24. Validation of conformal radiotherapy treatment planning systems using an antro-pomorphic phantom and thermoluminescence dosimetry

Within the requirements of a Quality Assurance programme in a radiotherapy department, the ability of a treatment planning system (TPS) to accurately calculate dose distributions under realistic conditions encountered in radiotherapy (RT) should be validated. This may be accomplished by thermoluminescence (TL) dosimetry in simulated treatment of antropomorphic phantoms. In our radiotherapy department, several planning systems are used concurrently in 3D conformal treatment of larger volumes (with irregular fields obtained via individual shielding or multileaf collimation) and of very small volumes (stereotactic technique), by external megavoltage photon beams. Realistic 3D treatment plans were prepared using CadPlan, Theraplan and BrainLab TPS for treating volumes in an Alderson phantom, which was prepared for topometry (CT-scanned) and irradiated in fully simulated conditions of patient RT. Suitably selected TL detectors (some custom-produced for these measurements), were placed inside and around the treated volumes in the phantom. For every photon beam applied (Co-60, 6 MV or 9 MV) the TL detectors, individually corrected, were calibrated in a standard solid phantom against ionisation chamber dosimetry. For irradiation of larger volumes, standard MTS-N (LiF:Mg,Ti) detectors were used. For stereotactic irradiation of small volumes in the head (6 MV) special miniature thermoluminescent LiF:Mg,Ti and LiF:Mg,Cu,P were developed. The technique of detector calibration, preparation of Alderson phantom for simulated RT, detector readout and interpretation of the measured versus calculated values of dose at measurement points inside the phantom, will be described

Experimental results on the environmental samples collected around sites in South Serbia, Kosovo and Montenegro where DU weapons were deployed in 1999

In a survey performed to estimate the presence of DU in regions where DU ammunition had been deployed, no clear evidence of its presence in the local environment or in the bodies of local inhabitants was observed, except in samples that came into direct or very close contact with DU penetrators. The activity ratios of particular interest (235U to 238U and 234U to 238U) in general tend to show typical values observed in the natural environment. The only environmental sample analyzed by alpha spectrometry to show an abnormal activity ratio suggesting the presence of DU was a piece of scrap metal covered with dust. This may have been an element of military equipment that had been fired at with DU armor-piercing ammunition. Samples of dust collected on air filters were too small to obtain conclusive results. Large volume air samplers should be used in the future to study the environmental pathways of DU over longer time periods

Measurement of stray neutron doses inside the treatment room from a proton pencil beam scanning system

International audiencePurpose To measure the environmental doses from stray neutrons in the vicinity of a solid slab phantom as a function of beam energy, field size and modulation width, using the proton pencil beam scanning (PBS) technique. Method Measurements were carried out using two extended range WENDI-II rem-counters and three tissue equivalent proportional counters. Detectors were suitably placed at different distances around the RW3 slab phantom. Beam irradiation parameters were varied to cover the clinical ranges of proton beam energies (100–220 MeV), field sizes ((2 × 2)–(20 × 20) cm2) and modulation widths (0–15 cm). Results For pristine proton peak irradiations, large variations of neutron H∗(10)/D were observed with changes in beam energy and field size, while these were less dependent on modulation widths. H∗(10)/D for pristine proton pencil beams varied between 0.04 μSv Gy−1 at beam energy 100 MeV and a (2 × 2) cm2 field at 2.25 m distance and 90° angle with respect to the beam axis, and 72.3 μSv Gy−1 at beam energy 200 MeV and a (20 × 20) cm2 field at 1 m distance along the beam axis. Conclusions The obtained results will be useful in benchmarking Monte Carlo calculations of proton radiotherapy in PBS mode and in estimating the exposure to stray radiation of the patient. Such estimates may be facilitated by the obtained best-fitted simple analytical formulae relating the stray neutron doses at points of interest with beam irradiation parameters. © 2017 Associazione Italiana di Fisica Medic