ESTRO 37 Abstract book

S1207

ESTRO 37

EP-2180 Total Skin Irradiation using helical tomotherapy: First experience A. Haraldsson 1,2 , J. Engleson 1 , S. Engelholm 1 , P.E. Enström 1 1 Skåne University Hospital, Department of haematology- oncology and radiation physics, Lund, Sweden 2 Lund university, Medical radiation physics, Lund, Sweden Purpose or Objective Mycosis fungoides is a cutaneous T cell lymphoma with low incidence but significantly higher prevalence due to the indolent nature of the disease. However, as the disease affects the skin, the quality of life for the patients affected is severely compromised. The current standard radiotherapy technique is total skin irradiation with electrons. As an alternative, we present total skin irradiation with helical tomotherapy (TTSI), the first treatment hitherto reported in Europe. Material and Methods The patient, a 62 year old male diagnosed with mycosis fungoides in 2003 had previously been treated with kV X- ray on several occasions and medicated with PUVA+methotrexate and retinoids. 12 Gy was prescribed to be delivered in 6 fractions over 30 days. The patient was immobilized in supine position using a large, whole body vacuum cushion and, thermoplastic mask. The patient was provided with a custom fit, neoprene diving suit of 7mm thickness to act as a bolus. CT was acquired in two sets; upper body head first and lower body feet first, with the two scans overlapping 10 cm at pelvis. The CTV extended from the skin surface to 5 mm into subcutaneous tissue, and the PTV was a 5 mm isotropic expansion of CTV. In-vivo dosimetry was performed using Gafchromic EBT3 film with FilmQAPro software. The patient setup was evaluated daily by recalculating the patient’s plan on the daily MVCT. The patient was monitored with weekly blood tests and clinical assessments.

Results The results, presented in table 1, show good target coverage apart from arms due to the patient’s width (54 cm). Beam on time for the treatment was 47 + 27 min with a total treatment time of 3 h per fraction. In-vivo dosimetry showed a median difference between TPS and film of 4% (SD:11%). Dose recalculated on daily MVCT is presented in figure 1. Weekly blood sample showed a transient decrease in white blood cell (WBC) (grade 4 according to CTCAE 4.0), neutrophils (grade 4) and platelets (grade 2) with full recovery within 1 month after treatment. The duration of the grade 4 toxicities regarding WBC (0.9x10e9) and neutrophils (0.4x10e9) lasted one week. The patient experienced grade 2 fatigue and grade 1 mouth dryness but both these symptoms were resolved 3 months after treatment. Follow up showed initial complete remission of disease with local in-field relapse after 5 months. Conclusion Treatment of TTSI is technically challenging but feasible, here showing good target coverage despite the patient’s size (187 cm, 100kg), with good agreement between planned and delivered dose. The largest difference is seen in extremities, where larger margins might be needed due to set-up uncertainties, especially outside the imaging field of view. Follow-up confirmed that the treatment affects bone marrow and should be given over an extended period of time. A large advantage of this technique is the possibility to assess the dose distribution, to give simultaneous integrated boost as well as avoid previously irradiated areas and organs at risks. EP-2181 Modeling and comparison the dosimetric impact of two couch model of iBEAM evo 415 in Monaco TPS R. Zhang 1 , J. Fleckenstein 2 1 Fourth Hospital of Hebei Medical University, Radiotherapy, Sijiazhuang- Hebei, China 2 University Medicineof Mannheim, radiation therapy and radio-oncology, Mannheim, Germany Purpose or Objective The aim of this study was to construct the uniform couch model (model A ED=0.25) and two components model (model B FD=0.5 and foam core=0.1) in the Monaco (Version 3.0) TPS for the iBEAM® evo Extension 415, and to assess which model can better quantified the couch transmission. Material and Methods The accuracy of each couches modelling was evaluated by comparing the measured and calculated attenuations in TPS with three phantom positions at A-B directions: on the left half (L), in the center (C) and on the right half (R) of the couch. The attenuation of the couch was evaluated by a 0.125cc semiflex ionization chamber, isocentrically placed in the center of a homogeneous