ESTRO 2020 Abstract book

S682 ESTRO 2020

(PCa). MR-depicted GTV regions have been correlated with the most common site of disease recurrence after RT. SABR with simultaneous integrated boost (SIB) to intraprostatic GTV is dosimetrically feasible without significantly increasing the dose to other OARs with the exception of the urethra. Herein, we hypothesized that rectal spacer may increase the degrees of freedom during SABR planning, thereby enabling a selective high-precision multiparametric MR (mpMR)-directed SIB SABR without incremental dose to the urethra. Material and Methods Ten randomly selected patients from a prospective study of whole-gland SABR plus focal brachytherapy dose- escalation to mpMR-defined GTV. Patients had intermediate/high-risk PCa, with a PI-RADS 4/5 lesion on MR (>5mm and < 1/3 of gland involved). Patients underwent insertion of 3 fiducial markers and rectal spacer. Simulation imaging: mpMR and computed tomography (CT), all co-registered using the fiducial markers. GTV and prostate CTV were contoured on mpMR, mapped onto planning CT using deformable image registration (Raystation v 6.1). 5mm isotropic expansion except laterally (3mm) was used to generate the PTVs. A dose of 36.25Gy/5 and 50Gy/5 were delivered using VMAT to the PTV_prostate and PTV_gtv, respectively. A second distribution was then generated with higher priority placed in reducing the urethra dose by allowing increased dose of up to 3Gy to the rectum and keeping the other OARs within planning constraints. Differences between planned and accumulated delivered doses (D Acc ) were assessed by dose accumulation analyses on treatment cone-beam CT images, assuming geometric relationship of urethra did not change relative to fiducial markers. Planning objectives were PTV D98% ≥ 34.4Gy and CTV D95% ≥40Gy; additional objective of PTV_boost D99% ≥ 47.5Gy for SIB; rectum D20% ≤ 29Gy and D1cc ≤ 36Gy; penile bulb D50 <29.5Gy, bladder D40 <18.1Gy and D10cc <37GY, and urethra D50 < 42Gy. Results The median (range) of GTV and CTV volumes (cc) were 3.5 (0.3-5.1) and 46.4 (21.2 – 85.7). Table 1 summarizes the mean and range of planned and D Acc to the urethra. Difference between planned and D Acc urethra was non significant. D Acc to 50% and 1% of urethra (Gy) were 43.9 (40.6 - 48.5) and 50.7 (45.3 - 52.3). After replanning to spare the urethra dose, D Acc was reduced to 41.4 (39.5 – 47.0) and D1 48.7 (43.1-52.7). The planned median rectal D50 and D1 (Gy) changed from 3.8 (1.9-8.6) to 7.7 (3.3- 12.6) and 31.7 (24.4-37.9) to 33.6 (26.2-39.2) respectively. Conclusion Urethral sparing is feasible with dose-escalation by MR- directed SIB to 50 Gy in this cohort of patients with rectal spacers without exceeding any other OAR dose constraints. This approach may allow selected dose escalation in the ultra-hypofractionated setting while minimizing urinary toxicity.

Purpose or Objective To evaluate clinical outcomes and prognostic factors in patients (pts) affected by localized prostate cancer (LPC) treated with 3D Conformal high dose rate (HDR) brachytherapy (BT) as monotherapy. Material and Methods Between March 2004 and October 2017, 277 pts with (LPC) (T1c-T2cN0M0) were treated in our institute with HDR BT. The mean age was 67 years (range=47-81). Of them, 166 pts were low risk, 145 intermediate risk, and 15 high risk. Overall, 149 patients received 38 Gy in 4 fractions (2 fractions/day in 2 days), 41 patients received 27 Gy in 2 fractions (1 fraction/day), and 87 patients received 19-20 Gy in 1 fraction. The treatment plan was elaborated using CT based software to perform 3D conformal dose planning using these dosimetric constraints: Rectum D2cc <75% of prescription dose (PD); D2cc of bladder <80%PD. For the urethra: (D1%)<115%PD and D10%<110%PD. The prescription for the target was D90%>95%PD. Results Overall survival and cancer specific survival rates were 90% and 97% respectively. The median follow-up was 6 years (range=6-160 months) and biochemical-free disease (BFD) rate was 78%. Patients with low and intermediate risk disease had one advantage in terms of BFD compared to pts with high risk disease ( p =0.04, HR=2.453). Also, in pts patients with (iPSA)<9.5 ng/ml there was one advantage in terms of BFD compared to pts with iPSA≥9.5 ( p =0.022, HR=2.042, 95% CI=1.123-4.081). Moreover, pts who reached a nadir of PSA <0.2 ng/ml and had a PSA value<0.5 ng/ml 3 months after BT treatment had a benefit in terms BFD ( p =0.003 and p =0.001, respectively). In the same way, pts who reached the nadir within 12 months after BT treatment reported a statistically significant advantage in terms of biochemical recurrence ( p =0.01). Patients treated with a total dose of 38 Gy in 4 ff or 27 Gy in 2 ff showed a benefit in terms of BFD compared to pts treated with a total dose of 19-20 Gy in one fraction ( p =0.0001, HR=6.813). Finally, pts with low-intermediate risk disease had an advantage in terms of OS compared to pts with high risk ( p =0.034). There were not statistically significant differences regarding the analyzed risk factors and overall survival. Conclusion High risk disease and total prescribed doses were prognostic factors regarding bochemical recurrences. PSA nadir <0.2 ng/ml, iPSA<9.5 ng/ml, PSA<0.5 ng/ml three months after BT and NADIR reached within 12 months after BT resulted predictive factors regarding biochemical control. PO-1205 Small cell carcinoma of the bladder: Retrospective long-term outcomes of chemoradiation J. Oh 1 , B. Eigl 2 , P. Black 3 , K. Sunderland 4 , S. Tyldesley 1 1 BC Cancer, Radiation Oncology, Vancouver, Canada ; 2 BC Cancer, Medical Oncology, Vancouver, Canada ; 3 University of British Columbia, Urologic Sciences, Vancouver, Canada ; 4 BC Cancer, Population Oncology, Vancouver, Canada Purpose or Objective To describe the epidemiology, cohort characteristics, and treatment patterns of limited stage small cell urothelial bladder cancer (SCUC) patients in British Columbia (BC) province, and to compare the oncologic outcomes of surgery and concurrent chemo-radiation (CRT) for SCUC treated in BC Material and Methods Charts of all patients who have been referred to BC Cancer from 1985 – 2018 with histologic diagnosis of SCUC were Poster: Clinical track: Urology-non-prostate

PO-1204 Clinical outcomes and prognostic factors in patients with localized prostate cancer treated HDR BT D. Delishaj 1 , C.P. Soatti 1 , C. Frigerio 2 , R. D'amico 1 , F. Bonsignore 2 , I.C. Fumagalli 1 , G. De Nobili 1 , A. Cocchi 1 , A. Vola 1 , G. Sangalli 2 , F. Declich 2 , A. Colombo 1 1 Hospital Alessandro Manzoni-Radiation Oncology Department- ASST LECCO- Lecco- Italy, Radiotherapy, Lecco, Italy ; 2 Hospital Alessandro Manzoni-Medical Physics Unit- ASST LECCO- Lecco- Italy, Radiotherapy, Lecco, Italy