ESTRO 2022 - Abstract Book

S1188

Abstract book

ESTRO 2022

Purpose or Objective With the increased use of PSMA-PET to direct treatment of oligorecurrent prostate cancer (ORPC) after radical prostatectomy (RP), we evaluated the results of stereotactic body or hypofractionated radiotherapy (SBRT / HFRT) for the treatment of patients with ORPC with ≤ 5 lesions using gallium prostate-specific membrane antigen positron emission tomography (68Ga-PSMA-PET/ CT). Materials and Methods We enrolled patients who suffered from biochemical failure and received 68Ga-PSMA-PET/CT before SBRT ( ≤ 12 fractions)/ HFRT (>12 fractions, minimal single dose 3 Gy) without androgen-deprivation therapy (ADT). We evaluated the effect of 68Ga-PSMA-PET/CT for the planning and the progression-free survival (PFS). Treatment related toxicity was measured using Common Terminology Criteria for Adverse Events (CTCAE, v4.0). For acute and late toxicities EQD2 a/b 10 Gy and a/b 3 Gy were assumed. Results 68Ga-PSMA-PET/CT modified the treatment in 70% of the patients. Median follow-up was 18 months (2-30 months). Of 35 patients with 42 lesions, 36% received radiotherapy only for the isolated lesion, while 64% of the patients received radiotherapy for the local regional nodal station with an EQD22 of 50 Gy with boost to the positive PSMA-LN. Mean high dose PTV -PSMA was 19 cc (range 2.54-147), mean dose was 50 Gy (30-74 Gy) in a mean of 14 fractions (6-24), High dose PTV median boost EQD22 of all patients was 72 Gy ( 52-78 Gy), EQD210 56 Gy and EQD23 67.2 (48-74,4). Non-boost median EQD2 values were 57.75 Gy, 47.25, and 54.6 Gy respectively (EQD22 , EQD210, EQD23 ). No patients suffered from recurrence in RT-field, SBRT / HFRT led to prolonged PSA decrease in 20/35 patients, however with 3 patients receiving repeated PSMA based irradiation of novel lesions during follow-up. Overall acute toxicity was low with 2 patients with reported toxicities > grade 1. Nevertheless, there was one patient with grade 4 acute toxicity and 1 patient with grade 3 toxicity, both bowels. Both were associated with large pelvic PTVs close to or at the prostatic bed. Late toxicity was ≤ grade 1 in all patients. Conclusion This study demonstrated the feasibility and safety of metastasis directed SBRT / HFRT to treat ORPC lesions defined by 68Ga-PSMA-PET/CT and promising results regarding intermediate-term PSA decrease were observed. Overall treatment related toxicity was well but PTVs close to RP regions should be restricted A. Castelluccia 1 , D. Marchesano 2 , G. Grimaldi 3 , I. Annessi 2 , F. Bianciardi 2 , A. Di Palma 2 , V. Confaloni 3 , F. Rea 3 , B. Tolu 3 , M. Valentino 2 , L. Verna 2 , M. Rago 2 , C. Borrazzo 2 , L. Capone 3 , M. Masi 2 , R. El Gawhary 2 , P. Gentile 2,3 1 San Pietro FBF, Radiantion Oncology, Rome, Italy; 2 San Pietro FBF, Radiation Oncology, Rome, Italy; 3 UPMC San Pietro FBF, Radiation Oncology, Rome, Italy Purpose or Objective The purpose of this study is to compare different techniques of SBRT for localized prostate cancer (PCa), stereotactic MR- guided adaptive RT (SMART) versus cone beam CT(CBCT)-guided SBRT, in terms of toxicity and time costs. Materials and Methods Patient with localized PCa (clinical stage T1-2bN0M0) underwent SBRT using CT-LINAC system (True Beam STx, Varian) or MR-hybrid LINAC system (MRIdian, Viewray). SBRT was prescribed to a dose of 40 Gy (8 Gy/fr) and 36.75 Gy (7.25 Gy/fr) to prostate and PTV, respectively, at 80% isodose, delivered on 5 days (3fr/week). An anisotropic 5mm-margin (3mm posterior) was created around the prostate for the PTV. Treatment was delivered using two different image guidance (IG) strategies. CT-guided SBRT strategy consisted of a pre-treatment CBCT acquisition with implanted fiducial markers and images matching using the ExacTrac® system. SMART consisted of indentification of target and OARs on pre-treatment MR images, with on-line calculation and delivery of a new plan for every fractions because of inter-fraction variation of bladder and rectal filling. Then an intra-fraction motion management strategy was applied, consisting of a gating approach based on the real-time acquisition of a sagittal cine MRI during the whole delivery time (temporal resolution: 8 frames/s). Mean time for each step of daily workflow was recorded. Common Terminology Criteria for Adverse Events was used to score gastrointestinal and genitourinary early toxicity during 3-month follow-up. Results Sixty patients (pts) treated with prostate SBRT were compared . Real-time adaptive MR-guided RT strategy was used for 30 pts (50%) . Pre-treatment CBCT was performed in 150 treatments. Using CBCT-IG, grade 2 acute rectal toxicity occurred in 3 pts ; 1 pts with Grade 2 and 1 pts with grade 3 urinary toxicity were observed . No grade 2 and 3 toxicity was recorded for SMART treatments. Mean total daily treatment time was about 13 (range 11-17) and 24 (range 22-30) minutes for CT- guided SBRT and SMART respectively. Treatment workflows are shown in table 1 and table 2. PO-1401 MR-guided adaptive versus CT-guided SBRT for prostate cancer: where is cost-benefit balance?