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KMID : 1164220130250010009
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Journal of Korean Society for Radiotherapeutic Technology
2013 Volume.25 No. 1 p.9 ~ p.14
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The Effect of Photoneutron Dose in High Energy Radiotherapy
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Park Byoung-Suk
Ahn Jong-Ho
Kwon Dong-Yeol
Seo Jeong-Min
Song Gi-Won
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Abstract
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Purpose: High-energy radiotherapy with 10 MV or higher develops photoneutron through photonuclear reaction.
Photoneutron has higher radiation weighting factor than X-ray, thus low dose can greatly affect the human body. An
accurate dosimetric calculation and consultation are needed. This study compared and analyzed the dose change
of photoneutron in terms of space according to the size of photon beam energy and treatment methods.
Materials and Methods: To measure the dose change of photoneutron by the size of photon beam energy,
patients with the same therapy area were recruited and conventional plans with 10 MV and 15 MV were each made.
To measure the difference between the two treatment methods, 10 MV conventional plan and 10 MV IMRT plan was
made. A detector was placed at the point which was 100 cm away from the photon beam isocenter, which was
placed in the center of 3He proportional counter, and the photoneutron dose was measured. 3He proportional
counter was placed 50 cm longitudinally superior to and inferior to the couch with the central point as the standard
to measure the dose change by position changes. A commercial program was used for dose change analysis.
Results: The average integral dose by energy size was 220.27 μSv and 526.61 μSv in 10 MV and 15 MV
conventional RT, respectively. The average dose increased 2.39 times in 15 MV conventional RT. The average
photoneutron integral dose in conventional RT and IMRT with the same energy was 220.27 μSv and 308.27 μSv
each; the dose in IMRT increased 1.40 times. The average photoneutron integral dose by measurement location
resulted significantly higher in point 2 than 3 in conventional RT, 7.1% higher in 10 MV, and 3.0% higher in 15 MV.
Conclusion: When high energy radiotherapy, it should consider energy selection, treatment method and patient
position to reduce unnecessary dose by photoneutron. Also, the dose data of photoneutron needs to be
systematized to find methods to apply computerization programs. This is considered to decrease secondary cancer
probabilities and side effects due to radiation therapy and to minimize unnecessary dose for the patients.
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KEYWORD
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photoneutron, 3He proportional counter, IMRT
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