ESTRO 2021 Abstract Book

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ESTRO 2021

late GI event was observed. The most common late GU symptom was nocturia. No significant decline in patient QoL was observed in any studied domain. Conclusion

The combination of 15Gy HDR prostate brachytherapy and prostate SBRT (25 Gy in 5 daily fractions) is a well- tolerated scheme without severe adverse events observed in our prospective phase II trial. Moreover, the majority of patients did not suffer from any adverse event. Patient reported outcomes confirm these results, we could not find any significant decline in any domain from baseline values. PD-0807 MRI-Guided focal boost to intraprostatic lesion using VMAT in prostate cancer. A Phase II Trial. A. Zapatero 1 , M. Roch 2 , P. Castro Tejero 2 , D. Büchser 3 , C. Martin de Vidales 4 , S. Gonzalez 5 , P. Rodríguez Carnero 5 , M.T. Murillo 4 1 Hospital Universitario de La Princesa; Instituto de Investigación Sanitaria IIS-IP, Radiation Therapy, Madrid, Spain; 2 Hospital Universitario de La Princesa, Medical Physics, Madrid, Spain; 3 Hospital Osakidetza, Radiation Oncology, Bilbao, Spain; 4 Hospital Universitario de La Princesa, Radiation Oncology, Madrid, Spain; 5 Hospital Universitario de La Princesa, Radiology, Madrid, Spain Purpose or Objective Evidence coming from prostate pathology studies suggest the existence of a dominant cancer focus or dominant intraprostatic lesion (DIL) within the gland that may be the nucleus of the aggressiveness of the cancer and therefore of recurrence post-treatment. Advances in the identification of the DIL with multiparametric magnetic resonance imaging (mpMRI) have enabled selective focal radiation dose intensification. The aim of this prospective phase II trial was to determine the PSA and mpMRI response, toxicity and quality of life (QOL) in men with localized prostate cancer (PCa) treated with MRI-guided focal boost. We report early results on local and biological control and toxicity. Materials and Methods Thirty patients with localized PCa with a visible DIL identified on mpMRI were enrolled in this study (NCT03030625). Matching point registration of planning TC and T2-weighted, diffusion-weighted and a gradient recalled echo (GRE) MRI images made in treatment position was used for prostate and tumor delineation. Treatment consisted on 35 daily fractions of 2.17 Gy with a concomitant focal boost to the intraprostatic nodule of 2.43 Gy using VMAT (volumetric modulated arc therapy) and IGRT with daily CBCT and intraprostatic fiducial markers. Androgen derivation therapy (ADT) was allowed for unfavorable intermediate and high risk tumors. Biochemical failure was analyzed using nadir+2 ng/ml criteria and local control using mpMRI evaluation at 6 and 9 months following RT. Acute and late toxicity were defined according to CTCAE v4.0 and RTOG/EORTC scales and QoL was assessed using IPSS, EPIC short-form and UCLA-PCI questionnaires. Results Dose intensification was feasible in the 30 patients. The median prostate dose was 77.6 Gy (IQR 77.3-78.1) and the median DIL RT dose was 85.2 Gy (IQR 85.0-85.4). With a median follow up of 30 months (IQR 23.5 – 40.5), all 30 patients remain free of biochemical relapse. A mpMRI complete response was observed in 23 patients during the first post-treatment evaluation performed at 6 months. The remaining 7 patients achieved a complete response in the second mpMRI made at 9 months a. Six out of 30 (20%) patients presented acute grade 2 urinary toxicity with no grade 3 acute complications. Acute rectal toxicity was only found in 2 (6.6%) patients (both grade 1). Only late grade 1 urinary and rectal complications were observed (3 patients respectively) with no grade 2 or more late toxicity. Conclusion Although preliminary, the present results show that focal dose escalation RT using mpMRI guided VMAT technique is associated with an encouraging local and biochemical control and a safe toxicity profile. PD-0808 Patterns of failure in Ga68-PSMA PETCT at rising PSA post radical radiotherapy for prostate cancer S. Sood 1 , P. Pathare 1 , P. Maitre 1 , A. Agarwal 2 , V. Rangarajan 2 , V. Murthy 1 1 Tata Memorial Centre, Homi Bhabha National Institute, Radiation Oncology, Mumbai, India; 2 Tata Memorial Centre, Homi Bhabha National Institute, Nuclear Medicine, Mumbai, India Purpose or Objective To study the patterns of failure on Ga68-PSMA PETCT at rising serum PSA after radical radiotherapy for non- metastatic prostate cancer. Materials and Methods Patients with non-metastatic prostate treated with radical external beam radiotherapy (EBRT) from February 2003 to October 2019 were identified from prospectively maintained institutional database for this IRB approved study. Treatment included moderate or extreme hypofractionation, and risk stratification- appropriate androgen deprivation therapy. Patients with Ga68-PSMA PETCT scan for biochemical and/or clinical progression post RT were eligible for analysis. Serum PSA level at the time of PETCT, and sites of abnormal radiotracer uptake in the scan were recorded. Recurrent lesions were defined using a combination of morphology and radiotracer uptake. Distant lesions ≤3 was considered as oligometastases. Results Of the total 114 patients included, 66% were high risk and 20% had regional nodal involvement at diagnosis. EBRT fractionation was conventional in 32%, moderately hypofractionated in 39% and extreme hypofractionated in 17% patients (median EQD2 1.5 78.5 Gy, IQR 74-82 Gy). Pelvic nodes were treated in 24.6% patients. Median time from RT completion to Ga68-PSMA PETCT was 4.2 years (IQR 2.5-6.3). Median serum PSA at scan was 4.7 ng/mL (IQR 2.6-9.4). Overall PETCT positivity was 88.6%. At PSA ≤2, ≤4 and ≤10 ng/mL, 67%, 82% and 85% patients respectively had an identifiable lesion. In patients with local failure, median SUVmax in prostate was 12.0 (IQR 6.5-21.1). For pelvic nodal failure, median SUVmax in the recurrent node was 11.7 (IQR