ESTRO 2023 - Abstract Book

S1072

Digital Posters

ESTRO 2023

We performed a retrospective analysis of 86 patients with Stage I - III (T1-4 N0 M0) proven or suspected NSLCL treated between October 2015 and December 2021. Patients treated with SBRT were nonsurgical candidates and/or patients who refused surgery. Advanced-stage T4 lesions were included in the study when all the nodules could be treated at the same time. Each patient had appropriate pretreatment staging with CT scans and FDG-18 PET-CT. Different motion management methods to account for respiratory motion were performed. Dose-prescription ranged from 55 to 60 Gy in 5 - 8 fractions. Treatment was delivered on Varian True-Beam® or Clinac DHX® linear accelerator, using volumetric modulated arc therapy (VMAT) with 6MV photons. Image guidance (IGRT) was performed by means of CBCT acquisitions prior to each treatment. After treatment, patients were followed with CTs or PET/CTs at least every 3 months for 2 year and every 6 months thereafter. The primary endpoints were Tumor Response, assessed via RECIST criteria, Local Control (LC), Disease-Free Survival(DFS), Overall Survival (OS) and treatment-related toxicity. The Kaplan Meir method and Log-Rank test were used to analyse the survival curves on SPSS v 25.0 (IBM Corp) was used for statistical analyses. Results Median age at treatment was 75 years (range 49 to 89 years), 82.5% males. The proportion of adenocarcinoma, squamous cell carcinoma, and unproven pathology was 36%, 25.6%, and 24.4% respectively. Most patients were early-stage (T1 69.8%; T2 19.8%), and the remaining 10.5% were T3-T4. The right upper lobe was the most involved (43%) whilst the right lower lobe was the least affected (7%). With a median follow-up of 19 months (range 1 to 80 months), the overall survival (OS) at 2y was 76%. The 2y OS rates for patients treated with T1compared to T2 lesions were 80% vs 76% (p=0.207). For early-stage and advanced cases 2y OS rates were 77% vs 58% respectively (p=0.926). When comparing OS in biopsy-proven vs unproven, the 2y OS rates were 82% vs 75% (p=0.407). The disease-free survival (DFS) was 72% at 2y; out of the 35 patients who relapsed a 62.8% presented local recurrence, 28.6% distant relapse (brain, liver and nodal) and 8.6% both local and distant disease. The 2y DFS for patients treated with T1 compared to T2 lesions was 50% vs 46% (p=0.750). The 2y DFS for advanced-stage and early-stage cases was 67% and 78% respectively (p=0.926). For patients with or without biopsy the 2y DFS rate was 52% and 43% respectively (p=0.506). Conclusion Outcomes after exclusive treatment with SBRT in patients with NSCLC are satisfactory with no disadvantage for empirically treated patients. Purpose or Objective At our institution, respiratory-gated SBRT (RG-SBRT) for lung tumors is performed using a real-time tumor monitoring system. Several fiducial markers (FMs) are inserted near the tumor for RG-SBRT. However, optimal FM as an internal surrogate cannot be selected to perform RG-SBRT. This study aimed to evaluate the relationship between FM and lung tumors to determine the optimal FM. Materials and Methods This study enrolled 41 patients who underwent RG-SBRT with real-time tumor monitoring for lung cancer. For each patient with 1-5 FMs, CT at end-exhalation (CTp) and 4DCT were acquired for treatment planning. CT at EE before treatment (CTfr) was also acquired. The dose prescription was 48-60 Gy/4-8 fr, and 145 FMs were analyzed. The FMs were divided into two groups based on the median distance between the centroid of the tumor and that of the FMs in CTp (Dp). First, to evaluate the relationship between the intra-fraction motion of the tumor and FMs during respiration, the intra-fraction motion was defined as the translation of the tumor and FMs between each phase and the 50% phase. The intra-fraction motion of the tumor and FMs were calculated in the left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. Pearson correlation coefficients between the relative coordinates of the tumor and FMs were calculated in each direction. Second, to evaluate the positional relationship between the tumor and FMs during respiration, the distance between the tumor and FMs was calculated in each direction for each 4DCT phase, and the maximum difference in distance was calculated based on the distance between tumor and FMs in the 50% phase (Dt-f). Third, to evaluate the inter-fraction variation of the tumor using the FM setup, the CTfrs were registered to CTp using each FM for patient setup. The differences between the tumor centroids in CTp and CTfr were defined as the inter-fraction variation and the mean inter-fraction variation was calculated in each direction. Results The median Dp was 27 mm. For the Dp ≤ 27 mm group, the intra-fraction motion of the FMs was significantly and strongly correlated with that of the lung tumor in all directions. However, for the Dp > 27 mm group, the intra-fraction motion of the FMs was significantly and strongly correlated with that of the lung tumor only in the AP and SI directions. In the LR direction, the intra-fraction motion of the FMs was significantly and moderately correlated with that of the lung tumor (Table 1). The Dt-f for the Dp ≤ 27 mm group was significantly smaller than that for the Dp > 27 mm group in all directions. The inter-fraction variation for the Dp ≤ 27 mm group were significantly smaller than that for the Dp > 27 mm group in all directions (Table 2). PO-1339 Comparing intra- and inter-fraction motion of tumors with fiducial markers for lung SBRT Y. Manabe 1 , T. Shiinoki 1 , K. Fujimoto 1 , K. Ueda 1 , M. Karita 1 , M. Kajima 1 , H. Tanaka 1 1 Yamaguchi University, Radiation Oncology, Ube, Japan