Abstract
BackgroundTo assess brachytherapy catheter positioning accuracy and to evaluate the effects of prolonged irradiation time on the tolerance dose of normal liver parenchyma following single-fraction irradiation with 192 Ir.Materials and methodsFifty patients with 76 malignant liver tumors treated by computed tomography (CT)-guided high-dose-rate brachytherapy (HDR-BT) were included in the study. The prescribed radiation dose was delivered by 1 - 11 catheters with exposure times in the range of 844 - 4432 seconds. Magnetic resonance imaging (MRI) datasets for assessing irradiation effects on normal liver tissue, edema, and hepatocyte dysfunction, obtained 6 and 12 weeks after HDR-BT, were merged with 3D dosimetry data. The isodose of the treatment plan covering the same volume as the irradiation effect was taken as a surrogate for the liver tissue tolerance dose. Catheter positioning accuracy was assessed by calculating the shift between the 3D center coordinates of the irradiation effect volume and the tolerance dose volume for 38 irradiation effects in 30 patients induced by catheters implanted in nearly parallel arrangement. Effects of prolonged irradiation were assessed in areas where the irradiation effect volume and tolerance dose volume did not overlap (mismatch areas) by using a catheter contribution index. This index was calculated for 48 irradiation effects induced by at least two catheters in 44 patients.ResultsPositioning accuracy of the brachytherapy catheters was 5-6 mm. The orthogonal and axial shifts between the center coordinates of the irradiation effect volume and the tolerance dose volume in relation to the direction vector of catheter implantation were highly correlated and in first approximation identically in the T1-w and T2-w MRI sequences (p = 0.003 and p < 0.001, respectively), as were the shifts between 6 and 12 weeks examinations (p = 0.001 and p = 0.004, respectively). There was a significant shift of the irradiation effect towards the catheter entry site compared with the planned dose distribution (p < 0.005). Prolonged treatment time increases the normal tissue tolerance dose. Here, the catheter contribution indices indicated a lower tolerance dose of the liver parenchyma in areas with prolonged irradiation (p < 0.005).ConclusionsPositioning accuracy of brachytherapy catheters is sufficient for clinical practice. Reduced tolerance dose in areas exposed to prolonged irradiation is contradictory to results published in the current literature. Effects of prolonged dose administration on the liver tolerance dose for treatment times of up to 60 minutes per HDR-BT session are not pronounced compared to effects of positioning accuracy of the brachytherapy catheters and are therefore of minor importance in treatment planning.
Highlights
To assess brachytherapy catheter positioning accuracy and to evaluate the effects of prolonged irradiation time on the tolerance dose of normal liver parenchyma following single-fraction irradiation with 192 Ir
Effects of prolonged dose administration on the liver tolerance dose for treatment times of up to 60 minutes per high-dose-rate brachytherapy (HDR-BT) session are not pronounced compared to effects of positioning accuracy of the brachytherapy catheters and are of minor importance in treatment planning
The angiographic sheaths containing the catheters were secured to the skin by suture, retraction of the brachytherapy catheters within the catheter tracks might potentially occur due to patient movement, e.g., when the patient is transferred from the Computed tomography (CT) unit to the brachytherapy unit, and liver movement during respiration
Summary
To assess brachytherapy catheter positioning accuracy and to evaluate the effects of prolonged irradiation time on the tolerance dose of normal liver parenchyma following single-fraction irradiation with 192 Ir. To prevent recurrence at the tumor margins, catheter placement and dwell positions of the 192 Ir point source have to be carefully planned [5]. The accuracy of dose application is predominantly dependent on catheter positioning. Computed tomography (CT) was used to monitor catheter implantation, and 3D CT datasets acquired in breath-hold were used for treatment planning. For irradiation patients were transferred from the CT unit to the brachytherapy unit. Dislocation of catheters during patient transfer might be a potential source of error with respect to correct dose application at the target site. The liver is an elastic organ and could be deformed between catheter implantation and irradiation
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