ESTRO 37 Abstract book

S132

ESTRO 37

Abstract text Radiotherapy is needed in the multidisciplinary management of cancer in children to improve local control, overall survival and symptom management; however, it is known that radiotherapy is associated with potential toxicities. For patients with a good long term prognosis, efforts to minimize late effects is critical and technological advances have provided opportunities improve our ability to deliver therapeutic radiation. Proton therapy is a powerful tool to improve radiotherapy delivery in an effort to decrease late effects while maintaining tumor control. There is a consistent reduction in overall radiation dose to the the patient in particular within the low and intermediate dose volumes. Children are most likely to benefit from an reduction in volume of irradiated tissue. Thousands of pediatric patients have now been treated with proton therapy and clinical evidence is now increasing to support the theoretical benefits that have been proposed through dosimetric studies. Proton therapy, however, it is not needed for all children requiring radiotherapy for management of their cancer. The patient's medical history, tumor radiosensitivity, tumor volume geometry, normal tissue anatomy, and treatment options should all be considered when considering radiation treatment modalities. In this session, we will review situations where proton therapy is not necessary, or maybe associated with higher uncertainties and risk. OC-0265 Effective tumor reoxygenation for combined treatment with radiotherapy I. Grgic 1 , F. Tschanz 1 , J. Ott 1 , S. Deschoemaeker 2 , M. Guckenberger 1 , A. Heyerick 2 , M. Pruschy 1 1 Universitätsspital Zürich, Radiation Oncology, Zürich, Switzerland 2 NormOxys, NormOxys Inc., Boston- MA, USA Purpose or Objective Reactive oxygen species are generated in response to ionizing radiation (IR) and produce amongst others irreversible DNA double-strand breaks. This IR-induced cytotoxic effect is less abundant under hypoxia and thus hypoxic cells are more resistant to IR. Hence, reoxygenation of the hypoxic tumor fraction by a combined treatment modality with a pharmaceutical agent is of high interest to reduce the required dose of IR and thereby to further minimize normal tissue toxicity. Here we investigated the combined treatment modality of the novel anti-hypoxia compound myo -inositol trispyrophosphate (ITPP) in combination with IR. Material and Methods ITPP was developed as an effector of hemoglobin lowering the oxygen/hemoglobin affinity thereby resulting in an enhanced release of oxygen e.g. in hypoxic tumors. ITPP’s capability for tumor reoxygenation was serially probed by a non-invasive hypoxia-directed ODD-luciferase-based bioimaging approach and by immunohistochemistry (pimonidazole, CAIX) in FaDu-HNSCC and A549-lung carcinoma-derived tumor xenografts. Tumor growth delay was determined on treatment with ITPP and either a single high dose fraction (10 Gy) or two fractions (2 x 10 Gy) of IR. Results Using our in vivo bioimaging approach, we confirmed increased pO 2 starting 2 hours after ITPP application. Dose-titration studies indicated that administration of ITPP at a maximal tolerable dose of 3g/kg on two consecutive days followed by immediate irradiation 2 Proffered Papers: RB 3: Imaging Hypoxia - Biology in Clinic

(AMORE) applied after brachytherapy. The purpose of the procedure is to provide therapeutic possibilities in case of recurrence, intensify local treatment and reduce late side effects such as cosmetic problems and / or loss of function. The treatment is mainly given to patients with (recurrence of) rhabdomyosarcoma at different locations such as the orbit, head-neck area or pelvis. In selected cases, patients with osteosarcoma, Ewing sarcoma, adenocarcinoma or rhabdoid sarcoma are eligible for this treatment. The procedure consists of two operations and brachytherapy during the intervening week with PDR fractions every two hours day and night. After the first operation, depending on the age of the patient, we make a CT scan under anesthesia. In this way the technicians are also able to measure the catheters without the patient being aware of the procedure being performed. The next morning the technicians make a treatment plan together with the radiotherapist. After this, the team that was involved in the operation, a radiologist and radiotherapist will discuss this plan. If everyone agrees, the physicist will do the final check and the treatment start at the end of the morning. It is an intensive treatment where good guidance of the child and parents is essential for the success of the treatment. Practicing the pulses without the parents presence in the room is essential as well. The children get used to the fact that they are from time to time, alone in the room but they are able to see and talk to their parents through videoconferencing. For nurses, doctors and brachytherapy technicians it is a matter of making the procedure as smooth as possible in order to make both the patient and parents feel at ease and well taken care of. The use of a patient-belt coupling is necessary so the young patients are able to move around during the 3 days of brachytherapy. In our experience, the freedom of movement contributes to a more successful treatment. On the other hand it is also extremely important that during all those days the catheters stay in good condition. To prevent them from kinking we load all the catheters during the intervals between fractions with check cables. The child and parents are supervised during the entire treatment by a pedagogical employee, so they have one contact person and a familiar face during the entire process. Our experience shows that it is possible to give this intensive treatment if the provided preconditions are correct. SP-0263 Every single paediatric patient needs to receive proton beam radiotherapy! G.O.R.J. Janssens 1 1 UMC Utrecht, Radiation Oncology, Utrecht, The Netherlands Abstract text Although a significant number of paediatric patients are candidate for proton therapy, criteria to prefer protons instead of photons or vice versa are lacking. As proton therapy is still not available in the majority of centers treating paediatric patients, better arguments to balance protons versus photons are needed. In order to tackle this issue a workshop with European experts in the field of paediatric (radiation) oncology was organized in Utrecht (NL), February 2018. A summary of this (consensus) workshop will be integrated in this session and should enhance radiation oncologists’ decisions. SP-0264 Not every single paediatric patient needs to receive proton beam therapy! A. Mahajan 1 1 MD Anderson Cancer Center, Proton Therapy Center, Houston, USA