Parametrial boosting in locally advanced cervical cancer: combined intracavitary/interstitial brachytherapy vs. intracavitary brachytherapy plus external beam radiotherapy

Parametrial boost (PB) with external beam radiotherapy (EBRT) aims to increase the dose in the parametrial regions where the contribution from intracavitary brachytherapy (IC BT) is insufficient. An alternative technique for parametrial boosting is combined intracavitary and interstitial (IC-IS) BT. We compared doses delivered by IC BT plus EBRT PB with doses delivered by IC-IS BT.

We reviewed 51 consecutive patients with locally advanced cervical cancer with parametrial involvement at diagnosis. At BT, 23 patients had persistent parametrial involvement and were treated with IC-IS BT. For the 23 patients, we simulated a treatment of IC BT combined with EBRT PB and compared it with the delivered IC-IS BT. Equivalent total doses in 2-Gy fractions of the target and organs at risk were evaluated, and the normal tissue volume irradiated to at least 60 Gy (V60).

The mean high-risk clinical target volume D90 was comparable (p = 0.8) for both techniques. However, with the EBRT PB scenario, 3 patients received high-risk clinical target volume D90 of <79 Gy, whereas IC-IS BT resulted in D90 of >84 Gy for all patients. Organs at risk D(2cm(3)) were significantly higher by a mean of 4-6 Gy (p < 0.001) with EBRT PB. The PB scenario resulted in a significantly higher V60 of 594 ± 596 cm(3) as compared with 228 ± 82 cm(3) with IC-IS BT (p = 0.004).

Combined IC-IS BT is superior than IC BT + EBRT PB both in terms of organ sparing and target coverage. The IC-IS BT was more conformal with less normal tissue exposure to intermediate doses (V60).