Inter-clinician variability in making dosimetric decisions in pediatric treatment: a balance between efficacy and late effects.

PURPOSE: To investigate variability of clinical target volume (CTV) delineation and deviations according to doses delivered in normal tissue for abdominal tumor irradiation in children. MATERIAL AND METHODS: For a case of nephroblastoma six French pediatric radiation oncologists outlined post-operative CTV, on the same dosimetric CT scan according to the International Society for Pediatric Oncology 2001 protocol. On a reference CTV and organs at risk (OAR), we performed dosimetric planning with the constraints as 25.2 Gy for CTV, V(20 max) to 50% for liver, V(12) <15% for kidney. Data were analyzed with Aquilab software. RESULTS: Final CTVs showed inter-clinician variability: 44.85-120.78 cm(3). The recommended liver doses were not respected in four cases: V(20) from 74% to 88% of the volume; for kidney, in two cases: V(12) of 17.6% and 25%, respectively. For vertebral bodies, no deviations were noted. CONCLUSION: Variability not only affected CTV delineation but also dose distribution to OAR with different compromises. This practice training demonstrates the hudge lack of data about correlation between dose, volume and risk of late effects in pediatric radiotherapy. We intend to record prospectively the dose/volume histogram of each OAR in a national database in order to characterize late effects occurring in relation to treatment modalities.