Measurements of doses from photon beam irradiation and scattered neutrons in an anthropomorphic phantom model of prostate cancer: a comparison between 3DCRT, IMRT and tomotherapy
Measurements of doses from photon beam irradiation and scattered neutrons in an anthropomorphic phantom model of prostate cancer: a comparison between 3DCRT, IMRT and tomotherapy
The rapid development of new radiotherapy technologies, such as intensity modulated
radiotherapy (IMRT) or tomotherapy, has resulted in the capacity to deliver a more homogenous dose in the
target. However, the higher doses associated with these techniques are a reason for concern because they may
increase the dose outside the target. In the present study, we compared 3DCRT, IMRT and tomotherapy to assess
the doses to organs at risk (OARs) resulting from photon beam irradiation and scattered neutrons. Material
and methods. The doses to OARs outside the target were measured in an anthropomorphic Alderson phantom
using thermoluminescence detectors (TLD 100) 6Li (7.5%) and 7Li (92.5%). The neutron fluence rate [cm–2·s–1]
at chosen points inside the phantom was measured with gold foils (0.5 cm diameter, mean surface density
of 0.108 g/cm3). Results. The doses [Gy] delivered to the OARs for 3DCRT, IMRT and tomotherapy respectively,
were as follows: thyroid gland (0.62 ± 0.001 vs. 2.88 ± 0.004 vs. 0.58 ± 0.003); lung (0.99 ± 0.003 vs.
4.78 ± 0.006 vs. 0.67 ± 0.003); bladder (80.61 ± 0.054 vs. 53.75 ± 0.070 vs. 34.71 ± 0.059); and testes
(4.38 ± 0.017 vs. 6.48 ± 0.013 vs. 4.39 ± 0.020). The neutron dose from 20 MV X-ray beam accounted for 0.5%
of the therapeutic dose prescribed in the PTV. The further from the field edge the higher the contribution of this
secondary radiation dose (from 8% to ~45%). Conclusion. For tomotherapy, all OARs outside the therapeutic
field are well-spared. In contrast, IMRT achieved better sparing than 3DCRT only in the bladder. The photoneutron
dose from the use of high-energy X-ray beam constituted a notable portion (0.5%) of the therapeutic dose
prescribed to the PTV.
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