Abstract Book

S1224

ESTRO 37

EP-2340 Using 3D printer technology to advance and optimize the use of bolus in the Radiotherapy workflow C. Malone 1 1 St.Luke's Radiation Oncology Network, Physics, Dublin, Ireland Purpose or Objective Bolus is commonly used in Radiotherapy to escalate the dose to the skin surface for the treatment of shallow tumours and to improve dose uniformity in the region of irregular body contours. There are many different commercial solutions currently available, each of which has their own disadvantages as an all-round bolus solution. First, sheets of uniform thickness bolus often result in air gaps between the bolus and skin surface, degrading the dosimetric build-up effect. Second, wet gauze, which is highly user dependent and is difficult to place during treatment. Finally, mouldable bolus such as wax, thermoplastic sheets or thermoplastic pellets, can be difficult to mould accurately to the desired thickness. One solution which does not have these shortcomings is 3D printed bolus, which can be generated directly from a contoured structure drawn on the patient’s CT dataset and then printed accurately using readily available 3D printing technology. Material and Methods Recent advancements in 3D printing technology have resulted in printer technology and materials that can be easily integrated into the radiotherapy workflow. In our clinic, we have opted to use the 3DBolus system which integrates with our existing TPS. 3DBolus uses the contours generated during the planning process and leverages the TPS dose calculation algorithms to create custom bolus that represents the planned bolus dose distribution accurately. The generated bolus structures are printed using an AirWolf Axiom 20 3D printer with a flexible filament called Ninjaflex. The 3D Printed bolus was evaluated using CBCT imaging over a number of fractions to assess fit throughout the patient’s treatment. Results 3D printed bolus was found to conform well to patient anatomy for a variety of treatment sites when compared to existing bolus methods used in our clinic. In particular, Head and Neck, vulva, and breast treatment sites benefited from the 3D printed bolus approach. Patient feedback confirmed the 3D printed bolus was comfortable for a variety of sensitive treatment sites. For sites of tumour response or change in anatomy, a new bolus structure could be created using the patients CBCT imaging and printed for the next patient fraction. Dosimetric comparisons between traditional bolus and 3D printed bolus using patient imaging found that using 3D printed bolus provides a more accurate representation of the planned dose distribution. Conclusion Our experience of integrating 3D printed bolus into our radiotherapy workflow found that 3D printed bolus offers four main advantages over traditional bolus methods. First, it conforms to difficult patient anatomy where traditional bolus would typically fail. Second, it can be quickly recreated or adapted if required using patient’s treatment imaging. Third, it offers the clinicians a consistent and accurate representation of the planned dose distribution on the treatment unit. Finally, it was found to be more efficient on the treatment units compared to current bolus techniques.

EP-2341 A Retrospective comparison of two immobilization systems for soft-tissue sarcomas of extremities M.M.O.M. Aly 1,2 , V.M. Gurusamy 1 , A.M. Maklad 1,3 , M. Tunio 1 , M. Shuja 1 , R. Mohammed 1 , A.A. AlHazineh 1 , Y. Bayoumi 1,4 1 King Fahad Medical City, Radiation Oncology Department, Riyadh, Saudi Arabia 2 South Egypt Cancer Institute- Assiut University, Radiotherapy and Nuclear Medicine, Assiut, Egypt 3 Faculty of Medicine- Sohag University, Department of Clinical Oncology, Sohag, Egypt 4 National Cancer Institute NCI- Cairo University, Department of Radiotherapy and Nuclear Medicine, Cairo, Egypt Purpose or Objective Our aim was to compare Vac-Lok™ and thermoplastic casts differences in interfraction set-up reproducibility in patients treated with three-dimensional conformal radiotherapy (3DCRT) for soft tissue sarcomas (STS) of extremities. Material and Methods Retrospective review of patients with STS of extremities treated with 3DCRT was performed. Immobilization was performed for 14 patients (Vac-LOKTM= 7; thermoplastic cast = 7). A total of 307 measurements of set-up errors in each direction (vertical, longitudinal, lateral and