ESTRO 2021 Abstract Book

S350

ESTRO 2021

The Netherlands

Abstract not available

Joint symposium: ESTRO-ASTRO: FLASH radiotherapy from a multidisciplinary prospective

SP-0456 – SP-0459 Abstracts not available for this session

Symposium: Salvage treatment for radiotherapy-recurrent primary prostate cancer

SP-0460 Immediate local or deferred therapy: The role of prognostic factors and novel imaging modalities W. Majewski 1 1 Maria Sklodowska-Curie National Research Institute of Oncology, Gliwice Branch, Radiotherapy Department, Gliwice, Poland Abstract Text Radio-recurrent prostate cancer is a great challenge. Recent meta-analysis of high-risk patients treated with radical radiotherapy (RT) revealed that local recurrence has the influence on overall, prostate cancer specific, and distant metastases-free survival. Therefore, local salvage treatment if possible should be considered in such patients. There are options of prostatectomy, brachytherapy, SBRT or other methods. The efficacy is quite good with a biochemical control (BC) around 60% at 5 years. However, an important issue is the diagnosis of a recurrence and defining the extent of a disease. PSMA PET/CT is currently the best way to detect the source of a biochemical recurrence and to select those patients who will be the best candidates for local treatment. It proved to be more accurate than choline- based PET/CT. The detection rate with PSMA PET/CT is around 60% in patients with biochemical recurrence after prostatectomy, 90% in those recurring after radiotherapy and 70% in combined groups. The detection rate is associated with a PSA value and increases from 40-50% for patients with PSA <0.5 ng/ml to 90% in those with PSA >2 ng/ml. It may be expected that around 30%-50% of biochemical recurrences after RT, detected with this imaging method, will be local and approximately 30% isolated local failures. It should be stressed that PSMA PET/CT is very accurate in a diagnosis of local failures with a PPV of almost 100%. What is important even in patients with progressing PSA, but not reaching the Phoenix criteria of a biochemical recurrence the anticipated detection rate will be around 80%. It results in a reasonable suggestion of an earlier diagnosis of radio-recurrent prostate cancer. The introduction of PSMA PET/CT into diagnostics leads to the change in a planned treatment of a recurrent prostate cancer in 50% of patients, which shows its clinical utility. Another diagnostic option for suspicious local recurrence is MRI. The diagnosis of radio-recurrence is based mainly on DWI, ADC and optionally contrast enhancement. However it may be confounded by post-irradiation changes like inflammation, atrophy, fibrosis. Nonetheless, multiparametric (mp) MRI has a capability to distinguish between recurrence and benign tissue. MRI is considered to have a comparable detection rate for local recurrences as PSMA PET/CT. Its sensitivity ranges from 50% to 90%, with PPV of around >90%. Concordant results of both PSMA PET/CT and MRI especially with corresponding PSA kinetics will be indicative of local recurrence and may raise the question on a necessity of a biopsy. Whether we can omit a confirmation biopsy is a matter of debate. It is reasonable to have a confirmation of a recurrence before second-line treatment, because it is often associated with an increased risk of sequalae. According to various guidelines confirmation biopsy is mandatory. Furthermore, the pathology findings of a recurrent prostate cancer may be of prognostic value. It is now well known that the primary pathology diagnosis often changes in a recurrent cancer. Local recurrences are usually more aggressive not only in terms of a Gleason score, but also other pathologic features. Those factors can be derived from the original pathology report as well, but because of the possibility that recurrent cancer will differ from the primary, the biopsy would be more accurate. However, there are many difficulties to exactly diagnose recurrent cancer cells; large proportion of cancer cells bears radiation effects which are not that straightforwardly related to clinical endpoints. The pathology features of a recurrent cancer may be also helpful in determining the role of a concomitant or deferred systemic treatment as for instance androgen deprivation therapy (ADT). The PSA kinetics may be useful to predict the treatment outcome. Probably the PSA doubling time (PSADT) at recurrence is most indicative of local vs systemic failure. Together with imaging and pathology findings it may serve as a predictive factor for adding for instance a systemic treatment. On general, PSADT < 6 months will rather suggest dissemination, whereas long PSADT and long time to the PSA recurrence will be rather indicative of a local recurrence. Who is the optimal candidate for local therapy? Should it be combined with a systemic treatment? These are the key question, which should be addressed and validated prospectively.

SP-0461 The role of EBRT: Can we give second chances? B. Jereczek-Fossa 1 1 European Institute of Oncology/University of Milan, Radiation Oncology , Milan, Italy

Abstract Text Between 30% and 47% of patients treated with definitive radiotherapy (RT) for prostate cancer are at risk of intraprostatic recurrence during follow-up. The routine approach consists in a life-long palliative androgen deprivation therapy. In some selected patients, local approach is being proposed, including surgery, cryotherapy, HIFU and re-irradiation by brachytherapy or external beam RT. Re-irradiation with stereotactic body RT (SBRT) is emerging as a feasible and safe option postponing androgen deprivation and disease