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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]

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]

Purpose: To assess the outcomes of a cohort of bone oligometastatic prostate cancer patients treated with PSMA-PET guided stereotactic body radiotherapy (SBRT) Methods: From April 2017 to January 2021, 40 patients with oligorecurrent prostate cancer detected by PSMAPET were treated with SBRT for bone oligometastases. Concurrent androgen deprivation therapy was an exclusion criterion. A total of 56 prostate cancer bone oligometastases were included in the present analysis. In 28 patients (70%), oligometastatic disease presented as a single lesion, two lesions in 22.5%, three lesions in 5%, four lesions in 2.5%. Results: 30.3% were spine-metastases, while 69.7% were non-spine metastases. SBRT was delivered for a median dose of 30 Gy (24-40Gy) in 3-5 fractions, with a median EQD2=85 Gy2 (64.3 - 138.9Gy2). With a median followup of 22 months (range, 2-48 months), local control (LC) 1- and 2-years rates were 96.3% and 93.9%, while distant progression-free survival (DPFS) rates were 45.3% and 27%. At multivariate analysis, the lower PSA nadir value after SBRT remained significantly related to better DPFS rates (p=0.03). In 7 patients, a second SBRT course was proposed with concurrent ADT, while 11 patients, due to polymetastatic spread, received ADT alone, resulting in 1- and 2-years ADT-free survival rates of 67.5% and 61.8%. At multivariate analysis, a lower number of treated oligometastases maintained a correlation with higher ADT-free survival rates (p=0.04). Conclusions: In our experience, PSMA-PET guided SBRT resulted in excellent results in terms of clinical outcomes, representing a helpful tool with the aim to delay the start of ADT. [ABSTRACT FROM AUTHOR]

Purpose or objective: Stereotactic Body Radiotherapy (SBRT) is widely used for treatment of uncomplicated spine metastases to palliate symptoms and prolong disease control. However, criteria for patient selection are not available. The aim of this study is to identify determinants of local failure and progression-free interval in patients treated with SBRT to spinal metastases. Materials and methods: Data from consecutive patients treated with Cyberknife-based spine SBRT between January 2019 and March 2020 were retrospectively collected. Dose was expressed as Biological Effective Dose for α/β=10 (BED10). Kaplan-Meyer method was used to calculate Local Control (LC) and Disease Free Survival (DFS) from date of SBRT to event. Univariate (UVA) and Multivariate analysis (MVA) were performed using log-rank and Cox model, respectively. Results: Sixty-two patients accounting for 70 spinal metastases were included. Median age was 66 (range 32- 87) years. Disease was metastatic at diagnosis in 21 patients (34%) : an active primary tumor was present in 17 patients (27%). Among treated sites, most represented primary malignancies were prostate (n=28, 40%) and breast (n=21, 30%). Dose regimens consisted of 25-30 Gy in 5 fractions and 21-30 Gy in 3 fractions in respectively 61 (87%) and 9 (13%) cases, resulting in a median BED of 43.2 (range 37.5-60) Gy10. Concurrent chemotherapy (including cytotoxic or targeted agents) was administered in 43% of cases (n=30). After a median follow up of 10 months (range 1-24 months), 9 local relapses and 40 distant progressions were observed. One year LC was 87% (Fig.1): nonprostate primary tumor (p=0.003, Fig.2) and concurrent chemotherapy (p=0.006, Fig.3) were associated to poorer LC at UVA, and an independent correlation was confirmed at MVA (respectively p=0.017 and p=0.024). One-year DFS was 43% (Fig.4). UVA showed a correlation between impaired DFS and active primary tumor (p=0.003), metastatic dissemination at diagnosis (p=0.02) and nonprostate primary tumor (p=0.009), although only an active primary tumor site was independently associated to DFS at MVA (p=0.007, Fig.5). Only G2 acute pain or nausea were observed. No late toxicity, in particular vertebral fracture, was reported. Conclusion: Spine SBRT results in high LC rates and durable progression-free survival with low incidence of mild toxicity. Clinical nomograms based on patient-related characteristics may help to select candidates for this approach. [ABSTRACT FROM AUTHOR]