ESTRO 38 Abstract book

S456 ESTRO 38

disease, 26% current or former smokers, and 20% with autoimmune disease. The median follow-up time is 15 months. Results are shown in Table 1 and Figure 1.

Conclusion DWI informed boost delineation for bladder radiotherapy planning improved normal tissue sparing at high dose bowel and bladder constraints by >60% compared to CT based GTV delineation. Acquiring DWI for radiotherapy planning may therefore complement target volume delineation and inform non-uniform dose delivery to biological sub-volumes for bladder radiotherapy dose escalation trials. Work is on-going to demonstrate this.

Conclusion

HDR-BT with surface applicators has important dosimetric and time advantages over other radiation modalities for NMSC. Based on our results, HDR-BT also offers excellent tumor control with exceptional cosmetic results in properly selected patients with NMSC. Future directions include a multi-institutional randomized trial comparing HDR-BT with EBRT. PO-0866 Cost-effectiveness analysis of stereotactic radiotherapy in melanoma brain metastases. A. Paix 1 , F. Thillays 2 , F. Courtault-Deslandes 3 , I. Pop 4 , J. Biau 5 , O. Briard 6 , A.L. Grosu 4 , E.A. Sauleau 7 , G. Noël 1 1 Centre Paul Strauss, Radiothérapie, Strasbourg, France ; 2 Institut Cancérologique de l'Ouest, Radiothérapie, Saint-Herblain, France ; 3 Centre Georges-François Strahlenheilkunde, Freiburg, Germany ; 5 Centre Jean Perrin, Radiothérapie, Clermont-Ferrand, France ; 6 Centre Henry Kaplan - Centre Hospitalier Universitaire de Tours, Radiothérapie, Tours, France ; 7 Centre Hospitalier Universitaire de Strasbourg, Groupe de méthodologie et recherche clinique GMRC, strasbourg, France Purpose or Objective Melanoma is the third cancer responsible for brain metastases in frequency. To treat these metastases, when a safe surgery could not be performed, there is a global agreement to prefer stereotactic radiotherapy, performed in either one single fraction (SRS) or several fractions (HFSRT), over whole brain irradiation, to preserve cognitive function with a better metastases response to treatment. Material and Methods We developed a Markov model, reported in Figure 1, based on retrospectively collected data of treatment delivered in 6 hospitals in France and Germany, to describe survival and treatment-related complications of patients treated for a single melanoma brain metastasis. This analysis was conducted from the French payer perspective on a lifetime horizon. Utility values, recurrence risks, and costs were adapted from the literature. Deterministic (DSA) and probabilistic (PSA) sensitivity analyses were performed to assess the influence of the assumptions made. Leclerc, Radiothérapie, Dijon, France ; 4 Universitätsklinikum Freiburg, Klinik für

Poster: Clinical track: Skin cancer / malignant melanoma

PO-0865 Curative HDR brachytherapy (HDR-BT) for non-melanoma skin cancers (NMSC) B. Emami 1 , C. Hentz 1 , I. Rashed 1 , K. Stang 1 , A. Gliniewicz 1 , M. Mysz 1 , D. Eilers 1 , R. Tung 1 1 Loyola University Medical Center, Radiation Oncology, Maywood, USA Purpose or Objective NMSC is the most common malignancy. Standard treatments are surgery; radiotherapy: external beam radiotherapy (EBRT) and brachytherapy with HDR-BT and electronic brachytherapy (e-BT ) sources. With some treatment modalities, incompatibility with certain anatomical sites (surgery and e-BT), operational/wound complications (surgery), dosimetric limitations (e-BT), and cosmetic/functional complications (surgery) often result in suboptimal cure rates or unacceptable sequela. In order to overcome these issues, we have used HDR-BT in treatment of selected NMSC patients. Material and Methods From July 2015 to June 2018, 105 NMSC lesions of basal cell carcinoma (BCC), squamous cell carcinoma (SCC), cutaneous T cell lymphoma (CTCL), or Merkel cell carcinoma in 75 patients were treated using HDR- BT(Iridium-192) using an Elekta Freiburg flap surface applicator according to an internal review board approved prospective protocol. Targeted lesions with 5-10mm margins were delineated at the time of CT simulation using radiopaque wires attached to thermoplastic mesh. The Freiburg flap is affixed to the mesh surface. A dose of 32-40 Gy in 8-10 fractions was delivered to a depth of 3-5 mm depending on lesion thickness. Patient and treatment characteristics, pain level and medication use, early (<3 month) and late toxicities (CTCAE v4.03), physician- and patient-reported cosmesis, and cancer outcomes were recorded in a prospective manner. Univariate generalized linear mixed effects models were used to estimate odds of suboptimal cosmesis (fair-poor vs. excellent-good). Results Median age of patients was 82 (range 74-88). Fifty-eight percent of lesions were SCC, 42% BCC. The median lesion size was 4mm (range 4mm - >5cm). Patient comorbidities were also recorded, with 51% of patients with vascular