Stereotactic Ablative Body Radiotherapy Research Articles

Curative intent Stereotactic Ablative Radiation Therapy (SABR) for treatment of lung oligometastases from head and neck squamous cell carcinoma (HNSCC): a multi-institutional retrospective study.

The aim of this retrospective study was to assess outcomes of SABR for metachronous isolated lung oligometastases from HNSCC. For patients who developed isolated, 1 or 2 lungs lesions (<5cm) consistent with metastases from HNSCC, the indication of SABR was validated in a multidisciplinary tumor board. All patients were monitored by CT or PET CT after SABR (Stereotactic Ablative Body Radiation) for HNSCC. Between November 2007 and February 2018, 52 patients were treated with SABR for metachronous lung metastases. The median time from the treatment of the primary HNSCC to the development of lung metastases was 18 months (3-93). The cohort's median age was 65.5 years old (50-83). The vast majority (94.2%) received 60 Gy in three fractions. Forty-one patients (78.5%) presented a solitary lung metastasis, while 11 patients (21.5%) had two lung metastases. With a median follow-up of 45.3 months, crude local and metastatic control rates were 74 and 38%, respectively. 1 year and 2 year Overall Survival (OS) were 85.8 and 65.9%, respectively. The median OS was 46.8 months. About one-fourth of patients were retreated by SABR for distant pulmonary recurrence. The treatment was well tolerated with only one patient who reported ≥ grade 3 toxicity (1.9%). In selected metastatic HNSCC patients, early detection and treatment of lung metastases with SABR is effective and safe. Prospective studies are required to validate this potential shift. Patients with oligometastases and controlled primary HNSCC seem to benefit from metastasis directed therapies.

Abstract PD10-02: A randomised phase II trial of single fraction or multi-fraction SABR (stereotactic ablative body radiotherapy) with atezolizumab in patients with advanced triple negative breast cancer (AZTEC trial)

Abstract A randomised phase II trial of single fraction or multi-fraction SABR (stereotactic ablative body radiotherapy) with atezolizumab in patients with advanced triple negative breast cancer (AZTEC trial) Abstract: BACKGROUND: In patients with advanced triple negative breast cancer (TNBC), immunotherapy has shown acceptable safety and efficacy in a PD-L1 (programmed death-ligand 1) positive population. Pre-clinical evidence has demonstrated that SABR can prime a more effective systemic anti-tumor response in combination with checkpoint inhibition. It is currently unknown if single or multi-fraction SABR scheduling synergises best with atezolizumab therapy. METHODS: This was a multi-centre, open label, phase 2 randomised trial of patients with advanced TNBC, unselected for (PD-L1) status, who had recurred at least 6 months post completion of (neo) adjuvant chemotherapy and received less than 2 lines of treatment in the metastatic setting. Participants were randomised to 20Gy SABR in 1 fraction or 24Gy SABR in 3 fractions to 1-4 sites of disease, with at least one metastasis left unirradiated. Within 5 days following the final fraction of radiotherapy atezolizumab was commenced at a dose of 1200 mg every 21 days and continued for up to 24 months, or until progression or intolerable toxicity. The primary endpoint is progression- free survival (PFS). Secondary endpoints include efficacy according to PD-L1 IHC status (positive: SP142 ≥1%) and TIL (tumour infiltrating lymphocyte) quantity, response assessment, overall survival and safety. Results presented are from interim analysis performed 18 weeks after the last patient commenced treatment. RESULTS: Fifty evaluable patients were recruited and randomised between 20th November 2018 and 12thApril 2021 with a median age of 57 [35 - 79] yrs. Thirty (60%) and 20 (40%) patients had received none or one previous line of chemotherapy in the metastatic setting, respectively. 14/40 (35%) patients were PD-L1 positive at baseline and 26/42 (62%) had TIL≥5%. Median follow-up was 17 months. The median PFS for the 20 Gy arm was 2.5 (90% CI: 1.7-4.5) months, 3.1 (90% CI: 1.8-3.9) months for the 24 Gy arm. For both arms combined, the PFS was 3.1 (90% CI: 1.8-3.9) months, with no difference between the arms, HR 1.2 (95% CI: 0.6-2.1), p=0.64. PFS by PD-L1 IHC status and TIL&amp;lt;5% vs ≥5% was similar. There were 11 (22%) patients with clinical benefit (no PD within 24 weeks of C1D1), these were not significantly different by arm (p=0.74), nor by PD-L1 status (p=0.44) or TIL quantity (p=0.92) (Table 1). Overall survival is immature: estimated 12 months was 78% (95% CI:54-90) for the 20 Gy arm and 57% (95% CI: 33-75) for the 24 Gy arm.. In patients who were PD-L1 positive the ORR was 1/12 (8%) and DC was 3/14 (21%) compared with ORR of 1/14 (7%) and DC of 3/26 (12%) in patients who were PD-L1 negative. CONCLUSIONS: The efficacy between single and multi-fraction SABR in combination with Atezolizumab was similar and toxicity was acceptable. Efficacy was seen in PD-L1 positive and negative patients. Longer follow-up is required to assess the effect on OS.. (Research support and funding provided by the imCORE Network on behalf of F. Hoffmann-La Roche; AZTEC ClinicalTrials.gov Identifier: NCT03464942) Table 1.Response AssessmentResponse, n (%)All patients (n = 50)Patients with measurable disease (n = 32)Best objective response (non-SABR lesion)CR3 (6)2 (6)PR2 (4)2(6)NCR/NPD8 (16)0SD13 (26)13 (41)PD24 (48)15 (47)ORR (CR + PR)5 (10); 95% CI: 3-224 (12%); 95% CI: 4-29DCR (CR + PR + SD + non-CR/non-PD ≥24 weeks)a11 (22%); 95% CI: 12-377 (23%); 95% CI: 10-41aOne patient withdrew at 8 weeks and was not assessable for DCR. Citation Format: Steven David, Peter Savas, Shankar Siva, Michelle White, Michael W Neeson, Shane White, Gavin Marx, Robyn Cheuk, Michelle Grogan, Maria Farrell, Jessica Foudoulis, Annette Dempsey, Paul J Neeson, Mathias Bressel, Sherene Loi. A randomised phase II trial of single fraction or multi-fraction SABR (stereotactic ablative body radiotherapy) with atezolizumab in patients with advanced triple negative breast cancer (AZTEC trial) [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD10-02.

Personalized Automation of Treatment Planning for Linac-Based Stereotactic Body Radiotherapy of Spine Cancer.

Purpose/Objective(s)Stereotactic ablative body radiotherapy (SBRT) for vertebral metastases is a challenging treatment process. Planning automation has recently reported the potential to improve plan quality and increase planning efficiency. We performed a dosimetric evaluation of the new Personalized engine implemented in Pinnacle3 for full planning automation of SBRT spine treatments in terms of plan quality, treatment efficiency, and delivery accuracy.Materials/MethodsThe Pinnacle3 treatment planning system was used to reoptimize six patients with spinal metastases, employing two separate automated engines. These two automated engines, the existing Autoplanning and the new Personalized, are both template-based algorithms that employ a wishlist to construct planning goals and an iterative technique to replicate the planning procedure performed by skilled planners. The boost tumor volume (BTV) was defined as the macroscopically visible lesion on RM examination, and the planning target volume (PTV) corresponds with the entire vertebra. Dose was prescribed according to simultaneous integrated boost strategy with BTV and PTV irradiated simultaneously over 3 fractions with a dose of 30 and 21 Gy, respectively. Dose-volume histogram (DVH) metrics and conformance indices were used to compare clinically accepted manual plans (MP) with automated plans developed using both Autoplanning (AP) and Personalized engines (Pers). All plans were evaluated for planning efficiency and dose delivery accuracy.ResultsFor similar spinal cord sparing, automated plans reported a significant improvement of target coverage and dose conformity. On average, Pers plans increased near-minimal dose D98% by 10.4% and 8.9% and target coverage D95% by 8.0% and by 4.6% for BTV and PTV, respectively. Automated plans provided significantly superior dose conformity and dose contrast by 37%–47% and by 4.6%–5.7% compared with manual plans. Overall planning times were dramatically reduced to about 15 and 23 min for Pers and AP plans, respectively. The average beam-on times were found to be within 3 min for all plans. Despite the increased complexity, all plans passed the 2%/2 mm γ-analysis for dose verification.ConclusionAutomated planning for spine SBRT through the new Pinnacle3 Personalized engine provided an overall increase of plan quality in terms of dose conformity and a major increase in efficiency. In this complex anatomical site, Personalized strongly reduce the tradeoff between optimal accurate dosimetry and planning time.

Preoperative stereotactic body radiotherapy combined with surgical treatment for renal cell carcinoma and inferior vena cava tumour thrombus: study protocol for a single-arm cohort trial

IntroductionAlthough surgery is currently the first choice for patients with renal cell carcinoma and vena cava tumour thrombus, the surgery is difficult, with many complications, and the prognosis of patients...

Treatment outcomes of stereotactic ablative body radiotherapy on oligometastases from colorectal cancer: early results of a single institution service evaluation.

ObjectiveStereotactic ablative radiotherapy (SABR) has been suggested to be an effective non-invasive ablative therapy for oligometastases originated from colorectal cancer (CRC). This study aimed to report CRC oligometastases SABR treatment outcomes in terms of overall survival (OS), progression-free survival (PFS) and post-treatment toxicities.Methods:Treatment records of patients with CRC metachronous oligometastases who underwent SABR at a single institution between February 2015 and December 2018 were retrospectively reviewed. OS and PFS were calculated using Kaplan–Meier statistics and post-RT toxicity data was scored following CTCAE v. 4.0. Analysis of prognostic factors on OS and PFS was performed based on site of primary cancer, types of treatment to primary cancer, number of oligometastases, SABR treatment sites, intervals between treatment to primary cancer and SABR to oligometastases, biological equivalent dose, cumulative gross tumour volume and planning target volume.Results75 patients with 86 CRC metachronous oligometastases (including liver, lung, lymph nodes and bone) were included. The median age was 65.5 years (range 42.5–87.2) with a median follow-up of 23.8 months (range 3.1–46.5). The estimated median PFS was 14.6 months (95% CI 9.6–19.6). and estimated median OS was 33.3 months (95% CI 22.9–43.7). Majority of patients tolerated SABR well with the most common acute side-effects of Grade 1 fatigue. No Grade 3 or higher toxicities were reported at any time points.Only SABR treatment sites (p = 0.03) and cumulative volumes of planning target volume (p = 0.02) were found to be statistically significant independent predictors of PFS and OS respectively.ConclusionThis study showed modest PFS, OS, and post-treatment toxicity outcomes on SABR to metachronous oligometastases from CRC. It has highlighted that cumulative tumour volume may be a stronger prognostic factor of OS comparing to the number of metastases.Advances in knowledge:There are limited data published on the efficacy and post-treatment toxicity of CRC oligometastases SABR with adequate length of follow-up. Our retrospective study suggests that cumulative tumour volume may be a stronger prognostic factor of OS comparing to the number of oligometastases.

The markerless lung target tracking AAPM Grand Challenge (MATCH) results.

Lung stereotactic ablative body radiotherapy (SABR) is a radiation therapy success story with level 1 evidence demonstrating its efficacy. To provide real-time respiratory motion management for lung SABR, several commercial and preclinical markerless lung target tracking (MLTT) approaches have been developed. However, these approaches have yet to be benchmarked using a common measurement methodology. This knowledge gap motivated the MArkerless lung target Tracking CHallenge (MATCH). The aim was to localize lung targets accurately and precisely in a retrospective in silico study and a prospective experimental study. MATCH was an American Association of Physicists in Medicine sponsored Grand Challenge. Common materials for the in silico and experimental studies were the experiment setup including an anthropomorphic thorax phantom with two targets within the lungs, and a lung SABR planning protocol. The phantom was moved rigidly with patient-measured lung target motion traces, which also acted as ground truth motion. In the retrospective in silico study a volumetric modulated arc therapy treatment was simulated and a dataset consisting of treatment planning data and intra-treatment kilovoltage (kV) and megavoltage (MV) images for four blinded lung motion traces was provided to the participants. The participants used their MLTT approach to localize the moving target based on the dataset. In the experimental study, the participants received the phantom experiment setup and five patient-measured lung motion traces. The participants used their MLTT approach to localize the moving target during an experimental SABR phantom treatment. The challenge was open to any participant, and participants could complete either one or both parts of the challenge. For both the in silico and experimental studies the MLTT results were analyzed and ranked using the prospectively defined metric of the percentage of the tracked target position being within 2mm of the ground truth. A total of 30 institutions registered and 15 result submissions were received, four for the in silico study and 11 for the experimental study. The participating MLTT approaches were: Accuray CyberKnife (2), Accuray Radixact (2), BrainLab Vero, C-RAD, and preclinical MLTT (5) on a conventional linear accelerator (Varian TrueBeam). For the in silico study the percentage of the 3D tracking error within 2mm ranged from 50% to 92%. For the experimental study, the percentage of the 3D tracking error within 2mm ranged from 39% to 96%. A common methodology for measuring the accuracy of MLTT approaches has been developed and used to benchmark preclinical and commercial approaches retrospectively and prospectively. Several MLTT approaches were able to track the target with sub-millimeter accuracy and precision. The study outcome paves the way for broader clinical implementation of MLTT. MATCH is live, with datasets and analysis software being available online at https://www.aapm.org/GrandChallenge/MATCH/ to support future research.

Variable and fixed costs in NHS radiotherapy; consequences for increasing hypo fractionation

Background/PurposeThe increased use of hypofractionated radiotherapy changes department activity. While expected to be cost-effective, departments’ fixed costs may impede savings. Understanding radiotherapy’s cost-drivers, to what extent these are fixed and consequences of reducing activity can help to inform reimbursement strategies. Material/MethodsWe estimate the cost of radiotherapy provision, using time-driven activity-based costing, for five bone metastases treatment strategies, in a large NHS provider. We compare these estimations to reimbursement tariff and assess their breakdown by cost types: fixed (buildings), semi-fixed (staff, linear accelerators) and variable (materials) costs. Sensitivity analyses assess the cost-drivers and impact of reducing departmental activity on the costs of remaining treatments, with varying disinvestment assumptions. ResultsThe estimated radiotherapy cost for bone metastases ranges from 430.95€ (single fraction) to 4240.76€ (45 Gy in 25#). Provider costs align closely with NHS reimbursement, except for the stereotactic ablative body radiotherapy (SABR) strategy (tariff exceeding by 15.3%). Semi-fixed staff costs account for 28.1–39.7% and fixed/semi-fixed equipment/space costs 38.5–54.8% of provider costs. Departmental activity is the biggest cost-driver; reduction in activity increasing cost, predominantly in fractionated treatments. Decommissioning linear accelerators ameliorates this, although can only be realised at equipment capacity thresholds. ConclusionHypofractionation is less burdensome to patients and long-term offers a cost-efficient mechanism to treat an increasing number of patients within existing capacity. As a large majority of treatment costs are fixed/semi-fixed, disinvestment is complex, within the life expectancy of a linac, imbalances between demand and capacity will result in higher treatment costs. With a per-fraction reimbursement, this may disincentivise delivery of hypofractionated treatments.

A customizable anthropomorphic phantom for dosimetric verification of 3D-printed lung, tissue, and bone density materials.

To design and manufacture a customized thoracic phantom slab utilizing the 3D printing process, also known as additive manufacturing, consisting of different tissue density materials. Here, we demonstrate the 3D-printed phantom's clinical feasibility for imaging and dosimetric verification of volumetric modulated arc radiotherapy (VMAT) plans for lung and spine stereotactic ablative body radiotherapy (SABR) through end-to-end dosimetric verification. A customizable anthropomorphic phantom slab was designed using the CT dataset of a commercial phantom (adult female ATOM dosimetry phantom, CIRS Inc.). Material extrusion 3D printing was utilized to manufacture the phantom slab consisting of acrylonitrile butadiene styrene material for the lung and the associated lesion, polylactic acid (PLA) material for soft tissue and spinal cord, and both PLA and iron-reinforced PLA materials for bone. CT images were acquired for both the commercial phantom and 3D-printed phantom for HU comparison. VMAT plans were generated for spine and lung SABR scenarios and were delivered as per departmental SABR protocols using a Varian TrueBeam STx linear accelerator. End-to-end dosimetry was implemented with radiochromic films, analyzed with gamma criteria of 5% dose difference, and a distance-to-agreement of 1mm, at a 10% low-dose threshold by comparing with calculated dose using the Acuros algorithm of the Eclipse treatment planning system (v15.6). 3D-printed phantom inserts were observed to produce HU ranging from -750 to 2100. The 3D-printed phantom slab was observed to achieve a similar range of HU from the commercial phantom including a mean HU of -760 for lung tissue, a mean HU of 50 for soft tissue, and a mean HU of 220 and 630 for low- and high-density bone, respectively. Film dosimetry results show 2D-gamma passing rates for lung SABR (internal and superior) and spine SABR (inferior and superior) over 98% and 90%, respectively. The end-to-end testing of VMAT plans for spine and lung SABR suggests the clinical feasibility of the 3D-printed phantom, consisting of different tissue density materials that emulate lung, soft tissue, and bone in kV imaging and megavoltage photon dosimetry. Further investigation of the proposed 3D printing techniques for manufacturability and reproducibility will enable the development of clinical 3D-printed phantoms in radiotherapy.

Stereotactic ablative body radiotherapy for ventricular tachycardia: An alternative therapy for refractory patients.

Stereotactic ablative body radiotherapy (SABR) allows the administration of ablative doses of radiation in a focused form with a low probability of side effects and is widely used for cancer treatment. However, in the recent years its usefulness in benign cardiac pathology is being studied. In this study, we aimed to guide the cardiologist in SABR and its applications in treatment of refractory ventricular tachycardia. In this review, we analyzed published literature on PubMed and MEDLINE with papers published in the past 5 years. We included papers in the English language with information about indications, radiotherapy plan, doses and fractionations, and outcomes. All citations were evaluated for relevant content and validation.

Dose calculation and reporting with a linear Boltzman transport equation solver in vertebral SABR.

Vertebral Stereotactic ablative body radiotherapy (SABR) involves substantial tumour density heterogeneities. We evaluated the impact of a linear Boltzmann transport equation (LBTE) solver dose calculation on vertebral SABR dose distributions. A sequential cohort of 20 patients with vertebral metastases treated with SABR were selected. Treatment plans were initially planned with a convolution style dose calculation algorithm. The plan was copied and recalculated with a LBTE algorithm reporting both dose to water (Dw) or dose to medium (Dm). Target dose as a function of CT number, and spinal cord dose was compared between algorithms. Compared with a convolution algorithm, there was minimal change in PTV D90% with LBTE. LBTE reporting Dm resulted in reduced GTV D50% by (mean, 95% CI) 2.2% (1.9-2.6%) and reduced Spinal Cord PRV near-maximum dose by 3.0% (2.0-4.1%). LBTE reporting Dw resulted in increased GTV D50% by 2.4% (1.8-3.0%). GTV D50% decreased or increased with increasing CT number with Dm or Dw respectively. LBTE, reporting either Dm or Dw resulted in decreased central spinal cord dose by 8.7% (7.1-10.2%) and 7.2% (5.7-8.8%) respectively. Reported vertebral SABR tumour dose when calculating with an LBTE algorithm depends on tumour density. Spinal cord near-maximum dose was lower when using LBTE algorithm reporting Dm, which may result in higher spinal cord doses being delivered than with a convolution style algorithm. Spinal cord central dose was significantly lower with LBTE, potentially reflecting LBTE transport approximations.

Quality of life after VATS lung resection and SABR for early-stage non-small cell lung cancer: A longitudinal study

IntroductionVideo-assisted thoracoscopic (VATS) lung resection is the recommended curative treatment for early-stage non-small cell lung cancer (NSCLC). Patients considered at high surgical risk, are treated with stereotactic ablative body radiotherapy (SABR) as a lower morbidity alternative. This study aims to investigate the impact of SABR and VATS resection on patients’ quality of life (QoL) over the first year after treatment. MethodsA prospective longitudinal observational study recruiting early-stage NSCLC patients from a single UK centre. QoL was assessed with EORTC QLQ-C30 and Lung Cancer Module LC13 at baseline, 6 weeks and 3, 6 and 12 months post-treatment. ResultsFrom 01.03.2017 till 01.03.2018, 244/281 patients (87%) consented to participate, 225 (95 SABR and 130 VATS) were included in the analysis.SABR patients had significantly worse baseline QoL scores than VATS patients, even after adjusting for preoperative clinical factors (C-30 Global Health mean: SABR = 53.8, VATS = 71.2; Physical Functioning mean: SABR = 57, VATS = 82.2; Fatigue mean: SABR = 43.5, VATS = 23.7; C30 Dyspnea mean: SABR = 49.5, VATS = 26.2). During the 12 months post SABR treatment patients’ QoL scores remained stable. In the VATS group, there was a deterioration 6-weeks after treatment in Role, Physical, Social Functions, Global Health, Fatigue, C30/LC13 Dyspnoea, Pain, Appetite loss, Constipation, LC13 Pain in Chest and Arms. The scores improved by 12 months without reaching the preoperative values. ConclusionsAlthough QoL outcomes for SABR and VATS are not comparable due to different medical selection criteria, the QoL impact of the two treatments during the first year showed different trends which will inform patients and clinicians during decision-making discussions.

A Randomized Phase 2 Trial of Nivolumab and Stereotactic Ablative Body Radiotherapy (SABR) in Advanced Non-Small Cell Lung Cancer, Progressing After First- or Second-Line Chemotherapy (NIVORAD)

A Randomized Phase 2 Trial of Nivolumab and Stereotactic Ablative Body Radiotherapy (SABR) in Advanced Non-Small Cell Lung Cancer, Progressing After First- or Second-Line Chemotherapy (NIVORAD)

Multi-Institutional Outcomes of Stereotactic Magnetic Resonance Image-Guided Adaptive Radiation Therapy (SMART) With Median Biologically Effective Dose of 100 Gy10 for Oligometastases

<h3>Purpose/Objective(s)</h3> Randomized data show an overall survival (OS) benefit of stereotactic ablative body radiation therapy (SABR) in addition to chemotherapy (CT) in selected patients with oligometastasis (OM). While ablative dose can be safely delivered to some lesions, others in proximity to some organs at risk (OARs) such as bowel may be treated with non-ablative dose to limit toxicity. Stereotactic magnetic resonance image-guided adaptive radiation therapy (SMART) may facilitate the delivery of ablative dose for OM lesions, especially those adjacent to historically dose-limiting OARs, which may improve long-term disease control. <h3>Materials/Methods</h3> The RSSearch Registry was queried for OM patients (1-5 metastatic lesions) treated with SMART. Patients with < 3 months (mo.) follow-up after SMART were excluded. Local control (LC), freedom from distant progression (FFDP), progression free survival (PFS), and OS were estimated using the Kaplan-Meier method. LC was evaluated using RECIST 1.1 criteria. Acute toxicity was defined as within 90 days of SMART and evaluated using CTCAE v4 criteria. <h3>Results</h3> 101 patients with 114 OM lesions were treated on a 0.35T-MR Linac at 2 institutions between 2018-2020. Median age was 62 years (range 23-89), and 99% were ECOG 0-1 performance status. The primary tumor was definitively managed in 34.7%, most commonly in the lung (30.7%), colon/rectum (22.8%), cervix/uterus/ovary (13.9%), or breast (5.9%). About 50% received CT for OM prior to SMART. SMART was delivered to 1 (87.7%) or 2 (10.5%) lesions, mostly involving abdominal/pelvic lymph nodes (40.4%), liver (17.5%), lung (17.5%), or adrenal gland (11.4%). All were treated without fiducial markers and with real-time tissue tracking and automated beam gating, typically in breath hold. The median prescribed RT dose was 45 Gy (range 24-60Gy) in a median 5 fractions (range 3-15). The median biologically effective dose (BED₁₀) was 100 Gy₁₀ (range 41.4-180). The median PTV was 14.5 cm³ (range 1.5-567.8). Median follow-up was 10 months (range 3-25) from SMART. One-year LC, FFDP, PFS, and OS were 88%, 38.2%, 36.1%, and 90.6%, respectively. Median PFS and OS were 9 months and not reached, respectively. No acute/late grade 3+ toxicities were recorded. <h3>Conclusion</h3> To our knowledge, this represents the largest analysis of SMART for OM. A median prescribed BED₁₀ of 100 Gy₁₀ resulted in excellent early LC and no significant toxicity, likely facilitated by continuous intrafraction MR visualization, breath hold delivery, and online adaptive replanning. These outcomes are noteworthy given the predominance of OM, especially LNs, treated with dose escalation in proximity to gastrointestinal OARs; such lesions are notably underrepresented in SABR OM trials. Prospective evaluation of dose-escalated SMART for OM is warranted.

A Prospective Clinical Trial Evaluating Stereotactic Magnetic Resonance Guided Adaptive Radiation Therapy (SMART) for Pancreatic Cancer

The use of ablative stereotactic body radiation therapy (SBRT) in pancreatic cancer is constrained by nearby radiation-sensitive organs. Magnetic resonance (MR)-guided adaptive radiation therapy (SMART) is an innovation that offers superior anatomical imaging during treatment allowing for daily plan adaptation based on the volumetric images prior to each treatment. We report results of a prospective phase 1 trial (NCT04115254) assessing feasibility of SMART and describe early outcomes of patients with pancreatic cancer. Secondary objectives included analysis of 90-day toxicity, local control, and patient-reported outcomes (PROMs) in patients undergoing SMART.In this prospective IRB approved study, patient eligibility criteria included: biopsy-proven diagnosis of pancreatic cancer, eligibility for SBRT, and ability to undergo and tolerate MRI imaging. Patients were ineligible if they had prior abdominal radiation, active ulcerative disease, or tumor invasion of the stomach, duodenum or bowel on endoscopy. Patients were monitored for acute and late grade ≥ 3 toxicity. PROMs included the FACT-HEP and PROMIS Physical and Mental Health batteries and were completed at baseline and during follow-up. Feasibility was defined as 1) enrolling patients and delivering SMART on the MR-Linac; 2) assessing tumor using MR guidance before, during and after MR-guided treatment and 3) generating adaptive plans.All 10 patients successfully completed SMART, receiving 40 Gy in 5 fractions with 48 of 50 fractions requiring adaptation to meet target or critical organ-at-risk metrics. The median follow up was 10.49 months (range 5.00 - 11.38). The median age was 72 (range 55 - 89), 60% were female, and 80% were white. Disease stages included 30% T1-T2, 10% T3, and 60% T4 disease, as well as 30% N0, 60% N1, 10% N2 disease, and 80% M0, 10% MX, and 10% M1. 90% of patients had other medical comorbidities. ECOG performance status was 0-1 in 90% of patients. There were no acute or late grade ≥ 3 treatment related toxicities. There were no local recurrences. The 6-month survival rate was 90% (95% CI 47.3-98.5) with two deaths due to progressive disease. The median change between baseline and follow-up within 6 months of treatment was -0.5 on FACT-HEP, -2.5 on PROMIS Physical, and -4.7 on PROMIS Mental Health (table 1).We successfully demonstrated the feasibility and safety of SMART with daily adaptation in patients with pancreatic cancer. PROMs highlight that patients tolerated treatment well with minimal toxicity. Further investigation in dose escalation in pancreatic cancer is warranted.

Stereotactic Ablative Body Radiotherapy Boost for Cervical Cancer When Brachytherapy Boost is Not Feasible

The purpose of this study was to analyze the treatment efficacy and safety of stereotactic ablative body radiotherapy (SABR) boost for cervical cancer patients not amenable to brachytherapy.A retrospective review of the medical records of 25 eligible patients was performed. The patients underwent pelvic radiotherapy in 25 or 28 fractions with a median dose of 45 Gy (range, 44-50.4 Gy). SABR boost was delivered after pelvic radiotherapy, with a median dose of 25 Gy (range, 20 to 33 Gy), and a median fraction number of 5 (range, 4-6). Patients with a follow-up period of more than one year were included in the toxicity analysis, and hematuria and hematochezia that occurred later than 3 months after the radiotherapy were graded.The median follow-up period after RT was 2.85 years (range, 0.33 to 6.60). The 3-year local control, locoregional control, disease-free survival, and overall survival rates were 80.9%, 75.8%, 40.9%, and 77.1%, respectively. The 3-year rates of freedom from hematuria and hematochezia were 58.5% and 29.6%, respectively. No grade 4-5 toxicity was reported. Receiver operating characteristic (ROC) curve analysis showed that simple summation of the mean biologically equivalent dose (BED) to the bladder was predictive of hematuria (P = 0.040), while the simple summation of the maximum BED to the rectum was marginally predictive of hematochezia (P = 0.057).SABR boost for cervical cancer was effective and tolerable. Although it cannot substitute brachytherapy, it can be a treatment option when brachytherapy is not possible.T. Lee: None. I. Kim: None. J. Kim: None. C. Song: None. Y. Kim: None. K. Kim: None. J. No: None. D. Suh: None. J. Chung: None. K. Eom: None.

Using 4DCBCT simulation and guidance to evaluate inter-fractional tumor variance during SABR for lung tumor within the lower lobe

Inter-fractional tumor variance would lead to insufficient dosage or overdose in tumor region during lung cancer radiotherapy. However, previous works have not considered influence of inter-fractional tumor amplitude variance at treatment position due to lack of effective evaluation method during radiotherapy, especially for lung tumor within the lower lobe. Our objective was to investigate inter-fractional tumor baseline shift and amplitude variance due to respiratory motion with 4DCBCT simulation and guidance during stereotactic ablative body radiotherapy (SABR) for lung tumor. Subject included 19 patients with lung tumor within the lower lobe. 4DCBCT-simulated images at treatment position were acquired sequentially to determine internal tumor volume (ITV) and reference tumor motion at simulation process. Compared with reference tumor motion, 95 4DCBCT-guided images were acquired during each treatment to evaluate inter-fractional tumor baseline shift and amplitude variance, which were − 0.0 ± 1.3 mm and − 0.2 ± 1.4 mm in left–right(LR) direction, 0.9 ± 2.3 mm and 0.4 ± 2.9 mm in superior-inferior (SI) direction, 0.1 ± 1.5 mm and − 0.4 ± 2.0 mm in anterior–posterior (AP) direction. ITV margin were 3.5 mm, 7.5 mm and 5.3 mm in LR, SI and AP directions with van Herk’s (Int J Radiat Oncol Biol Phys 52(5):1407–1422, 2002) formula. 4DCBCT simulation and guidance is a reliable method to evaluate inter-fractional tumor variance during SABR for lung tumor within the lower lobe. ITV margin of 3.5 mm, 7.5 mm and 5.3 mm in LR, SI and AP directions would ensure greater tumor coverage during SABR for lung tumor within the lower lobe.

Stereotactic ablative body radiotherapy as a bridge to liver transplantation for hepatocellular carcinoma: preliminary results of Baskent University experience

Stereotactic ablative body radiotherapy as a bridge to liver transplantation for hepatocellular carcinoma: preliminary results of Baskent University experience

ES02.04 Systemic Therapy Influenced Trials in Oligometastatic Disease

A working definition of Oligometastatic Disease (OMD) in Non-Small Cell Lung Cancer (NSCLC) is no more than 5 metastases involving 3 organs 1. This definition of OMD is largely for the purposes of offering local ablative therapy (LAT) - which includes surgery, or more frequently radiotherapy and, in particular Stereotactic Ablative Body Radiotherapy (SABR). However, OMD is a heterogenous state – which encompasses many clinical scenarios: at diagnosis of NSCLC with synchronous metastases; at recurrence after effective therapy; at progression after systemic therapy; and persistent site (s) of disease on therapy.

167: A Review of Stereotactic Ablative Body Radiotherapy Outcomes for Early Stage Non-Small Cell Lung Cancer at the Nova Scotia Cancer Centre to Determine the Role of [18F] Pet Metrics on the Prediction of Local Failure

167: A Review of Stereotactic Ablative Body Radiotherapy Outcomes for Early Stage Non-Small Cell Lung Cancer at the Nova Scotia Cancer Centre to Determine the Role of [18F] Pet Metrics on the Prediction of Local Failure

Patient-specific tumor and respiratory monitoring phantom design for quality controls of stereotactic ablative body radiotherapy in lung cancer cases.

The design, production and adaptability to clinical routine of a patient-specific tumor and respiratory monitoring phantom (TRMP) was investigated using 3D printer technology. TRMP and GTV modelling were done using 4D-CT images of the inhalation phase. The model was converted to STL (Stereolithography) format and printed with STH (Strong Herbal) biopolymer with HU (Hounsfield Unit) suitable for imaging purposes. The assembly of TRMP motorized parts and mechanical equipment has been completed and made suitable for clinical use. In the first part of the study, the deviations of radio-opaque markers attached to the TRMP sternum to perform mechanical quality control tests and T1-7 costal vertebrae in CC, AP, and LAT directions were evaluated. In the second part of the study, in order to evaluate the usability of the TRMP in quality assurance (QA), point dose measurements with BeO OSL dosimetry and EBT3 gafchromic film measurements were taken in Trilogy® radiotherapy accelerator and CyberKnife® robotic radiosurgery accelerator. In this study, we present a highly flexible TMRP capable of performing independent internal and external motions. TRMP was successfully tested in different treatment accelerators, both mechanically and dosimetrically.