Treatment accuracy without rotational setup corrections in intracranial SRT.

Eeva Boman,Mika Kapanen,Marko Laaksomaa,Hanna Mäenpää,Pirkko‐Liisa Kellokumpu‐Lehtinen,Simo Hyödynmaa

doi:10.1120/jacmp.v17i4.6149

Eeva Boman, Mika Kapanen + Show 4 more

Open Access

https://doi.org/10.1120/jacmp.v17i4.6149

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Abstract

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 (Auto6D); 2) an automatic 3D match (Auto3D); and 3) a manual 3D match from actual treatment (Treat3D). The mean conformity index (CI) was 0.92 for the original plans and 0.91 for the Auto6D plans. The mean CI decreased significantly (p<0.01) to 0.78 and 0.80 for the Auto3D and the Treat3D 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 Auto6D plans, while for the Auto3D and the Treat3D plans PTVmin decreased significantly (p<0.01) to 78.9% and 80.2%, respectively. No significant differences were seen between the Auto6D and the original treatment plans in terms of the dose parameters. However, the Auto3D and the Treat3D plans were statistically significantly inferior (p<0.01) to the Auto6D and the original plans. In addition, a significant negative correlation (p<0.01,|r|>0.38) was found in the Auto3D and the Treat3D 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

Highlights

Brain metastases occur in 10%–30% of all cancer patients.[1]
The mean distance between actual treatment positioning and the position obtained from Auto6D registration was 1.2 mm (± 0.6 mm), ranging from 2.6 mm to 0.1 mm, while the corresponding distance between treatment position and that obtained from the Auto3D was 1.7 mm (± 0.8 mm), altering from 3.8 mm to 0.2 mm
conformity index (CI), gradient index (GI), maximum, and minimum doses of planning target volume (PTV) and GTV (PTVmax, PTVmin, GTVmin) were investigated for each plan, and the mean, standard deviation (SD), minimum (Min), and maximum (Max) values are presented in Table 1 for each investigated group

Summary

Introduction

Brain metastases occur in 10%–30% of all cancer patients.[1]. Treatment options are whole brain radiotherapy, local therapies (SRT or surgery), and steroids. Several trials have shown a benefit in local control, quality of life, and even improved survival for single- or oligometastatic patients treated with SRT.[2,3,4]. Thermoplastic stereotactic masks are nowadays commonly used in SRT treatments. These have been validated in many studies as fulfilling the high accuracy standard of SRT.[8,9] Image-guidance with orthogonal kV‐images,(10) oblique images,(11) cone-beam computed tomography (CBCT) images,(12) reflecting markers with bite blocks,(13) and, more recently, patient surface matching systems[14] have shown to be sufficent in patient positioning in SRT keeping the residual setup errors under the desired limits. The use of flattering filter-free (FFF) beams decreases the treatment time even further in high dose per fraction treatments.[16]

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