ESTRO 2024 - Abstract Book

S2419

Clinical - Urology

ESTRO 2024

Maria Roch 1 , Sara Carroceda 2 , Pablo Castro 1 , Laura Zaragoza 3 , Rocio Simon 1 , Leopoldo Cogorno 4 , Pablo Chamorro 1 , Pablo Rodriguez 5 , Paloma Botella 1 , Alba Obesso 1 , Almudena Zapatero 3 1 H.U. La Princesa, Medical Physics, Madrid, Spain. 2 H.U. La Pricnesa, Radiation Oncology, Madrid, Spain. 3 H.U. La Princesa, Radiation Oncology, Madrid, Spain. 4 H.U. La Princesa, Urology, Madrid, Spain. 5 H.U. La Princesa, Radiology, Madrid, Spain

Purpose/Objective:

Dose – escalated stereotactic body ablative radiotherapy (SBRT) to the whole prostate has been reported to be feasible and safe but at a risk of increased toxicity, mainly urinary. We report preliminary results on local control using multi parametric magnetic resonance imaging (mpMRI), toxicity and quality-of-life (QoL) outcomes of a prospective phase 2 study of risk-adapted dose-escalation using ultra-hypofractionated SBRT in localized prostate cancer.

Material/Methods:

A total of 50 patients were enrolled in a prospective phase II study to determine the efficacy and safety of risk adapted dose intensification SBRT with 2 regimens. 13 patients with low risk disease received 36.25 Gy in 5 fractions and 37 intermediate risk patients received 40 Gy in 5 fractions. SBRT was delivered to the prostate with inclusion of 1/3 or 2/3 of the seminal vesicles and with an isotropic expansion of 5 mm (3 mm posteriorly). Exclusion criteria were IPSS > 18 and prior TUR of prostate. Treatment was delivered using volumetric modulated arc therapy (VMAT) and daily image-guided radiation therapy (IGRT) intrafractional control system with online tracking using intraprostatic fiducial markers. Biochemical failure was analyzed using PSA nadir +2 ng/mL criteria, and local control using mpMRI evaluation at 6 – 9 months following RT and comparing with pre-treatment mpMRI. Acute and late toxicity were defined according to CTCAE v.4.03 scale and QoL was assessed using the Expanded Prostate Cancer Index Composite (EPIC) form. A decreased of >0.5 standard deviation (σ) of baseline values for each domain score was considered clinically relevant (mild change). A change >1 σ of baseline values was considered moderately relevant (moderate change) and a change of >2 σ was considered a severe change. The median PTV-prostate dose was 40.0 Gy (IQR 37.3-40.8). With a median follow up of 17.0 months (IQR 13 – 30.6), all patients remain free of biochemical relapse. 25 patients were evaluable for mpMRI local response. A mpMRI complete response was observed in 23 patients and a partial response in 2 patients during the first post treatment assessment performed at 6 months (both treated 40 Gy). We have still no data of the second mpMRI at 9 months for these partial responders. CTCAE acute and late grade 2 urinary toxicity was observed in 9 (18%) and 1 (2%) patients respectively. No grade 3 or more urinary adverse events were observed. No grade 2 or more acute and late grade 2 rectal toxicity was reported within the analysis frame time. 38 patients completed EPIC questionnaire before treatment and during follow-up (every 3 and 6 months following RT). Questionnaires during and immediately post SBRT were no planned in the study. While a reduction in the QoL score was observed compared to the baseline situation in all the analyzed domains (see figure 1), the EPIC scores showed overall no significant differences for the urinary and sexual aspects between baseline and 24 months post treatment. Only at the 24 check-up, the bowel and hormonal QoL was slightly worse (0.6 σ, clinically relevant but mild). Though the number are small, when we compared both SBRT dose protocols, patients in the lower SBRT dose group (36.25 Gy) experienced no clinically significant reduction in the quality of life Results: