Rectal separation using hydroxypropyl methylcellulose in intracavitary brachytherapy of cervical cancer: an innovative approach

PURPOSE: This study was initiated to prove feasibility of hydrogel application in recto-vaginal space in intracavitary brachytherapy (ICBT) of cervical cancer in order to reduce rectal toxicity. MATERIAL AND METHODS: In a case of stage IIB cervical cancer, after external beam radiotherapy (EBRT), we planned ICBT 7 Gy × 3 fractions. In 1(st) fraction (Plan 1), due to narrow separation between rectum and cervix (0.18 cm), only 5 Gy was delivered at point A (with high-risk clinical target volume [HR-CTV] D(90) 5.94 Gy, intermediate risk clinical target volume [IR-CTV] D(90) 4.54 Gy, rectum D(2cc) 5.72 Gy, bladder D(2cc) 5.52 Gy, and sigmoid colon 5.82 Gy). In 2(nd) fraction (Plan 2), interstitial brachytherapy (ISBT) was attempted. For the prescription of 5 Gy, we get dose levels almost similar to the 1(st) insertion: HR-CTV D(90) (6.7 Gy), IR-CTV D(90) (3.06 Gy), bladder D(2cc) (5.7 Gy), rectum D(2cc) (4.8 Gy), sigmoid colon D(2cc) (1.3 Gy) (separation = 0.23 cm). During 3(rd) fraction (Plan 3), prior doing interstitial insertion, we instilled 50 cc of hydroxypropyl methylcellulose (Viscomet(®)) up to the tip of recto-vaginal septum. A repeat computed tomography (CT) scan was done 4 hours after Plan 3 treatment and it was re-planned (Plan 4) to find out migration of hydrogel if any and its dosimetric impact. RESULTS: 9 Gy was delivered to point A with a separation of 1.1 cm in Plan 3 (with HR-CTV D(90) 16.4 Gy, IR-CTV D(90) 11.3 Gy, rectum D(2cc) 3.6 Gy, bladder D(2cc) 6.9 Gy, and sigmoid colon 2.2 Gy). We achieved an optimum cumulative EQD(2) dose (HR-CTV D(90) 98.4 Gy, IR-CTV D(90) 76.1 Gy, rectum D(2cc) 67.7 Gy, bladder D(2cc) 73.2 Gy, and sigmoid colon 59.3 Gy). Hydrogel volume was decreased in Plan 4 without a major dosimetric changes. CONCLUSIONS: Hydrogel instillation is a useful tool for recto-vaginal separation during cervical cancer brachytherapy. It increases therapeutic ratio without any adverse event.