ESTRO 2022 - Abstract Book

S1329

Abstract book

ESTRO 2022

Conclusion A preliminary dosimetric characterization of PLA 3D-printed boluses was done and encouraging results were found for the use of 3D printed boluses in such a field. Optimization of parameters to obtain optimal values of infill pattern and density should be investigated to better correlate the entity of the maximum dose shift and to validate a substitute to the conventional bolus. Future perspectives include to test different materials and free-form shapes which can better adapt to the patient’s anatomy.

PO-1547 End to end tests for Volumetric Modulated Arc Therapy using a new modular phantom.

M.T. García Hernández 1 , A. Vicedo González 2 , R. García Mollá 3 , D. Planes Meseger 3 , B. Bordería Navarro 3 , P. Calatayud Cuesta 4 , M.L. Alcaraz Lozano 3 1 Consorcio Hospital General Universitario de Valencia, Radiofísica y Protección Radiológica, Valencia, Spain; 2 Consorcio Hospital General Universitario de Valencia, Servicio de Radiofísca y Protección Radiológica, Valencia, Spain; 3 Consorcio Hospital General Universitario de Valencia, Servicio de Radiofísica y Protección Radiológica, Valencia, Spain; 4 Consorcio Hospital General Universitaria de Valencia, Servicio de Radiofísica y Protección Radiológica, Valencia, Spain Purpose or Objective The increased complexity of the radiation therapy process makes essential to implement tests to commission the whole procedure, from de CT to the treatment administration in the radiation unit. In this work, we use a new modular phantom (RUBY phantom, PTW Freiburg, Germany) for the end to end testing of several VMAT irradiations. Materials and Methods End to end testing was made for different Vmat treatments: A non-coplanar cranial stereotactic treatment of one small centred lesion (volume of 0.5 cc), a cranial coplanar and non-coplanar stereotactic treatment for three lesions and a prostate SBRT. The main modules of the RUBY phantom were used for cranial (head phantom) and prostate (body phantom) treatments, combined with different inserts to check point dose and dose distributions, IGRT, heterogeneity corrections and volume calculations. For point dose measurements, an insert consisting of three detector positions that correspond to the centres of three assumed metastases was used, (MultiMet insert) with a PinPoint 3D ionization chamber (PTW Freiburg, Germany). MultiMet also contains three cylindrical volumes (made of bone equivalent material) positioned inside at different spatial angles (visible in planar MV, planar KV and CBCT images), to enable image registration with the reference data set. For dose distribution measurements, an insert that accommodates a film was used (Film insert) with radiochromic film EBT3 and Radiochromic software (radiochromic.com). To check heterogeneity corrections and volume calculations of treatment planning system (TPS), an insert with non-homogeneities (consisting of cylinders of different sizes around a detector, interrupted at different points to enable image registration) was used. Planning CT was acquired in a GE Discovery RT with 120 kV and 1.25mm slice thickness, the TPS used was Monaco (V.5.51) and the plans were irradiated in a VERSA Agility Linac (Elekta) with an energy of 6 MV. IGRT (kV/kV and CBCT) was checked positioning the phantom bodies using the engraved visible lines that indicate defined translational and rotational shifts in all three spatial directions. Results For IGRT using CBCT, differences between experimental and known shifts were smaller or equal than 0.5 mm and 0.5º. Higher differences were found when using Mosaiq (Elekta) fusion software (instead of Elekta-XVI software), due to rounding. Differences were lower or equal than 1.5 mm when using kV/kV IGRT. Differences in volume calculations (between TPS and Ruby phantom specifications) for heterogeneous inserts are lower than 1.5 %. Table 1 shows the results for point dose and dose distribution measurements.