Measurements of Secondary Radiation Doses Inside a Paediatric Anthropomorphic Phantom Exposed to Scanning Proton Radiotherapy, Activities within EURADOS WG9 (SG2)

Proton beams show an increase in energy deposition with penetration depth up to a sharp maximum at the end of their range and almost no dose is deposited in the normal tissue beyond the Bragg peak. Unwanted doses, deposited distantly from the target volume (out-of-field doses), may lead to an increasing probability of late effects of radiotherapy including the generation of secondary cancers which is of especial importance for children. Around 70 % of children with malignant diseases are successfully treated and radiotherapy is most frequent method of treating the tumors. The hadron therapy sub-group of EURADOS Working Group 9 (Radiation Dosimetry in Radiotherapy) is engaged in a measurement campaign designed to investigate the secondary radiation generated by a scanning proton beam. The measurement campaign was designed to measure out-of-field organ doses using 5 and 10 year-old anthropomorphic phantoms (CIRS) in the Bronowice Cyclotron Center in Krakow, Poland (IBA Proton Therapy System - Proteus 235). Doses were measured in different organs with thermoluminescent (MTS-7, MTS-6 and MCP), radiophotoluminescent (GD-352M and GD302-M), optically stimulated (OSL) and CR-39 track detectors. The isocenter (at the centre of a sphere 6 cm diameter, representing the tumour) was located in the head of the phantom and the applied target dose was 100 Gy. The detailed analysis of the results with different dosimetry systems combined with ongoing Monte Carlo simulations will give valuable information about out of field doses.(author).