Clinical factors affecting the therapeutic dose window in cervical cancer brachytherapy

Abstract

BACKGROUND AND PURPOSE: Although dose planning aims in cervical cancer brachytherapy are well-defined, variability in clinical practices makes it difficult to draw generalizable conclusions on achievable dosimetry. This review and meta-regression aim to assess clinical practices in terms of their therapeutic dose window, that is, the balance between target and organs-at-risk (OAR) doses. MATERIALS AND METHODS: A search of the literature was performed in Scopus, PubMed, and Web of Science databases. Peer-reviewed articles were included that described planning constraints and reported high-risk clinical target volume (CTV_HR) D_90% and OAR D_2cm³ for intracavitary (IC) tandem and ring (T&R) / tandem and ovoid (T&O) / mold (M) applicators, possibly supplemented with interstitial (IS) needles (+N). To determine factors associated with target volume coverage (D_90%) and OAR sparing (D_2cm³), multivariate meta-regressions were performed. RESULTS: Out of 1590 articles, 34 met the full inclusion criteria. In most studies, the CTV_HR D_90% aimed at ≥84–86 Gy EQD2_{α/β = 10Gy}, and constraints for the OARs were 80–90 Gy, 65–75 Gy and 70–75 Gy EQD2_{α/β = 3Gy} for the bladder, rectum and sigmoid D_2cm³, respectively. Studies using IC/IS applicators were associated with a ∼4 Gy increase in CTV_HR D_90% compared to IC only, with no effect on OAR dose. T&R studies achieved improvements of 3.2 Gy and 2.8–3.4 Gy at typical planning aims in comparison with T&O applicators in target and OAR doses. In 100% (15/15) of patient groups treated with T&R + N both CTV_HR and OAR objectives were met for the population average. For T&R, T&O, and T&O + N groups, this was the case in 89% (8/9), 43% (6/14), and 50% (4/8), respectively. CONCLUSION: Studies using interstitial needles with T&R applicators in MR-guided brachytherapy for cervical cancer seem to be associated with a favorable therapeutic target dose/OAR sparing ratio.