3D image-based adapted high-dose-rate brachytherapy in cervical cancer with and without interstitial needles: measurement of applicator shift between imaging and dose delivery.
OBJECTIVE
Using 3D image-guided adaptive brachytherapy for cervical cancer treatment, it often means that patients are transported and moved during the treatment procedure. The purpose of this study was to determine the intra-fractional longitudinal applicator shift in relation to the high risk clinical target volume (HR-CTV) by comparing geometries at imaging and dose delivery for patients with and without needles.


METHODS
Measurements were performed in 33 patients (71 fractions), where 25 fractions were without and 46 were with interstitial needles. Gold markers were placed in the lower part of the cervix as a surrogate for HR-CTV, enabling distance measurements between HR-CTV and the ring applicator. Shifts of the applicator relative to the markers were determined using planning computed tomography (CT) images used for planning, and the radiographs obtained at dose delivery. Differences in the physical D90for HR-CTV due to applicator shifts were simulated individually in the treatment planning system to provide the relative dose variation.


RESULTS
The maximum distances of the applicator shifts, in relation to the markers, were 3.6 mm (caudal), and -2.5 mm (cranial). There was a significant displacement of -0.7 mm (SD = 0.9 mm) without needles, while with needles there was no significant shift. The relative dose variation showed a significant increase in D90HR-CTV of 1.6% (SD = 2.6%) when not using needles, and no significant dose variation was found when using needles.


CONCLUSIONS
The results from this study showed that there was a small longitudinal displacement of the ring applicator and a significant difference in displacement between using interstitial needles or not.
School of Health and Medical Sciences; Department of Medical Physics, Faculty of Medicine and Health.
Leif
L
Karlsson
Department of Medical Physics, Faculty of Medicine and Health.
Per
P
Thunberg
Department of Medical Physics, Faculty of Medicine and Health.
Anders
A
With
School of Health and Medical Sciences; Department of Oncology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
Louise Bohr
LB
Mordhorst
School of Health and Medical Sciences; Department of Medical Physics, Faculty of Medicine and Health.
Jan
J
Persliden
HDR; brachytherapy; cervical cancer; intra-fraction