ESTRO 2021 Abstract Book

S753

ESTRO 2021

Institute, Department of Medical Physics, Milano, Italy; 4 Vita-Salute San Raffaele University, Medicine and Surgery, Milano, Italy

Purpose or Objective High dose (HD) radiotherapy (RT), with radical intent, is used more and more in prostate cancer (PCa) oligometastatic patients (pts) with good outcomes and low toxicity profile. The aim of this retrospective study is to evaluate the results of HD-RT in only lymph-nodal (LN) versus only bone (B) PCa oligometastatic disease. Materials and Methods Pts with 1-2 B or 1-5 LN metastases, treated with radical doses, were considered for this analysis. From February 2005 to June 2019, 192 oligometastatic PCa pts (150 LN, 42 B) were treated in our Institute. RT was delivered with helical IMRT (TomoTherapy®, Accuray, Sunnyvale, CA) prescribing high doses, with radical intent. All pts were treated with extended nodal radiotherapy (ENRT) (pelvic in 76 pts, para-aortic in 27 pts, mediastinal in 13 pts, pelvic + para-aortic in 76 pts) to a median dose of 51.8 Gy/28fr. In pts of the LN group a simultaneous integrated boost (SIB) on 11C-Choline PET/CT (PET/CT) positive nodes was prescribed to a median dose of 65.5 Gy/28fr. In B group, bone metastases were treated to a median dose of 51.8 Gy/28 fr. In all patients not previously treated, prostate or prostatic bed was irradiated (median EQD2 88 Gy and 74 Gy respectively). In 83% of pts androgen deprivation therapy (ADT) was prescribed, for a median of 35 months (range 0-84), but 38 o f them were already castration resistant. Acute and late toxicities were graded according to CTCAE v 5. Results Median follow up was 59.7 months (range 11.3-148.9). Late toxicity was acceptable and, in all cases, caused by prostate/prostatic bed irradiation: 12 pts presented grade (G) 3 genitourinary (GU) toxicity, 1 patient G 4 GU toxicity and 3 pts G 3 rectal toxicity. At the time of analysis 62 pts were dead, 26 of whom for PCa progression. ADT influences biochemical relapse free survival, thus disease free survival was used for outcome evaluation (see figure). However 41% of pts never experienced a biochemical relapse after RT. The 5 years- DFS was 60% in B group and 77% in LN group (p-value 0.05).

Conclusion In this large cohort of already metastatic patients with a long follow up, good results in term of systemic tumor control were observed after HD-RT, with radical intent. Apparently LN oligometastatic pts have a better outcome than B oligometastatic pts, but the results are satisfactory also in the later group. Further investigation, already scheduled, is warranted to identify the patients who most benefit from this treatment modality. PD-0911 Real world utilization of radical local therapy in metastatic castrate sensitive prostate cancer S. Malone 1 , C. Wallis 2 , B. Shayegan 3 , S. Morgan 4 , F. Saad 5 , S. Hotte 6 , K. Chan 7 , L. Park-Wyllie 8 , S. Roy 9 1 The Ottawa Hospital Cancer Centre, Radiation Oncology, Ottawa, Canada; 2 Vanderbilt University Medical Centre, Department of Urology, Nashville, USA; 3 St. Joseph's Health Care, Institute of Urology, Hamilton, Canada; 4 The Ottawa Hospital Cancer Centre, Department of Radiation Oncology, Ottawa, Canada; 5 University of Montreal Hospital Center, Department of Urology, Montreal, Canada; 6 Juravinski Cancer Centre, -, Hamilton, Canada; 7 Janssen Inc., -, Toronto, Canada; 8 Janssen Inc., Scientific Advisor, Toronto, Canada; 9 New York Medical College, Department of Medicine, New York, USA Purpose or Objective Based on the evidence provided by Stampede, receipt of radical local radiotherapy (RT) improves overall survival in low volume metastatic castrate sensitive prostate cancer (mCSPC). It is unknown to what extent the use of RT among men with de novo mCSPC has been adopted in routine practice. We performed a population-based study among patients in Ontario, Canada to determine if the Stampede publication changed utilization of RT in mCSPC and, second, if there was geographic variation in RT use. Materials and Methods We performed a population-based study of men diagnosed with de novo mCSPC between 2014 and 2019. We linked population-based healthcare databases, as administered at the level of Local Health Integration Networks (LHINs) in Ontario, to examine treatment patterns following diagnosis of mCSPC. We calculated the proportion of patients who received local RT within 6 and 12 mo of initial diagnosis. Multinomial logistic regression analyses were used to examine the association between receipt of RT with geographic region (LIHN), while adjusting for baseline patient and disease characteristics and socio-economic status. We