الفهرس 
TitleOnly 14 pages are availabe for public view
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Abstract
One of the most important and commonly used methods of cancer
treatment is radiotherapy. The aim of radiotherapy is to deliver a dose of
radiation into a volume of cancer cells that is sufficient enough to kill cancer
cells, but to do so in a way that spares the healthy tissues surrounding the
cancer.
The real revolution in radiotherapy came with the introduction of the
electron linear accelerator and the development of radiotherapy techniques as
SBRT (Stereotactic body radiation therapy), IMRT (Intensity modulated
radiation therapy), IGRT (Image guided radiotherapy) and VMAT (Volume
modulated arc therapy).
The main target of this study was to compare the dose coverage of
planning target volume (PTV) and organsatrisk (OAR) between
intensitymodulated radiation therapy (IMRT) with large and low number of
segments in prostate and head neck cancer patients.
This study included 40 cancer patients (20 prostate cancer patients and20
nasopharyngeal carcinoma) performed with radiotherapy. A total of 80 plans
were generated by performing IMRT large number of segments plan and
IMRT low number of segments plan for each patient.
Our results showed that:
Prostate Cancer:
The dosimetric results of the PTV were almost similar for IMRT low
number of segments and IMRT large number of segments plans. These results
illustrate that mean doses to PTV are identical for both plans.The uniformity
index and homogeneity index arealso have no significantly different.
Regarding dosimetric parameters for organs at risk, the comparison of
IMRT low number of segments with IMRT large number of segments plans in
the same percentage of volume showed that, the doses to the rectum, bladder,
right and left femoral head irradiated with both IMRT low number of
segments and IMRT large number of segments plans were almost the same.
The segment numbers was highly significantly lower in IMRT low
number of segments than IMRT large number of segments plans (p < 0.001).
Head and neck cancer (Nasopharyngeal carcinoma):
The dosimetric results of the PTV74 (D 95%), PTV64 (D 95%) and
PTV50(D 95%) were almost similar for IMRT low number of segments and
IMRT large number of segments plans. These results illustrate that mean
doses to PTV are identical for both plans. The uniformity index and
homogeneity index are show that there isno significantly different.
Regarding dosimetric parameters for organs at risk, the comparison of
IMRT low number of segments with IMRT large number of segments plans in
the same percentage of volume showed that, the doses to the brain stem, cord,
RT parotid, LT parotid, RT and LT optic nerve and RT and LT lenses
irradiated with both IMRT low number of segments than IMRT large number
of segments plans, insignificant difference was found between IMRT low
number of segments and IMRT large number of segments plan but both
results were in tolerance.
The segment numbers was highly significantly lower in IMRT low
number of segments than IMRT large number of segments plans.