ESTRO 2023 - Abstract Book

S456

Sunday 14 May 2023

ESTRO 2023

Purpose or Objective The acute toxicity risks associated with MR guided prostate stereotactic body radiotherapy with daily online plan adaptation (MRg-A-SBRT) compared to fiducial or CT-guided non-adaptive prostate SBRT (CT-SBRT) remain unknown. Materials and Methods We performed a PRISMA-compliant systematic review and meta-analysis of prostate stereotactic body radiotherapy (SBRT) studies that were published between 1/1/18-8/31/22. Inclusion criteria were: prospective study, samples >= 10 patients, prostate SBRT evaluated (4-5 fraction regimen), acute toxicity rates documented. Included studies were dichotomized into 2 groups: treatment delivery platform utilizing either MRg-A-SBRT or CT-SBRT as no studies meeting inclusion criteria of MR guided non-adaptive or CT/fiducial guided adaptive therapy were identified. Retrospective analyses were excluded as were studies of SBRT boost, SBRT re-irradiation or post-operative SBRT. Grade 2 or higher genitourinary (GU) and gastrointestinal (GI) acute toxicity rates were extracted from each study. A random effects model was utilized to estimate toxicity rates and meta-regression was performed to compare toxicity between MRg-A-SBRT and CT-SBRT. Results Twenty-nine unique prospective studies (9 MRg-A-SBRT, 20 CT-SBRT) were identified that met the inclusion criteria and included a total of 2547 patients (329 MRg-A-SBRT, 2218 CT-SBRT). MR-g-A-SBRT studies included 3 studies evaluating a 0.35T system and 6 evaluating a 1.5T system. Proportions of patients in the MRg-A-SBRT studies were higher for high risk prostate cancer (41% vs. 11%, p<0.01), use of androgen deprivation therapy (70% vs 22%, p<0.01), use of pelvic lymph node irradiation (16% vs 6%, p<0.01) and use of rectal spacers (10% vs 4%, p<0.01). The median posterior and non-posterior PTV margins were similar between groups (3mm vs 3mm posterior, p=0.41, and 5mm vs 5mm non-posterior, p=0.36). The median prescription dose (EQD2, a/b = 10) was similar between groups (MRg-A-SBRT 52.1 Gy vs. CT-SBRT 52.25, p=0.09). The ranges of acute G2+ GU toxicity were 5.0%-33.3% in the MRg-A-SBRT studies and 9.1%-46.7% in the CT-SBRT studies. The ranges of acute G2+ GI were 0%-8.3% in the MRg-A-SBRT group and 2.0%-23.3% in the CT-SBRT group. The pooled estimates for acute G2+ GU and GI toxicity for MRg-A-SBRT were 16% (95%CI 10-24%) and 4% (95%CI 2-7%) and for CT-SBRT were 28% (95%CI 23- 33%) and 9% (95%CI 6-12%), respectively. On meta-regression, the odds ratios for acute G2+ GU and GI toxicities comparing MRg-A-SBRT and CT-SBRT were 0.47 (95%CI 0.27-0.79, p<0.01) and 0.40 (95%CI 0.17-0.94, p=0.04), respectively. Conclusion MRg-A-SBRT is associated with reduced risk of both acute GU and acute GI toxicity compared to CT-SBRT. Further prospective studies are indicated to evaluate the clinical benefits of MR guided radiotherapy and adaptive radiotherapy for prostate SBRT. Longer follow up will be needed to evaluate late toxicity and disease control outcomes. PD-0575 UHRT for PCa with a DIL boost– a 5 year update with a focus on the impact of toxicity on QoL G. Corrao 1 , G. Marvaso 1,2 , M. Pepa 3 , M. Zaffaroni 3 , M.G. Vincini 3 , F. Bellerba 4 , S. Gandini 4 , S. Volpe 3 , D. Zerini 1 , C. Fodor 1 , P. Pricolo 5 , S. Alessi 6 , G. Petralia 7 , F.A. Mistretta 8 , R. Cambria 9 , F. Cattani 9 , O. De Cobelli 10 , R. Orecchia 11 , B.A. Jereczek- Fossa 1,12 1 IEO European Institute of Oncology IRCCS, Division of Radiation Oncology, Milan, Italy; 2 University of Milan, Department of Oncology and Hemato-oncology, Milan, Italy; 3 IEO European Institute of Oncology IRCCS, Division of Radiation Oncology, Milan, Italy; 4 IEO European Institute of Oncology IRCCS, Department of Experimental Oncology, Milan, Italy; 5 IEO European Institute of Oncology IRCCS, Division of Radiology, Milan, Italy; 6 IEO European Institute of Oncology IRCCS, Division of Radiology, Milan, Italy; 7 IEO European Institute of Oncology IRCCS, Precision Imaging and Research Unit - Department of Medical Imaging and Radiation Sciences, Milan, Italy; 8 IEO European Institute of Oncology IRCCS, Division of Urology, Milan, Italy; 9 IEO European Institute of Oncology IRCCS, Unit of Medical Physics, Milan, Italy; 10 IEO European Institute of Oncology IRCCS, Division of Urology, Milan, Italy; 11 IEO European Institute of Oncology IRCCS, Scientific Directorate, Milan, Italy; 12 IEO European Institute of Oncology IRCCS, Department of Oncology and Hemato-oncology, Milan, Italy Purpose or Objective Ultra Hypofractionated Radiation therapy (UHRT) represents a curative-intent treatment option in the management of localized prostate cancer (PCa), with disease progression and cancer-specific death rates comparable to radical surgery. The purpose of the present work is to report updated toxicity and oncological results at five years of Phase II prospective trial "Short-term high precision radiotherapy for early prostate cancer with a simultaneous boost to the dominant intraprostatic lesion (DIL) for patients with early-stage PCa”. The aim of the study is to identify clinically meaningful information through the analysis of validated questionnaires testing gastrointestinal (GI) and genitourinary (GU) RT-related toxicity and their impact on quality of life (QoL). Materials and Methods As part of the AIRC IG-13218 (NCT01913717), we analyzed data from patients with low- and intermediate-risk PCa treated with UHRT and simultaneous boost to the DIL. At the end of RT treatment, clinical assessment and prostate-specific antigen (PSA) measurements were performed every 3 months for at least 2 years and GI and GU toxicities were evaluated contextually. QoL of enrolled patients was assessed by the International Prostate Symptoms score (IPSS), European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire—Core 30 (EORTC QLQ-C30), EORTC QLQ prostate-specific (QLQ-PR25), and sexual activity by International Index of Erectile Function (IIEF-5). Patients’ score changes were calculated at the end of RT, at one, 12 and 60 months after RT Results At a median follow-up of 5.1 years (range 3.8-6.8 years), 7 patients died for other cancer causes, 3 patients experienced a clinical relapse of disease and for 45 patients updated data were available. Disease-free survival at 5 years was 82% with a median last PSA of 0.37 ng/ml. At the last follow-up, 32 QoL questionnaires were collected. Extensive analysis of different QoL and toxicity assessments showed that patients’ tolerance was satisfactory across all the considered time points, with a statistically significant improvement of QoL, IPSS and bowels symptoms from baseline to the last follow-up (p= .002, p=.004, p=.02, respectively) (Figure 1). Six grade (G)1 and two G2 gastrointestinal (GI) and one G1 and two G2 genitourinary (GU) toxicities were reported at the last follow-up, and no G ≥ 3 events were reported.