT slightly overestimating amplitude compared with 4D CT. The two imaging methods were determined to be significantly equivalent within ±1 mm based on two one‐sided t tests (p < 0.001). For patient‐specific motion, the mean difference was 1.5 ± 2.1 (0.8 ± 0.6 without outlier), 0.4 ± 0.3, and 0.8 ± 0.6 mm for superior/inferior (SI), anterior/posterior (AP), and left/right (LR), respectively.ConclusionIn cases where 4D CT is used to image mobile tumors, 4D CBCT is an attractive localization method due to its assessment of motion with respect to 4D CT, particularly for lung SBRT treatments where accuracy is paramount.

Racial and socioeconomic disparities in the use of stereotactic body radiotherapy for treating non-small cell lung cancer: a narrative review.

In the past two decades, there has been a steady increase in the use of stereotactic body radiotherapy (SBRT) as an alternative to surgical intervention for early-stage non-small cell lung cancer (NSCLC) patients; however, not much is known about the impact of race and socioeconomic status (SES) on the delivery of SBRT. Here, we conduct a narrative review to examine potential disparities in the use of SBRT. Keyword searches of MEDLINE/PubMed, Web of Science, Embase, and Google Scholar databases were performed for studies focused on race, SES, and the use of SBRT published between 2000 and 2020. Six studies were identified, and showed that minority patients, especially Blacks, were less likely to receive SBRT and had a significantly longer median time between diagnosis to SBRT treatment. Patients with lower income or lower education, as well as those from lower socioeconomic regions were less likely to receive SBRT; they were more likely to receive conventionally fractionated external beam radiation (CFRT) or no treatment. These racial and socioeconomic factors were associated with worse survival in other general early-stage NSCLC studies. In conclusion, the limited number of published studies suggest significant disparities in the treatment of early-stage NSCLC with SBRT. These factors potentially lead to worse survival outcomes among vulnerable patient populations. Equal access to SBRT should be a focus of healthcare delivery systems, to ensure optimal clinical outcomes for patients with early-stage NSCLC.

SBRT treatment of abdominal and pelvic oligometastatic lymph nodes using ring-mounted Halcyon Linac.

Purpose/objectivesThis work seeks to evaluate the plan quality, treatment delivery efficiency, and accuracy of single‐isocenter volumetric modulated arc therapy (VMAT) of abdominal/pelvic oligometastatic lymph nodes (LNs) stereotactic body radiation therapy (SBRT) on Halcyon Linac.Materials and MethodsAfter completing the in‐house multitarget end‐to‐end phantom testing and independent dose verification using MD Anderson’s single‐isocenter/multi‐target (lung and spine target inserts) thorax phantom, eight patients with two to three abdominal/pelvic oligometastatic LNs underwent highly conformal single‐isocenter VMAT‐SBRT treatment using the Halcyon Linac 6MV flattening filter free (FFF) beam. Targets were identified using an Axumin PET/CT scan co‐registered with planning CT images and a single‐isocenter was placed between/among the targets. Doses between 25 and 36.25 Gy in 5 fractions were delivered. Patients were treated every other day. Plans were calculated in Eclipse with advanced AcurosXB algorithm for heterogeneity corrections. For comparison, Halcyon VMAT‐SBRT plans were retrospectively generated for SBRT‐dedicated TrueBeam with a 6MV‐FFF beam using identical planning geometry and objectives. Target coverage, conformity index (CI), dose to 2 cm away from each target (D2cm) and dose to adjacent organs‐at‐risk (OAR) were evaluated. Additionally, various treatment delivery parameters including beam‐on time were recorded.ResultsPhantom measurements showed acceptable spatial accuracy of conebeam CT‐guided Halcyon SBRT treatments including compliance with MD Anderson’s single‐isocenter/multi‐targets phantom credentialing results. For patients, the mean isocenter to tumor center distance was 3.4 ± 1.2 cm (range, 1.5–4.8 cm). The mean combined PTV was 18.9 ± 10.9 cc (range, 5.6–39.5 cc). There was no clinically significant difference in dose to LNs, CI, D2cm and maximal doses to OAR between single‐isocenter Halcyon and Truebeam VMAT‐SBRT plans, although, Halcyon plans provided preferably lower maximal dose to adjacent OAR. Additionally, total monitor units, beam‐on time and overall treatment time was lower with Halcyon plans. Halcyon’s portal dosimetry demonstrated a high pass rate of 98.1 ± 1.6% for clinical gamma passing criteria of 2%/2 mm.ConclusionSBRT treatment of abdominal/pelvic oligometastatic LNs with single‐isocenter VMAT on Halcyon was dosimetrically equivalent to TrueBeam. Faster treatment delivery to oligometastatic LNs via single‐isocenter Halcyon VMAT can improve clinic workflow and patient compliance, potentially reducing intrafraction motion errors for well‐suited patients. Clinical follow‐up of these patients is ongoing.

Investigation of Buildup Region and Surface Dose: Comparison of Parallel Plane Ion Chamber, Treatment Planning System, and MC Simulation

In these days, Monte Carlo (MC) simulation is a method that can calculate the radiation dose that occurs in an environment in the most accurate way. The correct measurement of the dose occurring on the patient’s surface is of great importance to estimate the reactions that may occur on the patient’s skin. This importance encouraged us to do this study. The aim of this study is to determine buildup region and surface doses using MC simulation and to compare them with results of the parallel plane ion chamber and Treatment Planning System (TPS) measurements for 6-MV photon beams. Surface doses normalized to the maximum dose for the parallel plane ion chamber, MC simulation, fast photon (FP) algorithm, and collapsed cone convolution superposition (CC) algorithm are 13.6%, 30.28%, 0%, and 27.33%, respectively. The CC algorithm and parallel plane ion chamber measurements are compatible with MC simulation but the FP algorithm has calculated the dose less to a depth of 0.8 cm. Measuring the surface dose and the doses in the buildup region is of great importance in terms of accurately predicting the complications that may occur in the patient’s skin and taking precautions early. Using some methods and correction factors, the surface dose and the doses that may occur in the buildup region can be accurately calculated. It is recommended not to use the FP algorithm for stereotactic body radiation therapy and intensity-modulated radiation therapy treatments, as it cannot calculate doses correctly in the buildup region and surface.

Modeling of Tumor Control Probability in Stereotactic Body Radiation Therapy for Adrenal Tumors

Stereotactic body radiation therapy (SBRT) in the management of adrenal metastases is emerging as a well-tolerated, effective method of treatment for patients with limited metastatic disease. SBRT planning and treatment utilization are widely variable, and publications report heterogeneous radiation dose fractionation schemes and treatment outcomes. The objective of this analysis was to review the current literature on SBRT for adrenal metastases and to develop treatment guidelines and a model for tumor control probability of SBRT for adrenal metastases based on these publications. A literature search of all studies on SBRT for adrenal metastases published from 2008 to 2017 was performed, and outcomes in these studies were reviewed. Local control (LC) rates were fit to a statistically significant Poisson model using maximum likelihood estimation techniques. One-year LC greater than 95% was achieved at an approximated biological equivalent dose with α/β = 10 Gy of 116.4 Gy. While respecting normal tissue tolerances, tumor doses greater than or equal to a biological equivalent dose with α/β = 10 Gy of 116.4 Gy are recommended to achieve high LC. Further studies following unified reporting standards are needed for more robust prediction.

Stereotactic radiotherapy for early stage non-small cell lung cancer: current standards and ongoing research.

Stereotactic body radiation therapy (SBRT) allows for the non-invasive and precise delivery of ablative radiation dose. The use and availability of SBRT has increased rapidly over the past decades. SBRT has been proven to be a safe, effective and efficient treatment for early stage non-small cell lung cancer (NSCLC) and is presently considered the standard of care in the treatment of medically or functionally inoperable patients. Evidence from prospective randomized trials on the optimal treatment of patients deemed medically operable remains owing, as three trials comparing SBRT to surgery in this cohort were terminated prematurely due to poor accrual. Yet, SBRT in early stage NSCLC is associated with favorable toxicity profiles and excellent rates of local control, prompting discussion in regard of the treatment of medically operable patients, where the standard of care currently remains surgical resection. Although local control in early stage NSCLC after SBRT is high, distant failure remains an issue, prompting research interest to the combination of SBRT and systemic treatment. Evolving advances in SBRT technology further facilitate the safe treatment of patients with medically or anatomically challenging situations. In this review article, we discuss international guidelines and the current standard of care, ongoing clinical challenges and future directions from the clinical and technical point of view.

Monte Carlo as quality control tool of stereotactic body radiation therapy treatment plans.

The objective of this study was to verify the accuracy of treatment plans of stereotactic body radiation therapy (SBRT) and to verify the feasibility of the use of Monte Carlo (MC) as quality control (QC) on a daily basis. Using EGSnrc, a MC model of Agility™ linear accelerator was created. Various measurements (Percentage depth dose (PDD), Profiles and Output factors) were done for different fields sizes from 1x1 up to 40x40 (cm2). An iterative model optimization was performed to achieve adequate parameters of MC simulation. 40 SBRT patient's dosimetry plans were calculated by Monaco™ 3.1.1. CT images, RT-STRUCT and RT-PLAN files from Monaco™ being used as input for Moderato MC code. Finally, dose volume histogram (DVH) and paired t-tests for each contour were used for dosimetry comparison of the Monaco™ and MC. Validation of MC model was successful, as <2% difference comparing to measurements for all field's sizes. The main energy of electron source incident on the target was 5.8MeV, and the full width at half maximum (FWHM) of Gaussian electron source were 0.09 and 0.2 (cm) in X and Y directions, respectively. For 40 treatment plan comparisons, the minimum absolute difference of mean dose of planning treatment planning (PTV) was 0.1% while the maximum was 6.3%. The minimum absolute difference of Max dose of PTV was 0.2% while the maximum was 8.1%. SBRT treatment plans of Monaco agreed with MC results. It possible to use MC for treatment plans verifications as independent QC tool.

SEOR SBRT-SG survey on SRS/SBRT dose prescription criteria in Spain.

Stereotactic body radiotherapy (SBRT) and stereotactic radiosurgery (SRS) are essential tools in radiation oncology. In Spain, the use of these techniques continues to grow as older linear accelerators (linacs) are replaced with modern equipment. However, little is known about inter-centre variability in prescription and dose heterogeneity limits. Consequently, the SBRT-Spanish Task Group (SBRT-SG) of the Spanish Society of Radiation Oncology (SEOR) has undertaken an initiative to assess prescription and homogeneity in SRS/SBRT treatment. In the present study, we surveyed radiation oncology (RO) departments to obtain a realistic overview of prescription methods used for SBRT and SRS treatment in Spain. A brief survey was developed and sent to 34 RO departments in Spain, mostly those who are members of the SEOR SBRT-SG. The survey contained seven questions about the specific prescription mode, dose distribution heterogeneity limits, prescription strategies according to SRS/SBRT type, and the use of IMRT-VMAT (Intensity Modulated Radiation Therapy-Volumetric Modulated Arc Therapy). Responses were received from 29 centres. Most centres (59%) used the prescription criteria D95% ≥ 100%. Accepted dose heterogeneity was wide, ranging from 107 to 200%. Most centres used IMRT-VMAT (93%). This survey about SRS/SBRT prescription and dose heterogeneity has evidenced substantial inter-centre variability in prescription criteria, particularly for intended and accepted dose heterogeneity. These differences could potentially influence the mean planning target volume dose and its correlation with treatment outcomes. The findings presented here will be used by the SEOR SBRT-SG to develop recommendations for SRS/SBRT dose prescription and heterogeneity.

Impact of Age on Patient-Reported Outcomes Following Stereotactic Body Radiation Therapy for Prostate Cancer.

PurposeStereotactic body radiation therapy (SBRT) delivers large radiation doses to the prostate while minimizing exposure to adjacent normal tissues. Large fraction sizes may increase the risks of functional decrements. Elderly men may be at an increased risk of these toxicities due to poor baseline function and hence limited reserve. This study describes patient-reported outcomes following SBRT for clinically localized prostate cancer in the elderly.MethodsBetween 2007 and 2017, 179 hormone-naive elderly patients (≥ 70 years old) and 210 patients under 70 years old with clinically localized prostate cancer were treated with 35-36.25 Gy SBRT in five fractions utilizing the CyberKnife Radiosurgical System (Accuray Inc.). Quality of life (QOL) was assessed using the Expanded Prostate Index Composite-Short Form (EPIC-26) questionnaire at baseline and at 1, 3, 6, 12, 18, 24, 30, and 36 months following the completion of treatment. EPIC scores range from 0 to 100, with lower values representing worsening symptoms.ResultsEPIC scores in the elderly cohort mirrored those in the younger cohort. EPIC urinary obstructive/irritative scores declined at one month post-SBRT (mean change from baseline ≥70: -7.9; <70: -11.1) before returning to baseline at three months post-SBRT (mean change from baseline ≥70: -0.4; <70: -1.4). The EPIC urinary incontinence scores declined slowly over the three years following treatment without recovery (mean change from baseline ≥70: -6.6; <70: -4.8). EPIC Bowel scores transiently declined at one month post-SBRT (mean change from baseline ≥70: -8.5; <70: -9.1) and then experienced a second more protracted decline over the next three years without recovery (mean change from baseline ≥70: -4.5; <70: -1.8). Hormonal EPIC scores were not impacted by radiation treatment or age. Older men had lower baseline and post-treatment EPIC sexual summary scores at all time points. However, there was no clinically significant difference in the EPIC sexual bother score between younger and older men at baseline and following treatment.ConclusionsIn the first three years following treatment, the impact of SBRT treatment on patient-reported outcomes was minimal. Our findings suggest that SBRT for clinically localized prostate cancer should not be deferred in older men solely due to concerns of increased morbidity. Further studies should be conducted to evaluate the impact of age on outcomes or morbidity following SBRT.

P05.14 Dosimetric Impact of Using the Acuros XB for Planning of SBRT of Centrally Located NSCLC

Stereotactic Body Radiation Treatment (SBRT) of lung cancer is applied to a heterogeneous density gradient. Dose modeling is highly dependent on the accuracy of the calculation algorithm. This study aims to assess the dosimetric implications calculated by Acuros External Beam (AXB) instead of the Anisotropic Analytical Algorithm (AAA) in SBRT of centrally located-Non small cell lung cancer (CL-NSCLC). Twelve IMRT plans for SBRT of CL-NSCLC were investigated retrospectively. The prescribed scheme was 50 Gy in 5 fractions every 2 days. The plans originally calculated by AAA aimed to cover 95% PTV by varying prescription isodose lines at 70 to 90%. These plans were recalculated by AXB (Dose to medium) and verified by the benchmark Monte Carlo (MC) method. Dosimetric parameters e.g. V20Gy Lungs, D95%(PTV), D98%(GTV), dose gradient (the ratio of 50% prescription isodose volume to the PTV, R50%), and doses to organs at risk (spinal cord, heart, esophagus, trachea, bronchus, and major vessels) were compared. AAA has generally overestimated the PTV dose compared to AXB and MC. The mean differences for D95%(PTV) and D98%(GTV) is 3.1% and 2.8% higher than that of AXB, respectively. The differences were significant with p-value<0.05. They were further verified by MC method, the results agreed with that of AXB. The agreement between AXB and MC in all PTV parameters were within 1.6% and the differences were not significant. No significant differences were also noted on V20Gy Lungs between the three algorithms but three cases were observed with maximum point dose to the lung tissue 1cm surrounding the PTV increased over 11% after the recalculation of AXB. Moreover, two cases were reported exceeding in heart dose and three cases were found degrading from none to minor deviation in dose gradient R50%. AXB has been investigated intensively and found to perform superiorly to AAA especially in calculating the rapid change in heterogeneous density gradient e.g. in regions of re-buildup in soft tissue after passed through lung/air. Although AXB and MC have two completely different way in solving Linear Boltzmann Transport Equation (LBTE), the agreement between AXB and MC was widely acceptable, AXB provides an accurate but faster alternative to MC method. In this study, a significant under-dosage in PTV and large dose difference in modeling tissue/air interface were observed after remodeled with AXB and MC. Since the PTV of SBRT for NSCLC is relatively small, the PTV missed in AAA may lead to a reduction in treatment outcome. Hence, AXB should be used in preference to AAA to model SBRT for centrally located NSCLC.

Radiation-induced lung damage in patients treated with stereotactic body radiotherapy after EGFR-TKIs: is there any difference from stereotactic body radiotherapy alone?

To quantitatively evaluate lung damage after treatment of epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) and stereotactic body radiotherapy (SBRT) in patients with nonsmall cell lung cancer (NSCLC), and compare that of SBRT only treatment. Eligible patients from an IRB-approved prospective clinical trial had one month of EGFRTKIs treatment followed by SBRT (TKI + SBRT) and with 3-month follow-up high resolution CT. NSCLC patients treated with SBRT alone during the same time period without EGFR-TKIs or other systemic therapies were identified as controls. The lung damage was assessed clinically by pneumonitis and quantitatively using by CT intensity (Hounsfield unit, HU) changes. The mean HU values were extracted for regions of the lungs receiving the same dose range at 10 Gy intervals to generate dose-response curves (DRC). The relationship of HU changes and radiation dose was modeled using a Probit model. Four out of 20 (25%) TKI + SBRT patients and none of 19 (0%) SBRT alone patients had developed grade 2 and above pneumonitis (P=0.053), respectively. Sixty percent of TKI + SBRT patients and 30% SBRT alone patients had HU changes of the normal lung density >200 HU, respectively. There were significant differences in the DRC and in lung HU changes between the two groups (all P<0.05). The physical dose for a 50% complication risk (TD50) of CT lung damage was 52 Gy (CI: 46-59) in TKI + SBRT group versus 72 Gy (CI: 58-107) in SBRT alone group (P<0.01). Compared to patients treated with SBRT alone, patients treated with EGFR-TKIs followed by SBRT were more incline to develop radiation pneumonitis, and resulted in greater lung CT intensity changes and steeper dose-CT lung damage response relationship at 3 months post treatment. Future study with larger number of patients and longer follow-up period is warranted to validate this finding.

Interplay effect modeling in stereotactic body radiotherapy treatment of liver cancer using volumetric modulated arc therapy.

To model the interplay effect and minimize it by a selection of optimum parameters value using a predictive model for SBRT of liver cancers. Ten cases of liver tumors treated with the VMAT technique were selected retrospectively. The dosimetric error due to the interplay effect was measured with a micro ionization chamber (0.015cm3) in a Quasar phantom simulating the moving tumor. The interplay effect dependent parameter's viz. patient breaths per minute, the amplitude of respiration, fractional dose (FD), plan complexity due to different energies (Relative degree of modulation), degree of modulation due to a different level of dose optimization constraints, and dose rate (DR) were measured. For the predictive model, mathematical equations were modeled in python from 300 combinations of proposed parameters using multivariate regression analysis. It was observed that the dose variation reduced from -8.44% to -5.16% for change in the BPM values from 7 to 31 and similarly for amplitude, the dose variation reduced from -9.44% to -4.93% for change in amplitude value from 16mm to 2mm. The DR and FD have a prominent effect with R2 values of 0.990 and 0.880 respectively. The calculated mean square errors of equations excluding amplitude for the predictive model were 0.90 and 0.82 whereas those for equations excluding BPM were 1.31 and 1.41 for 6 MV and 10 MV beams respectively. The values of the parameters can be prospectively optimized by the use of the predictive model according to clinical situations, so dose variation can be minimized.

A protocol for absolute dose verification of SBRT/SRS treatment plans using Gafchromic™ EBT-XD films.

To provide a practical protocol for absolute dose verification of stereotactic body radiotherapy (SBRT) and stereotactic radiosurgery (SRS) treatment plans, based on our clinical experience. It aims to be a concise summary of the main aspects to be considered when establishing an accurate film dosimetry system. Procedures for film calibration and conversion to dose are described for a dosimetry system composed of Gafchromic™ EBT-XD films and a flatbed document scanner. Factors that affect the film-scanner response are also reviewed and accounted for. The accuracy of the proposed methodology was assessed by taking a set of strips irradiated to known doses and its applicability is illustrated for ten SBRT/SRS treatment plans. The film response was converted to dose using red and triple channel dosimetry. The agreement between the planned and measured dose distributions was evaluated using global gamma analysis with criteria of 3%/2mm 10% threshold (TH), 2%/2mm 10% TH, and 2%/2mm 20% TH. The differences between the expected and determined doses from the strips analysis were 0.9±0.6% for the red channel and 1.1±0.7% for the triple channel method. Regarding the SBRT/SRS plans verification, the mean gamma passing rates were 99.5±1.0% vs 99.6±1.0% (3%/2mm 10% TH), 96.9±3.5% vs 99.1±1.3% (2%/2mm 10% TH) and 98.4±1.8% vs 98.8±1.5% (2%/2mm 20% TH) for red and triple channel dosimetry, respectively. The proposed protocol allows for accurate absolute dose verification of SBRT/SRS treatment plans, applying both single and triple channel methods. It may work as a guide for users that intend to implement a film dosimetry system.

EUS-guided placement of fiducial markers for stereotactic body radiation therapy in pancreatic cancer: feasibility, security and a new quality score

Background and study aims In borderline resectable/locally advanced pancreatic ductal adenocarcinoma (PDAC), stereotactic body radiation therapy (SBRT) is an emerging neoadjuvant treatment option. Endoscopic ultrasound (EUS)-guided insertion of fiducial markers being a prerequisite, our aim was to assess its feasibility and safety and also to evaluate its success, from both the endoscopist’s and radiotherapist’s perspectives. Patients and methods We prospectively collected data concerning PDAC patients submitted to EUS-guided fiducial placement, from February 2018 to November 2019. Technical success was defined as at least one marker presumed inside the tumor. Quality success was assessed at pre-SBRT computed tomography, accordingly to the number of markers inside or < 1 cm from the tumor, number of markers at the tumor extremity, their location in different planes, the distance between them, and their distance from the biliary stent (if present). A new quality score was then proposed and high-quality success defined as at least six of 12 points. Results Thirty-seven patients were enrolled. A total of 97 fiducials were implanted, with a median of three fiducials per patient (0–4). The technical success rate was 92 %, with failure of fiducial placement in three patients. Three patients (8 %) had adverse events (fever, mild acute pancreatitis, and biliary stent migration). At pre-SBRT evaluation, two patients’ markers had migrated. The high-quality success rate was 62.5 %. Conclusions Our results contribute to demonstrating the feasibility and safety of EUS-guided fiducial placement for SBRT treatment in PDAC. It is hoped that the newly proposed quality score will pave the way for improving fiducial positioning and SBRT delivery.

Type of fiducial marker and clinical outcomes in stereotactic body radiation therapy for pancreatic cancer.

414 Background: Stereotactic body radiation therapy (SBRT) for pancreatic cancers has been shown to improve local control, and is an important option for treatment, especially for unresectable disease. Verifying the tumor location prior to delivery of SBRT is challenging, so fiducial markers are used to track tumor location. There is currently no standard of which fiducials to use in treatment. This study would like to compare outcomes of patients treated with SBRT using different fiducial markers. Methods: Records of patients diagnosed with primary pancreas cancer who were treated with chemotherapy and SBRT were reviewed from 2006-2019. Patients were excluded if they were treated with Cyberknife, were metastatic at presentation, recurrence /persistent disease after Whipple/radiation therapy, were secondary metastatic disease (from another primary), and if they were resected after SBRT. Patients were categorized according to the fiducial used for tumor tracking during SBRT treatment: gold seeds, intrabiliary stent, or both. Cumulative incidence of local recurrence (CIR) was analyzed with death as competing event, and time to over-all survival was estimated using Kaplan-Meier curves. Results: A total of 129 patients with available fiducial information were included in this study, of which 64 (49.6%) were treated with SBRT using gold seeds, 23 (17.8%) using intrabiliary stent, and 42 (32.6%) using both the seeds and stent. There were no difference between groups in terms of baseline characteristics such as age (p = 0.169), sex (p = 0.293), and stage grouping (p = 0.293). Median follow-up time was 15 months (range: 0.3-37.3 months). The 6- and 12-month CIR were 1.5% (95%CI, 0.1%-7.4%) and 11% (95%CI, 4.8%-20.2%) for patients treated with seeds, 4.3% (95%CI, 0.2%-18.6%) and 30.4% (95%CI, 13.1%-49.8%) for patients treated with stent, and 4.8% (95%CI, 0.8%-14.6%) and 19.5% (95%CI, 9.0%-32.9%) for patients treated with both (p = 0.007). Median time to overall survival was 15.3 months (95%CI, 13-17.8 months) for patients treated with seeds, 21.3 months (95%CI, 14.7-29.6 months) for patients treated with stent, and 15.7 months (95%CI, 11.5-19.7 months) for patients treated with both (p = 0.307). Univariate analysis for predictors of local failure did not show significance for age (p = 0.812), or advanced stage (p = 0.483), but was significant for the presence of seeds (p = 0.006). Conclusions: The type of fiducial marker used for tracking during pancreas SBRT treatment was associated with local failure but no difference in overall survival. Further analysis is warranted to see which clinical factors contribute to this difference.

Integrating stereotactic body radiation therapy (SBRT) and systemic treatments in oligoprogressive prostate cancer: new evidence from the literature.

Recent findings from literature evidenced that metastatic prostate cancer often shows heterogeneous response to therapy, with persistent sensibility to systemic treatments after biochemical, clinical, or radiographic progression. This highlights the advantage of integrated approaches in which local ablative treatments (e.g., stereotactic body radiation therapy) could prolong clinical benefit of systemic therapies beyond oligo-progression. Of course, development of predictive biomarker could be helpful in order to select patients who could much benefit from this treatment strategy. Circulating tumor cell detection and analysis could also have a crucial role in this field. A joint effort of two prospective ongoing trials (ARTO, clinical.gov identifier NCT03449719 and PRIMERA, clinical.gov identifier NCT04188275) might help to improve criteria to select patients in whom a local ablative approach might confer significant benefit. In this commentary, we summarized recent data from literature to support this thesis.

Commissioning of the TrueBeam STx 6 MV FFF Beam in the RayStation Treatment Planning System for SRS and SBRT Treatments

Purpose: The purpose of this study is to provide technical information on commissioning the TrueBeam STx 6 MV flattening-filter free (FFF) beam in the RayStation treatment planning system (TPS) for stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) treatments. Methods: For beam modeling, percent depth dose curves, profiles and output factors for jaw-collimated fields and stereotactic cones as well as X-jaws transmission were measured. For multi-leaf collimator (MLC) modeling, MLC model parameters such as offset, gain, curvature, leaf tip width, tongue and groove and transmission were determined and output factors for MLC-collimated fields were measured. Absolute dose calibration was also performed. For beam model and MLC model validation, the American Association of Physicists in Medicine Task Group-119 plans, clinical SRS and SBRT plans and end-to-end testing were performed. Results: Beam characteristics of the 6 MV FFF beam agreed well with those in the literature. Validation results showed that our beam model and MLC model were acceptable for SRS and SBRT treatments. Conclusions: The technical information and dosimetric data provided in this study will be a useful reference for other clinics/institutions which will commission the same machine energy in the RayStation TPS.

End-to-End Test of Respiratory Gated Radiation Therapy for Lung Stereotactic Body Radiation Therapy Treatments

End-to-End Test of Respiratory Gated Radiation Therapy for Lung Stereotactic Body Radiation Therapy Treatments

Efficacy and safety of sequential lenvatinib therapy after stereotactic body radiotherapy in treatment of advanced primary liver cancer

Objective To investigate the efficacy and safety of sequential lenvatinib therapy after stereotactic body radiotherapy (SBRT) in the treatment of advanced primary liver cancer. Methods A total of 18 patients with advanced primary liver cancer who were admitted to The Fifth Medical Center of Chinese PLA General Hospital from October 2018 to May 2019 were enrolled, among whom there were 4 patients with BCLC stage B liver cancer and 14 patients with BCLC stage C liver cancer. The prescribed dose of planning target volume was 48-55 Gy (median 50 Gy) in 6-9 fractions, and the median of single dose was 6 (5-9) Gy per fraction. Oral administration of lenvatinib was given since 1 week after SBRT was finished, with a median medication time of 9.5 (3.6-25.8) months. Follow-up was performed once a month for the first 3 months after treatment and once every 3 months after 3 months of treatment. The Kaplan-Meier method was used to calculate overall survival (OS) rate, progression-free survival (PFS) rate, and local control (LC) rate, and the incidence rates of adverse reactions and complications were also observed. Results Up to the follow-up on November 30, 2020, a total of 8 patients died, among whom 3 died of liver failure, 3 died due to tumor progression, 1 died of perforation of gallbladder, and 1 died of gastrointestinal bleeding. At 3, 6, 9, 12, and 18 months of treatment, the OS rates were 100%, 94%, 83%, 72%, and 67%, respectively, the PFS rates were 100%, 67%, 50%, 22%, and 17%, respectively, and the LC rates were 100%, 94%, 94%, 94%, and 94%, respectively; the median OS time was > 18 months, and the median PFS time was 9 months. Of all patients, 1 (6%) had a grade 3 adverse reaction during SBRT and 2 (11%) experienced a grade 3 adverse reaction during lenvatinib treatment, and no fatal adverse reaction was observed. Conclusion It is preliminarily proved that sequential lenvatinib therapy after SBRT is an effective and safe treatment method for advanced primary liver cancer.