Stereotactic reirradiation with CyberknifeR for locally recurrent prostate cancer, long-term toxicity and clinical outcomes from a monocentric cohort.

PURPOSE: Up to 47% of patients with localized prostate cancer (PCa) treated with radiotherapy (EBRT) eventually develop local recurrence. To date, no clear consensus exists on optimal management. A growing body of interest supports the use of stereotaxic re-irradiation (rSBRT), with promising oncological outcomes and low toxicity profile. We collected a single-center case series of locally recurrent PCa who underwent re-irradiation after a previous course of postoperative or definitive radiotherapy. METHODS AND MATERIALS: Data from 101 patients treated at our institution for locally recurrent PCa from June 2012 to June 2021 were retrospectively collected. Patients underwent rSBRT with CyberKnife system (Accuray Inc., Sunnyvale, CA, USA), delivered to intraprostatic or macroscopic recurrences within the prostate bed, for a total dose of 30 Gy in 5 fractions. RESULTS: All patients received prior EBRT. The median EQD2 total dose was 75.0 Gy (range, 60-80 Gy). Thirty-two (32%) patients were receiving androgen deprivation therapy (ADT) after prior biochemical recurrence. After a median follow-up of 57.8 months, BR occurred in 55 patients (54.5%), with a median BR-free survival (BRFS) of 40.4 months (95% C.I. 34.3-58.3). Thirty-two patients (31.7%) developed metastatic disease, with a median metastasis-free survival (MFS) not reached. PSA ≥ 2.5 ng/ml and ADT were associated with worst BRFS (26.06 vs. 39.3 months, p = 0.03 and 22.7 vs. 27 months, p = 0.01, respectively). Castration-resistant status and ADT were found to be predictive of worst MFS (34.1 vs. 50.5 months, p = 0.02 and 33.5 vs. 53.1 months, p = 0.002, respectively). Concomitant ADT was confirmed as an independent factor for MFS (HR 4.8, 95% CI 1.5-10.6, p = 0.007). No grade > /2 adverse were recorded. CONCLUSIONS: After almost 5 years of follow-up, with a median BRFS of 40.4 months and no grade ≥ 2 AEs, CyberknifeR rSBRT proved effective and safe in a cohort of 101 patients affected by locally recurrent PCa.

SBRT planning for spinal metastasis: indications from a large multicentric study.

BACKGROUND: The dosimetric variability in spine stereotactic body radiation therapy (SBRT) planning was investigated in a large number of centres to identify crowd knowledge-based solutions. METHODS: Two spinal cases were planned by 48 planners (38 centres). The required prescription dose (PD) was 3â€¯× 10 Gy and the planning target volume (PTV) coverage request was: VPD > 90% (minimum request: VPD > 80%). The dose constraints were: planning risk volume (PRV) spinal cord: V18Gy < 0.35 cm3, V21.9 Gy < 0.03 cm3; oesophagus: V17.7 Gy < 5 cm3, V25.2 Gy < 0.03 cm3. Planners who did not fulfil the protocol requirements were asked to re-optimize the plans, using the results of planners with the same technology. Statistical analysis was performed to assess correlations between dosimetric results and planning parameters. A quality index (QI) was defined for scoring plans. RESULTS: In all, 12.5% of plans did not meet the protocol requirements. After re-optimization, 98% of plans fulfilled the constraints, showing the positive impact of knowledge sharing. Statistical analysis showed a significant correlation (p < 0.05) between the homogeneity index (HI) and PTV coverage for both cases, while the correlation between HI and spinal cord sparing was significant only for the single dorsal PTV case. Moreover, the multileaf collimator leaf thickness correlated with the spinal cord sparing. Planners using comparable delivery/planning system techniques produced different QI, highlighting the impact of the planner's skills in the optimization process. CONCLUSION: Both the technology and the planner's skills are fundamentally important in spine SBRT planning optimization. Knowledge sharing helped to follow the plan objectives.

Treatment planning for spinal radiosurgery : A competitive multiplatform benchmark challenge.

PURPOSE: To investigate the quality of treatment plans of spinal radiosurgery derived from different planning and delivery systems. The comparisons include robotic delivery and intensity modulated arc therapy (IMAT) approaches. Multiple centers with equal systems were used to reduce a bias based on individual's planning abilities. The study used a series of three complex spine lesions to maximize the difference in plan quality among the various approaches. METHODS: Internationally recognized experts in the field of treatment planning and spinal radiosurgery from 12 centers with various treatment planning systems participated. For a complex spinal lesion, the results were compared against a previously published benchmark plan derived for CyberKnife radiosurgery (CKRS) using circular cones only. For two additional cases, one with multiple small lesions infiltrating three vertebrae and a single vertebra lesion treated with integrated boost, the results were compared against a benchmark plan generated using a best practice guideline for CKRS. All plans were rated based on a previously established ranking system. RESULTS: All 12 centers could reach equality (n = 4) or outperform (n = 8) the benchmark plan. For the multiple lesions and the single vertebra lesion plan only 5 and 3 of the 12 centers, respectively, reached equality or outperformed the best practice benchmark plan. However, the absolute differences in target and critical structure dosimetry were small and strongly planner-dependent rather than system-dependent. Overall, gantry-based IMAT with simple planning techniques (two coplanar arcs) produced faster treatments and significantly outperformed static gantry intensity modulated radiation therapy (IMRT) and multileaf collimator (MLC) or non-MLC CKRS treatment plan quality regardless of the system (mean rank out of 4 was 1.2 vs. 3.1, p = 0.002). CONCLUSIONS: High plan quality for complex spinal radiosurgery was achieved among all systems and all participating centers in this planning challenge. This study concludes that simple IMAT techniques can generate significantly better plan quality compared to previous established CKRS benchmarks.

Preoperative single fraction breast radiotherapy: Intra-fraction geometric uncertainties and dosimetric implications.

PURPOSE: A preoperative breast robotic radiosurgery trial was concluded in our centre. Purposes of the present study were to evaluate retrospectively over the enrolled patients: i) respiratory patterns ii) tracking uncertainties iii) necessity of respiratory compensation iv) tracking errors dosimetric effects. METHODS: 22 patients were treated in 21 Gy single fraction using CyberKnife (CK) respiratory modelling and tracking (SynchronyResp) and data extracted from log-files. Respiratory motion and baseline drifts (BD) were analyzed. SynchronyResp uncertainties were computed and compared with errors simulated for CK fiducial tracking without respiratory compensation. Plans were perturbed by tracking errors and perturbed doses calculated on the planning CT scan in order to simulate the dosimetric consequences of intra-fraction errors. RESULTS: After BD correction, respiratory amplitudes were below 5.5 mm except one value of 8 mm. 50% of patients showed BD above 3 mm. Standard deviations of SynchronyResp errors remained within 2.1 mm. Standard deviations of tracking errors without respiratory compensation were comparable and below 2.5 mm. Using a 3 mm PTV margin, perturbed CTV coverage was below 95% (93.7%) just for one patient. The latter case presented a large CTV-Skin interface. Perturbed OAR doses were always judged clinically acceptable. CONCLUSION: Intra-fraction geometric uncertainties and their effects were quantified for breast neoadjuvant CK treatments. Data indicated that in the majority of cases respiratory compensation may be disabled without increasing uncertainties and reducing treatment time, provided that fiducial intra-fraction tracking is performed to account for BD. Dosimetric effects are mostly not clinically relevant.

Preoperative robotic radiosurgery for early breast cancer: Results of the phase II ROCK trial (NCT03520894).

Background and purpose: Preoperative partial breast irradiation (PBI) has got the advantage of treating a well-defined target. We report the results of the phase II ROCK trial (NCT03520894), enrolling early breast cancer (BC) patients treated with preoperative robotic radiosurgery (prRS), in terms of acute and early late toxicity, disease control, and cosmesis. Material and methods: The study recruited between 2018 and 2021 at our Radiation Oncology Unit. Eligible patients were 50 + years old BC, hormonal receptors positive/human epidermal growth factor receptor 2 negative (HR+/HER2-), sized up to 25 mm. The study aimed to prospectively assess the toxicity and feasibility of a robotic single 21 Gy-fraction prRS in preoperative setting. Results: A total of 70 patients were recruited and 22 patients were successfully treated with pRS. Overall, three G1 adverse events (13.6 %) were recorded within 7 days from prRS. Three events (13.6 %) were recorded between 7 and 30 days, one G2 breast oedema and two G1 breast pain. No acute toxicity greater than G2 was recorded. Five patients experienced early late G1 toxicity. One patient reported G2 breast induration. No early late toxicity greater than G2 was observed. At a median follow up of 18 months (range 6-29.8), cosmetic results were scored excellent/good and fair in 14 and 5 patients, respectively, while 3 patients experienced a poor cosmetic outcome. Conclusions: ROCK trial showed that a single 21 Gy dose prRS represents a feasible technique for selected patients affected by early BC, showing an acceptable preliminary toxicity profile.

Robotic MLC-based plans: A study of plan complexity.

PURPOSE: The utility of complexity metrics has been assessed for IMRT and VMAT treatment plans, but this analysis has never been performed for CyberKnife (CK) plans. The purpose of this study is to perform a complexity analysis of CK MLC plans, adapting and computing complexity indices previously defined for IMRT plans. Metrics were used to compare the complexity of plans created by two optimization systems and to study correlations between plan complexity and patient-specific quality assurance (PSQA) results. Relationships between pairs of metrics were also analyzed to get insight into possible interdependencies. METHODS: Two independent in-house software platforms were developed to compute six complexity metrics: modulation complexity score (MCS), edge metric (EM), plan irregularity (PI), plan modulation (PM), leaf gap (LG), and small aperture score (SAS10). MCS and PM definitions were adapted to account for CK plans characteristics. The computed metrics were used to compare the existing optimization algorithms (sequential and VOLO) in terms of plan complexity over 24 selected cases. Metrics were then computed over a large number (103) of VOLO SBRT clinical plans from different treatment sites, mainly liver, prostate, pancreas, and spine. Pearson's r was used to study relationships between each pair of metrics. Correlation between complexity indices and PSQA results expressed as gamma index passing rates (GPR) at (3%, 1 mm) and (2%, 1 mm) was finally analyzed. Correlation was regarded as weak for absolute Pearson's r values in the range 0.2-0.39, moderate 0.4-0.59, strong 0.6-0.79, and very strong 0.8-1. RESULTS: When compared to VOLO, sequential plans exhibited a higher complexity degree, showing lower MCS and LG values and higher EM, PM and PI values. Differences were significant for 5/6 metrics (Wilcoxon P < 0.05). The analysis of VOLO clinical plans highlighted different degrees of complexity among plans from different treatment sites, increasing from liver to prostate, pancreas, and finally, spine. Analysis of dependencies between pairs of metrics showed a very strong significant negative correlation (P < 0.01), respectively, between MCS and PM (r = -0.97), and EM and LG (-0.82). Most of the remaining pairs showed moderate to strong correlations with the exception of PI, which showed weaker correlations with the other metrics. A moderate significant correlation was observed with GPR values both at (3%, 1 mm) and (2%, 1 mm) for all metrics except PI, which showed no correlation. CONCLUSIONS: Modulation complexity metrics were computed for CK MLC-based plans for the first time and some metrics' definitions were adapted to CK plans peculiarities. The computed metrics proved a useful tool for comparing optimization algorithms and for characterizing CK clinical plans. Strong and very strong correlations were found between some pairs of metrics. Some significant correlations were found with PSQA GPR, indicating that some indices are promising for rationalizing and reducing PSQA workload. Our results set the basis for evaluating new optimization algorithms and TPS versions in the future, as well as for comparing the complexity of CK MLC-based plans in multicenter and multiplatform comparisons.

Performance assessment of a new optimization system for robotic SBRT MLC-based plans.

PURPOSE: To assess the performance of a new optimization system, VOLO, for CyberKnife MLC-based SBRT plans in comparison with the existing Sequential optimizer. METHODS: MLC-plans were created for 25 SBRT cases (liver, prostate, pancreas and spine) using both VOLO and Sequential. Monitor units (MU), delivery time (DT), PTV coverage, conformity (nCI), dose gradient (R50%) and OAR doses were used for comparison and combined to obtain a mathematical score (MS) of plan quality for each solution. MS strength was validated by changing parameter weights and by a blinded clinical plan evaluation. The optimization times (OT) and the average segment areas (SA) were also compared. RESULTS: VOLO solutions offered significantly lower mean DT (-19%) and MU (-13%). OT were below 15 min for VOLO, whereas for Sequential, values spanned from 8 to 160 min. SAs were significantly larger for VOLO: on average 10 cm2 versus 7 cm2. VOLO optimized plans achieved a higher MS than Sequential for all tested parameter combinations. PTV coverage and OAR sparing were comparable for both groups of solutions. Although slight differences in R50% and nCI were found, the parameters most affecting MS were MU and DT. VOLO solutions were selected in 80% of cases by both physicians with 88% inter-observer agreement. CONCLUSIONS: The good performance of the VOLO optimization system, together with the large reduction in OT, make it a useful tool to improve the efficiency of CK SBRT planning and delivery. The proposed methodology for comparing different planning solutions can be applied in other contexts.

On-line image guidance for frameless stereotactic radiotherapy of lung malignancies by cone beam CT: comparison between target localization and alignment on bony anatomy.

INTRODUCTION: Free-breathing stereotactic radiotherapy for lung malignancies requires reliable prediction of respiratory motion and accurate target localization. A protocol was adopted for reproducibility and reduction of respiratory motion and for target localization by CBCT image guidance. Tumor respiratory displacements and tumor positioning errors relative to bony anatomy alignment are analyzed. MATERIALS AND METHOD: Image guided SRT was performed for 99 lung malignancies. Two groups of patients were considered: group A did not perform any breathing control; group B controlled visually their respiratory cycle and volumes on an Active Breathing Coordinator (ABC) monitor during the acquisition of simulation CT and CBCT, and treatment delivery. GTV on end inhale and exhale CT data sets were fused in an ITV and the extent of tumor motion evaluated between these 2 phases. A pre-treatment CBCT was acquired and aligned to the reference CT using bony anatomy; for tumor positioning the ITV contour on the reference CT was matched to the visible tumor on CBCT. Interobserver variability of tumor positioning was evaluated. ITV and CBCT tumor dimensions were compared. RESULTS: 3D tumor breathing displacement (mean+/-SD) was significantly higher for group A (14.7+/-9.9 mm) than for group B (4.7+/-3.1 mm). The detected differences between tumor and bony structure alignment below 3 mm were 68% for group B and 45% for group A, reaching statistical significance. Interobserver variability was 1.7+/-1.1 mm (mean+/-SD). Dimensions of tumor image on CBCT were consistent with ITV dimensions for group B (max difference 14%). CONCLUSIONS: The adopted protocol seems effective in reducing respiratory internal movements and margin. Tumor positioning errors relative to bony anatomy are also reduced. However bony anatomy as a surrogate of the target may still lead to some relevant positioning errors. Target visualization on CBCT is essential for an accurate localization in lung SRT.

CyberKnife MLC-based treatment planning for abdominal and pelvic SBRT: Analysis of multiple dosimetric parameters, overall scoring index and clinical scoring.

PURPOSE: This study evaluated the plan quality of CyberKnife MLC-based treatment planning in comparison to the Iris collimator for abdominal and pelvic SBRT. Multiple dosimetric parameters were considered together with a global scoring index validated by clinical scoring. METHODS AND MATERIALS: Iris and MLC plans were created for 28 liver, 15 pancreas and 13 prostate cases including a wide range of PTV sizes (24-643 cm3). Plans were compared in terms of coverage, conformity (nCI), dose gradient (R50%), homogeneity (HI), OAR doses, PTV gEUD, MU, treatment time both estimated by TPS (tTPS) and measured. A global plan quality score index was calculated for IRIS and MLC solutions and validated by a clinical score given independently by two observers. RESULTS: Compared to Iris, MLC achieved equivalent coverage and conformity without compromising OAR sparing and improving R50% (p < 0.001). MLC gEUD was slightly lower than Iris (p < 0.05) for abdominal cases. MLC reduced significantly MU (-15%) and tTPS (-22%). Time reduction was partially lost when measured. The global score index was significantly higher for MLC solutions which were selected in 73% and 64% of cases respectively by the first and second observer. CONCLUSION: Iris and MLC comparison was not straightforward when based on multiple dosimetric parameters. The use of a mathematical overall score index integrated with a clinical scoring was essential to confirm MLC plans advantages over Iris solutions.

CyberKnife beam output factor measurements: A multi-site and multi-detector study.

PURPOSE: New promising detectors are available for measuring small field size output factors (OFs). This study focused on a multicenter evaluation of two new generation detectors for OF measurements on CyberKnife systems. METHODS: PTW-60019 microDiamond and W1 plastic scintillation detector (PSD) were used to measure OFs on eight CyberKnife units of various generations for 5-60mm fixed cones. MicroDiamond and PSD OF were compared to routinely used silicon diodes data corrected applying published Monte Carlo (MC) factors. PSD data were corrected for Cerenkov Light Ratio (CLR). The uncertainties related to CLR determination were estimated. RESULTS: Considering OF values averaged over all centers, the differences between MC corrected diode and the other two detectors were within 1.5%. MicroDiamond exhibited an over-response of 1.3% at 7.5mm and a trend inversion at 5mm with a difference of 0.2%. This behavior was consistent among the different units. OFs measured by PSD slightly under-responded compared to MC corrected diode for the smaller cones and the differences were within 1%. The observed CLR variability was 2.5% and the related variation in OF values was 1.9%. CONCLUSION: This study indicates that CyberKnife microDiamond OF require corrections below 2%. The results are enhanced by the consistency observed among different units. Scintillator shows a good agreement to MC corrected diode but CLR determination remains critical requiring further investigations. The results emphasized the value of a multi-center validation over a single center approach.

Stereotactic body radiotherapy with CyberKnife for cardiac malignancies.

AIMS AND BACKGROUND: Radiobiological and technical considerations have traditionally limited the role of radiation therapy in the context of primary and secondary cardiac malignancies. Stereotactic body radiotherapy (SBRT) is a promising modality for the delivery of focused high-dose radiation with ablative potential to complex targets such as small, deep-seated, moving lesions, allowing also for re-irradiation. METHODS: Between January 2013 and October 2013, 3 patients underwent SBRT for cardiac lesions: 2 patients had recurrent, previously irradiated cardiac angiosarcomas (PCA) and 1 patient had a cardiac metastasis from melanoma. They were treated with fiducial-guided robotic radiotherapy with CyberKnife. As for dose prescription, 24 Gy in 3 fractions (80% isodose) and 30 Gy in 5 fractions (80% isodose) were administered to the recurrent PCAs and cardiac metastasis, respectively. RESULTS: At 2 months after SBRT, cardiac MRI showed a partial response in the patients treated for recurrent PCA while the cardiac metastasis remained stable. In all cases, absence of local progression was subsequently confirmed by contrast-enhanced cardiac MRI after 6 months, without any evidence of treatment-related side effects. CONCLUSIONS: Fiducial-guided SBRT proved to be feasible and effective in preventing local disease progression in selected patients with cardiac malignancies.

Salvage stereotactic re-irradiation with CyberKnife for locally recurrent head and neck cancer: a single center experience.

AIMS AND BACKGROUND: We report the toxicity and preliminary clinical outcome in patients affected by locally recurrent head and neck cancer treated with stereotactic re-irradiation. METHODS: Between February 2012 and August 2013, 17 patients were treated with CyberKnife as stereotactic re-irradiation for locally recurrent head and neck cancer. All patients had previously received a full dose radiation treatment with radical intent, with a median total dose of 66 Gy (range, 50-70) delivered with standard fractionation. The median interval between the primary radiotherapy and re-irradiation was 24 months (range, 10-168). RESULTS: All patients completed the prescribed treatment, which was delivered in 5 fractions. The median tumor dose administered was 30 Gy (range, 25-35) prescribed to the 80% isodose line. Treatment sites were as follows: neck lymph nodes in 5 patients, paranasal sinuses in 5, oropharynx in 2, nasopharynx, and larynx, oral cavity, nasal fossa and parotid gland each in 1 patient. The median target volume treated was 58.7 cm3 (range, 8.5-211.3). Sixteen patients (94%) were evaluated for response. At a median follow-up of 7.5 months (range, 2-17), 4 patients achieved complete response (25%), 5 had partial response (31%) and 7 showed stable disease (44%). No patient showed in-field progression after re-irradiation. Grade 3 acute toxicity was noted in one patient only; no late side effect was observed during the follow-up. CONCLUSIONS: Stereotactic re-irradiation with CyberKnife is an appealing non-surgical salvage treatment for selected patients with local-regionally recurrent head and neck cancer.

Impact of plan parameters on the dosimetric accuracy of volumetric modulated arc therapy.

PURPOSE: To evaluate the effect of plan parameters on volumetric modulated arc therapy (VMAT) dosimetric accuracy, together with the possibility of scoring plan complexity. METHODS: 142 clinical VMAT plans initially optimized using a 4° control point (CP) separation were evaluated. All plans were delivered by a 6 MV Linac to a biplanar diode array for patient-specific quality assurance (QA). Local Γ index analysis (3%, 3 mm and 2%, 2 mm) enabled the comparison between delivered and calculated dose. The following parameters were considered for each plan: average leaf travel (LT), modulation complexity score applied to VMAT (MCSv), MU value, and a multiplicative combination of LT and MCSv (LTMCS). Pearson's correlation analysis was performed between Γ passing rates and each parameter. The effects of CP angular separation on VMAT dosimetric accuracy were also analyzed by focusing on plans with high LT values. Forty out of 142 plans with LT above 350 mm were further optimized using a finer angle spacing (3° or 2°) and Γ analysis was performed. The average Γ passing rates obtained at 4° and at 3°∕2° sampling were compared. A further correlation analysis between all parameters and the Γ pass-rates was performed on 142 plans, but including the newly optimized 40 plans (CP every 3° or 2°) in place of the old ones (CP every 4°). RESULTS: A moderate significant (p < 0.05) correlation between each examined parameter and Γ passing rates was observed for the original 142 plans at 4° CP discretization. A negative correlation was found for LT with Pearson's r absolute values above 0.6, suggesting that a lower dosimetric accuracy may be expected for higher LT values when a 4° CP sampling is used. A positive correlation was observed for MCSv and LTMCS with r values above 0.5. In order to score plan complexity, threshold values of LTMCS were defined. The average Γ passing rates were significantly higher for the plans created using the finer CP spacing (3°∕2°) compared to the plans optimized using the standard 4° spacing (Student t-test p < 0.05). The correlation between LT and passing rates was strongly diminished when plans with finer angular separations were considered, yielding Pearson's r absolute values below 0.45. CONCLUSIONS: At 4° CP sampling, LT, MCSv, and LTMCS were found to be significantly correlated with VMAT dosimetric accuracy, expressed as Γ pass-rates. These parameters were found to be possible candidates for scoring plan complexity using threshold values. A finer CP separation (3°∕2°) led to a significant increase in dosimetric accuracy for plans with high leaf travel values, and to a decrease in correlation between LT and Γ passing rates. These results indicated that the influence of LT on VMAT dosimetric accuracy can be controlled by reducing CP separation. CP spacing for all plans requiring large leaf motion should not exceed 3°. The reported data were integrated to optimize our clinical workflow for plan creation, optimization, selection among rival plans, and patient-specific QA of VMAT treatments.

Clinical outcome of stereotactic body radiotherapy for abdominal lymph node metastases.

Aims and background. To report the clinical outcome of linac-based or robotic, image-guided stereotactic body radiotherapy in patients affected by abdominal lymph node metastases from different primary cancers. Methods and methods. Twenty-six patients with 32 abdominal lymph node metastases were consecutively treated at the University of Florence between April 2011 and May 2012. The mean follow-up was 4.6 months (SD, 3.9; range, 0.3-13). The dose prescription ranged between 24 Gy and 36 Gy delivered in 1-5 fractions. Results. In terms of local control, complete response to stereotactic body radiotherapy was obtained in 18 cases (66.7%), partial response in 7 (25.9%), and stable disease in 2 (7.4%). At the Cox univariate regression analysis, an increased risk of partial response or absence of local response to radiotherapy was found for subjects of the female sex (P = 0.036), age less than 50 years (P = 0.022), primary tumor of the genital tract (P = 0.007), and previous chemotherapy (P = 0.057). An excellent local control rate (90.9%) was obtained in patients affected by abdominal lymph node metastases of prostatic origin. Conclusions. Stereotactic body radiotherapy for abdominal lymph node metastases is a safe and effective treatment in terms of high rates of local control, especially in a subset of patients affected by prostate cancer.

Stereotactic radiotherapy for adrenal gland metastases: university of Florence experience.

PURPOSE: To evaluate a retrospective single-institution outcome after hypofractionated stereotactic body radiotherapy (SBRT) for adrenal metastases. METHODS AND MATERIALS: Between February 2002 and December 2009, we treated 48 patients with SBRT for adrenal metastases. The median age of the patient population was 62.7 years (range, 43-77 years). In the majority of patients, the prescription dose was 36 Gy in 3 fractions (70% isodose, 17.14 Gy per fraction at the isocenter). Eight patients were treated with single-fraction stereotactic radiosurgery and forty patients with multi-fraction stereotactic radiotherapy. RESULTS: Overall, the series of patients was followed up for a median of 16.2 months (range, 3-63 months). At the time of analysis, 20 patients were alive and 28 patients were dead. The 1- and 2-year actuarial overall survival rates were 39.7% and 14.5%, respectively. We recorded 48 distant failures and 2 local failures, with a median interval to local failure of 4.9 months. The actuarial 1-year disease control rate was 9%; the actuarial 1- and 2-year local control rate was 90%. CONCLUSION: Our retrospective study indicated that SBRT for the treatment of adrenal metastases represents a safe and effective option with a control rate of 90% at 2 years.