Abstract Book

ESTRO 37

S375

within day 7 + maintenance therapy with rituximab2 infusion every 2 months for 2 years

images to the planning CT scan was performed for each patient (18 patients: 5 CBCTs, 2 patients: 4 CBCTs), using automatic registration on sternum and anterior ribs and including both translations and rotations. Distances from the isocenter to the edge of the CTV in each plane were assessed. Rotations were converted to translational components and added to the translations to find the total uncertainty for each registration. The overall set-up uncertainty was derived according to van Herk [van Herk 2004], The systematic uncertainties considered in this study was the contouring and set-up uncertainties, the random uncertainties were the setup and the intrafraction uncertainties. A contouring uncertainty of 3 mm [Aznar et al 2017] and an intrafraction uncertainty of 2 mm, 2 mm, and 3 mm (lateral, anterior-posterior and superior-inferior displacement in DIBH [Remouchamps et al 2003 and 2007], respectively) were assumed. Results The contributions from each type of uncertainty and the resulting margins are presented in Ta ble 1. Table1. Contribution from different uncertainties to overall PTV margin Direction

Major Inclusion Criteria: • FL •

Grades I-IIIA according to WHO 2008 classification

• • • •

Stage II-IV according to Ann Arbor

High tumor burden

ECOG performance status 0-2

No previous lymphoma treatment Primary endopoint is the feasibility (patients completing the therapeutic schema with dose intensity>90 %). Secondary endopoints are: overall response rate according to Lugano classification criteria, progression free survival, overall survival, event free survival, frequency of adverse events according to CTCAE 4.03, quality of life according to EORTC QLQ - C30 instrument. Regarding statistical considerations, in the absence of criteria for sizing the sample in formal terms, the study sample (20 cases) is defined according to criteria of opportunity and feasibility. We hypothesize that 80% of patients will complete treatment without any problems, with a minimum acceptance rate of 50%. Based on the binomial distribution the study will provide an encouraging result if at least 15 out of 20 pts will complete the treatment schedule. Results Between March 2017 and October 2017 10 patients were enrolled in the study. Stage was III for 9 patients and II for 1. Bulky site outside mediastinum was present in 5 patients. No mediastinal bulky site was present. All patients completed LD-RT and are currently undergoing immuno-chemotherapy. One patient completed both with unconfirmed complete response and is currently in maintenance therapy. No LD-RT toxicity was seen except for G1 nausea in one patient. No increase in hematologic toxicity compared to R-chemo alone was seen with prevalence of grade 1 or 2 haematological adverse effects. Conclusion Early results show excellent feasibility and safety of LD- RT and standard R-chemo as first-line therapy in FL. After completion of the this pilot study, if the feasibility and safety of this scheme are confirmed, we will start a multicentre phase 2 study PO-0733 PTV margins for mediastinal lymphoma in deep inspiration breath-hold using daily image guidance M. Maraldo 1 , L. Rechner 1 , M. Josipovic 1 , P. Petersen 1 , L. Specht 1 , M. Aznar 2 1 Rigshospitalet, Department of Clinical Oncology, Copenhagen, Denmark 2 Manchester Research Cancer Centre, Division of Cancer Science, Manchester, United Kingdom Purpose or Objective Radiotherapy for mediastinal lymphoma has evolved over the last decades with reductions in dose and field size, the advent of intensity modulated radiotherapy or volumetric modulated arc therapy, as well as daily image guidance (IGRT) which ensures the ability to accurately position the patient before each treatment. Also, the use of deep inspiration breath hold (DIBH) has provided a dosimetric benefit for mediastinal lymphoma patients with respect to sparing normal tissue. In this modern context, an assessment of the appropriate planning target volume (PTV) margins is required. Material and Methods 20 sequential patients with mediastinal lymphoma treated with radiotherapy at our hospital were selected retrospectively for analysis. Inclusion criteria were: treatement in DIBH and daily imaging available for analysis. Offline registration of cone beam CT (CBCT)

Anterior- Posterior

Superior- Inferior

Lateral

Type

of

uncertainty Systematic (mm) Contouring

3

3

3

Set-up

0.5

0.5

0.5

Random (mm) Set-up

3.7

2.7

2.5

Intrafraction

2

2

3

Resulting margin (mm)

10.5

10.0

10.3

Conclusion Including both systematic and random uncertainties, the resulting PTV margin was approximately 1 cm in all directions. As radiotherapy for mediastinal lymphoma has evolved from fixed fields with 2-dimensional planning and into the era of modern, highly conformal radiotherapy it is appropriate to consider all types of uncertainties when deciding the institutional PTV margins. PO-0734 Clinical outcome of Durie-Salmon Stage III multiple myeloma patients treated with radiotherapy S. Jeong 1 , S.H. Kim 2 , H.S. Jang 3 , J.H. Lee 2 1 Mokdong Hospital- Ewha Womans University, Radiation Oncology, Seoul, Korea Republic of 2 St.Vincent's Hospital- College of Medicine- the Catholic University of Korea, Radiation Oncology, Suwon, Korea Republic of 3 St.Mary's Hospital- College of Medicine- the Catholic University of Korea, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Radiotherapy is a very useful modality for palliation in multiple myeloma, especially in mass forming lesion in that size reduction and resolving skeletal mass effect of radiotherapy. We evaluated overall number and sites of radiotherapy from diagnosis to death and overall survival time from the first radiotherapy to death in multiple myeloma patients. For mass forming lesion, we evaluate association factors for response rate. Material and Methods We retrospectively reviewed medical records of patients who are treated with radiotherapy in our institutions