ESTRO 2021 Abstract Book

S1090

ESTRO 2021

PO-1328 VMAT-SIB boost to the dominant intraprostatic lesion: preliminary results of a dose escalation trial P. Bonome 1 , G. Macchia 2 , M. Ferro 1,1 , S. Cilla 3 , C. Romano 4 , A. Re 1 , V. Picardi 1 , M. Boccardi 1 , D. Pezzulla 1 , S. Cammelli 5,6 , M. Buwenge 5,6 , L. Tagliaferri 7,8 , A.G. Morganti 5 , A. Morganti 6 , V. Valentini 7,9 , F. Deodato 7,1 1 università Cattolica del Sacro Cuore, Gemelli Molise Hospital, Radiation Oncology Unit, Campobasso, Italy; 2 Università Cattolica del Sacro Cuore, Gemelli Molise Hospital, Radiation Oncology Unit, Campobasso , Italy; 3 Università Cattolica del Sacro Cuore, Gemelli Molise Hospital, Medical Physics Unit, Campobasso, Italy; 4 Università Cattolica del Sacro Cuore, Gemelli Molise Hospital, Medical Physics Unit, Campobasso, Italy; 5 Alma Mater Studiorum Bologna University, Department of Experimental, Diagnostic and Speciality Medicine - DIMES, Bologna, Italy; 6 IRCCS Azienda Ospedaliera - Università di Bologna, Radiation Oncology, Bologna, Italy; 7 Università Cattolica del Sacro Cuore, Istituto di Radiologia, Roma, Italy; 8 Fondazione Policlinico Universitario A. Gemelli IRCCS, UOC di Radioterapia, Dipartimento di Scienze Radiologiche, Radioterapiche ed Ematologiche Roma, Italy, Roma, Italy; 9 Fondazione Policlinico Universitario A. Gemelli IRCCS, UOC di Radioterapia, Dipartimento di Scienze Radiologiche, Radioterapiche ed Ematologiche Roma, Italy Roma, Italy, Roma, Italy Purpose or Objective To evaluate the safety and feasibility of stereotactic ablative radiotherapy (SABR) on prostate cancer patients treated with escalating doses to the dominant intraprostatic lesion (DIL). Materials and Methods A Phase I clinical trial was performed in patients with low and intermediate – risk prostate carcinoma (NCCN risk classes), and American Urological Association (AUA) score ≤ 15. Rectal voiding, bladder filling and gold fiducials were mandatory for patients’ set-up. A Volumetric Modulated Arc with simultaneous integrated boost (VMAT-SIB) technique was used with progressively increased total dose to the DIL defined by magnetic resonance imaging (MRI). The prescribed dose to the prostate plus 3-mm margin (PTV2) was 35 Gy (7 Gy per fraction) and remained unchanged. The MRI enhancing lesion with 3-mm margin (PTV1) received the dose escalation in five fractions (planned dose levels: 40, 42.5, 45, 47.5, 50 Gy) (Figure 1). Dose-limiting toxicity (DLT) was defined as any grade ≥ 3 gastrointestinal (GI) or genitourinary (GU) toxicity by Common Terminology Criteria of Adverse Events. Rectal sigmoidoscopy was performed in all patients 12 months after SABR. The Vienna Rectoscopy Score (VRS) was used to grade the 1 year-late rectal toxicity outcome, such as telangiectasia, congested mucosa and ulcers.

Results Thirteen patients (median age: 73 years, range: 58-78) were enrolled between May 2014 and December 2020. All patients had T2a-c N0 M0 clinical stage and/or a Gleason score of ≤ 7; patients were treated as follows: 8 patients (40 Gy), 5 patients (42.5 Gy). Prostate volumes ranged from 28.9 to 97.7 cc, with a median DIL volumes of 4.6 cc (range 1.4-14.3). With a median follow-up of 28 months (range 2 -72 ), no patients experienced dose-limiting toxicity (Table 1). Rectal bleeding (2 patients) and pollachiuria (4 patients) were mainly reported as late toxicity, none higher than grade 2. One-year VRS score was available in 12 of 13 patients and grade 0, 1, 2, 3 were recorded in 3 (25%), 4 (33.3%), 3 (25%) and 2 (16.7%) patients, respectively. Ten of 13 patients (76.9%) underwent short course androgen deprivation therapy (from 3 months before to 3 months after SABR). The median PSA value decreased from 5.4 ng/ml (range 4.2–9.6 ng/ml) (values at diagnosis) to 0.21 ng/ml (range 0.05–2.28 ng/ml) (values at the last follow-up). According to Phoenix definition , one biochemical failure was registered at the first dose level. One year-actuarial local control (defined as irradiated site progression-free) was 100%.