Treatment accuracy without rotational setup corrections in intracranial SRT

The aim of this study was to evaluate the impact of actual rotational setup errors on dose distributions in intracranial stereotactic radiotherapy (SRT) with different alternatives for treatment position selection. A total of 38 SRT fractions from 18 patients were retrospectively evaluated with rotational setup errors obtained from actual treatments. The planning computed tomography (CT) images were rotated according to online cone‐beam CT (CBCT) images and the dose distribution was recalculated to the rotated CT images using three different patient positionings derived from: 1) an automatic 6D match neglecting rotation correction [Formula: see text]; 2) an automatic 3D match [Formula: see text]; and 3) a manual 3D match from actual treatment [Formula: see text]. The mean conformity index (CI) was 0.92 for the original plans and 0.91 for the [Formula: see text] plans. The mean CI decreased significantly [Formula: see text] to 0.78 and 0.80 for the [Formula: see text] and the [Formula: see text] plans, respectively. The mean minimum dose of the planning target volume (PTVmin) was 91.9% of the prescribed dose for the original plans and 92.1% for the [Formula: see text] plans, while for the [Formula: see text] and the [Formula: see text] plans PTVmin decreased significantly [Formula: see text] to 78.9% and 80.2%, respectively. No significant differences were seen between the [Formula: see text] and the original treatment plans in terms of the dose parameters. However, the [Formula: see text] and the [Formula: see text] plans were statistically significantly inferior [Formula: see text] to the [Formula: see text] and the original plans. In addition, a significant negative correlation [Formula: see text] was found in the [Formula: see text] and the [Formula: see text] cases between the rotation error and CI, PTVmin or minimum dose of gross tumour volume. In SRT, a treatment plan of comparable quality to 6D rotation correction can be achieved by using 6D registration without a rotational correction in the selection of patient positioning. This was demonstrated for typical rotation errors seen in clinical practice. PACS number(s): 87.55, 87.57