Four-dimensional cone-beam computed tomography-guided radiotherapy for gastric lymphoma

We describe a treatment method with four-dimensional cone-beam computed tomography (4D-CBCT)-guided radiotherapy for gastric lymphoma. We performed image-guided radiotherapy (IGRT) with 15 fractions for a gastric mucosa-associated lymphoid tissue lymphoma patient, using 4D-CBCT. The stomach was delineated based on 4D-CT images. For image guidance, an automatic registration between planning CT and 4D-CBCT images was performed based on the bony anatomy (bone matching), followed by manual registration based on the stomach in 4D-CBCT images of all 10 phases (4D matching). We calculated the covering ratio (CR) with variable stomach-to-planning target volume (PTV) margins, based on the images of all phases [CR (%) = the number of covering phases/all 150 phases x 100]. The patient underwent radiotherapy (RT) as scheduled, without any significant adverse effects. The appropriate PTV margins (CR ae<yen> 95%) were 25 mm (CR 99.3%) and 15 mm (CR 98.7%) for bone and 4D matching, respectively. 4D matching using 4D-CBCT is appropriate for IGRT of gastric lymphomas.