Stereotactic Radiotherapy for the Treatment of Recurrent Refractory Vt in Chagas Disease Patients

Background: Stereotactic radiotherapy (SBRT) is a new therapeutic option for patients with scar related ventricular tachycardia (VT). Objective(s): To describe our experience with the use of SBRT for the treatment of recurrent VT in patients with Chagas Cardiomyopathy (CCM) in whom catheter ablation is not an option. Method(s): We selected patients with Chagas Disease that underwent SBRT for recurrent VT treatment. The target sites of SBRT were planned based on CMR and CT reconstruction on ADAS software, bipolar voltage maps from previous CA procedures and VT morphology induced on a electrophysiologic study performed SBRT planning. Target sites were decided together by electrophysiology and radiation oncology group. Result(s): We performed SBRT in six CCM patients July 2021 to July 2022. Most patients were male (66.7%), mean age 62.3+/-5.7 years-old and EF 28.5% (Q1: 20 Q3:42.7). One patient (16.7%) had two prior catheter ablation, four (66.7%) had one and one patient had no prior ablation, but had severe pulmonary fibrosis after COVID and was O2 dependent. The mean PTV (planning target volume) was 85+/-14 mL and the ITV (internal target volume) was 29+/-4 ml, with safe constraints regarding the esophagus and stomach. In a mean FU of 244+/-173days, 3 (50%) patients presented VT recurrence after blanking period. Two patients died 86 and 50 days after SBRT. The median number of VT episodes reduced from 13 (6.25;44.75) to 7.5 (3;7.5) (P = 0.093). All alive patients stop presenting VT in a median period of 174 (Q1: 44.75: Q3: 199) days, being at the end of the follow-up in a median of 196 (Q1: 137;Q3: 246) days without new VT episodes. Conclusion(s): SBRT presents a high rate of early recurrence in Chagas disease patients that improves during timeCopyright © 2023

Stereotactic Body Radiotherapy for Primary and Metastatic Lung Cancer, Cyberknife-M6 Experience

Introduction: It was aimed to evaluate the efficacy, local control and survival in patients with inoperable primary or metastatic lung cancer who underwent stereotactic body radiotherapy (SBRT) using the Cyberknife-M6 (CK-M6) with lung optimized treatment (LOT) module. Methods: Ethics committee (no: 2018-7/6) and scientific research project (OUAP (T) 2019/1) approval were obtained. 23 lesions of 21 patients were treated between April 2019 to December 2020 at our department. The patients were immobilized in the supine position by wearing a Synchrony vest, with the hands at their sides. A planning 4D-CT was obtained in a free breathing modality. The gross target volumes was created both on the full-inhale and full-exhale phases and internal target volume (ITV) was created. By taking an image of patients on the treatment device, tracking modality was selected according to the visibility of the target. Zero-View tracking was applied in 10 patients, 1-View in 10 patients, 2-View in 1 patients. 3 to 5 mm margin added for planning target volume (PTV) according to tracking method. Median ITV and PTV was 9,38 (2-52,34) and 20,27 (9,25-82,7) cc, respectively. An InCise2 multileaf collimator optimized by the Monte Carlo algoritm was used in all patients. A pair of the orthogonal kV X-ray imaging systems were used for simultaneous target tracking. Median prescribed dose was 48 Gy in 4 fractions (30-54 Gy in 3-6 fractions) administered consecutively or every other day. Prescription isodose covering 95% of PTV was 82,5% (77,4-99,3). Median conformity and homogeneity index was 1,17 (1,02-1,77) and 1,22 (1,09-1,29), respectively. Median BED10 was 100 Gy (53,62-151,2) and median beam on time was 26 minutes (12-42). Results: Patients were evaluated on January 2022. The median follow-up was 21 months (2-33). The median age was 68 (53-80) and 40% of the cases were adenocarcinoma. Two patients diagnosed with radiologically. Median lesion size was 13 mm (9-27). SBRT was applied to 13 primary tumors, 3 lung metastases and 7 lymph nodes. At initial evaluation, complete, partial and stable response was found 30%, 65% and 5%, respectively. During the follow-up, 3 patients locally recurred at a median of 11 months (9-14). The median and one-year local recurrence free survival was 22 months, and 89%. Acute and late grade 1-2 pulmonary complications was seen in 10 patients in a median of 7 months (2-13). While the cause of death in 6 cases was existent cardiac morbidity, covid19 pneumonia, lung infection (2) and progression (2), it was unknown in 1 patient. The median and one-year survival was 23 months and 95%. Conclusions: LOT module of the CK-M6 Xsight lung tracking system allows for the application of fiducial-free motion management strategies. The advantage of our study is that the most appropriate tracking modality can be selected prospectively before treatment. In our study, excellent local control with a median survival of 23 months for primary and metastatic lung cancer. With a median treatment time 26 minutes, noninvasive CK-M6 based SBRT was efficient, safe and comfortable treatment in lung cancer. Keywords: lung cancer, Cyberknife-M6, stereotactic body radiotherapy

Quantitative benefit of centralised quality assurance for the implementation of Lung SABR

Purpose or Objective SABR has become standard of care for early stage lung cancer where surgery is contraindicated. As a result of the COVID- 19 pandemic access to surgery was limited and demand for SABR as primary treatment has increased. A national program to implement lung SABR in all radiotherapy centres was commissioned and an associated QA program was developed. One of its components was a planning benchmark case to ensure optimal planning of target volumes whilst sparing organs at risk following the SABR Consortium Guidelines. Results of the benefits of the QA process are presented here. Materials and Methods A dual-lesion planning benchmark DICOM dataset was circulated amongst 24 participating centres, including a planning CT and a structure set. Centres had to plan the lesions to 55Gy in 5# and meet dose constraints, coverage and conformity criteria outlined in the Guidelines. All plans were reviewed on Velocity v4.1 (Varian Medical Systems) and PTV coverage, dose distribution, plan conformity and OAR dose constraints were assessed. Prescription Dose Spillage (PDS) was used to define conformity in the high dose area as Body V100(cc)/PTV V100(cc) and Modified Gradient Index (MGI) was defined for conformity in low dose area as Body V50(cc)/PTV V100(cc). The Mann Whitney test was used to evaluate differences in conformity across plans, with statistical significance set at 5%. Results Mean V100% for first submissions for lesions 1 and 2 were 97.26% (S.D. 1.86) and 98.19 % (S.D.1.61), respectively. All mandatory OARs were well within tolerance. The largest variation across centres was plan conformity, which is summarised in Table 1. (Table Presented) Ten plans failed their first attempt and centres were asked to resubmit following detailed feedback. Mean PDS for these plans changed from 1.19 (S.D. 0.09) to 1.13 (S.D. 0.05), although this was not statistically significant (p=0.12). Mean MGI was significantly improved on resubmission, decreasing from 7.08 (S.D. 0.8) to 6.16 (S.D.0.84), (p=0.03). Figure 1 shows increase in consistency and improvement in conformity across centres after resubmission. On completion of the QA process, the final set of accepted plans had improved conformity indices from initial PDS and MGI, however these were not statistically significant (p=0.31 and p=0.13, respectively). (Figure Presented) Conclusion A national QA program for lung SABR is critical for the safe implementation of this technique and to ensure standards are consistently high across multiple centres. The planning benchmark has highlighted differences in plan conformity and technique, in particular for MGI, however feedback within the QA process has allowed for increased consistency across departments through improved quality.