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  5. Validation of Total Skin Irradiation Using Two Monte Carlo Systems

Validation of Total Skin Irradiation Using Two Monte Carlo Systems

W Tseng1*, R Li2 , Q Wu3 , D Sawkey4 , (1) Duke University Medical Center, Durham, NC, (2) Duke University Medical Center, Durham, NC, (3) Duke University Medical Center, Durham, NC, (4) Varian Medical Systems, Palo Alto, CA

Presentations

(Monday, 7/15/2019) 3:45 PM - 4:15 PM

Room: Exhibit Hall | Forum 1

Purpose: Stand-up technique is the standard procedure for total skin irradiation (TSI) in our clinic. This study aims to validate the commissioning dosimetric data using two Monte Carlo (MC) systems for the standard TSI technique.

Methods: MC simulations were performed with EGSnrc and VirtuaLinac. EGSnrc has been the standard MC system used in radiotherapy field, but it is not common to be used for simulations of particles transport at an extended source to skin distance (SSD). VirtuaLinac is a web-based application based on GEANT4 from Varian. Beam parameters of VirtuaLinac were specified by an XML file and API.py to control the gantry rotation and MU delivery. Dual beam with gantry angle of ±19º and jaws setting of 36x36 cm² were used. For each field/direction at treatment SSD, the percent depth dose (PDD), profiles at dmax, absolute dosimetric output on a water phantom and composite dose distribution on a 30 cm diameter cylindrical phantom were studied and compared with the commissioning measurements.

Results: For one dual beam, the average difference in profiles between EGSnrc/VirtuaLinac and measurement were -5.5%/0.9%. Both dmax (1.1 cm) and Râ‚…â‚€ (2.1 cm) in PDD of both MC systems agreed with measurements within 1 mm. X-ray contamination at 15 cm depth was less than 1% for EGSnrc/VirtuaLinac (0.5%/0.6%) and the measurement (0.8%). The output was -2.4%/-3.2% for EGSnrc/VirtuaLinac, compared with measurements. B-factor was 3.1 for both MC systems and measurement. For composite fields, the dmax shifted toward the surface (0.15 cm). The maximum x-ray contamination was 1.2 %/1.3% for EGSnrc/VirtuaLinac, compared with measurements (2%).

Conclusion: The results from both MC systems generally agree with the measurement. In addition to these measurable quantities, MC simulations can provide further information such as the full dose distribution of the patient phantom, thus become the foundation for investigations in future technique optimizations.

Keywords

Monte Carlo, Total Skin Irradiation, Electron Therapy

Taxonomy

TH- External beam- electrons: Monte Carlo dosimetry

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