ESTRO 37 Abstract book

S1204

ESTRO 37

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 For historic comparison, a total of 10 patients with 19 metastases were identified with a mean PTV volume of 4.7 cm 3 (range, 0.6-12.5cm 3 ). Prescribed dose ranged from 14.25Gy to 20Gy delivered in a single fraction. After implementation of the QA program 30 patients over an 18month period were evaluated. These had 50 metastases, with a mean PTV volume of 3.9cm 3 (range , 0.4-12.7 cm 3 ) and receiving a single fraction of radiosurgery (16Gy – 20Gy dose range). There was an observed difference in both the RTOG prescription isodose to target volume ratio (PITV) and Paddick conformity indices (CI pad ), showing a better conformity after the implementation of the program (see table 1). When assessing individual lesions for deviation to conformity indices (see Table 2), the PITV was assessed before and after QA program implementation as 58% vs 98%(acceptable), 21% vs 2%(minor deviation), 21% vs 0 (major deviation). For the CIpad 5% vs 74%(acceptable) and 95% vs 26%(deviation). The dose to normal brain was also lower with the V5Gy(%) normal brain historic vs post-implementation being 13.1(± 8.4) vs 8.2(± 7.4) and the V12Gy(%) being 1.8(± 1.4) vs 1.5(± 0.8).

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 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

Conclusion Implementation of a multi-disciplinary dosimetric QA program with scorecard early in the planning process showed a significant improvement in RS plan quality with improvements in plan conformity and decreased dose to normal brain.