ESTRO 37 Abstract book

S352

ESTRO 37

SP-0673 Multi-parametric imaging for dose targeting in salvage radiotherapy of prostate cancer U. Van der Heide 1 , C. Dinis Fernandes 1 1 Netherlands Cancer Institute, Radiation Oncology, Amsterdam, The Netherlands Abstract text Multi-parametric MRI, combining T2-weighted MRI, Diffusion-weighted MRI and dynamic contrast-enhanced MRI, is widely used for localizing prostate cancer. In focal boost treatments such as investigated in the FLAME trial, these images are used to delineate the GTV inside the prostate as target for dose escalation. For patients with a post-radiotherapy recurrence focal treatment strategies including radiotherapy are considered. Here, multi-parametric MRI is also attractive for delineation of the intraprostatic GTV. However, for patients with a post-radiotherapy recurrence, the changes that the radiotherapy has caused in the tissue result in changes in mp-MRI. It is necessary to distinguish the effects of radiation on the images from those of the recurrent intraprostatic cancer. In this presentation, data from patients treated with a salvage prostatectomy will be presented. These patients were treated for primary prostate cancer with either external-beam radiotherapy or brachytherapy. The multi- parametric MRI data will be compared to histology. To differentiate between radiation effects and recurrent prostate cancer, we conducted a matched case control study, where MRI from patients with biopsy-proven recurrent PCa and matched controls without evidence of recurrence are compared. The localization of recurrent prostate cancer on mp-MRI is confounded by radiation effects. T2 values in the peripheral zone tend to be lower than those observed in untreated patients. Tumor T2 values are lower but not significantly different than PZ, and comparable to CG. Mean K trans and k ep seem to be the most informative to distinguish tumour, even in the presence of elevated values around the urethra that appear in both cases and controls. SP-0674 Rectum tolerance dose and repair after previous radiotherapy A.H. Ree 1 1 Akershus University Hospital, Department of Oncology, Lørenskog, Norway Abstract text In radiation oncology, the success in eradicating tumor depends on the ability to deliver the cytotoxic radiation effects in a focused tumor volume. There is a steep dose- response relationship, and small dose escalations may translate into clinically relevant improvements. In prostate cancer, the corollary to more efficacious radiotherapy is that the rectum is at higher risk of suffering morbidity. This is a particular concern when prescribing prostate reirradiation. The combined insights into vulnerable anatomical structures of the pelvic cavity and classic principles of radiobiology, together with the utilization of modern radiotherapy technology, may improve patient outcome related to rectum tolerance following radiotherapy of prostate cancer. In this context, the presentation will address a number of central topics: The therapeutic ratio principle: - Tumor control probability (TCP) versus normal tissue complication probability (NTCP) - An anatomy tour of the (male) pelvic cavity - Radiotherapy technology/technique and the pelvic cavity Rectum tolerance dose: - Assessment of radiation volume - Toxicity assessment tools -Dose-limiting toxicities relevant for salvage prostate-

radiotherapy Repair: Late toxicities relevant for salvage prostate radiotherapy - Normal genetic variation Predictive modeling and evaluation of radiation tolerance: - The REQUITE project - Example of a Morbidity and Mortality Review (MMR) procedure SP-0675 Salvage high-dose-rate brachytherapy for prostate cancer recurrence P. Wojcieszek 1 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Brachytherapy Department, Gliwice, Poland Abstract text Radiotherapy has become one of the most important methods in the prostate cancer treatment. Despite its advantages and efficacy there are patients suffering from failure. Patients with confirmed localized (i.e. organ- confined±regional lymph nodes) recurrence need radical approach, especially those with long life expectancy or good performance. There are questions to be raised, before we consider what to do or which modality should be chosen in our management. Radiotherapy failure inside target volumes means that there are cancer cells resistant to irradiation. However there are data showing efficacy of ablative (dose per fraction>7Gy) regimens. This is probably due to enhanced multi-hit effect and shorter overall treatment time. Unlike external-beam radiotherapy, interstitial high dose rate brachytherapy is delivered from the inside of the target volume. This may mean that biological effect is much beyond the linear- quadratic model conception. If doses are exceeding familiar schedules, toxicity rates, hypothetically, should be high. Data shows that genitourinary/gastrointestinal toxicity is acceptable for the salvage brachytherapy patients. In conclusion, salvage brachytherapy schedules are efficient and safe, however we need uniform approach combined with modern imaging. SP-0676 Cellular senescence: when multitasking becomes dangerous M. Demaria 1 1 University Medical Center Groningen, European Research Institute for the Biology of Ageing, Groningen, The Netherlands Abstract text Cellular senescence is a complex stress response whereby cells lose irreversibly their capacity to proliferate. Senescent cells develop the senescence-associated secretory phenotype (SASP), characterized by the expression and secretion of inflammatory cytokines, chemokines, growth factors and proteases. Cellular senescence is a potent tumor suppressive mechanism, and a desired outcome of anti-cancer therapies. However, mounting evidence indicates that senescent cells participate in multiple physiological and pathological stages, including aging and cancer. To more critically determine the diverse functions of senescent cells in vivo , we created a mouse model (p16-3MR) in which senescent cells can be detected and inducibly eliminated using the pro-drug ganciclovir (GCV). In mice, senescent cells induced by anti-cancer therapies such as radiation or chemotherapy drugs persist for several weeks in tissues and promote local and systemic inflammation. The presence of senescent cells favours Symposium: Radiation induced senescence