Establishment of linear accelerator-based image guided radiotherapy for orthotopic 4T1 mouse mammary tumor model

Abstract

This study was conducted to assess the feasibility of image guided radiotherapy (IGRT) for orthotopic 4T1mouse mammary tumor using linear accelerator (LINAC). Eighteen Balb/C mice were inoculated with 4T1cells on left mammary fat pad and nine of them were irradiated using LINAC. Tumors, planning targetvolumes (PTV), bowels adjacent to tumors, bones and lungs were delineated on planning CT images. IGRT plans were generated to irradiate prescription dose to at least 90% of the PTV and then comparedwith conventional 2-dimensional plans with anterior-posterior and posterior-anterior beams with 5 mmmargins (2D AP/PA plan). Homemade dose-build-up-cradle was designed to encompass mouse bed forhomogeneous dose build up. To confirm the irradiated dose, tumor doses were measured using diodedetector placed on the surface of tumors. Plan comparison demonstrated equivalent doses to PTV whilesparing more doses to normal tissues including bowel (from 90.9% to 40.5%, median value of meandoses) and bone marrow (from 12.9% to 4.7%, median value of mean doses) than 2D AP/PA plan. Qualityassurance using diode detector confirmed that IGRT could deliver 95.3-105.3% of the planned doses toPTV. Tumors grew 505.2-1185.8% (mean 873.3%) in the control group and 436.1-771.8% (mean 615.5%)in the irradiated group. These results demonstrate that LINAC-based IGRT provides a reliable approachwith accurate dose delivery in the radiobiological study for orthotropic tumor model maintaining tumormicroenvironment.