ESTRO 2020 Abstract Book

S617 ESTRO 2020

PO-1173 Long term results of IG-IMRT in high risk prostate cancer patients: a monoinstitutional experience N. Di Muzio 1,2 , C.L. Deantoni 2 , C. Cozzarini 2 , I. Dell'Oca 2 , F. Zerbetto 2 , P. Mangili 3 , S. Broggi 3 , M. Pasetti 2 , A. Chiara 2 , F. Borroni 2 , R. Tummineri 2 , L. Perna 3 , R. Calandrino 3 , C. Fiorino 3 , A. Fodor 2 1 Vita e Salute University, Medicine and Surgery, Milano, Italy ; 2 San Raffaele Scientific Institute, Radiotherapy, Milano, Italy ; 3 San Raffaele Scientific Institute, Medical Physics, Milano, Italy Purpose or Objective To evaluate long-term toxicity and outcomes in patients (pts) affected by unfavourable intermediate-, high- and very high- risk prostate cancer (PCa) according to NCCN 2019 classification, treated with image guided- intensity modulated radiotherapy (IG-IMRT) with radical intent. Material and Methods From December 2006 to May 2011, 100 PCa pts underwent a moderately hypofractionated IG-IMRT with radical intent. All pts underwent prophylactic irradiation on pelvic nodes to 51.8 Gy in 28 fractions (EQD2 52.2 Gy, for α/β=1.5 for prostate cancer), with simultaneous integrated boost to seminal vesicles up to 65.5 Gy (77.7 Gy EQD2) and to prostate up to 74.2 Gy (88 Gy EQD2). Neoadjuvant and/or adjuvant androgen deprivation therapy (ADT) was prescribed in 90/100 pts for a median of 28.9 months (3- 120 months). All pts were treated with helical IMRT (Tomotherapy®, Accuray, Wisconsin) and daily IGRT (MVCT). Pts’ characteristics are reported in Table 1.

Hospital Heidelberg, Department of radiation Oncology, Heidelberg, Germany Purpose or Objective During radiotherapy for prostate cancer, interfractional variability results from changes in bladder and rectal position and filling. As a result, the delivered dose may deviate from the planned dose, resulting in reduced dose coverage of the target volumes and increased doses to the organs-at-risk. However, the effects of interfractional variability on dose deviations are largely unknown especially for hypofractionated radiation therapy concepts. Material and Methods For ten consecutive patients receiving intensity- modulated radiotherapy for low- or intermediate-risk prostate carcinoma hypofractionated radiation treatment was planned to atotal dose of 60 Gy in 3 Gy fractions using the commercial TPS RayStation (RaySearch). Patients were instructed to present to treatment with an empty rectum and a comfortably filled bladder; all patients received daily in-room diagnostic CT imaging (fxCT) in treatment position for position verification (total of 200 fxCTs). GTV, CTV, PTV as well as bladder, rectum, sigma and femoral heads were contoured on all fxCTs, and the pelvic anatomy was compared to that on the respective planning CT scans. Applied fractional doses were calculated based on each fxCT, and doses were mapped to the planning CT and accumulated over the course of treatment using deformable registrationPlanned and delivered doses were compared on a voxel-by-voxel basis regarding dose volume parameters and and γ-analysis to a level of 3mm/3%. Results The mean CTV volume was 74 ± 41 ml; the mean volume for the PTV was 140 ± 90 ml. The delivered dose D 50 to the CTV was 0.13 ± 0.57 Gy higher than prescribed with a p- value of 0,13941, while both the D 2 (mean 1,45 ± 3,33 Gy, p-value 0,28450) and the D 98 (mean -0,26 ± 0,57 Gy, p- value 0,72127) were lower. For the PTV the delivered dose D 50 was 0.03 ± 0.47 Gy lower than prescribed with a p-value of 0,72127 and the D 2 (mean -0,43 ± 0,54 Gy, p-value 0,05933) and the D 98 (mean -10.34 ± 7,96 Gy. p-value 0,00506 ) were also lower. The bladder volume showed the biggest interfractional volumetrical variability. On average, the bladder volume ranged at 286 ± 168 ml, resulting in a dose deviation of 1,96 ± 4,8 Gy (D 50 ) with a p-value of 0,11412. The average rectal volume was 76 ± 33 ml, leading to an increase in the median delivered dose of 0.29 ± 2,76 Gy (p-value 0,57506). The γ-analysis to a tolerance level of 3mm and 3 % dose difference resulted in 96,08 ± 3,4 %.

Median ( range) age at diagnosis 75 (58-90) years Median (range) iPSA

10.9 (1.68-206) ng/ml

6:

13 14 28 25

7 7

(3+4): (4+3):

Median ( range) Gleason Score

8:

9: 1710: 3

cT1c: cT2a:

32

13

T Stage

cT2b-c: cT3: 13

42

Results Median follow up was 94 (23-215) months. Cumulative late gastro-intestinal (GI) toxicity was acceptable: 13% G2 and 6% G3 (rectal bleeding), the latter requiring Argon Plasma Coagulation (APC). At the last follow up none of the pts presented G3 GI toxicity. Cumulative late genito-urinary (GU) toxicities was 15% G2 and 13% G3-G4; 11 pts presented G3 urinary stenosis and in 7 the G3 toxicity was solved with urethrectomy, thus only 4 % of pts presented G3 GU toxicity at the last follow up. Two patients presented G4 events (1 urethrostomy, due to repeated urethrectomies, and 1 cystectomy, due to hyperactive bladder). Thirty pts were dead at the last follow up, but only 5 due to PCa progression. Eleven pts experienced biochemical relapse, 1 of whom also with an intraprostatic relapse and 2 with bone metastases. Fifty-nine pts are alive and free from biochemical progression. Conclusion IG-IMRT in high-risk PCa pts allows dose escalation and pelvic nodal irradiation, with very good long term outcomes, with 8-year biochemical relapse free survival of 89% and 8-year cancer specific survival of 95%. Rectal G3 toxicity was acceptable, and solved in all pts with APC. Genito-urinary G3 toxicity was fair, limited by the presence of the urethra in the field, and solved in 7 out of 11 pts.

Conclusion The observed anatomical variabilities of bladder, rectum and target volumes resulted in significant dose deviations only of the PTV (p-value 0,00506) at low doses, while both the D 50 and D 2 of the PTV were comparable. For the bladder and the rectum only non-significant dose deviations occurred. Thus in case of daily CT-based repositioning, regular adaptive re-planning may not be necessary in the majority of cases.