Abstract Book

ESTRO 37

S435

Conclusion The change in GFR after SBRT for primary RCC was similar to that observed in other kidney-directed treatment modalities. A recent meta-analysis reported a mean decrease in GFR after thermal ablation and partial nephrectomy of -4.5 mL/min and -6.2 mL/min respectively. Uninvolved renal cortex was the only dosimetric feature related to changes in renal function. Patients with better renal function and higher kidney volume at baseline have higher rates of deterioration in renal function post-SBRT.

cancer. The 5 and 10-year OS rates were 67.1% and 43.2% respectively, whereas the 5 and 10-year MFS rates were 84.4% and 79.2% and the 5 and 10-year CSS rates were 81.4 % and 76.3 %, respectively. There was no statistically significant difference in OS between treatment protocols. On MVA, mTUR of the bladder and the complete response (CR) after induction therapy were independent correlates of improved OS (mRTU p=0.012, HR=0.444; CR p=0.039, HR=0.478) and of MFS (mTUR p=0.021, HR=0.303; CR p=0.022, HR=0.300), the development of invasive bladder recurrence was independently associated with worse CSS survival (p=0.001, HR: 6.164) and MFS (p=0.016, HR: 3.504). Conclusion This long-term report indicates that bladder-sparing treatment is a successful approach for MIBC in terms of survival an distant metastasis. The results confirm that mTUR of the bladder tumor and the complete response after induction therapy remain the most significant predictive clincal factors. PO-0833 Dosimetric analysis of renal toxicity after stereotactic body radiotherapy for renal cell carcinoma M. Niglas 1 , P. Cheung 1 , A. Swaminath 2 , R. Koro l 1 , D. Erler 1 , D. Vesprini 1 , W. Chu 1 1 Sunnybrook Odette Cancer Centre, Radiation Oncology, Toronto, Canada 2 Juravinski Cancer Centre, Radiation Oncology, Hamilton, Canada Purpose or Objective Stereotactic body radiotherapy (SBRT) is an emerging treatment option for localized, inoperable renal cell carcinoma (RCC). Previous reports have demonstrated favourable toxicity profiles, with a recent meta-analysis showing an eventual decrease in glomerular filtration rate (GFR) of 5.5 mL/min after SBRT. Currently, clinical predictors and dosimetric parameters have not been well-defined in the literature for SBRT fractionation schedules. Material and Methods After institutional research ethics board approval, patients with inoperable RCC who were treated with a 5- fraction SBRT protocol between June 2012 and July 2017 were analyzed. Patient characteristics, dosimetric parameters and serum markers were prospectively collected. “Uninvolved renal cortex” was defined as the volume of renal cortex outside of the 17.5 Gy isodose line. Toxicity was defined as GFR deterioration crossing at least one chronic kidney disease (CKD) stage. Absolute change in GFR was also examined. Kaplan-Meier estimates and Cox proportional hazards regression were used to examine toxicity outcomes. Results Fifty-two patients with a median GFR of 62 mL/min were treated with a median dose of 35 Gy in 5 fractions (range 30-45 Gy). Median follow-up time was 9.4 months. Mean change in GFR at the time of last follow-up was -6.3 mL/min (p=0.02). 14 patients (27%) developed a worsening of their CKD stage by the time of last follow- up. Median time to toxicity was 24.8 months based on Kaplan-Meier estimates. Those who experienced progression of CKD stage had a mean pre-treatment GFR of 77.2 mL/min, compared to 57.2 mL/min in those who had stable CKD stage (p=0.02). 20 patients had improvements in GFR at the time of last follow-up, and 4 had transient improvements in CKD stage. On univariate analysis, higher rates of deterioration in CKD stage were seen in patients with stage 1-2 CKD (HR = 5.9, p=0.02), and those with more than 250cc of uninvolved renal cortex (HR = 4.4, p<0.001). No other dosimetric parameters were associated with increased rates of renal toxicity. No significant effects were seen on multivariate analysis.

Poster: Clinical track: Skin cancer / malignant melanoma

PO-0834 Hypofractionated electron beam RT in non- melanoma-skin-cancer (229 pts): exclusive or postoperative. V. Mazzotti 1 , C. Menichelli 1 , A. Fanelli 1 , G. Pastore 1 , F. Casamassima 1 1 Centro di Radioterapia - Ecomedica, Radiotherapy, Empoli, Italy Purpose or Objective Non-melanoma skin cancer (NMSC) represents the most common type of malignancy in white population with an estimated 100 000 new cases per year in Italy. The 99% of the NMSC is represented by keratinocyte carcinomas (BCC) and squamous cell carcinomas (SCC). There are many treatment options in the management of NMSC and radiotherapy (RT) represents nowadays an important modality both in definitive and adjuvant settings. The aim of this study is to evaluate the effectiveness and the safety of hypofractionated electron beam RT in terms of local control (LC), toxicity and cosmetic outcome both as definitive treatment or in association with surgery. Material and Methods Between January 2011 and December 2016, 229 pts (77% men and 33% women) were treated in our center with electron beam RT for NMSC. The median age was 83 years (range 41-98). Lesions were localized in most cases on the scalp, front, cheekbone, ear, eyelid or nose. In 112 pts (49%) RT was the unique treatment, instead in 117 pts (51%) RT was delivered after surgical excision with or without persistence of local disease. The treated lesions were BCC in 71 cases (31%), SCC in 148 cases (64,6%) and not histoligical characterized in 10 cases (4,4%). In the 82% of cases the tumor dimensions were between 2 and 5 cm. The lesion treatment to a depth of 3-5 mm with a 4 or 6 MeV electron beam was produced by a Linear Accelerator. The delivered dose was 60 Gy/10fx in definitive treatments and 30,48 or 60 (6Gy/fx) in post-operative cases. Toxicities were assessed by CTCAE 4.0 criteria and results were evaluated every 2 months for the first 6 months after the end of RT and then every 6 months. Results Median follow-up was 9,8 months. 23 pts were lost at the follow-up. LC ratio was 93% (144 complete response at the first control and 47 complete response achieved at the second/third control). 12 pts presented local progression (4 BCC and 8 SCC) with a mean time to progression of 16 months. 2 pts developed lymph nodal metastases (SCC with local complete response on primary cancer). A comparison between pts who received definitive RT and those who received RT as a post-operative treatment