Jh. Bahena et al., SPATIAL REPRODUCIBILITY OF THE RING AND TANDEM HIGH-DOSE-RATE CERVIX APPLICATOR, International journal of radiation oncology, biology, physics, 41(1), 1998, pp. 13-19
Citations number
14
Categorie Soggetti
Oncology,"Radiology,Nuclear Medicine & Medical Imaging
Purpose: High-dose rate (HDR) applicators for uterine cervix brachythe
rapy are used with increasing frequency. Because multiple HDR fraction
s are required for treatment, the applicator position reproducibility
is of most importance. To study this effect, the clinical data from pa
tients with uterine cervix cancer were examined retrospectively to eva
luate the interfraction geometric variation of the HDR applicator and
its potential treatment impact. Methods and Materials: Eighteen patien
ts with invasive cervical cancer who were treated with definitive radi
otherapy at William Beaumont Hospital were included in the study. Pati
ents were treated with 45-50.4 Gy megavoltage external beam to the pel
vis, and 35 Gy to the prescription point A from 7 fractions of HDR bra
chytherapy. The 3-dimensional (3D) interfraction geometrical variation
of the ring and tandem (R & T) applicator was measured using predefin
ed reference points in the 7 sets of orthogonal simulation films obtai
ned prior to each HDR application. Spatial reproducibility of the R &
T insertion and time-trend of the R & T position variation related to
patient's anatomy during the treatment course were analyzed with respe
ct to different groups of patients who had either early or advanced di
sease. Results: The translational variation of the applicator position
for all patients was 6.5, 5.9, and 7.7 mm (one standard deviation), r
espectively, in the patient's superior-to-inferior (SI), right-to-left
lateral (RL), and anterior-to-posterior (AP) direction. The rotationa
l variation was 3.4, 4.6, and 6.0 degrees (one standard deviation) in
the patient's coronal, transverse, and sagital planes. When the patien
ts were grouped based on early disease or advanced disease, the latter
demonstrated substantially larger variation (factor of 2) in the appl
icator position than the former. Furthermore, the time-trend of positi
on variation was observable for both groups of patients. The variation
s occurred primarily during the first 3 fractions. Conclusions: Based
on the good spatial reproducibility observed in our study, the current
clinical procedure for the HDR R & T applicator placement is reliable
. Positional reproducibility of the R & T applicator is highly depende
nt upon the size of tumor volume, which, in turn, deviates the applica
tor during the early course of HDR brachytherapy. Attention to the con
struction of the midline block is of paramount importance. (C) 1998 El
sevier Science Inc.