ESTRO 36 Abstract Book

S731 ESTRO 36 2017 _______________________________________________________________________________________________

Due to rarity of the disease, our data did not show significant improvement of LC after RT. GTR should be pursued and adjuvant RT after STR is a resonable approch. Further investigations are needed to determine the optimal therapeutic strategy.

Electronic Poster: Clinical track: Paediatric tumours

EP-1379 Heart volume reduction in paediatric cancer patients during radiotherapy I. Van Dijk 1 , J. Visser 1 , J. Wiersma 1 , J. Van Boggelen 1 , B. Balgobind 1 , L. Feijen 2 , S. Huijskens 1 , L. Kremer 2 , C. Rasch 1 , A. Bel 1 1 Academic Medical Center, Radiation Oncology, Amsterdam, The Netherlands 2 Academic Medical Center, Pediatric Oncology- Emma Children's Hospital, Amsterdam, The Netherlands Purpose or Objective Radiation to the heart is associated with adverse cardiac effects in long-term cancer survivors. In adult patients with oesophageal cancer, a decrease in heart volume was observed already early during radiotherapy. Based on this observation we investigated whether similar heart volume changes occur during radiotherapy in paediatric cancer patients as well. Therefore, we retrospectively assessed heart volume change during thoracic radiotherapy in paediatric cancer patients. Material and Methods We included 13 females and 14 males who received radiotherapy to the thoracic region for a primary paediatric cancer, a recurrence, or metastatic disease between 2010 and 2016; median age at treatment was 11.0 (range 4.0-17.3) years. Median height and weight were 1.4 (range 1.0-2.0) meter and 40 (range 14-69) kilogram, respectively. Primary cancer diagnoses included CNS tumours (n=15), bone tumours (n=4), lymphomas (n=3), rhabdomyosarcomas (n=2), neuroblastomas (n=2), and 1 blastoma. Heart contours were delineated and volumes were measured on cone beam (CB)CTs, considering an interval of at least 3 treatment days between the scans. Relative volume changes were determined by normalizing the volumes with respect to the volume as measured on the first CBCT (i.e., baseline 100%). Cardiac radiation doses were converted into equivalent doses of 2 Gy per fraction (EQD2 for α/β = 3 Gy), after which radiation dose parameters were calculated from dose volume histograms. Chemotherapy was administered to 23 of the 27 children (in 13 cases concurrently with radiotherapy), and was categorized as follows: anthracyclines, alkylating agents, vinca-alkaloïds, and other. We tested possible correlations between heart volume change and patient characteristics (gender, age, height, weight), cardiac radiation dose, and category of chemotherapy. Results Heart volumes were measured on 90 CBCTs (range 2-6 per patient). Figure 1A shows the volume change during the radiation course. The overall median volume reduction from the first to the last CBCT was 3.6% (IQR 0.3-8%) (Figure 1B) this reduction was significant (Wilcoxon signed-ranks tests, p<0.01). No correlations were found between the reduction of the heart volume and patient characteristics, cardiac radiation dose, or category of chemotherapy.

Conclusion We found a significant heart volume reduction in children during thoracic radiotherapy for cancer. Correlations with patient- or treatment-characteristics were not found. Elucidation of the underlying mechanism and clinical relevance of early heart volume reduction during thoracic radiotherapy require a prospective follow-up study. EP-1380 Impact of radiobiological models in decision making to individualize proton and photon radiotherapy A. Chaikh 1 , J. Balosso 2 , J. Blouzard 3 , J. Bondiau 4 1 CHU de Grenoble - A.Michallon, Radiothérapie et physique médicale, Grenoble, France 2 University Hospital of Grenoble- University Grenoble- Alpes, Department of Radiation Oncology and Medical physics, Grenoble, France 3 IPNL, France HADRON national research infrastructure, Lyon, France 4 Centre Antoine Lacassagne, Department of Radiation Oncology, Nice, France Purpose or Objective The aim of this study is to assess the impact of radiobiological models and their clinical parameters on the medical decisions. This include TCP, NTCP, UTCP (substitute of QALY) and secondary cancer risk estimation 17 pediatric patient’s cases with medulloblastoma were studied. Two treatment plans were generated with conformal photon radiotherapy and proton therapy. The same dose prescriptions for posterior fossa and craniospinal irradiation were used for both plans. Two radiobiological models were used for NTCP (LKB and Niemierko) and the EUD model for TCP. The organ equivalent dose model was used to estimate secondary cancer risk. The in-silico dose based estimation of toxicity and cancer risk derived from dose volume histogram (DVH). Wilcoxon paired test was used to calculate p-value. Results Overall, proton plans achieved lower dose for most of the OARs. Consequently, the NTCPs were significantly lower, p < 0.05. However, the variation, due to the model and radiobiological parameters choice, showed a significant impact on UTCP based on TCP/NTCP regarding medical decision. Similarly the variation of TCP/NTCP can reach 20-30% and 100% for secondary cancer, depending on the model. Conclusion The considerable impact of radiobiological model on the radiotherapy outcomes urges us, once again, to measure specific (CTCAE scale) and global (QoL as EQ-5D) clinical outcomes, to tune the parameters of TCP/NTCP in pediatric patients. Material and Methods