Abstract Book

S840

ESTRO 37

Conclusion Available data support the hypothesis of lower rates of acute toxicity and reduced economic burden associated with SBRT compared to CF-EBRT. Oncological outcomes for patients treated with SBRT appear at least equivalent to outcomes associated with CF-EBRT. Randomised data and longer follow-up is needed to determine whether SBRT is clinically more effective than CF-EBRT. EP-1558 Hypofractionated helical tomotherapy for older aged prostate cancer patients: a phase I-II trial L. Ma 1 , D. Cui 2 , H.X. Liu 3 , L. Du 4 , W. Yu 1 , B.N. Cai 1 , S.P. Xu 1 , C.B. Xie 1 1 301 Hospital, Radiation Oncology, Beijing, China 2 International Hospital of Beijing University, Radiation Oncology, Beijing, China 3 Xuanwu Hospital, Radiation Oncology, Beijing, China 4 Hainan Branch of 301 Hospital, Radiation Oncology, Sanya, China Purpose or Objective To evaluate the feasibility and outcome of hypofractionated radiation therapy realized with helical tomotherapy (HT) in older aged prostate cancer (PC) patients. Material and Methods Between February 2009 and February 2014, 67 patients (older than 65 years) were enrolled in a prospective phase I-II study (registered number ： ChiCTR-ONC- 13004037). Patients in Cohort-1 (n=33) and Cohort-2 (n=34) received 76 Gy in 34 fractions (2.25 Gy/F) and 71.6 Gy in 28 fractions (2.65 Gy/F), respectively, to the prostate and seminal vesicles (SV). While 25 patients, with a risk of lymph node involvement of >15% according to Roach et al, in Cohort-2 also received integrated elective lymph node irradiation (50.4 Gy). All patients were treated with HT and daily image guidance was performed before each treatment. Acute and late toxicities were assessed with the established RTOG/EORTC criteria. Survival rates were assessed with Kaplan-Meier method. Results The median follow-up was 109 months and 84 months in Cohort-1 and Cohort-2, respectively, with one patient lost to visit in Cohort-2. In Cohort-1, the incidences of late grade 1 / grade 2 genitourinary (GU) and gastrointestinal (GI) toxicities were 30.4% / 4.4% and 13.0% / 4.4%%, respectively; without grade 3-4 toxicities. In Cohort-2, the incidences of late grade 1 / grade 2 GU and GI toxicities were 30.0% / 0% and 6.7% / 10.0%, and that of late grade 3-4 GU and GI toxicities were 3.3% and 3.3%, respectively, without significant difference between the two cohorts. The 3- and 5-year overall survival were 94% and 80% in Cohort-1, 94% and 83% in Cohort-2, respectively (p= 0.965). The 5-year biochemical relapse free survival was 90% and 88%, and the 5-year disease-free survival was 89% and 88%, with a prostate cancer specific mortality of 4% and 3% in Cohort-1 and Cohort-2, respectively. No local or pelvic lymph node failure was noted in both cohorts Conclusion The two hypofractionation regimens, 76Gy/34F and 71.6Gy/28F, delivered with HT technique, were well tolerated in older aged PC patients with minor severe toxicities and satisfied outcome. This study also suggests that a prophylactic irradiation of pelvic lymph nodes might be not necessary in intermediate- and high-risk patients with PC.

fractal dimension features (only a trend) were statistically associated to PSA decrease in percent between M0 and M12 (p=0.012, p=0.015 and p=0.05, respectively). The two last features were also associated to PSA level at M12 in ng/ml (p=0.010 and p=0.022, respectively) such as variance with only a trend (p=0.051). Kurtosis variation was also significantly associated with both PSA level at M18 and PSA variation between M0 and M18 (p=0.042 and 0.020, respectively). No other significant results were found but some trends for kurtosis variation and fractal dimensions with PSA threshold of 1ng/ml at M12 (p=0.07 and p=0.06, respectively). Conclusion With some limitations such as statistical biases due to population size, it seems that delta-radiomics on T2w-MRI could be a potential tool as a very early biomarker of biological outcome for patients with PCa treated by EBRT. EP-1557 SBRT is a safe and effective treatment option for early stage prostate cancer. H. Linney 1 , S. Barret 1 1 Trinity College, Discipline of Radiation Therapy, Dublin, Ireland Purpose or Objective Stereotactic body radiation therapy (SBRT) is emerging as a new treatment option for the treatment of early stage prostate cancer. It theoretically poses clinical and economic benefits compared to conventionally fractionated external beam radiation therapy (CF-EBRT), which is the current standard of care. This debate aims to evaluate available clinical data to determine if the proposed theoretical benefits translate clinically. Material and Methods A systematic search strategy was employed across three databases using predefined search terms to identify articles for inclusion is this debate. Predefined exclusion criteria were used to filter results of this search. Reference lists of included studies were also reviewed for relevant material. Results Sixteen articles were included. Biochemical progression free survival rates ranging 77.1%-100% were reported in SBRT studies compared to 55%-98% in CF-EBRT studies. Incidence of acute grade one, two and three genitourinary toxicities were reported in the range of 13.3%-71%, 12-25% and 0%-3% respectively in the SBRT cohort in comparison to 28.7%-51.9%, 15.6%-41.4%. and 1.1%-8.1% respectively in the CF-EBRT cohort. Incidence of acute grade one, two and three gastrointestinal toxicities were reported in the range of 13%-67%, 1%-27% and 0%-9% respectively of the SBRT cohort compared to 16.1%- 51.1%, 6.3%-20.7% and 0%-3% respectively of CF- EBRT cohort. Mean treatment costs estimates associated with SBRT reported ranged $22,152 to $24,873 mean costs ranging $33,068 to $35,431 for CF-EBRT. Results SBRT CF-EBRT

Reported bPFS rates ranged 77.1% to 100%

Reported bPFS rates ranged 55% to 98%.

Treatment efficacy

Mean costs

treatment

Mean costs

treatment

Cost Effectiveness

ranged $22,152 to $24,873.

ranged $33,068 to $35,431.