Liver stereotactic body radiation therapy without fiducial or retained ethiodized oil guidance warrants greater than 5 mm planning target volumes

Abstract Introduction For liver stereotactic body radiation therapy (SBRT), the placement of fiducial markers or retained ethiodized oil by transarterial chemoembolisation (TACE) provides a landmark for consistent target localisation. TACE and fiducial markers are invasive procedures that harbour additional risks. We hypothesise that liver SBRT can be accurately delivered without the use of these invasive surrogate markers. Methods We retrospectively identified 50 consecutive patients who underwent liver SBRT with respiratory motion management to a single lesion which exhibited retained ethiodized oil per prior TACE delivery. For each SBRT fraction, two manual rigid image registrations were performed by the treating physician. One using the liver contour as a surrogate for the target and second aligning only to the radio‐opaque retained ethiodized oil of the treated lesion. The magnitude of the displacement vector between the two registration methods was used to assess the accuracy of target localisation if ethiodized oil was not present. Results For the 50 patients, a total of 244 analysable cone‐beam CTs (CBCTs) were included (six CBCTs excluded due to poor ethiodized oil visualisation). Respiratory motion management techniques consisted of active breathing control for 13 and abdominal compression for 37 patients. Forty‐two patients had peripheral lesions and eight had central lesions (