Document Type : Original Paper
Authors
1
Ph.D. Student in Medical Physics Dept., Cancer Reserch Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran.
2
Associate Professor, Cancer Reserch Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran
3
M.Sc. in Nuclear Engineering, Azad University Tehran, Iran
4
Assistant Professor, Cancer Reserch Center, Cancer Institute, Tehran University of Medical Sciences, Tehran, Iran.
Abstract
Introduction: Esophageal cancer is one of the most frequently occurring cancers in Iran and having a
high incidence rate among other countries. Radiotherapy is one of the three methods (surgery,
radiotherapy and chemotherapy) for radical or palliative treatment of esophageal cancer. In this method
of treatment, the organs such as heart and spinal cord are regarded as organs at risk (OAR) which their
dose should be kept below the tolerance level.
Different techniques have been used in conventional radiotherapy, among which two parallel opposed
fields (POP) is used more often either for the whole course of the treatment or 2/3 of the fractions. In
this technique, a great portion of the spinal cord may be involved in the treatment volume.
The rate of treatment success may depend on the tolerance dose of heart and cord which act as the
limiting factor.
Materials and Methods: In this study, 10 patients with S.C.C. of esophagus having indication for
external radiotherapy were selected. The CT scan simulations were performed for all the cases and
their data were digitized to be used in computerized treatment planning system. Treatment planning for
three photon beam energies (Co-60, 6 and 10 MV) are obtained for each individual patient under the
same geometry and dose. The integral dose, absorbed dose and dose volume histogram (DVH) of the
heart and target were calculated for all the cases.
Results: The maximum point dose in the heart is 140, 125 and 115% of the reference point for Co-60,
6 and 10 MV, respectively. The integral dose for the largest A-P patient was found to be 55.33, 54.17
and 51.66 Gy.Kg for Co-60, 6 and 10 MV, respectively. In using 10 MV beam, 7% reduction in the
integral dose of the heart was obtained. Alternatively, by using 6 MV beam, a reduction of only 2%
was observed. The integral dose of the heart for the 10 MV beam had a 5% reduction in comparison to
6 MV beam.
Discussion and Conclusion: Since lower energy beams cause a higher integral dose to the heart and
cord, the use of higher energy photon beams in the case of deep seated tumors and large size patients
are unavoidable. In spite of the advantages of cobalt machines, its energy is not suitable for deeply
suited tumors.
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