Clinical and dosimetric consequences of imperfect applicator insertion in cervical cancer brachytherapy

Introduction
This study analyzes clinical consequences and dosimetric variations after imperfect brachytherapy insertions. It examines treatment decisions after such insertions in patients having difficult anatomy, which leads to good subsequent insertions with acceptable dose volume parameters.

Material and methods
We reviewed images of all insertions performed during last one year and sorted faulty ones out. Clinical outcome was assessed, analyzing original treatment records. Repeat three-dimensional planning using identical dose-optimization-technique compared their dosimetry. Statistical analysis using SPSS®-Statistics-software included Fisher’s-exact-test to analyze predisposing factors for faulty insertions and predictive factors for subsequent satisfactory insertion. Friedman test was used to compare dose-volume-effects of normalization.

Results
Eighteen of 292 brachytherapy plans revealed imperfect insertions, including thirteen perforations (4.5%). Lack of pre-planning, obstructing mass, narrow vagina, acute anteversion of uterus, and multi-parity were significant (p ≤ 0.05) predisposing factors for atypical insertions. Satisfactory optimization was possible after correcting acute anteflexion or positioning tandem in retroverted direction in uncorrectable retroverted uterus. Dose normalization at point A shifted optimized dose from contoured volume to point of normalization, often undesirably. This difference, however, was statistically not significant (p = 0.121). In patients having obstructing mass, subsequent insertions were perfect, and dose volume parameters were acceptable only when full prescribed dose was delivered to at least 60% volume of the mass after a faulty insertion (p < 0.001).

Conclusions
Pre-planning by imaging is suggested in all cases of brachytherapy. Insertion of adequate length of tandem aligned to uterine axis is warranted for adequate tumor coverage. Whenever detected, acute anteflexion and mobile retroversion should be corrected. Tandem inserted in retroverted direction in uncorrectable retroverted uterus generates acceptable dose volume parameters. In cases with obstructive cervical mass, good subsequent insertion is possible with acceptable dose volume parameters, if planned dose can be delivered to its 60% volume.