Commissioning of Elekta 6MV FFF Versa HD and Pinnacle Poster No.: R-0044 Congress: Type: Authors: Keywords: DOI: 2014 CSM Scientific Exhibit L. Bendall, I. Patel, N. McGrath, C. Rowbottom; MANCHESTER/ UK Radiotherapy techniques, VMAT and Tomotherapy, Physics, Radiation therapy / Oncology, CT, Radiation physics, Oncology 10.1594/ranzcr2014/R-0044 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply RANZCR/AIR/ACPSEM's endorsement, sponsorship or recommendation of the third party, information, product or service. RANZCR/AIR/ ACPSEM is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold RANZCR/AIR/ACPSEM harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies,.ppt slideshows,.doc documents and any other multimedia files are not available in the pdf version of presentations. Page 1 of 8
Aim To commission the first 6MV FFF beam within Pinnacle 9.6 at The Christie, Manchester, UK. Methods and materials Linac matched to manufacturer "golden dataset" A 3D water tank with dimensions 50cmx50cmx50cm was used with Farmer chambers with vented sensitive volumes of 0.125cm 3 (for fields #10x10cm 2 ) and 0.015cm 3 (for fields #10x10cm 2 ) Data was collected across range of field sizes 2x2-40x40cm 2, including Open field profiles (Figure 1) Percentage depth doses (Figure 2) Output factors Tissue Standard Ratios (Tissue Phantom Ratio normalised to standard set up; 10x10cm field, 10cm deep, 90cm FSD) cgy-mu factor For Pinnacle model, we started with a conventional flattened beam model previously produced at The Christie for the same linac and adjusted (in order): Arbitrary profile Energy spectrum (Figure 3) Small change to build up (electron contamination) Off-axis softening factor set to zero MLC and jaw transmission reduced FFF flag updated Maximum dose rate increased to 1500MU/min Model validation measurements Chamber measurements, EDR2 film and Delta 4 used for model validation All Pinnacle calculations made with Collapsed Cone Convolution algorithm, with a dose grid resolution of 1mm. Page 2 of 8
Tissue Standard Ratios; measured compared to calculated in Pinnacle. Test fields including those listed in Table 1. Point doses for test fields were measured in a water phantom and compared to Pinnacle calculated doses. Test fields were delivered to film and compared to Pinnacle fluences Clinical plan verification 4 field brick dose measurements, off-axis, various depths etc IMRT plans - fluence and dose point comparisons Images for this section: Fig. 1: 40x40cm^2 profiles at varying depths Page 3 of 8
Fig. 2: Comparison of measured Percentage Depth Doses for 6MV and 6MVFFF Page 4 of 8
Fig. 3: Comparison of 6MV and 6MVFFF modelled energy spectrum Fig. 4: Test fields used and the parameters they verify Page 5 of 8
Results A model was produced in Pinnacle for use with the 6MVFFF beam. Generally good agreement was seen between modelled and measured data, an example can be seen in Figure 5 and Table 2. The maximum difference between calculated (Pinnacle) and measured TSRs over a range of areas (16-900cm 2 ) and depths (1.6-20cm) was found to be <1%. All model validation measurements were within acceptable values. The department is currently working on implementing Lung SABR VMAT treatments with 6MVFFF. Images for this section: Fig. 5: Bar test results for 6MVFFF at 10cm deep Page 6 of 8
Fig. 6: Bar test comparison data measured vs. calculated in Pinnacle Page 7 of 8
Conclusion The 6MVFFF model was successfully produced and commissioned. The introduction of FFF treatment delivery into clinical use at The Christie will include a change in technique from conventional 11-field Lung SABR planning with 6MV to Lung SABR VMAT planning with 6MVFFF. The work required to introduce the new technique is currently in progress. Further work may involve the commissioning of paediatric treatment sites and 10MVFFF. Personal information L. Bendall worked at The Christie NHS Foundation Trust, Manchester, UK, where this work was undertaken, until the end of June 2014. She now works with the Institute of Medical Physics, University of Sydney, the Crown Princess Mary Cancer Care Centre, Westmead Hospital, and Nepean Cancer Centre, Nepean Hospital. References. Page 8 of 8