ESTRO 36 Abstract Book

S787 ESTRO 36 2017 _______________________________________________________________________________________________

3 Kangbuk Samsung Hopital, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Tissue equivalent material commonly used in the electron radiation therapy was developed its own by using a 3- dimensional printer (3DP). We fabricated a customized bolus using a 3DP and evaluated for usefulness and accuracy of the Customized Bolus. Material and Methods Treatment with an electron beam 20MeV according to the virtual Clinical Target Volume (CTV) and Organ at Risk (OAR) planed with a treatment plan system (TPS). The 3D printed customized bolus was then fabricated Bolus A, B and C, respectively, and its quality and clinical feasibility were evaluated by visual inspection and by assessing dosimetric parameters such as Dose Volume Histogr(DVH), D max , D min , D mean , V 90% , and V 80% . Test electron field was measured using Gafchromic TM EBT3 film. And then was scanned by using a film scanner and compared with TPS data by applying Gamma (γ) analysis to verify their geometric accuracy. Results In all cases, the CTV volume is encompassed within 90% of the prescribed dose 3Gy. There was a difference in the CTV volume, D max up to 0.12Gy, D min up to 0.09Gy, D mean up to 0.12Gy. In the OAR volume, D max up to 0.29Gy, D min up to 1.24Gy, D mean up to 0.66Gy. The dose distribution difference between the measured and TPS dose was within 3%/3mm criteria with Gamma evaluation for EBT3 film. The pass rate for the test were 92.46%, 95.23%, 98.41% for Bolus A, B and C, respectively. It showed a more than 90% pass rate.

EP-1489 Effect of the thermoplastic mask on patient skin dose in tomotherapy V. Ravaglia 1 , A. Giuliano 2 1 San Luca Hospital, Medical Physics, Lucca, Italy 2 Istituto Nazionale di Fisica Nucleare INFN- Pisa, Pisa, Pisa, Italy Purpose or Objective The Treatment Planning Systems (TPS) do not accurately model skin dose, and several studies in vivo have demonstrated that the TPS overestimates skin dose in tomotherapy treatments. The bolus effect due to thermoplastic masks, which are commonly used in Tomotherapy head & neck (H&N) treatments, has sometimes been reported in literature. The aim of this study was to report results of in vivo measurements of skin dose in tomotherapy using EBT3 Gafchromic films with and without thermoplastic mask. Material and Methods Surface dose measurements were performed with the application of EBT3 pieces of size 2x2 cm 2 . Films were read with a flatbed scanner Epson 10000XL and images were analyzed using the red channel calibration. Preliminarily, reproducibility of surface dose measurements was assessed on Cheese phantom, then the thermoplastic mask effect was investigated using fine, normal and coarse calculation dose grids on phantom (see Figure 1). Skin doses were measured in vivo with the application of radiochromic film pieces directly on the skin of patients or in the inner side of thermoplastic mask, if used during the treatment. The target lesions included H&N, brain and sarcoma. For each patient films were located in 1 to 3 reproducible points and measurements were repeated on average for three fractions. Measured doses were compared with doses calculated with the TPS using fine grid.

Conclusion In this study, we fabricated a customized starchy bolus in powdered form using a 3DP to dose build up and evaluated for usefulness and accuracy of the Customized Bolus. The result showed that 3D printed customized bolus could significantly improve the dose homogeneity in the CTV and reduce the dose in the OAR for patients treated with electron therapy effective in clinical trials.

Results