ESTRO 36 Abstract Book

S18 ESTRO 36 _______________________________________________________________________________________________

PV-0043 Radiotherapy to the mediastinum in Hodgkin's lymphoma: Is B-VMAT the only arc solution? C. Hanna 1 , C. Featherstone 1 , S. Smith 2 1 NHS Greater Glasgow and Clyde, Clinical Oncology, Glasgow, United Kingdom 2 NHS Greater Glasgow and Clyde, Radiotherapy planning and imaging, Glasgow, United Kingdom Purpose or Objective Patients treated for Hodgkin’s lymphoma have a long life expectancy. It is therefore essential to restrict dose to organs at risk (OARs) to reduce long-term toxicity when using consolidation radiotherapy treatment. Smaller volumes and lower doses have made an impact but it is also crucial that the correct radiotherapy technique is chosen. "Butterfly" arc therapy (B-VMAT) is a technique that has gained popularity with the claim of reducing dose to heart, lung and breast tissue. This project aims to assess if B-VMAT offers any advantage over 3D conformal or alternative arc techniques as a solution to reduce long- term toxicity in these patients. Material and Methods Review of case records and planning CT scans for 8 patients with mediastinal lymphoma treated with radiotherapy in the past 12 months. We produced a list of "aspirational" dose constraints (DCs) (Table 1) after review of current literature. These DCs were used to compare five different planning techniques (Figure 1) for each patient (Varian/Eclipse Version 13). Mean OAR dose values were calculated for each technique and a paired t-test was used to compare conformity of B-VMAT to the other techniques. Results Patients were aged between 20-42 years; 4 male and 4 female. Heart Dmean of 15Gy was met for all plans except one (AP:PA) and 10Gy was mostly achievable. B-VMAT and ARC-A were the optimal plans in terms of OAR dose except for one patient when there was most overlap between heart and PTV. In this case the ARC-F was superior. Lung-PTV Dmean of 12Gy was achieved in all but one plan (AP:PA). Arc therapies achieved better V20 doses compared to 3DCRT. Arc therapy, in general, did not generate high V5s except for ARC-F which failed to meet the V5 constraint for all patients. Breast doses were similar for arc and 3D conformal plans except when using ARC-F which was inferior. Dmean of 2Gy was always met. V4 <5% was met for all plans except ARC-F. Table 1 displays mean OAR doses for all 8 patients for each technique. ARC-A and B-VMAT both consistently out- perform 3D-CRT, ARC-F and hybrid without a substantial increase in dose bathing. Conformation number (CN) was significantly better for ARC-F, significantly worse for AP:PA and equivalent for ARC-A and hybrid when compared to B-VMAT. Although superior or equivalent in conformality compared to B-VMAT, both ARC-F and hybrid techniques were nevertheless inferior in reducing OAR doses.

France 6 Centre Hospitalier Lyon Sud, Service Hématologie, Lyon, France 7 Hôpital Saint Louis, Hematology and BMT-, Paris, France 8 Nijmegen Medical Centre, Heamtology, , The Netherlands 9 Erasmus MC Cancer Institute- University Medical Center, Hematology, Rotterdam, The Netherlands 10 CHU de Lille and Université de Lille II., Hematology and BMT- INSERME U955, Lille, France 11 Chaim Sheba Medical Center, Hematology division BMT and cord blood bank, Tel-Hashomer, Israel Purpose or Objective Total-body irradiation (TBI) has an historical established role in preparative regimens used before allogeneic transplant in both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia (AML). The most popular myeloablative conditioning consists of 12Gy delivered in 6 fractions (2Gy twice daily for 3 days) in combination with cyclophosphamide. This schedule of treatment delivery is, however, time-consuming and became less popular in the radiation oncology community in the era of development of new technologies. The aim of the SARAZIN study was to analyze the impact of the modified myéloablative fractionated TBI regimens as compared to the standard 6 fractions-schedule on outcome of patients undergoing allotransplant for ALL and AML. Material and Methods We retrospectively compared myeloablative TBI regimens of 3126 patients registered in the EBMT database transplanted between 2000 and 2014 for ALL (n=1783) or AML (n=1343). Pre-transplant chemotherapy consisted mainly of cyclophosphamide (Cy) in 92% and 97% of ALL and AML patients, respectively. TBI was delivered as either 12Gy in 6 fractions (group 1; ALL, n=1362 and AML, n=857), or single dose TBI (STBI) (group 2; ALL, n=54 and AML, n=79), or 9-12Gy in 2 fractions (group 3; ALL, n=173 and AML, n=256), or 12Gy in 3-4 fractions (group 4; ALL, n=194 and AML, n=151). The majority (70%-79%)* of ALL and AML (57%-79%) patients were grafted in 1 st complete remission (CR1). The rate of transplants from unrelated donors was higher in ALL (24%-50%) vs AML (20%-37%). Results The median follow-up was 61 months and 85 months in the ALL and AML patients, respectively. At 5 years, leukemia free survival (LFS), overall survival (OS), relapse incidence (RI) and non-relapse mortality (NRM) were 46.5%, 50.4%, 29%, 24.5% in ALL and 45.7%, 48%, 30.4% and 23.8%, respectively. LFS at 5y in AML and ALL patients were respectively: 48% and 45%, 32% and 45%, 45% and 53%, 42% and 50% in the 4 TBI groups (p=0.082 for AML and p=0.32 for ALL). Additionally, for both AML and ALL, no statistical significance was found between the 4 TBI groups for OS (p=0.82 in ALL; p=0.11 in AML), RI (p=0.29 in ALL; p=0.23 in AML) and for NRM (p=0.58 in ALL; p=0.12 in AML). In multivariate analyses of TBI schedules, comparing the different schedules to the standard 12Gy in 6 fractions (group 1 vs group 2; group 1 vs group 3; group 1 vs group 4), fractionation was not found as independent prognostic factor neither in ALL nor in AML patients for LFS, OS, RI or NRM. Conclusion The SARASIN study showed that using a TBI dose of 12Gy as pre allogeneic transplantation, fractionation has no impact on relapse or survival neither in ALL, nor in AML patients. The reduction of the number of fractions even in this rather high TBI dose level is not associated with increased risk of NRM. Altogether, our data suggests that 12Gy could be delivered safely in less than 6 fractions. This may lead to increase TBI availability as pre transplantation conditioning regimens in acute leukemia patients.