ESTRO 2020 Abstract Book

S605 ESTRO 2020

diagnostic modalities: CT, MRI, PET-CT. In 2009 we developed and implemented in clinical practice variant of SRT in classical fractionation, which consists in irradiating the regional pelvic lymph nodes to 44 Gy, the fossa of prostate gland to 66 Gy and the area of recurrence to 72 Gy. In 2013 we created and patented the technique of hypofractionation SRT. Radiotherapy have been prescribed to the pelvic lymphatic nodes to 46.8 Gy of 1.8 Gy per fraction, to the prostate bed - 61.1 Gy of 2.35 Gy per fraction and clinical recurrence in prostate bed - 65 Gy of 2.5 Gy each, in 26 fractions using simultaneous integrated boost. Some patients receive сombination SRT and hormonal therapy (HT) (6-8 months (agonists LHRH). Results 411 patients were treated from March 2009 to December 2018. 42 (10.2%) patients were treated by classic fractionation SRT, 369 (89.8%) - by hypofractionation SRT. 3-year and 5-year disease free survival (DFS) were 81.3% and 77.6%, respectively. Locoregional control - 100%. The results of our study indicate two main negative factors in the prognosis of the efficacy of SRT – the period of prostate specific antigen (PSA) doubling time less than 6 months (p = 0.035) after RP and a higher PSA level, especially more than 0.5 ng/ml before SRT (p = 0.037). In our study, 247 (60.1%) of 411 patients were treated combination SRT and HT. It was found that 5-year DFS among patients who received a combination of SRT and HT, is higter rates - 81%, compared with patients who were treated by monotherapy SRT - 73.5% (p = 0.5). However, retrospectively analyzing, we noted that patients who were treated by combination SRT and HT had more unfavorable prognosis factors: pT3a-b, pN1, Pn1, PSA level> 1 ng/ml at time the beginning of treatment, the period of PSA doubling time less than 6 months,the presence of regional relapses after RP, the size of the recurrent tumor more than 10 mm. We also have found that pN1 is a reliable adverse prognosis factor effectiveness of SRT. So, a 5-year DFS is significantly lower in patients with pN1 than with pN0, it is 52% and 83%, respectively. Conclusion This study is the result of the use of modern high-precision radiation therapy equipment and advanced clinical approaches in the treatment of patients with locoregional prostate cancer recurrence after radical prostatectomy PO-1150 Biological target volume delineated and 3D UI guided hypofractional radiotherapy for prostate cancer J. Wang 1 , J. Ma 1 , Y. Wang 1 1 University of Electronic Science and Technology of China, School of Medicine- Sichuan Cancer Hospital and Institute, Chengdu, China Purpose or Objective This study aims to evaluate the clinical significance of MRS and PET CT based biological target volume (BTV) delineation in the hypofractionated radiotherapy (HR) with simultaneously integrated boost (SIB) for prostate cancer. The 3D ultrasound imaging (UI) is also proposed for intra- fraction motion management during the HR for prostate cancer. Material and Methods 13 patients with moderate to high risk localized prostate cancer, all examined with MRS or PET-CT (18F-FDG/11C- CHO ） ) before radiotherapy, were investigated. Image fusion was conducted between MRI, MRS, PET CT and the localized CT. We delineated the tumor target volume for GTV MRI , BTV MRS , and BTV PET-CT , respectively, while recoding their volume values correspondingly as shown in Fig. 1(a). For the five patients having explicit BTV, the prescription for prostate and seminal vesicles (GTV) was 2.6Gy/f in 28 fractions, while the other patients received 2.5Gy/f *28f dose for GTV. The prescription of pelvie lymph nodes (CTV) was kept 1.8Gy/f*28f for all patients. CBCT (Elekta XVI

guided), and 3D UI (Elekta Clarity guided) were applied to modify the setup error before each fraction, as shown in Fig.1(b)(c). The 3D UI was also applied for intra-fraction motion management as displayed in Fig. 1 (d).

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.