Monte Carlo-based software for 3D personalized dose calculations in image-guided radiotherapy.

Abstract

Image-guided radiotherapy (IGRT) involves frequent in-room imaging sessions contributing to additional patient irradiation. The present work provided patient-specific dosimetric data related to different imaging protocols and anatomical sites. We developed a Monte Carlo based software able to calculate 3D personalized dose distributions for five imaging devices delivering kV-CBCT (Elekta and Varian linacs), MV-CT (Tomotherapy machines) and 2D-kV stereoscopic images from BrainLab and Accuray. Our study reported the dose distributions calculated for pelvis, head and neck and breast cases based on dose volume histograms for several organs at risk. 2D-kV imaging provided the minimum dose with less than 1mGy per image pair. For a single kV-CBCT and MV-CT, median dose to organs were respectively around 30mGy and 15mGy for the pelvis, around 7mGy and 10mGy for the head and neck and around 5mGy and 15mGy for the breast. While MV-CT dose varied sparsely with tissues, dose from kV imaging was around 1.7 times higher in bones than in soft tissue. Daily kV-CBCT along 40 sessions of prostate radiotherapy delivered up to 3.5Gy to the femoral heads. The dose level for head and neck and breast appeared to be lower than 0.4Gy for every organ in case of a daily imaging session. This study showed the dosimetric impact of IGRT procedures. Acquisition parameters should therefore be chosen wisely depending on the clinical purposes and tailored to morphology. Indeed, imaging dose could be reduced up to a factor 10 with optimized protocols.