ESTRO 37 Abstract book

S1095

ESTRO 37

Purpose or Objective To analyze and compare normal tissue complication probability (NTCP) models in their ability to predict late urinary toxicity at 5 years follow-up, in a series of patients having received 3D conformal radiotherapy (3DCRT) or intensity-modulated radiotherapy (IMRT) for prostate cancer. Material and Methods Clinical data and dose-volume histograms (DVH) were collected in a series of 434 patients, following the same dose-volume recommendations (from the GETUG group). Bladder toxicity endpoints were: ≥Grade 2 (LENT/SOMA grading system) and bleeding (at least one episode). The correlations between toxicity and patient characteristics or DVH were investigated. Parameters of 6 NTCP models (LKB, Logit-EUD, Poisson-EUD, Källman, Schultheiss and Parallel) were identified at 5 years follow-up. Toxicity prediction performance of each model was compared by Receiver Operating Characteristic methods. Results LKB, Logit-EUD, Poisson-EUD, Källman, Shcultheiss and Parallel models predicted late bladder toxicity (≥Grade 2) and bladder bleeding with similar capabilities (area under curve ranges from 0.661 to 0.665 and 0.623 to 0.627, respectively). Multivariate analysis shown that: no DVH bin was significant when considering any of the six NTCP models at the same time; NTCP values and EUD were also stronger predictors than the maximum dose and the total dose.

Material and Methods Eight GC patients, previously treated with photon-beam VMAT, were included in this study. The prescribed dose was 45 Gy, given in 25 fractions of 1.8 Gy. For each patient, a proton plan was generated with the single-field uniform-dose (SFUD) method, using field-specific planning target volumes (PTV) derived from the clinical target volumes (CTV). A two-field configuration with one frontal and one lateral field (incident from the left) was used. The dose calculation and robust optimization to create the SFUD opt plans were done on CT sets in which the Hounsfield units (HUs) of the air cavities along the beam path and within the target volume were replaced with tissue-equivalent HUs. These plans were prepared accounting for 1.0 cm of setup uncertainty and a proton range uncertainty of 3.5 %. To evaluate the plan robustness against possible density changes, the SFUD opt plans were recalculated on the original CT sets which contained gas cavities, to produce the SFUD ver plans. The dose-volume values obtained for relevant organs at risk (OARs) with the VMAT and SFUD plans were then compared. Thereafter, the LKB-model was used to estimate the normal-tissue complication probability (NTCP) for different toxicity endpoints for the kidneys, liver, spinal cord, heart and bowel. A generic RBE of 1.1 was assumed for the proton beams. Results For all the patients, the SFUD plans fulfilled the robustness objectives set for the CTV dose coverage (V 95 > 98% for all scenarios) and for the normal-tissue constraints. The dose-volume values determined for all the OARs, in the SFUD opt - and SFUD ver -plans, were of comparable sizes, showing that robustness against density changes was achieved. For the SFUD plans, significant reductions of the dose-volume values were determined for the kidneys, spinal cord and liver, compared to the VMAT plans ( p < 0.05). For the heart and bowel, the dosimetric values obtained in the VMAT and SFUD plans were comparable ( p > 0.05). In terms of the estimated NTCPs, risks of 0 % were obtained with both the VMAT- and SFUD-plans for the right kidney, liver, spinal cord, heart and bowel ( p > 0.05). However, for the left kidney, a median NTCP value of 9.6 % (range 0 – 86.3 %) was estimated for the VMAT plans and a median NTCP value of 0 % (range 0 – 20.7 %) was estimated for the SFUD ver plans ( p < 0.05). Conclusion The risks for treatment-related side effects were found to be negligible for the two treatment techniques studied, except for the left kidney. The risk reductions obtained for the left kidney with proton-beam therapy could be of clinical relevance for preserving the renal function after radiotherapy of GC. EP-2007 Radiomics based method to predict overall survival of inoperable NSCLC patients L. HUANG 1 , M. Fan 1 , J. Chen 1 , J. Wang 1 , X. Xu 1 , J. Lu 1 , G. Qin 1 , J. Wen 1 1 Fudan University Shanghai Cancer Center, Radiation Oncology, Shanghai, China Purpose or Objective It could be difficult to predict prognostics of inoperable ALK+ mutated patients as they are in large part complicatedly affected by diverse factors in treatment process. The lack of a high-performance and pragmatic indicator for prediction make it imperative to investigate any further. So that we focused on a cohort of inoperable ALK+ mutated patients received targeted or non-targeted therapy and probed into the radiomics based methods for prognostics. Material and Methods Two cohort of clinic patients in Netherlands (n=317) and Chinese (n=54) cancer center was enrolled respectively. The former for model training, received radiotherapy or

Conclusion All the six NTCP models present a similar significant capabilities at predicting late bladder toxicity (≥Grade 2) and bladder bleeding with the identified parameters. Both NTCP and DVH parameters are useful to assess late bladder toxicities. EP-2006 Normal-tissue toxicity following gastric cancer radiotherapy with photon- or scanned proton- beams G.A. Mondlane 1 , A. Ureba 1 , M. Gubanski 2 , P. Lind 2,3 , A. Siegbahn 1 1 Stockholm University, Department of Physics, Stockholm, Sweden 2 Karolinska University Hospital, Department of Oncology and Pathology, Stockholm, Sweden 3 Södersjukhuset, Department of Oncology, Stockholm, Sweden Purpose or Objective The aim of this study was to evaluate the potential of scanned proton-beam therapy to reduce the normal- tissue toxicity after gastric cancer (GC) treatment, compared to photon-beam therapy.