Program Information
Dose Distribution Reconstruction for Respiratory Controlled Radiosurgery
W Osewski , L Dolla , K Slosarek*, Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice, Poland
Presentations
SU-I-GPD-J-13 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: Now days VMAT technique is commonly used for radiosurgery. High fraction doses requires high precision. Standard dose distribution verification methods are problematic because of the small size of treatment fields. Additionally respiratory controlled VMAT technique usage causes difficulties because of not continues radiation delivery. Dose distribution can be distorted by beam interruptions. To solve this problem new dose distribution reconstruction method, based on data from Trajectory Log Files (TLF), was developed.
Methods: Homemade software DDcon combines TLF files with RTPlan dicom file, exported form Eclipse TPS. In new RTPlan dicom file planned leaves positon, gantry angles and MU values were converted to actual one from TLF files. Recalculation of the dose, using same algorithm as it was done during treatment plan preparation, gives reconstructed dose distribution. The example of the dose reconstruction for gated VMAT technique will be presented on the example of a patient with lung tumour were total planned dose was 30 Gy delivered in three 10 Gy fractions.
Results: During treatment plan verification measured dose distribution was compared with calculated one using gamma index (3%, 2 mm) and it was less than one in 97.4% of analyzed dose distribution area. TLFs were also used to reconstruct QA plan and all treatment fractions. Differences between calculated dose distribution and reconstructed for QA plan were small (gamma index(3%,2mm) was 100%). Summed reconstructed dose distribution for all fractions was compared with: calculated dose distribution where gamma index(3%,2mm) was 100% and with measured dose distribution where gamma index (3%,2mm) was 97.7%.
Conclusion: Developed method is consistent with phantom measurements but in some cases it is even more sensitive and precise. When standard methods fails then presented dose distribution reconstruction method is very helpful in acceptance process.
Funding Support, Disclosures, and Conflict of Interest: K. Slosarek - Scientific Consultant - Varian Medical Systems Poland
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