Effect of patient size on image quality in radiotherapy kV planar verification imaging: a phantom study

Introduction This study aimed to determine a maximal pelvic separation and waist circumference in pelvic patients to guide radiation therapists in acquiring kilovoltage (kV) planar images of acceptable quality for treatment verification. Methods A pelvic anthropomorphic phantom modified with different bolus thicknesses was imaged at various default kV exposure settings. Radiation therapists rated image quality and acceptance/rejection of these images for treatment verification. Results Sixteen radiation therapists participated in the study. Image quality was inversely proportional to phantom size. AP and lateral kV images were acceptable for treatment verification up to a waist circumference of 143 cm. Conclusions Exposure settings for kV image verification of large patients should be individualised to avoid unnecessary patient radiation dose through repeated imaging. Exposure settings for radiotherapy image verification of large patients should be individualised to avoid unnecessary patient radiation dose through repeated imaging. This study found that radiation therapists rated image quality to be unacceptable for use in image verification beyond pelvic AP separation of 46.5 cm, lateral separation of 60 cm and the corresponding waist circumference of 169 cm.