SPATIAL REPRODUCIBILITY OF THE RING AND TANDEM HIGH-DOSE-RATE CERVIX APPLICATOR

Citation
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
ISSN journal
03603016
Volume
41
Issue
1
Year of publication
1998
Pages
13 - 19
Database
ISI
SICI code
0360-3016(1998)41:1<13:SROTRA>2.0.ZU;2-D
Abstract
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.