ESTRO 2021 Abstract Book

S685

ESTRO 2021

Conclusion Conclusion. Toxicity after adjuvant radiotherapy post-RC with VMAT is acceptable. Preliminary survival data are encouraging and underline the importance of further evaluating the place of adjuvant RT in well-selected MIBC patients post-RC. PD-0851 Clinical outcomes of online adaptive RT and conventional RT for muscle invasive bladder cancer. J. Yeh 1,2 , F. Foroudi 2 , K.H. Tai 1 , M. Bressel 1 , T. Kron 1 1 Peter MacCallum Cancer Centre, Radiation Oncology, Melbourne, Australia; 2 Olivia Newton-John Cancer Wellness & Research Centre, Austin Health, Radiation Oncology, Melbourne, Australia Purpose or Objective To report long-term outcomes of online image-guided (IG) adaptive radiation therapy (aRT) versus conventional IG radiation therapy (cRT) for bladder preservation in muscle-invasive bladder cancer (MIBC). Materials and Methods A retrospective review of patients with histologically proven MIBC who were prescribed radical intent radiation therapy (RT) following trans urethral resection of bladder tumour (TURBT) was conducted. There were three groups based on their RT treatment modality: conventional RT (cRT), margin 5mm adaptive RT (aRT5mm) and margin 7mm adaptive RT (aRT7mm). Results 171 patients were included in this study, with median age of 79.4 years (41 - 90). Approximately half of all patients received concurrent chemotherapy. N=57 underwent cRT, n=39 underwent aRT5mm, and n=75 underwent aRT7mm. Response evaluable patients in all three groups (n=133) had high rates of complete response (CR, 83%) on first post-RT cystoscopy with no significant differences between the groups. At a median follow-up of 54 months, the 5-year freedom from muscle-invasive failure survival (FFMIFS) in the cRT, aRT5mm, and aRT7mm groups were 75%, 59%, and 98%, respectively. The estimated cancer specific survival (CSS) at 5 years were 60%, 30%, and 59%, respectively. The estimated overall survival (OS) at 5 years were 43%, 26%, and 38%, respectively. The incidence of late grade 3 + toxicity was n=4 in aRT5mm, and n=1 in cRT group. Conclusion IG aRT with 7mm expansion for MIBC provides higher rates of FFMIFS, similar 5-year CSS and OS, as well as toxicity outcomes when compared to cRT. aRT with 5mm expansion with this RT protocol is not recommended to be used for treatment. PD-0852 Recommendations and clinical validation of inguinal CTV delineation in penile cancer R. Mittal 1 , V. Murthy 1 , R. Krishnatry 1 , P. Maitre 1 1 Tata Medical Centre, Department of Radiation Oncology, Mumbai, India Purpose or Objective Optimal clinical target volume (CTV) for inguinal nodal irradiation in penile cancer is unclear. This study determines the patterns of distribution of inguinal nodes and optimal margin needed around the femoral vessels to propose guidelines for inguinal CTV delineation in penile cancer. Materials and Methods Patients with biopsy proven penile squamous cell carcinoma (SCC) with inguinal node metastases were identified on a CT scan using predefined standard criteria. Distribution of nodes and distance from the center of nodes to the nearest femoral vessel and inferior edge of pubic symphysis (IPS) was obtained. A three- dimensional CTV margin to cover 95% of the nodes was estimated to evolve contouring guidelines for patients with both non-operated and post-operative groin. A comprehensive contouring guide with a visual atlas for inguinal CTV delineation was created. The proposed CTV was prospectively validated in 14 consecutive patients of penile SCC treated with post-operative radiotherapy to the inguino-femoral region. Results Of the 222 inguinal lymph nodes analyzed in 33 patients, 99% (220) were located anterior to femoral vessels of which, 81% (181) of the nodes were antero-medially and 18% (39) of the nodes were antero-laterally located (Figure 1) . Seventy percent nodes (n=155) were located superior (n=147) and at the level (n=8) of IPS. The remaining 30% (n=67) were located inferior to IPS. A majority (95%) of the antero-laterally located nodes were superior to IPS. No nodes were present antero-laterally to the femoral vessel inferior to the IPS. Margin around