Purpose: Advances in three-dimensional image-guided brachytherapy technique allow for using intra-cavitary and interstitial brachytherapy (ICIS-BT), and sole interstitial brachytherapy (ISBT) in addition to conventional intra-cavitary brachytherapy (ICBT). However, no consensus has been reached regarding the choice of these techniques. The aim of this study was to propose the size criteria for indication of interstitial techniques.
Material and methods: We examined initial gross tumor volume (GTV) at presentation and at each brachytherapy session. Also, dose volume histogram parameters for each modality were compared in 112 patients with cervical cancer treated with brachytherapy (ICBT, 54; ICIS-BT, 11; and ISBT, 47).
Results: The average GTV at diagnosis was 80.9 cm3 (range, 4.4-343.2 cm3), which shrank to 20.6 cm3 (25.5% of initial volume, range, 0.0-124.8 cm3) at initial brachytherapy. GTV > 30 cm3 at brachytherapy and high-risk clinical target volume > 40 cm3 were good threshold values for indication of interstitial technique, and tumors with initial GTV > 150 cm3 could be candidates for ISBT. An ISBT dose of 89.10 Gy can be prescribed in equivalent dose in 2 Gy fractions (range, 65.5-107.6 Gy), which was higher than those of ICIS (73.94 Gy, range, 71.44-82.50 Gy) and ICBT (72.83 Gy, range, 62.50-82.27 Gy) (p < 0.0001).
Conclusions: Initial tumor volume is an important predictor for indication of ICBT and ICIS-BT. ISBT or at least an interstitial technique is recommended for initial GTV > 150 cm3.
Keywords: HDR-RALS; ICBT; ICIS-BT; ISBT; brachytherapy; cervical cancer; chemoradiotherapy.
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