Program Information

Efficient Verification Method for Modulated Electron Radiotherapy Treatment Plans

D Henzen¹*, C Chatelain¹ , P Manser¹ , D Frei¹ , W Volken¹ , H Neuenschwander² , A Joosten¹ , K Loessl¹ , D M Aebersold¹ , M K Fix¹ , (1)Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern, Switzerland (2)Clinic for Radiation-Oncology, Lindenhofspital Bern, Switzerland

Presentations

SU-E-T-148 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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 0.2x0.2x0.2 cmÂ³, 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.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Varian Medical Systems.

Contact Email: