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Funding Acknowledgements Type of funding sources: None. Background Ventricular tachycardia (VT) is a life-threatening condition. Usual management of VT is based on anti-arrhythmic drugs or catheter ablation. In this scenario, stereotactic body radiation therapy (SBRT) is arising as an attractive non-invasive alternative for the treatment of VT in some patients (pts). Purpose The aim of this study was to assess safety, feasibility and outcomes of SBRT in fragile pts admitted in our centre for VT storms. Methods Pts with implantable cardioverter-defibrillator (ICD), presenting with VT storms and not responsive to drugs or suitable for catheter ablation were enrolled for SBRT. All pts underwent a computed tomography (CT) and an 18F-fluorodeoxyglucose positron emission (FDG PET)-CT scan in order to detect a possible area of scar responsible of the VT. All pts had also an electrophysiological study and ventricular programmed stimulation inducing clinical VT while wearing a multi-electrodes ECG vest. Merging the CT scan imagines and the VT 3D reconstruction, we identified the possible circuit of the VT and its exit sites. Treatment planning was performed for a total dose of 21-25 Gy delivered in a single session. For the first year, follow-up (FU) were scheduled every 3 months since the SBRT treatment. Toxicity was prospectively assessed. Results From January 2020 to March 2021, we treated 6 (5 males) pts. Mean age was 78±4. NYHA class was II for 3 pts, 2 were class III and only one pts was class IV. Four pts had an ischaemic heart disease background, two had dilated cardiomyopathy (DCM). Mean ejection fraction (EF) was 31±6%. The mean FU was 17 months, with the longest of 23 months. Of these 6 pts, only one died because of end stage heart failure, no VT/VF were recorded on his ICD. This was the pts with DCM and class NYHA IV at the time of procedure. Of the 5 pts remaining, 2/5 reported new therapies delivered by their ICDs. One pts had a single ICD shock during acute urine tract infection and sepsis at one month since SBRT. ICD interrogation documented inappropriate shock on fast conducted atrial fibrillation. No VTs have been recorded after 7 months. The other pts was admitted after 5 months since SBRT. The ICD showed appropriate therapies on VTs. This pts had the biggest scar volume compared to the others (anterior wall of the left ventricle with aneurysmatic apex). On the other 3 pts, no VTs were recorded by ICDs. Of these 3 pts, interestingly, 2 had class NYHA III and the mean EF 28.6±3%. The overall outcome with no appropriate ICD shocks due to VTs is above 70%. No radiotherapy toxicity was documented. Conclusion To the best of our knowledge this is one of the biggest groups of pts treated with this technology and the longest FU so far, of a single centre in Italy. SBRT seems to be a safe and feasible approach to treat fragile pts with VTs when not suitable for standard catheter ablation or responsive to medications. It also shows a good outcome even in pts with more advanced heart failure.

Background The current therapy of recurrent ventricular tachycardia (VT) and arrhythmic storms is the radiofrequency catheter ablation (RFCA). The first experiences of stereotaxic radioablation of arrhythmia (STAR) as an alternative in patients (pts) with defibrillator (ICD) and Arrhythmic Storms are emerging. However, a standardized method for STAR is not yet available and many issues are still under discussion. We present the preliminary results of STAR in the pts of our Center. Material and method Pts with ICDs and Arrhythmic Storms, excluded from RFCA, were referred to STAR. Diagnostics performed were Electrophysiological study (EPS) using 3D electroanatomical mapping (3DEAM) using CardioInsightTM vest (Medtronic, Minneapolis, MN), cardio–CT scan and 18F–fluorine–2–deoxy–D–glucose positron emission tomography (18FDG – PET scan) in order to identify the target area of the ventricle. In all pts a sustained monomorphic VT was induced during EPS, and 3DEAM was used to identify the exit point of the VT (Fig. 1). In all cases, a 3 mm thick 4D CT scan was used (Fig. 2) with the aid of an abdominal thermoplastic mask. Each patient was treated with a TrueBeam Linac (Varian Medical Systems, Palo Alto, CA). The prescription of the dose from 21 to 25 Gy in a single delivery. Ethics committee approval was obtained prior to each treatment. Results From January 2020 to March 2021, 6 patients (5 M, 1 F), mean age 78 years (58–80) were treated with STAR. The median delivered dose was 25 Gy (range 21–25 Gy). In follow–up (FU) one patient died from end–stage heart failure after 30 days. At a median FU of 13 months, STAR treatment efficacy was observed in 3/5 patients, in whom no defibrillator activation was recorded. 2/5 patients had recurrence of TV, 2 and 6 months after STAR. No severe acute toxicity was recorded after radiotherapy. Conclusions Arrhythmic stereotaxic radioablation appears to be a safe and effective therapy in PTS with ICDs and arrhythmic storms. Completely non–invasive diagnostics and therapy make it very interesting and ambitious. Additional data is needed to improve the definition of the target zone and to standardize it in patients not eligible for RFCA.

Cancer cachexia is a syndrome characterized by weight loss (WL) and sarcopenia. Aim of the study was to assess the impact of cachexia on head and neck changes during definitive cisplatin and image-guided volumetric-modulated arc radiation therapy in a series of locally advanced oropharyngeal cancer.Volume variations of sternocleidomastoid muscle (SCM) were considered as surrogate of muscle changes related to sarcopenia. Two head and neck diameters, encompassing the cranial limits of II and III nodal levels (defined as 'head diameter' and 'neck diameter', respectively), were measured. All parameters were defined retrospectively by means of on-board cone beam computed tomography images at 1-8th to 15-22th and at last fraction (fx) of radiotherapy (RT). Cachexia was defined as WL5% during treatment. Analysis was conducted correlating the parameter changes with three WL ranges:5, 5-9 and10%.Thirty patients were evaluated. One hundred and fifty contoured SCMs and three hundred diameters were collected. Median WL was 6.5% (range, 0-16%). The most significant SCM shrinkage was recorded at 15th fx (mean 1.6 cc) related to WL 5-9% and WL10% (P 0.001). For 'head diameter', the peak reduction was recorded at the 15th fx (mean 8 mm), statistically correlated to WL10% (P 0.001). The peak reduction in 'neck diameter' was registered at the 22th fx (mean 6 mm), with a gradual reduction until the end of treatment for WL5%.In a homogeneous cohort of patients, present study quantified the impact of cachexia on head and neck changes. Present data could provide adaptive RT implications for further investigations.

Purpose To investigate possible predictive anatomical features correlating to cardiac and left-lung dose sparing by deep inspiration breathhold (DIBH) technique compared to freebreathing (FB) for left-sided whole breast radiation therapy (RT). Materials and Methods Twenty consecutive patients who underwent (DIBH) left-sided breast RT had both FB and DIBH CT simulation. All patients were planned with two 6 MV-flattening-filter-free FFF (DIHB) and two/four (FB) 6 MV IMRT tangential fields, with prescription of 50 Gy/25 fr to whole breast and 60 Gy to simultaneous integrated boost (SIB). Mean dose and dosevolume metrics (V5Gy, V10Gy, V20Gy) were analyzed and compared for heart and left-lung for both FB and DIBH techniques. Correlation analyses were performed between such dose metrics and patient (FB) anatomic features: maximal heart distance and length (MHD, MHL), maximal lung distance (MLD), chest wall rise (CWH) (Fig. 1). Paired t-test or Wilcoxon signed-rank test was applied to compare differences in the dose metrics between the two techniques and linear regression was used for data analysis with significance level of p ≤ 0.05. Results All dose metrics for the heart and left-lung were significantly reduced (p Conclusion In this patient cohort, DIBH technique has been shown to reduce dose to the heart and left-lung. MHL(FB) and CWH served as significant predictors for heart and left-lung dose sparing by DIBH. These parameters can be easily measured at the time of CT simulation and thus may be used as simple and quick tool to determine which patient may benefit from a DIBH technique.

To analyze clinical-dosimetric predictors of genitourinary (GU) toxicity in a cohort of prostate cancer (PC) patients treated with moderate hypofractionation and simultaneous integrated boost (SIB) using volumetric modulated arc therapy (VMAT) technique.60 patients were selected. Patients were stratified into low (43 %), intermediate (30 %) and high-risk (27 %) groups. Low-risk patients received 73.5 Gy to PTV1; intermediate-risk received 73.5 Gy to PTV1 and 60 Gy to PTV2; high-risk received 73.5 Gy to PTV1, 60 Gy to PTV2, and 54 Gy to PTV3. All patients were treated in 30 fractions. Androgen deprivation therapy (ADT) was prescribed upfront in intermediate and high-risk categories. Toxicity was scored according to Common Terminology Criteria for Adverse Events v4.0 scoring system.Median follow-up was 30 months (range 16-36 months). GU acute toxicity was recorded as followS: G0 = 16/60 (27 %), G1 = 18/60 (30 %); G2 = 26/60 (43 %). GU late toxicity was recorded as follows: G0 = 20/60 (34 %); G1 = 29/60 (48 %); G2 = 11/56 (18 %). The risk of acute G2 GU toxicity was three times higher for prostate volume ≥80 cc. In 60 % of the patients with a prostate volume ≥80 cc, the first 3 weeks are at particular risk for toxicity onset. In the late setting, no statistical significance was found between GU toxicity and prostate gland dimension.Prostate volume ≥80 cc resulted a predictive factor of acute G2 GU toxicity, in moderate hypofractionation and volumetric modulated arc radiation therapy for definitive PC.

To investigate the feasibility and tolerance in the use of adjuvant intensity modulated radiation therapy (IMRT) and simultaneous integrated boost in patients with a diagnosis of breast cancer after breast-conserving surgery.Between September 2011 to February 2013, 112 women with a diagnosis of early breast cancer (T1-2, N0-1, M0) were treated with IMRT and simultaneous integrated boost after breast-conserving surgery in our institution. A dose of 50Gy in 25 fractions was prescribed to the whole breast and an additional dose of radiation was prescribed on the tumour bed. A dose prescription of 60Gy in 25 fractions to the tumour bed was used in patients with negative margins after surgery, whereas if the margins were close (1mm) or positive (without a new surgical resection) a dose of 64Gy was prescribed. All patients were followed with periodic clinical evaluation. Acute and late toxicity were scored using the EORTC/RTOG radiation morbidity score system. Both patient and physician recorded cosmetic outcome evaluation with a subjective judgment scale at the time of scheduled follow-up.The median follow-up was 28 months (range 24-40 months). The acute skin grade toxicity during the treatment was grade 0 in 8 patients (7%), grade 1 in 80 (72%), grade 2 in 24 cases (21%). No grade 3 or higher acute skin toxicity was observed. At 12 months, skin toxicity was grade 0 in 78 patients (70%), grade 1 in 34 patients (30%). No toxicity grade 2 or higher was registered. At 24 months, skin toxicity was grade 0 in 79 patients (71%), grade 1 in 33 patients (29%). No case of grade 2 toxicity or higher was registered. The pretreatment variables correlated with skin grade 2 acute toxicity were adjuvant chemotherapy (P=0.01) and breast volume ≥700cm(3) (P=0.001). Patients with an acute skin toxicity grade 2 had a higher probability to develop late skin toxicity (P0.0001). In the 98% of cases, patients were judged to have a good or excellent cosmetic outcome. The 2-year-overall survival and 2-year-local control were 100%.These data support the feasibility and safety of IMRT with simultaneous integrated boost in patients with a diagnosis of early breast cancer following breast-conserving surgery with acceptable acute and late treatment-related toxicity. A longer follow-up is needed to define the efficacy on outcomes.