Abstract Book

S1204

ESTRO 37

Two different coefficients were introduced: DCpre and DCpost for comparison between CT and pre- and post- treatment CBCT images, respectively. The average DCpre is representative of the inter-fraction reproducibility whereas DCpost of the intra-fraction reproducibility The method was validated using CT and CBCT images of IMRT thorax phantom (CIRS Inc, Norfolk, USA). The method was then applied to 2 breast cancer and 2 Hodgkin’s Lymphoma (LH) patients who received VMAT treatments by means of a Agility linear accelerator (Elekta Instruments AB, Stockholm) under HFV. For breast patients VLung referred to the ipsi-lateral lung while for LH patients it encompassed both lungs. Pre-treatment CBCT were performed on daily basis (25 and 15 fractions for breast and LH, respectively) while post-treatment CBCT on weekly basis. The same method was also applied to 2 control patients who received breast irradiation under Active Breath Controlled (ABC) System (Elekta Instruments AB, Stockholm) as well as to 2 LH patients in free-breathing conditions. Results In-phantom evaluation returned a DCpre of 0.989±0.010 confirming the reliability of the thresholding method applied for lung segmentation. For breast patients, mean DCpre and DCpost were 0.970±0.152 and 0.975±0.023, respectively (see Figure 1). For control ABC patients, mean DCpre and DCpost were 0.976±0.090 and 0.978±0.025, respectively. For LH patients, mean DCpre and DCpost were 0.948±0.035 and 0.951±0.041, respectively. For free-breathing control patients DCpre and DCpost were 0.951±0.041 and 0.942±0.037. No statistically significant differences were observed between case and control groups (p<0.005). Conclusion Thresholding lung method may be considered as appropriate to assess inter- and intra-fraction lung reproducibility under HFV. According to our results, HFV system is able to provide a degree of reproducibility similar to existing breathhold devices. It could therefore be used as an alternative to free-breathing irradiation techniques with a potential improvement of OARs dose sparing. 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