ESTRO 2020 Abstract Book

S492 ESTRO 2020

management of indolent NHL has not been defined yet. Taking advantage of the radiosensitivity of indolent NHL, particularly of marginal zone (MZL) histology, and the fact that local relapses of these diseases are commonly salvageable and non life-threatening, there has been a recent trend towards reducing radiation doses to as low as 2 successive fractions of 2 Gy, in order to reduce long term RT complications. We report our experience about clinical outcomes in terms of survival and local control among a population of nodal and extranodal MZL treated in our Institution. Material and Methods All patients treated at our Institution with low dose RT for MZL, mostly mucosa-associated lymphoid tissue (MALT) lymphomas, between January 2015 and July 2019 were included in this analysis. Overall, we included 27 patients (9 males and 18 females, respectively). Disease was located in nodal or extranodal sites (such as orbit, stomach, lung, breast, spleen and head and neck region). The vast majority had a limited disease at the time of diagnosis: 23 patients were stage I (85.2%) and there was very low percentage of bulky presentations (2/27, 7.4%) at baseline. Assessment was performed with CT-scan, MRI or US, at the time of the diagnosis and throughout the follow up. All patients received a primary treatment based on curative low dose RT, administrated with 3DCRT technique. Progression-free survival (PFS), local and systemic disease control rates were evaluated. Results With a median follow up time of 12 months, we observed an excellent outcome in our cohort, with PFS rates of 92% at 1 year and 81.8% at 2 years (fig. 1). Also, low dose RT entails a very good disease control: local control was 96.3% at 12 months (fig.2a) with only one patient who did not respond to low doses and required a retreatment with full- dose RT up to 24 Gy. Furthermore, systemic disease control amounted to 96.3% at 1 year and 88.3% at 2 years (fig.2b): indeed, one patient experienced disease progression and received CT, with good response. Both of them were alive at the time of the last follow-up. Actually, there were no lymphoma related deaths, and only 2 patients (7.4%) died, due to other comorbidities. No acute and late toxicities were reported.

Conclusion Our study confirms that low dose radiation therapy with 2 Gy x 2 is effective and well tolerated in the treatment of MZL with high response rates in term of local control and progression-free survival. PO-0921 Total Body Irradiation and adoptive immunotherapy in pediatric HLA-haploidentical transplantation S. Saldi 1 , B.M. Panizza 1 , M.S. Massei 2 , I. Capolsini 2 , C. Fulcheri 3 , G. Ingrosso 4 , S. Chierchini 4 , C. Mariucci 4 , E. Perrucci 1 , M. Caniglia 2 , C. Aristei 4 1 Radiotherapy Oncology Centre, Santa Maria della Misericordia Hospital, Perugia, Italy ; 2 Pediatric Oncology and Haematology Centre, Santa Maria della Misericordia Hospital, Perugia, Italy ; 3 Medical Physics Unit, Santa Maria della Misericordia Hospital, Perugia, Italy ; 4 Radiotherapy Oncology Centre, University of Perugia, Perugia, Italy Purpose or Objective Hematopoietic stem-cell transplantation (HSCT) is the standard treatment for pediatric patients with high-risk acute lymphoid leukemia (ALL) . As the best donor, the matched sibling, is not always available, the 1-haplotype mismatched relative (haploidentical) is a valid alternative. In conditioning to T-depleted haploidentical HSCT, total body irradiation (TBI) is essential. In this setting we designed an inoculum which included a megadose of CD34+