Magnetic resonance (MR) image-guided radiotherapy (MRIgRT) has been recently implemented in routine clinical practice in our department. Treatment workflow for MRIgRT differs substantially from other radiotherapy systems and consists of set-up, MR imaging, re-contouring, re-optimization & plan QA and treatment delivery. We hypothesized that delivery of total on table treatment time will be less than 60 minutes for >75% of fractions. Aforementioned treatment components were recorded in 44 patients (304 fractions), treated between September 2018 and January 2019 with our linear accelerator based MRIgRT. Effect of treatment parameters (treatment site, dose per fraction, being first or last fraction, being treated with adapted plan or not, using breath hold technique or not) on total treatment time were analyzed. Median age was 66 years (28-83). Upper abdomen (21 patients, 41.1%) and pelvic (17 patients, 33.3%) regions were most common sites treated. Most common diagnosis was prostate cancer (14 patients - 31.8%). Majority of patients (40 patients, 91%) were treated with stereotactic body radiotherapy (SBRT), with fraction number 8 or less. Twenty-nine patients (56.8 %) were treated with audio-visually coached breath-hold gating method. Median total dose was 36.25 Gy (24 – 70 Gy) and median fraction number is 5 (3 – 28). Median total treatment time for all fractions was 43.5 minutes (range, 21-125 ) with 85% of patients being treated in less than 1 hour. Median patient setup time was 10 minutes (range 5-31), contouring time was 8 minutes (range 1-45), re-optimization + QA time was 4,5 minutes (range 1-16). Median time lost due to technical problems was 7 minutes (range 2-49) and occurred in 86 fractions. The longest component of the workflow was found to be radiotherapy treatment delivery; median 18 minutes (range 8-76). There was correlation with the treatment site and the total treatment time (p<0.0001) Median total treatment durations for upper abdomen, pelvis, thorax and spine were 48.3, 40.9, 42.2 and 53 minutes, respectively. As expected, lower fraction doses (< vs > 6 Gy) resulted in shorter treatment time (median 39.4 vs 47.2, p<0.0001). Breath hold technique resulted in longer overall treatment time compared to non-breath hold techniques (median 41.7 vs. 45.1, p=0.01). Similar difference was noticed in total treatment time between fractions treated with the original plan or the adapted plan (median 38.9 vs. 45.3, p<0,0001). There was a gradual decrease in treatment time between the first and last fraction (median 51 vs 41.7, p<0.0001). Total treatment time was found to be longer for SBRT compared with non-SBRT fractions (median 45 vs 40.5, p=0.001). MRIgRT can be easily delivered in less than 1 hour in 85% of fractions if appropriate precautions are taken. Radiotherapy delivery time remains the longest component of overall treatment. Optimization of the workflow and future hardware changes are expected to further reduce overall delivery times.

S765ESTRO 37was a significant predictor for OS (median, 55.6 vs 24.5 months, p=0.04).Low PLR (≤ 153.1) was associated with longer PFS (45.2 vs 9.8 months, p=0.009).Low NLR (≤ 2.97) showed a trend toward better OS (45.5 vs 24.5 months) and PFS (18.7 vs 10.4 months) with no statistical difference (p=0.19,0.28). ConclusionPretreatment PLR and LMR could be prognostic markers for OS and PFS in patients with non-small cell lung cancer treated with chemoradiotherapy.

To evaluate factors associated with local control (LC), overall survival (OS) and toxicities after SABR to centrally located primary non-small cell lung (PL) and oligometastatic (OM) tumors. Seventy centrally located tumors (abutting tracheobronchial tree [TBT], <2cm from TBT, or intersecting mediastinum) in 65 patients treated with linear accelerator-based SABR between 2009 and 2016 were retrospectively studied. Impact of patient, tumor, and treatment parameters on LC, OS and toxicity-free survival (TFS) were evaluated by multivariate analyses. Forty-eight PL and 22 OM lesions were analyzed, including 20 (28%) re-irradiation (Re-RT) cases. Median total, fractionated, and biological equivalent doses in BED10 and BED3 were 55 (30-60), 9.75 (4-18), 110 (41-151), and 228 (90-378) Gy, respectively. Doses given as Re-RT were lower (median Re-RT BED10 dose 94 vs. 110 Gy, P=0.009). Complete response (CR) was obtained in 43 (61%) lesions. None of the analyzed factors correlated to CR. After a median follow-up of 57 (48-65, 95%CI) months, 10 (14%) lesions had relapsed and 37 (57%) patients had died (2 and 5-year LC and OS rates were 84/70% and 52/28%, respectively). In univariate analysis, 2-year LC was lower for lesions with no CR and for colorectal cancer lesions. Only “no CR” was significant (100 vs. 51%; HR=18.2, CI 2.3-146, P=0.006) in final multivariate analyses. Median OS was significantly lower in patients with grade 3+ toxicity (5 months after grade 3+ toxicity, vs. 39 months in others [HR 4.7, CI 2-11.2,P<0.0001]). OS was marginally lower in patients with primary lung cancer compared to patients with OM tumors (19 vs. 49 months, HR 2.3, CI 1-5.6, P=0.06). Among 17 toxicities, 5 reached grade 5. For patients with grade 3+ toxicities, TFS was lower after Re-RT (2-year TFS 63% vs. 96%, HR 5.1, CI 1.3-20.3, P=0.022) but did not differ significantly for lesions abutting TBT (2-year TFS 69% vs. 93.4%, HR 3.5, CI 0.9-13.9, P=0.08). SABR is an effective treatment modality in centrally located lung tumors. SABR to re-irradiated lesions and possibly lesions abutting TBT may have the higher risks for serious toxicities. Further studies are indicated.

Stereotactic lung radiation therapy is an established technique that has been shown to be effective in early stage lung cancer. In this study, we aimed to compare conformal arc (3DCA) and volumetric modulated arc (VMAT) techniques according to RTOG 0915 protocol guideline using either flattened (FF) or unflattened (FFF) photon beams Twenty stage I non-small cell lung cancer patients were included to this dosimetric study. 3DCA and VMAT non-coplanar plans were generated both with FF and FFF modes using 6 MV photons and two arcs. 95% of PTV is conformally covered by the prescription line. Plans were compared in terms of various dosimetric parameters; ratio of prescription isodose volume to the PTV volume (Conformity index-CI), ratio of 50% prescription isodose volume to the PTV (Intermediate spillage volume-ISV), maximum dose in % of dose prescribed at 2 cm from PTV (intermediate dose spillage location-ISL), and percent of lung receiving 20 Gy (V20) total or more. Deviations were classified as minor and major according to the volume of PTV. All plans were acceptable and no deviation was observed according to RTOG criteria. CI ranged between 0.97 – 1.26 (Median: 1.06), 1.00 – 1.19 (Median: 1.04), 1.04 – 1.43 (Median: 1.22) and 1.00 – 1.37 (Median: 1.18) for VMAT-FF, VMAT-FFF, 3DCA-FF and 3DCA-FFF, respectively. VMAT-FFF have significantly better conformality index compared to others. (p=0.001) ISV values ranged between 3.64 and 5.82 (Median: 4.30), 3.37 – 5.04 (Median: 3.96), 3.87 – 6.30 (Median: 4.80) and 3.69 – 5.33 (Median: 4.44) for VMAT-FF, VMAT-FFF, 3DCA-FF and 3DCA-FFF, respectively. VMAT-FFF has significantly lower ISV values which indicates superior falloff gradient. (p=0.001) ISL values in percentage ranged between 47.8%-71.8% (Median: 60.45%), 47.4%-66% (Median: 58.25%), 47.8%-84.7% (Median: 61.35%) and 47.4%-82.7% (Median: 60.5%) for VMAT-FF, VMAT-FFF, 3DCA-FF and 3DCA-FFF, respectively. VMAT-FFF has significantly lower ISL values which show a better falloff gradient 2 cm away from PTV. (p=0.001) V20 values for lung ranged between 0.77% – 9.07% (Median: 3.06%), 0.72% – 8.76% (Median: 2.91%), 0.96% - 8.92% (Median: 3.06%), 0.8% – 8.76% (Median: 2.95%) for VMAT-FF, VMAT-FFF, 3DCA-FF and 3DC-FFF, respectively. No difference was found between 4 techniques. (p=0.069) Results of the this study have shown that VMAT-FFF technique demonstrated better conformality for high dose spillage region and higher dose falloff gradient for intermediate dose spillage regions with shortest treatment time compared to VMAT-FF and 3DCA FF/FFF using RTOG 0915 guidelines. We believe that VMAT-FFF is the optimal technique for lung SBRT treatments due to high quality SBRT plans obtained and shorter treatment time

PURPOSE: Robotic stereotactic hypofractionated radiotherapy (SRT) become an important modality in the treatment of cranial meningiomas. In this study, we analysed the treatment parameters and outcomes of our cranial meningioma patients treated with SRT. MATERIALS AND METHODS: Between 2009 and 2013, 103 cranial meningioma lesions of 93 patients were treated with CyberKnife (Accuray®) Stereotactic Radiosurgery Unit. 42 patients (45%) received SRT as primary modality, and 51 patients ( 55 %) received postoperatively. Six patients have treated with external beam radiotherapy. Of the 103 cases, 69 of the lesions were located basally, 34 of them nonbasally. The most common symptoms in patients with basal tumours (38 patients, 58%) was detoriation in the visual field and the restriction of the eye movements and in patients with non-basal tumours (8 patients, 26%) was headache. In 33 patients (32%) tumours were located just adjacent to the optic apparatus or brain stem, 27 of them (26%) were located close (<1cm) to the optic apparatus or brain stem. SRT dose and fractionation were determined according to tumor localization. Optical apparatus and brainstem maximum point dose constraints for one fraction were 10 Gy and 14 Gy; 25 Gy and 30 Gy were for 5 fractions. RESULTS: The median age was 44 (16-81). The female to male ratio was 73/20 (3.6/1). Median follow-up was 10 months (1-37 months). The median dose was 2500cGy (1500 - 3000 cGy). The median number of fraction was 5 (1-5 fractions) fraction. GTV volume ranged between 0.66 cm3 and 80.6 cm3 (Median 12.4 cm3). Median conformity index was 1.4 (1.06 to 2.03) and the median homogeneity index was 1.25 (1.09 to 1.56). Among the patients with follow up, local control rate was 98%. Only one patient with parasagittal meningioma underwent decompressive surgery due to radiation induced edema. All other side effects were either grade I or II. The most common side effect was headache associated with brain edema in 10 patients (11%). CONCLUSION: Hypofractionated SRT is an effective treatment method in patients with cranial meningiomas with excellent rate of local control and minimal side effects.

We aimed to compare dosimetric characteristics of conventional linear accerator-based treatment plans to those created using the robotic CyberKnife® (CK) treatment planning system for patients with early-stage lung cancer. Eight early-stage lung cancer patients treated with stereotactic body radiotherapy (SBRT) using a conventional linac-based (LIN) system were included in this study. New treatment plans were created for the patients with the CK treatment planning system in order to compare the two platforms' dosimetric characteristics. Planning computed tomographies (CT) were obtained in three phases: free-breathing, full exhalation and inhalation. The three GTVs were then added together for internal target volume (ITV) with LIN, whereas no ITV was used for CK. Planning target volumes (PTV) were constituted by adding 5-mm margin to GTV and ITV. Treatment plan was 54 Gy in three fractions. Five-field, seven-field, and dynamic-conformal arc planning techniques were used in LIN plans. Plans were compared according to dose heterogenity (D(max)-maximum dose), volume of 54 Gy (V54) and 27 Gy isodose (V27), conformity index (CI(54) and CI(27)) and lung volumes. PTVs were significantly smaller in CK plans (p=0.012). D(max) was significantly lower in ARC plans (p=0.01). Among all plans, CK had significantly tightest isodose shell received 54 Gy and 27 Gy (p=0.0001). Among LIN plans, V54 was significantly (p=0.03) smaller in ARC plans; but no difference was observed for V27 values. LIN plans have better plan quality (CI(27) and CI(54)) than CK. No statistically significant difference was observed for lung volumes. CK plans had superior V54 and V27 values compared to LIN plans due to smaller PTV. LIN plans had better CI(27) and CI(54) values. Advantages of LIN treatment were no neccessity for fiducial marker use, which may cause pneumothorax, and significantly shorter beam-on treatment times. Both CK and LIN methods are suitable for lung SBRT.