ESTRO 2022 - Abstract Book

S1353

Abstract book

ESTRO 2022

Conclusion We have designed, fabricated and tested a high-resolution phantom for QA process. The proposed instrumented phantom can be used for quick PDD measurement or verification. It can also serve to study inhomogeneity effect on PDD. References: [1] Smilowitz, J.B., Das, I.J., Feygelman, V., Fraass, B.A., Kry, S.F., Marshall, I.R., Mihailidis, D.N., Ouhib, Z., Ritter, T., Snyder, M.G. and Fairobent, L. (2015), AAPM Medical Physics Practice Guideline 5.a.: Commissioning and QA of Treatment Planning Dose Calculations — Megavoltage Photon and Electron Beams . Journal of Applied Clinical Medical Physics, 16: 14- 34.

PO-1571 Proton therapy dose distributions around cardiac implant leads measured with 3D dosimeters and films

L. Valdetaro 1 , L. Bjerregaard Stick 2 , M. Krzysztof Sitarz 3 , L. Paul Muren 1 , P. Balling 4 , P. Sandegaard Skyt 3 , J. Breede Baltzer Petersen 5 , M. Fulgsang Jensen 3 1 Aarhus University, Department of Clinical Medicine, Danish Center for Particle Therapy, Aarhus, Denmark; 2 Aarhus University Hospital , Danish Center for Particle Therapy, Aarhus, Denmark; 3 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus, Denmark; 4 Aarhus University, Department of Physics and Astronomy, Interdisciplinary Nanoscience Center, Aarhus, Denmark; 5 Aarhus University Hospital, Medical Physics, Department of Oncology, Aarhus, Denmark Purpose or Objective Due to their proximity to lymph nodes, cardiac implantable electronic device leads can present a challenge to target coverage in proton therapy of breast cancer patients. Moreover, shortcomings in treatment planning dose calculations when modelling the interaction of proton beams with metal components can result in greater uncertainty in the delivered dose. The aim of this study was therefore to dosimetrically investigate the dose degradation caused by two types of leads with 3D radiochromic dosimeters and 2D gafchromic films. Materials and Methods Radiochromic dosimeters (5 × 5 × 7 cm 3 ) were fabricated from silicone, curing agent, chloroform and leucomalachite green (LMG). Before curing, a cylindrical insert with a 3 mm diameter was placed in the centre of each dosimeter, to fit the lead during irradiation. Leads of two different widths (Ø1.6 mm and Ø2.2 mm) were used. EBT3 gafchromic films (5 × 7 cm 2 ) were placed 1 cm above and 1 cm below the leads (see Fig 1). The entire setup was CT-scanned and imported to Eclipse (Varian Medical Systems) where two spot-scanning proton therapy plans were prepared using 2.5 or 7.5 cm thickness solid water (SW) build-ups, such that the leads were positioned at the spread-out Bragg peak. A 5 cm range shifter (water equivalent thickness of 5.7 cm) was used in both plans that also delivered 6 fractions of 2 Gy (RBE dose) to the region containing the lead. Following our previously established dosimetry protocols, gafchromic films were scanned 24 hours before and after irradiation with an Epson Expression Pro scanner while the radiochromic dosimeters were scanned 2 hours before and after irradiation using an optical CT scanner (Modus Medical) with 1000 projections over a 360° rotation. Subsequent data reconstruction for the 3D dosimeters was performed with 0.5 mm 3 voxel size.

Results