Can Online Adaptive Radiation Therapy Eliminate Intrafractional Deformation in Gastric Mucosa-Associated Lymphoid Tissue Lymphoma?

Abstract

We hypothesized that online adaptive radiation therapy (oART) could eliminate errors associated with interfractional deformation in gastric mucosa-associated lymphoid tissue (MALT) lymphoma, but errors in intrafractional deformation remained in 6 directions (anterior, posterior, superior, inferior, left, and right). This study aimed to quantify the anisotropic deformation errors of the clinical target volume (CTV) for MALT lymphoma using oART to determine deformations in the planning target volume (PTV) margins. Thirty fractional scans from 4 consecutive patients (a total of 120 cone beam computed tomography scans) with gastric MALT lymphoma treated with oART were chosen for this retrospective study. The CTV contours were manually delineated on the pretreatment and posttreatment cone beam computed tomography images. The center-of-mass matching of the CTVs was performed following the bone anatomy matching. Systematic and random errors of intrafractional deformations of the CTV were quantified using displacement vectors between the pretreatment and posttreatment CTV surfaces for each fraction. The PTV margins for oART were anisotropically calculated using the van Herk formula: 2.5Σ + 0.7σ, accounting for intrafractional errors. For intrafractional deformation, the means of standard deviations of systematic errors ranged from 1.2 mm to 2.2 mm, whereas those of random errors ranged from 2.9 mm to 3.6 mm. The PTV margins were up to 13.1 mm in the inferior direction, whereas in other directions, they ranged from 9.7 mm to 12.8 mm. The PTV margin in integer achieved posttreatment CTV coverage for 90% of the fractions, with undercoverage volumes remaining below 0.6 cm³ in all fractions. This study suggests that the impact of intrafractional CTV deformation can not be eliminated even with oART. This highlights the need to set the appropriate anisotropic PTV margins.