Impact of the frequency of online verifications on the patient set-up accuracy and set-up margins

Abstract

PurposeThe purpose of the study was to evaluate the patient set-up error of different anatomical sites, to estimate the effect of different frequencies of online verifications on the patient set-up accuracy, and to calculate margins to accommodate for the patient set-up error (ICRU set-up margin, SM).Methods and materialsAlignment data of 148 patients treated with inversed planned intensity modulated radiotherapy (IMRT) or three-dimensional conformal radiotherapy (3D-CRT) of the head and neck (n = 31), chest (n = 72), abdomen (n = 15), and pelvis (n = 30) were evaluated. The patient set-up accuracy was assessed using orthogonal megavoltage electronic portal images of 2328 fractions of 173 planning target volumes (PTV). In 25 patients, two PTVs were analyzed where the PTVs were located in different anatomical sites and treated in two different radiotherapy courses. The patient set-up error and the corresponding SM were retrospectively determined assuming no online verification, online verification once a week and online verification every other day.ResultsThe SM could be effectively reduced with increasing frequency of online verifications. However, a significant frequency of relevant set-up errors remained even after online verification every other day. For example, residual set-up errors larger than 5 mm were observed on average in 18% to 27% of all fractions of patients treated in the chest, abdomen and pelvis, and in 10% of fractions of patients treated in the head and neck after online verification every other day.ConclusionIn patients where high set-up accuracy is desired, daily online verification is highly recommended.

National survey on image‐guided radiotherapy practice in New Zealand

“…Online IGRT strategies aim to reduce both systematic and random errors and can achieve a larger reduction in random errors compared to offline corrections. 16 Daily online image verification maximizes the benefit of random error reduction achieved by online IGRT. 17,18 There are currently no guidelines addressing the optimal verification strategy (online vs. offline).…”

The Empirical Foundations of Teleradiology and Related Applications: A Review of the Evidence

“…A Saudi study (observational, n = 148, slightly less than the target of 150) evaluated the effects of different frequencies of online verifications on patient setup accuracy and margins among patients receiving radiotherapy in the head and neck region, chest, abdomen, and pelvis, using electronic portal imaging. 125 Online verification intervals varied from zero, once a week, and every other day. The data show an effective improvement of both the systematic and the random errors with increasing frequency of online verifications.…”

Application of Cone Beam Computed Tomography to Conventional Radiotherapy: Limited Angle of Projections for Lymph Nodes Located above or below the Collarbone

“…Because residual set-up errors larger than 5 mm were observed on average in 18% to 27% of all fractions of patients treated in the chest, abdomen and pelvis, and in 10% of fractions of patients treated in the head and neck [13], it is necessary to correct the set-up error by CBCT in conventional RT. Therefore, it is important to investigate the limited angle of projections for the auto-image registration.…”