ESTRO 2020 Abstract book

S653 ESTRO 2020

PO-1151 Is the dose-distribution in bladder really unimportant for GU toxicity in prostate cancer patients? W. Majewski 1 , A. Napieralska 1 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiotherapy Department, Gliwice, Poland Purpose or Objective In patients with prostate cancer there is a well- documented dose-volume-effect for rectal toxicity. However, data on GU toxicity did not reveal a clear dose- volume-effect relationship in a bladder. We assumed that a lack of such relationship may be caused by many confounding factors, which influence GU toxicity. Therefore the analysis was restricted to patients presenting no dysuria and no urinary infections at the beginning of radiotherapy which are factors that seem to In a group of 180 patients with prostate cancer treated with a radical 3DCRT or IMRT between 2008 and 2011, 99 patients (55%) had no dysuria and urinary tract infections before radiotherapy. Those patients formed the group for further analysis. Mean patients’ age was 68 years, there were 16%, 39% and 45% of patients in low, intermediate and high-risk group, respectively. Patients were treated with conventionally fractionated radiotherapy to the total dose of 76 Gy with 2 Gy per fraction, in 45% of patients pelvic lymph nodes irradiation was performed. Patients were planned and treated with a comfortably filled bladder (2 h after urination). Bladder dose constraints were as follows: V70 ≤20%, V60 ≤35%, V50 ≤50%. We assessed Grade 2+ acute GU toxicity and Grade 2+ late GU toxicity in relation to various parameters representing dose distribution in the bladder: volume of the target (CTV), V30-V75Gy, Dmax, D2% (near maximum dose). The evaluation of the dose-effect relationship was performed with logistic regression for acute toxicity and Cox proportional hazard model for late toxicity. Results Acute G2+ GU toxicity was observed in 37 patients (37%), and late G2+ GU toxicity was observed in 7 patients (7%) with an actuarial rate of 7% at 5-years. With respect to the acute toxicity only D2% had statistically significant (p=0.033) impact on the incidence of acute G2+ GU toxicity. The volume of the target (CTV) had some statistical trend (p=0.098). With respect to late G2+ GU toxicity only D2% had statistically significant impact (p=0.017) with some statistical trend for Dmax (p=0.074). Conclusion In the purified group of patients presenting neither dysuria nor urinary infections before RT some impact of the dose distribution in the bladder on GU radiation toxicity may be observed. Only very high-dose regions were important. Probably during treatment planning much effort should be put on reducing very high dose volumes and “hot-spots” because they seem to be more important than other dose- volume parameters in a bladder. PO-1152 Postoperative Prostate Cancer treated with High-dose Radiotherapy. E. Amaya 1 , P. Samper 1 , M. Hernández 1 , M.D. De Las Peñas 1 , J. Zapatero 1 1 Rey Juan Carlos Universitary Hospital., Radiation Oncology, Madrid, Spain Purpose or Objective To analyze and release our center outcomes about prostate cancer patients with Biochemical Failure (BF) after radical prostatectomy, treated with postoperative high-dose radiotherapy through daily IGRT system. Material and Methods Restrospective study of 57 patients with a mean age 62.39 (range 49-72) years. All patients underwent surgery and influence GU toxicity. Material and Methods

Results For the five patients having explicit BTV, GTV MRI was 3.52±1.69cm 3 , BTV MRS was 6.64±2.27cm 3 , and BTV PET-CT was 5.47±2.60cm 3 .Significant difference was only found between GTV MRI and BTV MRS （ P = 0.046). Compared with GTV MRI, the average increasing volumes of BTV MRS and BTV PET-CT were 89.07%, 55.52%, respectively. For BTV MRS ， the prescription dose (PD) and biological effective dose (BED) ranged from 70.09 to 73.45Gy and 129.06 to 135.54Gy. For CTV ， the PD and BED ranged from 66.02 to 69.40Gy and 113.3 to 124.82Gy, respectively. In all cases, bladder and rectum were irradiated within the safe limitation. We analyzed the serum PSA at first diagnosis, before HR and after HR, and the results were demonstrated in Fig. 2. After a median follow-up of 7 months (3-12 months), the average PSA was reduced from 47.4±30.3 ng/ml (before HR) to 0.8±1.1 ng/ml (after HR) ． four of the patients (30.7%) experienced Grade 2 acute gastrointestinal (GI) toxicity, 1 of the patients (7.7%) experienced Grade 3 acute GI toxicity. 3 of the patients (23%) experienced Grade 2 acute genitourinary (GU) toxicity and none of the patients were observed Grade 3 GI and GU toxicity.

Conclusion The MRS and PET CT have been demonstrated clinically beneficial for delineating BTV of prostate cancer. The potential ability where 3D UI image are utilized for prostate intro fraction motion management has also been validated. Compared with the conventional CBCT guided scheme, the proposed 3D UI scheme is non-irradiative and therefore more clinically secure.