ESTRO 36 Abstract Book

S723 ESTRO 36 2017 _______________________________________________________________________________________________

The results demonstrate that bladder filling helps limit dose to the small bowel, and therefore is of paramount importance that every effort is made to ensure consistency of bladder filling for patients who are undergoing pelvic IMRT. EP-1363 Clinical efficacy of a dose escalated and hypofractionated pelvic IMRT study in prostate cancer A. Khan 1,2 , K. Thomas 3 , L. Truelove 4 , M. Ferreira 1,2 , S. Gulliford 5 , H. McNair 6 , C. Parker 2 , R. Huddart 1,2 , D. Dearnaley 1,2 1 Institute of Cancer Research, Division of Radiotherapy and Imaging, Sutton, United Kingdom 2 Royal Marsden NHS Trust, Academic Urology Unit, Sutton, United Kingdom 3 Royal Marsden NHS Trust, Research Data management and statistics unit, London- United Kingdom, United Kingdom 4 Institute of cancer research and Royal Marsden NHS Trust, Bob Champion Unit, Sutton, United Kingdom 5 Institute of cancer research and Royal Marsden Hospital, Joint Department of Physics, London, United Kingdom 6 Institute of cancer research and Royal Marsden NHS trust, Department of physics, London, United Kingdom Purpose or Objective The role of pelvic lymph node (PLN) radiotherapy in high- risk localised prostate cancer remains controversial. The dose to PLN is limited by bowel toxicity and the use of intensity modulated radiotherapy (IMRT) has been developed to improve the therapeutic ratio. The IMRT trial was a phase I/II trial conducted in 426 patients at a single centre, with the aim of exploring dose- escalated and hypofractionated regimes of pelvic irradiation. We report the long term outcomes of this trial cohort. Material and Methods Eligible patients had high risk (>T3a, Gleason ≥8 or PSA ≥20) disease with an estimated risk of lymph node involvement of ≥30%, or lymph node positive disease. IMRT was inverse planned to give 70-74Gy in 35- 37 fractions to the prostate and sequential patient cohorts received 50Gy (n=25), 55Gy (n=70) and 60Gy (n=138) to the pelvis in 35-37 fractions using a simultaneous integrated boost technique. Positive lymph nodes received an additional 5Gy boost. The remaining patients received 60Gy in 20 fractions to the prostate and 47Gy in 20 fractions over 4 weeks (n=64) or 47Gy in 20 fractions over 5 weeks (n=129) with an additional 4Gy boost to positive lymph nodes. All patients received long course androgen deprivation therapy, commencing at least 6 months before radiotherapy. Biochemical failure was defined according to the Phoenix criteria of the nadir +2ng/ml. Local recurrence was confirmed with MRI and/or histological confirmation. Distant staging with CT, MRI, nuclear medicine bone scan or choline-PET CT was performed in patients with biochemical relapse to establish all sites of 426 patients were recruited between 09/08/2000 and 09/06/2010 and the median follow up for the whole cohort at the time of analysis was 7.6 years. Median age was 65 years (IQR 60-70 years) and median presenting PSA was 21.4 ng/ml (IQR10.2-42.8 ng/ml). The total number of failure events was 169. Freedom from biochemical /clinical failure at 5 years was 71% (95% CI 66%-75%). The 5 year prostate cancer specific survival was 92% (95% CI 89%-94%) and overall survival was 87% (95% CI 84%-90%). Table 1 demonstrates the distribution of all documented relapse. Results

sites

of

relapse

in

each

cohort.

Conclusion Pelvic IMRT with dose escalation and hypofractionation is associated with a low rate of pelvic recurrence. Freedom from biochemical/clinical failure , cancer specific survival and overall survival appear favourable, but high dose pelvic IMRT requires testing in a phase 3 trial. EP-1364 Substratification of prostate cancer risk groups by core involvement and T stage may alter prognosis A.B. Hopper 1 , J.P. Einck 1 1 University of California San Diego, Radiation Medicine and Applied Sciences, San Diego, USA Purpose or Objective Stratification of prostate cancer patients into low, intermediate and high risk groups has shown to be an important tool for prognostic outlook and treatment planning. The intermediate and high risk groups have been shown to be quite heterogenous though, and substratification of these two groups may offer improved guidance. Recent research has shown that a five group risk stratification system may outperform the traditional three group system in predicting prostate cancer specific mortality, though this study did not use detailed staging information or % core involvement (Gnanapragasam et al. PLoS Medicine 2016). We sought to evaluate a five tiered system, specifically substratification of intermediate (IR) and high risk (HR) patients, using more detailed information with regard to stage and biopsy core involvement. Material and Methods 378 intact PCa patients classified as IR or HR were treated with radiotherapy at our institution between Jan 2005 and Dec 2013, excluding any patients with prior metastases or positive nodes on imaging. 48 patients were designated as favorable (fIR) within the IR category with only one IR factor, no predominant Gleason 4 pattern and % of cores involved ≤ 50%. 147 patients were unfavorable IR (uIR) with any Gleason pattern 4+3, >50% of cores involved or multiple IR factors. 78 patients were favorable HR (fHR) with only one of Gleason 4+4, PSA > 20, or clinical stage T3. 105 patients were unfavorable HR (uHR) with a combination of multiple HR factors or any Gleason 5 pattern (GS 9 or 10). Recurrence was defined using the Phoenix criteria of PSA nadir + 2 ng/mL. Kaplan-Meier analysis was used to compare biochemical progression free survival (bPFS) between substratification groups. Median follow up was 47 months. Results Log-rank testing showed no significant difference in total bPFS between fIR and uIR groups (p=0.293). fHR and uHR groups were found to have significantly different bPFS (Figure 1, p=0.036). Overall comparison between the 4 groups showed a significant effect on bPFS (p = 0.038). Pairwise analysis showed that there was not a significant