Introduction/Background A midline block (MB) used in whole pelvic RT (WPRT) hinders accurate interpretation of the treatment outcome due to uncertainty of the RT dose delivered to cervical tumours.

Methodology Patients with cervical cancer of FIGO stages IB1-IVA were eligible for this prospective study. The treatment protocol consisted of WPRT (non-IMRT) without a MB (45 Gy/25 fractions) and CT-based high-dose-rate intracavitary brachytherapy (HDR-ICBT; 15 Gy/3 fractions or 20 Gy/4 fractions, prescribed to point A). The total EQD2 to point A was 63 or 69.3 Gy. The HR-CTV was contoured at the time of the present analyses. If optimisation (manual adjustment of the dwell times) was inadequate to meet the organ-at-risk dose constraints, the point A dose was decreased. Graphical optimisation was not performed.

Results A total of 40 patients were enrolled. The FIGO stage distribution was IB1, 11; IB2, 13; IIA2, 1: IIB, 11; IIIB, 3; IVA, 1. The median pretreatment tumour diameter was 47 mm (14–81 mm). No patients underwent hybrid ICBT. The point A dose was decreased in 19 of 153 ICBT sessions (12%). Twenty-nine patients received concurrent chemoradiotherapy. After a median follow-up of 33 months, the 2-year pelvic progression-free survival (PPFS), and overall survival rates were 83%, and 85%, respectively. A HR-CTV D90 threshold of 70 Gy was correlated with the PPFS: 93% for patients receiving ≥70 Gy (n=29) versus 64% for those receiving <70 Gy (n=11) (P=0.018). Late adverse events (grade ≥3) were observed in three patients (bladder in two, rectum in one).

Conclusion Definitive RT consisting of WPRT without a MB and HDR-ICBT was feasible in our cohort of Japanese patients. A low RT dose might be adequate for patients with non-bulky tumours. Proper 3D-IGBT using graphical optimisation and a suitable hybrid technique, based on appropriate HR-CTV contouring, is recommended to improve outcomes further.

Disclosure Nothing to disclose.