ESTRO 2020 Abstract book

S684 ESTRO 2020

consisted of grade II mucositis that dissolved during 8 weeks after the treatment. Local recurrence occurred in 6 patients, 5 of them were successfully treated with partial amputation. In one case, the local recurrence was combined with recurrence in inguinal node, the patient underwent partial penectomy, lymphadenectomy and radiotherapy, but shortly afterwards he died on duplicate lung cancer. One patient had a nodal recurrence successfully salvaged by lymphadenectomy. One patient developed a necrosis of the glans requiring partial amputation. Currently, there are 24 patients alive without signs of disease. One patient died of cardiac comorbidity, one died of duplicate lung cancer. Nineteen patients have a preserved penis (73%), 18 of them sexually active before treatment report satisfactory intercourse. Conclusion Hyperfractionated interstitial high-dose rate brachytherapy with 18 times 3Gy per fraction twice daily is promising method in selected patients with penile carcinoma and deserves further evaluation in larger prospective study. PO-1209 A novel liquid fiducial marker for image- guided adaptive radiotherapy in bladder cancer. M. De Ridder 1 , L.C. Gebrandy 2 , T.M. De Reijke 2 , K.A. Hinnen 3 , M.C.C.M. Hulshof 3 1 LUMC, Radiation Oncology, Leiden, The Netherlands ; 2 Amsterdam UMC, Urology, Amsterdam, The Netherlands ; 3 Amsterdam UMC, Radiation Oncology, Amsterdam, The Netherlands Purpose or Objective To optimize Image Guided Adaptive RadioTherapy (IGART) for bladder preservation in bladder cancer, fiducial markers at the margins of the bladder tumor are needed to improve the precision of planning and delivery. All currently available fiducial markers have disadvantages like migration (titanium and gold fiducials), fading during treatment (hydrogel) or blurring (lipiodol, see fig 1). So, there is a need for a safe, feasible, visible and positionally stable marker. BioXmark® is a novel liquid injectable and adherent fiducial marker. This study evaluated the clinical performance of BioXmark for IGRT of bladder cancer. Material and Methods Prospective, single center phase I-II trial, including 20 patients with muscle-invasive bladder cancer treated with chemo-radiotherapy (55 Gy/20 fractions). BioXmark® liquid markers were injected in an outpatient setting using a flexible cystoscope. Visibility and stability of BioXmark® liquid markers on CT and cone-beam CT (CBCT) were evaluated. Results In total 77 markers were implanted in 20 patients; 60 markers (78%) in 19 patients (95%) were visible on treatment planning CT-scan. Invisible markers at the CT scan were mainly encountered during the first 4 patients, suggesting a learning curve for the application of markers. All visible markers after CT-acquisition were still visible at the last CBCT at the same position, without any signs of migration or fading. In 15/20 (75%) of the patients, 3 or more markers were visible on CT and thereby applicable for an daily automatic matching procedure. No BioXmark® related adverse-events were reported.

histology. 32/43 (74%) had neoadjuvant chemotherapy and 42/43 (98%) had concurrent chemotherapy. All patients completed radiotherapy. 39/43 (91%) patients had a post- radiotherapy cystoscopy at 3-4 months post-treatment; 26/39 (67%) had a biopsy result available from this procedure. NMF analysis identified 5 molecular subtypes. At a median follow-up of 3.8 years, 1/20 (5%) patients within subtypes 4-5 had a documented invasive locoregional recurrence compared to 8/23 (35%) of patients in subtypes 1-3 (p = 0.0243). 2-year invLR_RFS was 100% and 71% respectively (p=0.028). There was no significant difference in OS. With regards to post-radiotherapy biopsy results, the pathological complete response rate, defined as pT0, was 100% for the 11 patients in subtypes 4-5 compared to 60% for the 15 patients in subtypes 1-3 (p = 0.0237). On applying our classifier to publically available data, the 2-year OS for subtype 4 in the primarily surgically managed TCGA cohort was <50%. In our radiotherapy cohort, the 2- year OS for subtype 4 was 85%. This difference may suggest that patients in subtype 4, which displayed basal features, may derive greater benefit from radiotherapy +/- chemotherapy than surgery alone. Conclusion Data from this pilot study suggests that molecular subtype could be associated with response to radiotherapy in MIBC. Cohort numbers were small and further work is warranted. PO-1208 High-dose rate brachytherapy in the treatment of early stages of penile carcinoma D. Pohanková 1 , I. Sirak 1 , L. Kašaová 1 , J. Grepl 1 , P. Paluska 1 , M. Louda 2 , L. Holub 2 , J. Špaček 2 , P. Prošvic 3 , J. Petera 1 1 University Hospital Hradec Kralove, Oncology and Radiotherapy Department, Hradec Kralove, Czech Republic ; 2 University Hospital Hradec Kralove, Department of Urology, Hradec Kralove, Czech Republic ; 3 Hospital Náchod, Department of Urology, Náchod, Czech Republic Purpose or Objective Interstitial low-dose rate (LDR) brachytherapy (BT) allows a conservative treatment of T1-T2 penile carcinoma. High- dose rate (HDR) BT is often considered as a dangerous method for interstitial implants because of higher risk of complications. However, numerous reports suggest that results of HDR BT may be comparable to LDR. We present our first experience with HDR brachytherapy in the treatment of penile cancer. Material and Methods Twenty six patients with early penile carcinoma (T1- 2N0M0) were treated by HDR BT at dose 18 times 3Gy per fraction twice daily between years 2002-2018. The target volume encompassed tumor with 0.5 – 1.0 cm margin. In 7 patients the stainless hollow needles were inserted in 1 plane, in 12 patients in 2 planes and in 7 patients in 3 planes. The square pattern geometry and separation of 10 mm between needles were used. The distance of urethra was kept at least 5 mm from the plane of needles. Breast interstitial brachytherapy template was used for fixation and precise geometry reconstruction. The distance between both plates, between needle tip and plate, needle tip and mucosa exit point and needle tip and mucosa entry point were measured directly. The dose distribution was calculated with program for template with square pattern geometry on Brachyvision planning system (Varian, USA). The irradiation was performed by GammaMed afterloading device (GammaMed, Germany). Results The median number of implanted catheters was 4 (2; 12). The median volume covered by 3 Gy isodose was 7 cm 3 (2.1;11). The median V150 was 2.1 cm 3 (0.9; 5.0) and the mean dose homogeneity index was 0.62 (0.46; 0.87). Median follow up was 95 months (17; 210). Acute reaction