Abstract Book

ESTRO 37

S499

Material and Methods We developed an easy-to-use platform which enables simple and reliable recalculations of treatment plans using FLUKA. Starting from the export of the CT images to the voxel-phantom geometries, the Flair particle therapy framework allows now to export the entire set of RT DICOM files, including ROI structures, TPS based calculated doses and pencil beam scanning datasets. To better comply with the realistic irradiation settings, the framework exports into the FLUKA also the geometry or characteristic of the beam delivery system with a minimal user effort. In order to prove the reliability of our toolkit, we selected several proton cases from two different facilities - synchrotron and cyclotron based ones, which use two different TPSs. We recalculated 5 proton cases (2 chordoma cases, 1 head and neck and 2 phantom cases) for which we obtained information on physical/biological dose deposition simulating 1% of the planned beam intensity. Data were evaluated using DVH plots and presented with the graphical RTViewer comparison tool.

presents a compelling evidence that an additional independent dose re-calculation is essential for assuring treatment quality. Our study provides the MC particle therapy platform, which due to its simplicity and thoroughly validated FLUKA physical models, can enhance the popularity of the MC in the clinical environment for both research and QA purposes. Finally, this framework can be easily extended to other ion species and other than only physical dose scoring. multileaf collimator and variable aperture collimator in renal SBRT K. Morrison 1 , D. Henderson 1 , V. Khoo 1 , N. Van As 1 1 Royal Mardsen NHS Trust, Department of Clinical Oncology, London, United Kingdom Purpose or Objective SBRT is being investigated as a treatment alternative for patients with primary renal carcinoma unsuitable for surgery, which is the standard of care. The aim of this planning study was to compare CyberKnife® M6 System plans using the InCise TM Multileaf Collimator (MLC) with the Iris TM variable circular aperture collimator. Hypothesis: Dosimetrically equivalent plans can be achieved with MLC in comparison to Iris, with a reduction in estimated delivery time and total monitor units (MU). Material and Methods 15 renal cancer cases were selected (maximum tumour diameter of ≤6 cm and total kidney volume > 200 cc). Diagnostic CT imaging was used to contour CTV and OARs and a 5 mm CTV – PTV margin was applied. Images were imported to the MultiPlan® treatment planning system, where Iris and MLC plans were created for each case. Plans were setup for Synchrony respiratory motion management and fiducial tracking. A ray-tracing algorithm was used for dose calculation. The aim was to achieve ≥ 95% PTV coverage at a dose of 45 Gy in three fractions, prescribed to the 78 – 82 % isodose. Required dose constraints for dose limiting structures (kidney, small bowel, colon) are shown in Table 1 . The prescribed dose could be reduced in 3 Gy increments to a minimum of 36 Gy in order to meet constraints. The primary objective was to compare the proportion of plans achieving 45 Gy prescription dose. Secondary objectives were to compare coverage, conformality (nCI), OAR dose, estimated treatment time and total monitor units (MU). PO-0926 Comparison of CyberKnife

Results With several performed tests we proved the reliability and the usability of the developed particle therapy platform. Homogeneous phantom cases and proton chordoma patient cases showed a good agreement with the commissioned TPSs. No significant discrepancies were noticed, neither in the DVH plots, nor in the RTViewer dose deposition representation. As expected, for cases with more heterogeneous tissue structures (i.e. head and neck) especially in the areas with empty cavities discrepancies were non negligible - reaching up to 5-10% difference in dose-to-water deposition between MC and TPS for full plan simulations. In this study we aimed also to demonstrate an extended possibilities of the presented platform, thus we show an example (chordoma patient case) of the dose-weighted LET distribution, which can serve as a simplified indicator for the biological response.

Results The mean PTV volume was 44.7 cc (range 15.0 – 156.9 cc). Prescription dose of 45 Gy was achieved in 14 out of 15 MLC and IRIS plans. In one case, the dose was reduced to 42 Gy in both plans in order to meet constraints. Plans were equivalent in terms of coverage and conformality,

Conclusion Quantification and identification of the discrepancies, especially taking into consideration more complex cases,