ESTRO 2023 - Abstract Book

S716

Monday 15 May 2023

ESTRO 2023

Majority of patient cases do not benefit clinically from daily adaptation, assuming the initial plan is good quality and option of efficient replan is available. References 1. Hafeez S, Webster A, Hansen VN, McNair HA, Warren-Oseni K, Patel E, et al. Protocol for tumour-focused dose- escalated adaptive radiotherapy for the radical treatment of bladder cancer in a multicentre phase II randomised controlled trial (RAIDER): Radiotherapy planning and delivery guidance. BMJ Open. 2020; 10(12) doi:10.1136/bmjopen-2020-041005. 2. Foroudi, F, Wong J, Haworth A, Baille A, McAlpine J, Rolfo A, et al. Offline adaptive radiotherapy for bladder cancer using cone beam computed tomography. J Med Imaging Radiat Oncol. 2009 Apr; 53(2): 226-33. doi:10.1111/j.1754- 9485.2009.02066.x. 3. Murthy V, Gupta P, Baruah K, Krishnatry R, Joshi A, Prabhash K, et al. Adaptive radiotherapy for carcinoma of the urinary bladder: long-term outcomes with dose escalation. Clin Oncol (R Coll Radiol). 2019 Sep; 31(9): 646-652. doi:10.1016/j.clon.2019.06.005. 4. Cabaille M, Khalifa J, Tessier AM, Belhomme S, Crehange G, & Sargos P. A review of adaptive radiotherapy for bladder cancer. Cancer Radiother. 2021 May; 25(3): 271–278. doi:10.1016/j.canrad.2020.08.046. 5. Murthy V, Master Z, Adurkar P, Mallick I, Mahantshetty U, Bakshi G, et al. ‘Plan of the day’ adaptive radiotherapy for bladder cancer using helical tomotherapy. Radiother Oncol. 2011 Apr; 99(1):55-60. doi:10.1016/j.radonc.2011.01.027. 6. Shepherd M, Graham S, Ward A, Zwart L, Cai B, Shelley C, Booth J. Pathway for radiation therapists online advanced adapter training and credentialing. Tech Innov Patient Support Radiat Oncol. 2021 Dec; 20:54-60. doi:10.1016/j.tipsro.2021.11.001. MO-0869 The impact of the ADC for the early prediction of treatment response after definitive radiotherapy C. Onal 1 , G. Erbay 2 , O.C. Guler 3 , E. Oymak 4 1 Baskent University Faculty of Medicine, Department of Radiation Oncology, Adana, Turkey; 2 Baskent University, Department of Radiology, Adana, Turkey; 3 Baskent University, Department of Radiaition Oncology, Adana, Turkey; 4 Iskenderun Gelisim Hospital, Radiation Oncology Clinic, Hatay, Turkey Purpose or Objective Few studies have demonstrated changes in apparent diffusion coefficient (ADC) values during or after definitive radiotherapy (RT) in prostate cancer (PC) patients; however, its role in evaluating treatment response and prognostic significance on biochemical control in patients with PC treated with definitive RT has not been adequately investigated. We assessed early changes in ADC and serum prostate specific antigen (PSA) values after definitive RT in low- and intermediate-risk PC patients. Materials and Methods The clinical data and ADC parameters of 229 PC patients were retrospectively evaluated. All patients underwent DW-MRI for initial staging and RT planning, and after the completion of RT. All patients were treated with 78 Gy to the prostate ± seminal vesicles, 78 Gy to the prostate ± seminal vesicles, and 86 Gy to the intraprostatic lesion. No patient received pelvic nodal irradiation and hormonoterapy. Receiver operating characteristic curves were generated for primary tumor post- treatment ADC response to determine the cutoff for predicting recurrence. The prognostic factors predicting freedom from biochemical failure (FFBF) and progression-free survival (PFS) were analyzed using univariable and multivariable analyses. Results Most patients (75.1%) had Gleason 6 tumor, had low-risk disease (64.4%), and were treated with SIB technique (85.6%). The median pretreatment serum PSA level was 8.3 ng/mL (range: 1.6–20.0 ng/mL). The primary tumor was found in the peripheral zone in 137 patients (59.8%) and in the central zone in 92 patients (40.2%). The mean pretreatment ADC value was 0.76 ± 0.16 × 10 ˗ ³ mm ² /sec, which is significantly lower than the post-treatment ADC value (1.09 ± 0.20 × 10 ˗ ³ mm ² /sec; p < 0.001) With a median follow-up time of 80.8 months, the 5-year FFBF and PFS rates were 95.9% and 89.3%, respectively. Eleven patients (4.8%) had PSA relapse, with a median of 34.4 months after the completion of RT. A statistically significant difference in post-treatment ADC values was noted between patients with and without recurrence (0.94 ± 0.07 vs. 1.10 ± 0.20 × 10 ˗ ³ mm ² /sec; p < 0.001). Patients with a Gleason score of 6 and low-risk disease had significantly higher post- treatment ADC and PSA levels than their counterparts. The progression rate was 90.9% for patients with ADC ≤ 0.96 × 10 ˗ ³ mm ² /sec and 25.2% for patients with ADC > 0.96 × 10 ˗ ³ mm ² /sec (p < 0.001). In the multivariable analysis, a lower ADC value and intermediate-risk disease were independent predictors of worse FFBF. However, there were no significant prognostic factors for predicting PFS. Conclusion To the best of our knowledge, this is the first study to evaluate the feasibility of ADC values measured with DW-MRI for treatment response evaluations in PC patients undergoing definitive RT. Our findings suggest that the tumor ADC value measured four months after definitive RT could be used as a quantitative imaging modality for therapy monitoring. MO-0870 HPV subtypes and integration not prognostic in p16+ oropharyngeal squamous cell carcinoma J. Lilja-Fischer 1 , M.H. Kristensen 1 , T. Steiniche 2 , T. Tramm 2 , J.G. Eriksen 1 , J. Overgaard 1 , M. Stougaard 2 1 Aarhus University Hospital, Experimental Clinical Oncology, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Pathology, Aarhus, Denmark Purpose or Objective Treatment response and prognosis after primary (chemo-)radiotherapy for oropharyngeal squamous cell carcinoma (OPSCC) is affected by Human Papillomavirus (HPV) status, with a markedly better prognosis in HPV-positive OPSCC. There are numerous HPV subtypes, and it is still debated if prognosis depends on this. Further, HPV DNA may be integrated into the Mini-Oral: Biomarkers