U. Isacsson et al., POTENTIAL ADVANTAGES OF PROTONS OVER CONVENTIONAL RADIATION BEAMS FORPARASPINAL TUMORS, Radiotherapy and oncology, 45(1), 1997, pp. 63-70
Citations number
23
Categorie Soggetti
Oncology,"Radiology,Nuclear Medicine & Medical Imaging
Background and purpose: Conformal treatment planning with megavoltage
X-rays and protons was studied in an attempt to determine if there are
advantages of boost therapy with protons instead of X-rays for a pati
ent with a tumour growing around the cervical spinal cord. Materials a
nd methods: A patient with a Ewing sarcoma was selected for the model
study. The proton boost plan was realised with a six beam patched tech
nique. Several X-ray boost techniques were planned, some not yet pract
ically realisable. The techniques giving the best dose distributions a
nd the best tumour control probabilities in the absence of significant
late toxicity were looked for. The boost techniques were added to two
large lateral X-ray beams covering the planning target volume (PTV) a
nd the main risk organ, the spinal cord. The evaluation was made with
two biological models, i.e. the tumour control probability (TCP) model
, proposed by Webb and Nahum (Webb, S. and Nahum, A.E. A model for cal
culating tumour control probability in radiotherapy including the effe
ct of inhomogeneous distributions of dose and clonogenic cell density.
Phys. Med. Biol. 38: 653-666, 1993), and the normal tissue complicati
on probability (NTCP) model, first derived by Lyman (Lyman, J.T. Compl
ication probability as assessed from dose-volume histograms. Radiat. R
es. 104: s13-s19, 1985). Results: The comparison showed small but clea
r advantages of protons for the boost. At 1% NTCP in the spinal cord,
the calculated TCP was on average 5% higher. However, depending on the
values of the parameters chosen in the biological models, the gain fo
r protons varied from 0-10%. The smallest gains were seen in radiosens
itive tumours for which the TCP was close to 100% with any of the tech
niques and in radioresistant tumours for which neither technique resul
ted in any appreciable probability of local cure. Conclusion: Protons
appear to have therapeutic advantages over conventional radiotherapy i
n tumours with relatively high radiosensitivity situated close to the
spinal cord. (C) 1997 Elsevier Science Ireland Ltd.