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Stereotactic radiosurgery (SRS) is a highly precise form of radiation therapy initially developed to treat small intracranial lesions. The principles of cranial SRS is high precision radiation where delivery is accurate to within one to two millimeters applied with dedicated devices in one fraction. This treatment is only possible due to the development of highly advanced radiation technologies that permit maximum dose delivery within the target while minimizing dose to the surrounding healthy tissue. The goal is to deliver doses that will destroy the tumor and achieve permanent local control. Intracranial SRS can be done in an excellent way with dedicated machines. Gamma Knife and Cyberknife are two of these dedicated machines for this approach. In this study, SRS planning was performed to 11 intracranial metastases of 9 patients with the two dedicated treatment planning system. The dose volume histograms and dosimetric parameters were compared. Those parameters included heterogenity index (HI), conformality index (CI), gradient index (GI), volume of the normal brain receiving 8Gy (V8), 10 Gy (V10) and 12 Gy (V12) . The mean RTOG CI of the CK and GK treatment plans were 1.14±0,07 and 1.16±0.17 respectively where the mean Paddick CI was 0,82 ± 0,04 and 0,85 ± 0,10 (0.64-0.95) (NS). The mean GI of the CK and GK treatment plans were 3,26 ± 0,47 and 3.05±0.51 respectively (NS). GK plans were more heterogeneous than CK plans with a HI 1.98 ± 0.19 vs 1.09 ± 0,05 (p=0.003). V8, V10 and V12 values of the normal brain was not found to be different in the two treatment planning systems. GK and CK treatment planning systems are two excellent tools for stereotactic radiosurgery of solitary intracranial lesions in terms of universal dosimetric parameters. Disclosure: No significant relationships. [ABSTRACT FROM AUTHOR]

Stereotactic body radiotherapy (SBRT) is an effective treatment for adrenal metastases, but it is technically challenging and there are concerns about toxicity due to the proximity of organs at risk. We hypothesized that MR-guided SBRT (MRgSBRT) using a 0.35 T MR-Linac for adrenal metastases can achieve durable local control (LC) with a low probability of toxicity. In an ethics-approved study, we analyzed clinical and dosimetric data of patients treated with MRgSBRT at 10 institutions between 2016-2022. LC, local progression-free survival (LPFS), distant progression-free survival (DPFS) and overall survival (OS) were estimated using Kaplan-Meier method and log-rank test. Responses were evaluated using RECIST criteria. Toxicity was graded according to CTCAE (v4.0). OS and DPFS were calculated on a per-patient basis, while LC and LPFS were calculated on a per-lesion basis. A total of 249 patients (260 adrenal lesions) were included; median age was 65 years (range 28-91), 65.5% were male, 83.9% had ECOG PS 0-1. The most common primary tumor was lung cancer (69.1%). Adrenal metastases were synchronous, metachronous, oligoprogressive or oligopersistent in 20%, 41.5%, 35.8% and 2.7% of patients, respectively. Metastatic pattern was solitary in 26.9%, oligometastatic in 57.3% and polymetastatic in 15.8% of patients. Right-sided metastases comprised 40%, left-sided 51.5% and lesions were bilateral in 8.5%. Chemotherapy and immunotherapy were administered in 67.1% and 60.6% of patients, respectively. Median gross tumor volume was 21.8 cc (range 1.1-383.2) and median planning target volume was 36.9 cc (range 3.6-516.9). Median total dose was 45 Gy (range 16-60), median fraction number was 5 (range 1-8) and median fraction dose used was 10 Gy (range 5-24). Median BED 10 was 100 Gy (range 37.5-132); 87.8% of fractions used adapted plans. At a median follow-up was 17.7 months (IQR 5.5-21.7), local responses were scored as complete response (CR), partial response (PR), stable disease (SD) or progressive disease (PD) in 36.9%, 28.2%, 25.7%, and 9.1%, respectively. Median OS was 30.4 months, with 1- and 2- year OS rates of 75.3% and 57.1%, respectively. On multivariate analysis, significantly higher OS rates were seen in patients achieving a CR (p = 0.007, HR 0.50) and with ECOG scores of 0-1 (p = 0.001, HR 0.43). One- and 2- year LPFS rates were 94.5% and 88.8%, respectively. No local recurrences were observed after treatment to a BED 10 >100 or with single fraction (range 16-24 Gy). Only 2 patients (0.8%) had ≥grade 3 chronic toxicity. This multi-institutional study of MRgSBRT outcomes for adrenal metastases revealed a 2-year LPFS of 89%, with a <1% risk of ≥grade 3 toxicity. Daily adaptation was performed in 90% of plans, indicating a beneficial role for MR guidance. [ABSTRACT FROM AUTHOR]

Purpose/objective(s): Stereotactic MR-guided Adaptive Radiotherapy (SMART) is an appealing treatment option for irradiation of intra-abdominal tumors. Daily adaptation with SMART has the advantage of dose escalation while protecting organs at risk (OARs). We aimed to document dosimetric parameters during SMART and analyze local control for adrenal metastases.Materials/methods: Fifteen patients treated between September 2018 and October 2020 for adrenal metastases were included in the study. The institutional constraints were used to evaluate the doses to OARs and target volumes. For each fraction, an adaptive plan was generated following registration and delineation of the daily disposition. A comparison was done between predicted plans (original plan on the daily anatomy) and adapted plans (new plan after re-optimization accounting the new contours) in terms of target volumes coverage and OARs doses. Patients were treated every other day.Results: The median age was 63 years (range 36-74 years) and 73.3% of patients were male. The median delivered total dose was 50 Gy (range 35-50 Gy); with a median fraction number of 5 (range 3-5 fractions) and the median fraction dose was 10 Gy (range 7-15 Gy), corresponding to a median BED10 of 100 Gy (range 60-113 Gy). Nine patients presented with a left-sided lesion, five with right-sided and one patient with both left and right-sided lesions. All of the initial plans met target and OARs constraints. Among 70 fractions 56 fractions (80%) were re-optimized. The dosimetric findings for PTV and OARs on predicted and re-optimized fractions were compared. PTV V100 (90.9% vs 94.3%) and PTV D98 (40.8 Gy vs 44.5 Gy) were better with re-optimization and the differences were statistically significant (P < 0.05). The OARs doses for 0.5 cc, 1 cc, 5 cc and 10 cc were compared. The right and left sided lesions were analyzed separately. For the left sided metastases there was OARs dose violation for stomach in one patient and for bowel in one patient. For the right sided metastases there was OARs dose violation for duodenum in two patients and for bowel in two patients. After re-optimization all dosimetric parameters met the institutional constraints. Local control rate was 93.8% with a median follow up time of 11.7 months (range 4.5-26.4 months). One patient with progressive disease underwent adrenalectomy. All treatments were well tolerated. The most common radiation induced acute toxicities were grade 1-2 fatigue and nausea. There were no grade 3 or higher acute or late toxicities experienced during the treatment and follow-up course.Conclusion: The use of re-optimization with SMART improved the PTV coverage and OARs doses for treatment of adrenal metastases. SMART has some advantages when compared to other radiotherapy techniques due to its better visualization of soft tissue, real-time tumor tracking without fiducial markers and potentially reduced toxicity to OARs. These results need to be confirmed with more patients and longer follow-up. [ABSTRACT FROM AUTHOR]