ESTRO 36 Abstract Book

S374 ESTRO 36 _______________________________________________________________________________________________

Tsu, Japan 4 Mie University Graduate School of Medicine, radiation oncology, Tsu, Japan Purpose or Objective To investigate the value of the apparent diffusion coefficient (ADC) on pre- and mid-treatment MRI in predicting the prognosis (local recurrence/metastasis) of stage IIIB uterine cervical cancer patients who receive concurrent chemoradiotherapy (CCRT). Material and Methods Twenty-three patients with stage IIIB cervical cancer (the International Federation of Gynecology and Obstetrics, FIGO) underwent 1.5T MRI, including T2 weighted imaging (T2WI) and diffusion-weighted imaging at a b-value of 0 and 1,000 (s/mm 2 ) before and 3 weeks after the initiation of treatment. Twenty-two of the 23 patients received standard CCRT (chemotherapy including weekly cisplatin and concurrent radiotherapy including external body radiation therapy and brachytherapy). When measuring the ADCs, the regions of interest (ROIs) were manually drawn to include as much of the tumor as possible in two slices; the two mean values were recorded and averaged. The pre ADCs and mid ADCs were defined as the ADCs measured on pre- and mid-treatment MRI, respectively. The ΔADC values were obtained by subtracting the pre- ADC from the mid- ADC, and the %ADC values were determined by dividing the ΔADC values by the pre-ADC values. The sizes of the tumors were also measured on pre- and mid-treatment T2WI. The %size was defined as the rate of decrease in the longest diameter of the tumor. These parameters were statistically analyzed in relation to the prognosis (local recurrence/metastasis) of the patients. The statistical analyses included the Mann- Whitney U test, Fisher’s exact test, and a receiver operating characteristics (ROC) analysis. Results In the study population (n=23), local recurrence or metastasis (R/M) was found during follow-up (12-64 months, median: 40 months) in 7 patients (30%); 2 of these patients had local recurrence, 4 had metastasis and 1 had both. The ΔADC values of the patients with and without R/M were 0.210 ± 0.070 and 0.331 ± 0.126, respectively, which amounted to a statistically significant difference (p=0.013). The %ADC values of the patients with R/M were significantly lower (mean ± SD: 23.5 ± 8.25) in comparison to the patients without R/M (37.9 ± 16.4) (p=0.012). The area under the ROC curve of the %ADC was 0.835, and the sensitivity and specificity were 87.5% and 85.7%, respectively, when using an optimal cutoff value of 25.7. The proportion of patients who had %ADC values of <30% was significantly greater among the patients with R/M (6/7, 86%) than it was among those without R/M (4/16, 25%) (p=0.019). The %size values of the two groups did not differ to a statistically significant extent (p= 0.483).

Conclusion For patients with positive pelvic lymph nodes LACC, prophylactic PALN irradiation up to the level of renal vessels could reduce PALN recurrence and improve outcomes with few severe late toxicities. A prospective study investigating the risk stratification based optimal radiation field in patients with LACC is warranted. PO-0713 Diffusion-weighted MRI for predicting prognosis after radiotherapy in stage IIIB cervical cancer Y. Watanabe 1 , N. Ii 1 , T. Kawamura 1 , Y. Toyomasu 1 , T. Takada 1 , H. Tanaka 1 , E. Kondo 2 , T. Tabata 2 , H. Sakuma 3 , Y. Nomoto 4 1 Mie University Hospital, radiation oncology, Tsu, Japan 2 Mie University Hospital, Obstetrics and Gynecology, Tsu, Japan 3 Mie University Graduate School of Medicine, radiology,