3rd ESTRO Forum 2015 S365 Acute toxicity was defined as up to 18 weeks from the start of RT and was assessed using the modified RTOG toxicity criteria weekly during RT and then at week 10, 12 and 18. The NCI CTCAE v4 scoring system was used pre-RT and at week 18. Patients were also asked to complete IPSS questionnaires at these times. Peak toxicity grade (G) was dichotomized: modified RTOG G0&1 (n=13) vs G2&3 (n=37) and NCI CTCAE v4 (G0 vs G1&2). The Mann Whitney U test was used to compare

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... ity groups using a range of dosimetric descriptors for each GU pelvic structure. Data was analysed in SPSS, v22 (IBM SPSS, Armonk, NY). Results : 36 patients (72%) experienced a peak G2 RTOG acute toxicity and 1 patient G3. At week 18, half of the patients had no toxicity according to the NCI CTCAE v4. IPSS median and IQR at pre-RT and 18 weeks (n=45) were 5 (4-9) and 7 (5-9) respectively. There were statistically significant differences in a number of dose surface parameters for WB and BT using NCI CTCAE v4. No urethral dose parameters related to toxicity (Table 1) . There were no statistically significant results for RTOG peak toxicity. Conclusions: Our technique to produce the dose surface map of the BT has enhanced the dosimetric information available for analysis of acute GU toxicity. The results suggest that modifying dose surface parameters to WB and BT may impact on the incidence of acute toxicity. PO-0737 Adjuvant hormone therapy in intermediate-high risk prostate cancer: LH-RH agonist versus anti-androgens