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Robotic Stereotactic Body Radiotherapy (SBRT) employs radiopaque fiducial markers implanted near the tumor for real-time tracking. Fiducials are usually placed before simulation under CT or ultrasound guidance. This represents a limitation to treatment availability and may result in potential treatment delay. In our Institution, an in-house percutaneous CTguided fiducial placement procedure was implemented for pelvic SBRT. The aim of our study is to evaluate the performance and side effects of in-house fiducial placement. Methods: Patients underwent percutaneous fiducial insertion with a 18 G needle under CT guidance, using a radiopaque skin marker to calculate the depth of target location from body surface (Figure 1). One week after placement, simulation CT and orthogonal X-ray imaging were acquired to verify fiducial usability for SBRT tracking. Data from a consecutive cohort of patients treated with fiducial-guided, robotic-arm pelvic SBRT were collected from January 2018 to September 2021. Success rate was defined as the implanted/tracked fiducials ratio. Kruskal Wallis-test was used to compare median success rate over time. Results: In the observed time frame, 282 patients underwent CT-guided fiducial placement, accounting for 883 implanted fiducials (median 3, range 1-4). Implantation sites were the prostate bed, extra-spinal bones and pelvic lymph nodes in 158 (56%), 37 (13%) and 87 (31%) patients, respectively. Side effects consisted of minor bleeding at the insertion site and transient pain requiring medication after 24 hours in 5 patients (2%). No grade >2 toxicity was observed. Overall success rate was 86% (719/833); median success rate per procedure was 100% (range 50-100%). Among the 114 fiducials rejected for tracking, failure was due to migration in 63 cases (55%) and misplacement in 51 cases (45%). Overall success rate increased across the observed time window from 2018 (53/73, 74%) to 2019 (245/293, 84%) to 2020 (246/272, 90%) to 2021 (175/195, 90%) (Figure 2). A consistent, statistically significant improvement in median success rate was observed over time from 2018 (75%, Interquartile Range, IQR 67-100%) to 2019 (100%, IQR 75-100%) to 2020 (100%, IQR 75-100%) to 2021 (100%, IQR 100- 100%) : p= 0.0008. Conclusions: Our in-house percutaneous CT-guided fiducial placement is a safe procedure requiring minimal standard equipment, resulting in success rates comparable with published experiences performed in a dedicated interventional radiology setting. A consistent improvement in median success rate was observed over 4 years, suggesting the need for appropriate interventions to shorten the learning curve. [ABSTRACT FROM AUTHOR]

Aims: Re-irradiation with stereotactic body RT (re-SBRT) is a valid treatment option for local relapse in prostate cancer after postoperative or definitive radiotherapy (RT). However, we need predictive factors to prevent the onset of late adverse events. Here we present a retrospective analysis conducted on a cohort of patients treated with re-SBRT through Cyberknife ® robotic system. The correlation between dosimetric data and incidence of late genitourinary (GU) toxicity was evaluated to establish a model to predict late GU Grade >2 adverse events in this population. Methods: We collected data of 50 consecutively patients treated from June 2012 to February 2016. All patients were affected by biochemical relapse defined by European Urology Association Criteria after definitive or postoperative radiotherapy, and macroscopic evidence of intra-prostatic or prostate bed recurrence was detected by 18F-choline PET/CT and MRI. Patients with metastatic or regional nodal disease were excluded. All patients underwent reSBRT using the CyberKnife ®robotic system, for a total dose of 30 Gy in 5 fractions every other day. Toxicity was assessed by the Common Terminology Criteria for Adverse Events (CTCAE) toxicity scale v.5. Relationship between late GU G>2 and Gross Target Volume (ccGTV), Dose to 50% of urinary bladder volume (DB50), Maximum dose within Planning Target Volume (Dmax), urethra Dmax (UDmax) and Total Equivalent Dose (tEQD2) administered to prostate or prostate bed was explored with logistic regression. A receiver operating characteristic (ROC) curve was used to find the optimal cut-off point for continuous variables significantly predictive for late GU adverse events. Results: After a median follow up of 48.2 months (6.4-86.3), late G> 2 GU toxicity occurred in 13 (26%) patients. At Univariate Analysis, no significant impact of ccGTV (p=0.38), DB50 (p=0.25), Dmax (p=0.88), and tEQD2 total was detected (p=0.76 ). Only UDmax showed significant association with Late G> 2 GU toxicity (p=0.02). ROC analysis showed that UDmax >34.12 Gy best predicted GU toxicity, with a positive and negative likelihood ratio of 3.56 (95% CI 1.1-11.3) and 0.69 (95% CI 0.4-1.1), respectively (AUC 0.66, p=0.06). Conclusion: These data suggest that higher urethral dose may be associated to higher risk of late G> 2 GU toxicity. Thus, due to the low number of events, larger series with long term follow up would be needed to better identify a model to predict late GU adverse events after re-SBRT. [ABSTRACT FROM AUTHOR]

Background: Breast-conserving surgery (BCS) followed by postoperative radiation therapy (RT) to the residual breast represents the current standard of care for most women affected by early breast cancer. However, standard postoperative regimens are characterized by postsurgical waiting time and potential acute and late locoregional adverse events. Several studies suggested that breast cancer cells can be more sensitive to high doses administered in short intervals. Preoperative robotic stereotactic radiotherapy (SBRT) followed by BCS may yield potential advantages in selected patients. An exploratory phase II study (ROCK trial – NCT03520894) was conducted in our institution. Materials: Women with histologically proven unifocal invasive hormonal receptors positive, HER2 negative breast cancer, sized less than 25 mm, with negative clinical nodal status, aged 50+ and eligible for BCS were enrolled. Fiducial markers were introduced in peri/ intralesional position. Magnetic resonance imaging (MRI) was used in addition to standard CT-based planning. Patients received 21 Gy in single fraction with CyberKnife® followed by BCS two weeks after preoperative SBRT. The primary endpoint was the acute skin toxic effect rate. Secondary objectives were the pathological response rate and the late adverse events rate. Echocardiography and spirometry were performed before preoperative SBRT and yearly thereafter. Translational research was conducted to identify correlations between radiogenomic, immunological and biochemical biomarkers with treatment-related response and toxicity. Results: From August 2018 to September 2021, a total of 70 patients were screened on mammography; 29 of them were eligible following inclusion criteria. Seven were excluded due to multiple foci disease at basal MRI, and 22 patients were successfully treated. All required dosimetric parameters and normal tissue constraints were met in all cases. Median age at diagnosis was 68 years (range 50-86) and median tumor size was 13 mm (range 7.5-25). All treated patients received surgery within 14 days from preoperative SBRT without any delay or complication. No patients experienced acute skin toxicity of grade (G) 2 or higher; only one patient had a G1 erythema one month after BCS. Two patients reported a pathological complete response, according to Chevallier’s classification. At a median follow up of 18 months, no patients experienced locoregional recurrence or distant metastases. No clinically meaningful changes were observed regarding left-ventricular ejection fraction and spirometric parameters. Conclusion: Results from the ROCK trial showed that single fraction preoperative robotic SBRT is a feasible technique in selected breast cancer patients with a good safety profile and encouraging activity. This new approach warrants further investigations. [ABSTRACT FROM AUTHOR]

Purpose: Stereotactic body radiotherapy (SBRT) has emerged as a novel therapeutic option to improve outcome of patients with locally advanced pancreatic cancer (LAPC). More intensive schedules are often challenging due to proximity of organs at risks (OARs). Local control is closely related to a biologically effective dose (BED) of 100 Gy10, corresponding to a dose of 50 Gy in 5 fractions. An in-silico study was performed to evaluate the feasibility of dose escalation in SBRT treatments of LAPC through inhomogeneous dose prescription, and to identify patients suitable for this strategy, based on anatomical proximity between target volumes and OARs. Materials and methods: We collected dosimetric data from 14 patients treated at our center for LAPC. For each patient, a CyberKnife (CK) Synchrony re-planning for fiducial-guided pancreatic SBRT treatment was developed for a planned dose of 50 Gy and 40 Gy in 5 fractions to gross tumor volume (GTV) and target volume planning (PTV), respectively. Priority was given to OAR constraints. Criteria for acceptable coverage of the target were: a) 50 Gy and 47.5 Gy to ≥90% and ≥95% of the GTV, respectively, and b) 40 Gy to ≥95% of the PTV. For each plan, a Expansion-Intersection Volume (EIV), corresponding to the intersection volume between PTV and OARs expanded by 5 mm, was calculated. The planned doses to the target volumes and the OARs were evaluated and statistically analyzed. Results: Median GTV and PTV sizes were 40.8 (range 22.3-205.3) cc and 73.7 (range 36.1-266.7) cc, respectively. Treatment plans have been optimized to keep a V35 in the duodenum, stomach and intestines below 0.5cc in all cases. Median V50 and V47.5 for GTV was 91.0% (range 82.4% -97.8%) and 96.8% (range 92.5% -99.9%), respectively: GTV coverage was acceptable in 10 out of 14 cases. Median V40Gy for PTV was 96.8% (range 90.0% -99.8%): PTV coverage was acceptable in 11 of 14 cases. Median EIV was 12.9 (3.9- 25.1) cc. Spearman correlation showed a significant association between EIV and V47.5Gy for GTV (rho -0.77228, p<0.001) and V40Gyfor PTV (rho -0.68352, p <0.001), respectively (Figure 1). Conclusions: Inhomogenous dose escalated prescription to a BED≥100Gy10 is a feasible treatment strategy in selected patients with LAPC (Figure 2). EIV represents a simple tool to identify suitable patients for this approach [ABSTRACT FROM AUTHOR]

Introduction: Only 30% of patients with liver metastases (LM) may be suitable for surgery due to unfavourable location, comorbidities or extrahepatic disease burden. Patients treated with stereotactic radiotherapy (SBRT) reported excellent local control (LC) and low toxicity rate although data on global disease control are missing. The aim of this preliminary analysis was to assess patterns of failure in a cohort of patients treated with SBRT for LM. Method: Data from patients treated between 2018 and 2020 at our Institution with SBRT to LM receiving at least an EQD2 of 50 Gy (α/β=10) as per ESTRO consensus were collected. Failure patterns following SBRT and rates of local control (LC), intrahepatic relapse (excluding treated site, IHR), extrahepatic relapse (EHR), and overall survival (OS) were evaluated. Results: Forty-three patients received liver SBRT due to oligometastatic (20,46%) and oligoprogressive (23,54%) disease. Most common primary tumors were breast (n=18,42%) and colon (n=10,23%) cancer. SBRT was performed using Cyberknife real-time tumor tracking(n=30,70%) or abdominal compression-assisted VMAT (n=13,30%) delivering 35-60 Gy in 3-5 fractions, corresponding to median EQD2 of 94 (50-150) Gy. Twelve (28%) patients were chemotherapy-naïve, while the remaining patients received 1(20,46%), 2(5,12%) or ≥3(6,14%) chemotherapy lines. Median follow-up was 12 months. Patterns of failure are reported in Table 1. One-year LC, IHR, EHR and OS were 80%,51%,49% and 87% respectively. At multivariate analysis LC was significantly correlated with EQD2≥94Gy(p=0.009) and ≥3 chemotherapy lines(p=0.04). IHR and EHR were significantly associated with local failure (p=0.0013) and intrahepatic progression (p=0.03), respectively. A significant correlation between OS and local relapse was shown (p=0.026). Conclusion: In our experience, improved LC using high BED in non-heavily pretreated patients was correlated to reduced risk of IHR and to improved OS. IHR was the dominant mode of failure in patients treated with SBRT for LM,and was correlated to further progression at extrahepatic sites. Our findings suggest that IHR may result from uncontrolled macroscopic LM rather than ubiquitous micrometastatic dissemination, and preceed further systemic spread at distant sites. Our findings support the use of SBRT as an efficient tool to block stepwise metastatic spread from uncontrolled isolated LM to liver, and from liver to distant site, thus extending global disease control. [ABSTRACT FROM AUTHOR]