Needle use and dosimetric evaluation in cervical cancer brachytherapy using the Utrecht applicator

Background and purpose: To analyse the clinical use of needles and examine the feasibility to meet the planning criteria in three fractions of cervical cancer brachytherapy. Furthermore, to investigate whether the needles with the largest discrepancy between application and loading are essential to treatment planning.

Materials and methods: For 22 patients we analysed the applied and loaded needle patterns, and examined the dosimetric results for small (<30 cm³) and large (≥30 cm³) CTV_HR. We removed from the clinical plans (CP) the needles applied most, but with the lowest loading frequency and intensity and re-optimized these plans (RP).

Results: On average 5.8 needles were applied and 4.8 loaded per fraction, with average intensity 22% (17% for small, 29% for large CTV_HR). Mid-lateral needles were applied and loaded most frequently and intensely. The average CTV_HR D_90% prescribed dose was 88.8 Gy (SD 4.2) EQD2₁₀, the average OAR [Formula: see text] limit was respected. Omitting the mid-ventral needles, minimal statistically significant differences were found in dose distributions between RP and CP.

Conclusions: Applying on average 5.8 needles per fraction it was possible to meet the planning criteria for targets and OARs in three BT fractions for both small and large CTV_HR. The mid-ventral needles were not essential in treatment planning, unless situated in the vicinity of the GTV_res.