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KMID : 1164220130250010001
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Journal of Korean Society for Radiotherapeutic Technology
2013 Volume.25 No. 1 p.1 ~ p.8
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The Effect of Partially Used High Energy Photon on Intensity-modulated Radiation Therapy Plan for Head and Neck Cancer
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Chang Nam-Joon
Seok Jin-Yong
Won Hui-Su
Hong Joo-Wan
Choi Ji-Hun
Park Jin-Hong
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Abstract
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Purpose: A selection of proper energy in treatment planning is very important because of having different dose
distribution in body as photon energy. In generally, the low energy photon has been used in intensity-modulated
radiation therapy (IMRT) for head and neck (H&N) cancer. The aim of this study was to evaluate the effect of
partially used high energy photon at posterior oblique fields on IMRT plan for H&N cancer.
Materials and Methods: The study was carried out on 10 patients (nasopharyngeal cancer 5, tonsilar cancer 5)
treated with IMRT in Seoul National University Bundang Hospital. CT images were acquired 3 mm of thickness in the
same condition and the treatment plan was performed by Eclipse (Ver.7.1, Varian, Palo Alto, USA). Two plans were
generated under same planing objectives, dose volume constraints, and eight fields setting: (1) The low energy
plan (LEP) created using 6 MV beam alone, (2) the partially used high energy plan (PHEP) created partially using
15 MV beam at two posterior oblique fields with deeper penetration depths, while 6 MV beam was used at the rest
of fields. The plans for LEP and PHEP were compared in terms of coverage, conformity index (CI) and homogeneity
index (HI) for planning target volume (PTV). For organs at risk (OARs), Dmean and D50% were analyzed on both
parotid glands and Dmax, D1% for spinal cord were analyzed. Integral dose (ID) and total monitor unit (MU) were
compared as addition parameters. For the comparing dose to normal tissue of posterior neck, the posterior-normal
tissue volume (P-NTV) was set on the patients respectively. The Dmean, V20Gy and V25Gy for P-NTV were evaluated by
using dose volume histogram (DVH).
Results: The dose distributions were similar with regard to coverage, CI and HI for PTV between the LEP and PHEP.
No evident difference was observed in the spinal cord. However, the Dmean, D50% for both parotid gland were slightly
reduced by 0.6%, 0.7% in PHEP. The ID was reduced by 1.1% in PHEP, and total MU for PHEP was 1.8% lower
than that for LEP. In the P-NTV, the Dmean, V20Gy and V25Gy of the PHEP were 1.6%, 1.8% and 2.9% lower than those
of LEP.
Conclusion: Dose to some OARs and a normal tissue, total monitor unit were reduced in IMRT plan with partially
used high energy photon. Although these reduction are unclear how have a clinical benefit to patient, application of
the partially used high energy photon could improve the overall plan quality of IMRT for head and neck cancer.
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KEYWORD
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head and neck cancer, IMRT, high energy photon, integral dose, normal tissue of posterior neck, ID
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