Locally advanced cervical cancer: Is it relevant to report image-guided adaptive brachytherapy using point A dose?

PURPOSE:To evaluate the usefulness of reporting the point A dose in patients with locally advanced cervical cancer treated with image-guided adaptive brachytherapy (IGABT). METHODS AND MATERIALS:Dosimetric data from patients treated with a combination of chemoradiation and intracavitary IGABT were examined in light of their outcomes. Prescribing followed the Groupe Européen de Curiethérapie-European Society for Radiation Oncology recommendations. All doses were converted in 2-Gy equivalent. The relationships between the D90 high-risk clinical target volume (CTVHR) and intermediate-risk clinical target volume (CTVIR) and point A doses were studied. Dose-effect relationships based on the probit model and log-rank test were assessed. RESULTS:Two hundred twelve patients were included with a median followup of 53.0 months. A total of 28 local relapses were reported, resulting in a local control rate of 86.6% at 3 years. Mean D90 CTVHR, CTVIR, and point A doses were: 79.7 ± 10.4 Gy, 67.4 ± 5.8 Gy, and 66.4 ± 5.6 Gy, respectively. The mean D90 were significantly different and independent from the mean point A dose, even in bulky tumors at diagnosis or in large CTVHR lesions. Point A dose appeared correlated with TRAK, and finally with the D90 CTVHR through a complex formula including the CTVHR volume (R2 = 0.55). Whereas significant relationships between the probability of achieving local control and the D90 CTVHR and CTVIR (p = 0.08 and 0.025) were observed, no similar relationship was found with point A dose except a trend of an inverse relation. After sorting patients according to three dose levels, highest local control rates were observed in patients with D90 CTVHR ≥85 Gy, whereas those with point A doses ≥70 Gy had the worst outcomes. CONCLUSIONS:In patients treated with IGABT, point A dose is not predictive of local control but a surrogate of the irradiated volume. Its relationships with the D90 CTVHR are indirect and complex rising the question of relevance of its reporting in routine.