ESTRO 36 Abstract Book

S71 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective Results from a Bayesian-randomized trial on intensity modulated radiotherapy (IMRT) vs. passively scattered 3D proton therapy (3DPT) show no significant difference in protocol failure (i.e., either grade>=3 radiation pneumonitis (RP) or local recurrence within 12 months). We intend to analyze the differences in dose distribution between modalities, relations between dosimetric parameters and radiation-induced toxicities. The objective is to identify dosimetric constraints that would limit normal tissue complications in future trials. Material and Methods We analyzed 149 (57 3DPT, 92 IMRT) randomized trial patients. DVH parameters for 3DPT and IMRT treatment plans were compared for lung, esophagus, and heart. To measure the predictive value of high- and low-dose parameters for toxicity in lungs and esophagus, we fitted V5 and V50Gy to RP and grade>=3 radiation esophagitis (RE). Heart dose data was missing for 5 IMRT patients. Results RP and RE are not significantly different between modalities (p>0.1, two-tailed Wilcoxon rank-sum test). The difference between mean doses planned for IMRT and 3DPT plans was tested: Lung V5, V50, V60, V70Gy (in %), esophageal V5Gy, and heart V5, V10Gy are significantly different (p<0.005, two-tailed Wilcoxon rank-sum test). The significant esophageal and heart dose parameters are smaller for 3DPT, lung V5Gy is smaller, while lung V50,V60,V70Gy are larger. 3DPT plan V5 and V50Gy are computed for each OAR and compared to the respective median values of IMRT plans. The percentage of 3DPT plans with V5Gy below or equal to the IMRT median and V50Gy above the IMRT median are reported: <=V5Gy IMRT Median >V50Gy IMRT Median 3DPT Lung 0.93 0.68 Esophagus 0.67 0.49 Heart 0.93 0.54 3DPT plans yield smaller low dose regions in all three OARs. However, 3DPT yields larger high dose regions in the lungs. To assess the relationship between low/high dose regions and toxicity, V5 and V50Gy of lung and heart were fitted to RP, esophageal V5 and V50Gy were fitted to RE:

Joint Symposium: ESTRO-JASTRO: Oligometastatic disease

SP-0145 Biological rationale and clinical evidence P. Ost 1 1 University Hospital Ghent, Gent, Belgium In 1995, Hellman and Weichselbaum hypoth esized that the number and location of the metastases are an important prognostic factor reflecting the metastatic phenotype and hence prognosis of the cancer patient. They suggested this based on the historical observation that some metastatic patients have a durable survival in case their limited metastases are surgically removed. For these cases, they proposed the term oligometastases, suggesting that eradicating oligometastases with metastasis-directed therapy (MDT) would have the potential to improve survival. This hypothesis would shift the paradigm for oligometastatic patients from a palliative to a potentially curable disease. Recent data in several solid tumors support the notion that patients with oligometastatic disease have a more favorable prognosis as compared to their counterparts and that these different phenotypes probably require a different therapeutic approach. Clinical data indicate that the number of patients with oligometastatic disease receiving aggressive treatment is increasing rapidly. We will discuss the key evidence supporting or refuting the existence of an oligometastatic state. SP-0146 Oligometastatic disease: Radiophysics implementation and pitfalls D. Verellen 1 1 GZA- Ziekenhuizen - St. Augustinus Iridium Kankernetwerk Antwerpen, Radiotherapy, Wilrijk, Belgium As clinical evidence in favor of SBRT for treatment of oligometastatic disease increases, SBRT proves to be a safe and effective treatment modality to achieve local control and delay progression, which in turn also postpones the need for further treatment. Basically SBRT refers to a high-dose-per-fraction-high-precision technique and the mainstream adaptation of SBRT is the result of combined developments in image guided motion management, treatment planning and delivery. This presentation will cover some of the main issues related to clinical implementation of SBRT and quality assurance. A critical overview will be provided comparing dedicated equipment against mainstream technology. The different treatment modalities will be benchmarked allowing to assess an appropriate balance between technological needs and patient compliance. As the efficacy of SBRT in the management of the oligometastic state increases, the need for treatment of multiple metastases and re- irradiation requires extra attention. In this presentation, some of the issues related to dose accumulation for this particularly challenging situation will also be highlighted. SP-0147 Interpretation and management of oligometastases H. Onishi 1 1 Yamanashi University, Department of Radiology, Chuo, Japan All of cancer state with metastases is judged as stage IV even if the number of metastases is only one. However, it has been known that some of patients with a limited number of metastatic lesions regions have a good prognosis by a locally radical therapy combined with systemic chemotherapy, and the disease state was named “oligometastases” by Hellman in 1995. In addition, a limited disease state of oligometastases with primary

There appears to be a stronger relationship between toxicity and high dose regions in the affected OAR. Heart doses have a weaker relationship with RP. Conclusion Tucker et al. (2013) showed that high dose regions in lung tissue in lung IMRT have a pronounced effect on toxicity. This is also observable in this trial cohort of IMRT and 3DPT patients. In order to reduce toxicities, high dose regions in normal tissues need to be reduced. 3DPT reduces low dose regions significantly in all three OARs but high doses regions are significantly higher in the lungs. Future investigations should focus on stricter high dose constraints for 3DPT plans. If such constraints are not achievable due to penumbral and scattering characteristics of protons and the usage of passive scattering techniques, intensity modulated proton therapy should be considered.