ESTRO 36 Abstract Book

S954 ESTRO 36 _______________________________________________________________________________________________

comparison of planned to delivered plans for all TG-119 targets for IMRT and VMAT deliveries are shown in Figures 1 and 2 below, and for the two MLC systems. The prototype MLC system produced higher passing rates for both IMRT and VMAT than the TB MLC system for the various test plans. In addition, the prototype MLC system performs equally well for IMRT and VMAT, whereas the TB MLC is less optimum for VMAT delivery compared to IMRT (Fig. 1 and Fig. 2).

phantom was covered with a 7 mm thick wet suit made of Neoprene (AquaLung) and CT scanned in two sets; from vertex to thigh and from toes to hip. The CTV was defined as skin with 5mm depth, with PTV as a 7 mm expansion. An optimization bolus was added from the body and 12 mm expansion, defined as mass density 1.0 g/cm 3 . The prescribed dose was 12 Gy delivered in 6 fractions. The dose planning was aimed to keep D 95% > 95% to PTV and minimizing dose to organs at risk, which was defined as the rest of the body. An optimization structure was used to create a tangential irradiation of the skin, minimizing the dose to normal tissue. We tested the bolus effect of Neoprene with Gafchromic EBT3 film by irradiating slabs of 7mm, dry and soaked in water. To verify skin doses, the phantom with wet suit was irradiated with several 2x2 cm 2 slabs of film taped to the body. The film were evaluated at least 24 hours after irradiation. Corresponding detector array measurements (Delta4, Scandidos) were done and evaluated with gamma analysis. Further, a robustness test was done by moving the phantom 10 mm in the x, y and z directions, to evaluate the effect of mispositioning. Results Results of planning and robustness tests are presented in table 1. Measured data fit to depth dose data yields a dose maximum at 28 mm for Neoprene. Hence, 7 mm is equivalent to 3 mm thick water bolus and lightly soaked Neoprene adds another 1.2 mm thickness of water. Delta4 gamma analysis with 2 mm and 3%, global dose, is clinical acceptable with regards to deliverability (M = 93%, SD = 3%). The verification of 27 film slabs for skin dose gave an average difference from TPS dose of 4% (SD = 3%), figure 1.

Conclusion The TG-119 test plans were performed on a prototype MLC system in comparison to the well-understood TB Millennium MLC. Our investigation showed, in the context of TG-119, this prototype MLC performs well for both IMRT and VMAT plans. 1 Ezzel G., et al., 'IMRT commissioning: Multiple institution planning and dosimetry comparisons, a report from AAPM Task Group 119.” Med. Phys. 36 :5359-5373 (2009). EP-1735 Total skin irradiation with helical Tomotherapy: Planning and dosimetry feasibility aspects A. Haraldsson 1 , P. Engström 1 1 Skåne University Hospital, Radiation physics, Lund, Sweden Purpose or Objective Mycosis fungoides (MF) is a lymhpatic disease that attacks the skin. The primary treatment for treating MF is total skin electron therapy (TSET). The procedure is technically challenging both in terms of dosimetry and treatment delivery. Helical TomoTherapy (HT) is due to its design especially advantageous when irradiating very long and complex targets. In this study we have explored the possibility of employing HT in the treatment of total skin irradiation (TSI). Material and Methods We used an anthropomorphic whole body phantom (PBU- 60 Kyoto Kaguka). The phantom was immobilized with whole body vacuum bag, a five-point open head net mask fixated to the couch and an individual neck rest. The

Conclusion The difference of measured dose compared to TPS, for both film and Delta4 dosimetry is larger than most types of targets treated with HT which is to be expected considering the technique and size of target. The deliverability is within limit of our clinic action levels (gamma pass rate < 90%) and neoprene is feasible as bolus. The benefits, in comparison with reported electron treatments, are target homogeneity and target coverage with good immobilization and complete irradiation with two positions. The higher dose to organs at risk than reported with electrons needs to be addressed if acceptable with regards to toxicity.