Clinical Investigations
Extracranial stereotactic radiation therapy: set-up accuracy of patients treated for liver metastases

Parts of the contents of this paper have been presented at the 40th annual ASTRO meeting in Phoenix, AZ, 1998.
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Abstract

Purpose: Patients with liver metastases might benefit from high-dose conformal radiation therapy. A high accuracy of repositioning and a reduction of target movement are necessary for such an approach. The set-up accuracy of patients with liver metastases treated with stereotactic single dose radiation was evaluated.

Methods and Materials: Twenty-four patients with liver metastases were treated with single dose radiation therapy on 26 occasions using a self-developed stereotactic frame. Liver movement was reduced by abdominal pressure. The effectiveness was evaluated under fluoroscopy. CT scans were performed on the planning day and directly before treatment. Representative reference marks were chosen and the coordinates were calculated. In addition, the target displacement was quantitatively evaluated after treatment.

Results: Diaphragmal movement was reduced to median 7 mm (range: 3–13 mm). The final set-up accuracy of the body was limited to all of median 1.8 mm in latero-lateral direction (range: 0.3–5.0 mm) and 2.0 mm in anterior-posterior direction (0.8–3.8 mm). Deviations of the body in cranio-caudal direction were always less than the thickness of one CT slice (<5 mm). However, a repositioning was necessary in 16 occasions. The final target shift was median 1.6 mm (0.2–7.0 mm) in latero-lateral and 2.3 mm in anterior-posterior direction (0.0–6.3 mm). The median shift in cranio-caudal direction was 4.4 mm (0.0–10.0 mm).

Conclusions: In patients with liver metastases, a high set-up accuracy of the body and the target can be achieved. This allows a high-dose focal radiotherapy of these lesions. However, a control CT scan should be performed directly before therapy to confirm set-up accuracy and possibly prompt necessary corrections.

Introduction

Radiation therapy has played a minor role in the treatment of patients with liver metastases. The tolerance dose of the whole liver to radiation is limited to 30 Gy, which does not result in longer survival (1). Higher doses could safely be applied to a liver tumor if functional liver tissue can be spared from high radiation doses (2). Stereotactic and conformal techniques made high-dose radiation therapy possible in the brain. However, in the brain, set-up accuracy of less than 2 mm can be achieved using invasive or non-invasive fixation methods 3, 4. In the bodytrunk, and especially in the liver, normal tissue sparing conformal therapy is complicated by an exact body-fixation and intra-corporal target movement. For paraspinal tumors, invasive and non-invasive methods for body fixation have been published 5, 6. However, these techniques are time consuming and not suitable for liver metastases, because they do not reduce the intra-corporal liver movement. Other repositioning devices have been used for conformal therapy of prostate cancer (7). Lax et al. (8) published a set-up for stereotactic radiation therapy of liver tumors using a vacuum pillow in a stereotactic frame. Using this device, an acceptable accuracy of repositioning for hypofractionated therapy could be achieved (8). We have used a similar approach for stereotactic treatment of liver metastases. We present our experience of set-up accuracy of the first 26 single dose treatments in patients with liver metastases.

Section snippets

Methods and materials

Between April 1997 and January 1999, 24 patients (17 male, 7 female) with inoperable metastases in the liver have been stereotactically treated in a phase I/II study in 26 occasions. The ethics committee of the University of Heidelberg approved the study, and all patients gave their written consent. The study design was in consent with the declaration of Helsinki (1975/1983). The median age was 60 years (range 49–84 years). The patients had a median body mass index [BMI = weight (kg)/(length (m)

Reduction of intra-corporal target movement

Fluoroscopy showed a median shift of the right diaphragm of 7 mm (range: 3–13 mm, mean 7.3 mm, standard deviation 2.7 mm). In seven patients, the movement of the posterior part of the diaphragm was also measured with lateral fluoroscopy since these patients had metastases in posterior parts of the liver. The posterior part of the right diaphragm showed a 2 mm (median; range 0–4 mm) stronger cranio-caudal shift than the frontal parts of the diaphragm in these patients.

There was a statistically

Discussion

Patients with metastases in the liver may benefit from surgery (10). However, liver resections are accompanied by a relatively high morbidity and mortality (11). Alternative methods to surgery have been developed for patients with inoperable hepatic disease. These included locoregional chemotherapy (12), laser-induced thermotherapy (LITT) (13), cryotherapy (14), alcohol injection (15), and also radiation therapy 1, 16, 17, 18, 19, 20. Due to the radiosensitivity of normal liver tissue,

Acknowledgements

The authors would like to thank Mrs. A. Fuxa, Mrs. M. Jochim, Mrs. S. Kuhn, and Mrs. C. Weyrich for their excellent technical support.

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