Program Information
Out-Of-Field Dose Measurement for Advanced Post-Mastectomy Radiotherapy Techniques
J Yoon1*, R Zhang1,2 , (1) Louisiana State University, Baton Rouge, LA, (2) Mary Bird Perkins Cancer Center, Baton Rouge, LA
Presentations
TU-L-GePD-TT-4 (Tuesday, August 1, 2017) 1:15 PM - 1:45 PM Room: Therapy ePoster Theater
Purpose: Normal tissue dose reconstruction is challenging for advanced post-mastectomy radiotherapy (PMRT) because these techniques increase the low dose clouds and the current commercial treatment planning systems (TPS) have limited dose calculation accuracy in the out-of-field (OF) dose areas. We aim to measure and model the OF radiation doses for various advanced PMRT techniques.
Methods: Various PMRT plans, including several volumetric modulated arc therapy (VMAT) plans (standard 6MV, flattening-filter-free (FFF) with 6 and 10 MV), mixed beam therapy with electron, intensity modulated radiotherapy (IMRT) and VMAT beams, 4-field IMRT and Tomotherapy, were generated for an anthropomorphic phantom using Pinnacle 9.8 and TomoTherapy Hi∙Art (for tomotherapy) TPSs. Thermoluminescence dosimeters (TLDs) were loaded in the anthropomorphic phantom. The plans were delivered by Elekta Versa HD and TomoTherapy. To correct over-response of TLDs in low dose region, additional energy-response correction factors, namely in-beam OF correction factor K(IBOF) and out-of-beam OF correction factor K(OBOF), were used. A simple analytical model was developed to predict OF dose as a function of distance from field edge for each PMRT technique.
Results: OBOF doses for VMAT plans showed similar trend,while IBOF doses were highly scattered and did not follow any obvious trend. For mixed beam therapy, the differences between IBOF and OBOF doses were less than those in VMAT plans due to the less dose contribution from VMAT beam. IMRT showed wider dose distribution than VMAT plans. Tomotherapy showed highest OF dose among all tested treatment techniques.
Conclusion: Based on our measurement, one can easily combine the measured OF dose here with in-field dose calculated by the local TPS to reconstruct organ doses for a specific PMRT patient if the same treatment apparatus and technique were used.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by National Cancer Institute Award 1 K22 CA204464-01, Louisiana State University (LSU) Faculty Research Grant and LSU Economic Development Award.
Contact Email: