ESTRO 2021 Abstract Book

S343

ESTRO 2021

MRI in 41 patients before radiotherapy treatment. Patients received a total dose delivered with external beam of 45-50.4 Gy, with daily 1.8 Gy fractionation on the pelvis +/- para-aortic region and 54 Gy (50-56 Gy, 2-2.16 Gy/fractionation) with simultaneous integrated boost (SIB) on 18 FDG-PET/CT positive nodes. Results Local lymph nodal involvement was detected in 29 out of 43 patients (67%). In 11 patients (26%), 18FDG- PET/CT showed pelvic positive lymph nodes in one or more areas, not detected in the other imaging techniques, such as CT and/or MRI: common iliac lymph nodes (LN) in 3 pts, internal iliac LN in 4 pts, obturator LN in 4 pts, external iliac LN in 3 pts and perirectal LN in 2 pts. Clinical Target Volume (CTV) was modified including para-aortic region in 8 patients whose 18 FDG-PET/CT detected metabolically active nodes not evidenced in CT and MRI reports (Tab.1, Fig.1).

Conclusion In our study, 18 FDG-PET/CT allowed to modify the clinical target volume in 8/43 (19%) patients with positive para-aortic nodes not detected on CT or MRI. It provided clinical staging optimization and intensification dose in involved lymph nodes. PH-0444 Optimal use of radiotherapy in the definitive treatment of non-bulky IB ‒ IIA cervical cancer Y.J. Lim 1 1 Kyung Hee University School of Medicine, Radiation Oncology, Seoul, Korea Republic of Purpose or Objective Although the current clinical guidelines recommend either surgery or radiotherapy for non-bulky IB ‒ IIA cervical cancer, the role of radiotherapy as a curative treatment method has not been established. This study aimed to evaluate the prognostic implications of definitive radiotherapy and determine its optimal use in clinical practice. Materials and Methods Patients with non-bulky (<4 cm) IB ‒ IIA cervical cancer who underwent hysterectomy or primary radiotherapy were identified from the Surveillance, Epidemiology, and End Results database. We compared disease-specific survival after surgery to that after radiotherapy in three discrete cohorts as follows: hysterectomy vs. radiotherapy or chemoradiotherapy overall with/without brachytherapy (cohort A); radio- or chemoradiotherapy with brachytherapy (cohort B); and chemoradiotherapy with brachytherapy (cohort C). Results Among the 9,391 initially identified patients, 1,762, 1,244, and 750 patients were categorized into cohorts A, B, and C, respectively, after propensity score matching. In cohort A, the disease-specific survival after primary radiotherapy was inferior to that after hysterectomy ( P = 0.001). In cohort B, a trend toward differential survival in favor of hysterectomy was observed with marginal significance ( P = 0.061). However, in cohort C, disease-specific survival after primary radiotherapy was comparable to that after hysterectomy ( P = 0.127). According to hazard rate function plots, patients receiving external beam radiotherapy alone had an increased short-term risk of disease-specific mortality, whereas patients without evidence of chemotherapy had a distinct late risk surge at approximately 15 years of follow-up. Conclusion For long-term curative efficacy of primary radiotherapy in non-bulky IB ‒ IIA cervical cancer, optimizing radiotherapy methods with brachytherapy and the combined use of chemotherapy should be considered.