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SU‐E‐T‐148: Efficient Verification Method for Modulated Electron Radiotherapy Treatment Plans
Author(s) -
Henzen D,
Chatelain C,
Manser P,
Frei D,
Volken W,
Neuenschwander H,
Joosten A,
Loessl K,
Aebersold D M,
Fix M K
Publication year - 2014
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.4888478
Subject(s) - imaging phantom , quality assurance , monte carlo method , computer science , voxel , pentium , dosimetry , nuclear medicine , medical imaging , photon , radiation treatment planning , inverse , medical physics , physics , radiation therapy , mathematics , optics , artificial intelligence , statistics , medicine , external quality assessment , pathology , geometry , parallel computing
Purpose: For shallow tumors, modulated electron radiotherapy (MERT) promises a reduction of dose to distal organs at risk. At our institution a framework was developed in order to create treatment plans for MERT employing both forward and inverse optimization. In this work, an efficient quality assurance (QA) process is established. Methods: Treatment plans for three different tumor sites were created using an inverse optimization. These plans consist of 6–12 segments and energies between 6 and 18 MeV. An already established QA process for photon IMRT plans is now extended to additionally handle MERT plans. First, the dose distributions are calculated in a homogenous water phantom. For this task a dedicated Monte Carlo (MC) framework for MERT is used. Second, the segments are applied on a stand‐alone amorphous silicon electronic portal imaging device (EPID) using a source‐to‐surface distance of 70 cm. This device was calibrated for electron beams in a previous work. An in‐house developed analysis software, is then utilized for comparisons and evaluation of the measured and calculated dose distributions. Results: For all three plans the calculated dose distributions agree well with the measured ones. Using a 2D gamma comparison (2% of dose max/2 mm and 10% dose threshold) passing rates >98% are achieved. The dose calculation for each plan on the water phantom, using voxels of 0.2×0.2×0.2 cm 3 , takes at maximum 30 min on a single core Pentium 2.66 GHz system with 6 GB RAM, to reach a statistical uncertainty of 2% (1 std. dev.). Conclusion: An already established QA procedure for IMRT photon plans was applied for MERT. The dedicated MC framework and the use of EPID measurements allow an efficient QA procedure in a clinical environment. This work was supported by Varian Medical Systems.