Abstract Book

S1201

ESTRO 37

EP-2174 Fabrication of three-dimensional printed customized bolus for the irregular shape of the outer ear M. Baeza Trujillo 1 , G. Gomez 2 , J.C. Mateos 3 , J.A. Rivas 2 , S. Velazquez 3 , J. Simon 3 , D. Mesta Ortega 4 , M.A. Flores Carrión 4 , M.J. Ortiz Gordillo 4 , T. Gómez-Cía 5 , J.L. Lopez Guerra 4 1 Hospital Universitario Virgen del Rocío, Servicio de Radiofísica Hospitalaria, Seville, Spain 2 University Hospital Virgen del Rocio, Group of Technological Innovation, Seville, Spain 3 University Hospital Virgen del Rocio, Radiation Physics, Seville, Spain 4 University Hospital Virgen del Rocio, Radiation Oncology, Seville, Spain 5 University Hospital Virgen del Rocio, Plastic Surgery, Seville, Spain Purpose or Objective The skin-sparing effect of megavoltage-photon beams in radiotherapy reduces the target coverage of superficial tumours. Consequently, a bolus is widely used to enhance the target coverage for superficial targets. Commercial bolus cannot easily be applied on irregular surfaces. A three-dimensional (3D)-printed customized bolus (3D bolus) can be used for radiotherapy application to irregular surfaces. This study examines the possibility of the fabrication of a 3D customized bolus for an irregular surface. Material and Methods We fabricated a bolus using a computed tomography (CT) scanner and evaluated its efficacy. The head of an Alderson Rando phantom was scanned with a CT scanner. A 3D bolus of 5-mm thickness designed to fit onto the ear was printed with the use of a Stratasys Objet260 Connex3 with the use of PolyJet technology (Stratasys Ltd., Eden Prairie, MN, USA) with the malleable `rubber-like' printing material, Agilus (Stratasys Ltd.). CT simulations (Figure 1) of the Rando phantom with and without the 3D and a commercial high density bolus (eXaSkin©) were performed to evaluate the dosimetric properties of the 3D bolus. The ear was delineated as the target (15 cc). Radiotherapy plans with two beams were generated in the Oncentra Masterplan v4.1 radiotherapy treatment planning system with the use of the enhanced collapse cone algorithm. The prescription dose was normalized for 95% of the prescribed dose to cover 90% of the target volume in the plan without bolus. The plans with the bolus were normalized to ensure that the target dose lie within 95% and 107% of the prescription dose. The following dosimetric parameters were estimated for all cases: maximal dose (Dmax), mean dose (Dmean), minimum dose (Dmin), V95% (volume receiving at least 95% of the prescription dose), V90%, and homogeneity index (HI) proposed in ICRU-83.

ear anatomy, there was some air gap between the bolus and the phantom surface with both the commercial and the 3D bolus. Figure 1 shows the isodose lines corresponding to the plans with and without the bolus. We observe that the target coverage is better with the bolus and it is similar between the commercial and the 3D bolus. Table 1 summarizes the relevant dosimetric parameters for the three plans.

Conclusion We successfully fabricated a customized 3D bolus for an irregular surface using a CT scanner. The fabrication process was simple and fast. The bolus, made of the malleable material Agilus, suitably fitted the surface, and the surface dose was sufficiently enhanced. Thus, we believe that the use of malleable materials can be seriously considered for the fabrication of customized boluses. EP-2175 Improvement in radiosurgical plan dosimetry with implementation of a quality assurance program. A.L. Salkeld 1,2 , W. Wang 1 , N. Nahar 1 , E.K.C. Hau 1 , N. Nahar 1 , J.R. Sykes 2,3 , T. Moodie 1 , D.I. Thwaites 1,2 1 Sydney West Radiation Oncology Network, Radiation Oncology, Westmead, Australia 2 The University of Sydney, Institute of Medical Physics - School of Physics, Sydney, Australia 3 Sydney West Radiation Oncology Network, Radiation Oncology, Blacktown, Australia Purpose or Objective Quality assurance (QA) check points are vital to ensure high quality treatment of brain metastases with radiosurgery (RS). The small margins used require rigorous attention to all clinical and technical steps contributing to treatment quality. Poor quality radiotherapy has been reported to impact overall survival and increase treatment failure. In 2015, an internal audit of RS plans demonstrated that minimal dosimetric QA parameters were being formally reported during RS planning for brain metastases. The purpose of this 18 month study was to determine if implementation of a dosimetric QA checkpoint, with joint clinician/physicist/radiation therapist review and using a dosimetric QA program early in the planning process led to improvement in RS plan quality. Material and Methods A committee comprising a radiation oncologist, physicist and radiation therapist performed a literature review of RS practice standards and recommended reporting of conformity indices (see table 1), as well as organs at risk (including normal brain). A scorecard / template was developed indicating each plan’s compliance with QA measures (acceptable/minor deviation/major deviation and this was built into the work-flow to streamline the process. The plan and scorecard were assessed by the planner during the planning process and reviewed by the multi-disciplinary QA team prior to plan approval. 12 months of RS plans (January 2014 to December 2014) for brain metastases were reviewed as a historical comparator. The QA program was introduced in January 2015. Fractionated radiosurgery and tumour resection cavity lesions were excluded from both groups.

Results We fabricated the customized 3D bolus, and further, a CT simulation indicated an acceptable fit of the 3D bolus to the ear (Figure 1). Due to the irregular shape of the outer