ارزيابي خطر سرطان ثانويه ي تيروئيد ناشي از دز معادل نوترون در درمان تومور مغزي به روش )3D-CRT 3 يا D-Conformal Radiation Therapy( تطبيقي سه بعدي

Evaluation of Risk of Secondary Thyroid Cancer Caused by Neutron Dose Equivalent from Brain Tumor 3D-Conformal Radiation Therapy (3D-CRT)

ﻘﺪﻣﻪ: ﺳﺮﻃﺎن ﺗﯿﺮوﺋﯿﺪ، ﯾﮑﯽ از ﻓﺮاوانﺗﺮﯾﻦ ﺑﺪﺧﯿﻤﯽﻫﺎي ﺛﺎﻧﻮﯾﻪ در ﻧﺘﯿﺠﻪ ي درﯾﺎﻓﺖ دزﻫﺎي درﻣﺎﻧﯽ در ﻧﺎﺣﯿﻪ ي ﺳﺮ و ﮔﺮدن اﺳﺖ. ﻫﺪف از اﻧﺠﺎم اﯾﻦ ﻣﻄﺎﻟﻌﻪ، ﺗﺨﻤﯿﻦ ﺧﻄﺮ ﺳﺮﻃﺎن ﺛﺎﻧﻮﯾﻪ ي ﺗﯿﺮوﺋﯿﺪ ﻧﺎﺷﯽ از آﻟﻮدﮔﯽ ﻧﻮﺗﺮوﻧﯽ ﺷﺘﺎب دﻫﻨﺪه ي زﯾﻤﻨﺲ 15 ﻣﮕﺎوﻟﺘﯽ در درﻣﺎن ﺗﻮﻣﻮرﻫﺎي ﻣﻐﺰي ﺑﻪ روش ﺗﻄﺒﯿﻘﯽ ﺳﻪ ﺑﻌﺪي )3D- Conformal Radiation Therapy ﯾﺎ 3D-CRT( ﺑﻮد. روش ﻫﺎ: ﺷﺎر و دز ﻧﻮﺗﺮون در ﻧﻘﺎط ﻣﺨﺘﻠﻒ ﺗﺤﺖ درﻣﺎن ﺑﺎ اﺳﺘﻔﺎده از ﯾﮏ آﺷﮑﺎرﺳﺎز ﻧﻮﺗﺮون ﻣﺴﺘﻘﻞ از اﻧﺮژي، ﻣﺘﺸﮑﻞ از ﯾﮏ ﮐﺮه ي ﺗﻌﺪﯾﻞ ﮐﻨﻨﺪه )Moderator( و ﺷﻤﺎرﺷﮕﺮ ﺑﻮران ﺗﺮي ﻓﻮﻟﻮراﯾﺪ )Boron Trifluoride ﯾﺎ BF3( اﻧﺪازه ﮔﯿﺮي ﺷﺪ و دز ﻣﻌﺎدل ﻧﻮﺗﺮون در ﺗﯿﺮوﺋﯿﺪ ﺑﻪ ﻫﺪف ﻣﺤﺎﺳﺒﻪ ي ﺧﻄﺮ ﺳﺮﻃﺎن ﺛﺎﻧﻮﯾﻪ ي آن ﺗﻌﯿﯿﻦ ﺷﺪ. ﯾﺎﻓﺘﻪ ﻫﺎ: ﻣﻘﺪار دز ﻣﻌﺎدل ﻧﻮﺗﺮون در ﻣﺤﻮر ﻣﺮﮐﺰي )0/030 ﻣﯿﻠﯽ ﺳﯿﻮرت ﺑﺮ ﮔﺮي( و ﻓﻮاﺻﻞ 4 ﺳﺎﻧﺘﯽﻣﺘﺮ )0/285 ﻣﯿﻠﯽ ﺳﯿﻮرت ﺑﺮ ﮔﺮي(، 15 ﺳﺎﻧﺘﯽﻣﺘﺮ )0/229 ﻣﯿﻠﯽ ﺳﯿﻮرت ﺑﺮ ﮔﺮي(، 45 ﺳﺎﻧﺘﯽ ﻣﺘﺮ ) 0/125 ﻣﯿﻠﯽ ﺳﯿﻮرت ﺑﺮ ﮔﺮي( و 150 ﺳﺎﻧﺘﯽ ﻣﺘﺮ )0/020 ﻣﯿﻠﯽ ﺳﯿﻮرت ﺑﺮ ﮔﺮي( ﭘﺎﯾﯿﻦ ﺗﺮ از ﻣﺤﻮر ﻣﺮﮐﺰي ﺑﻪ دﺳﺖ آﻣﺪ. دز ﻣﻌﺎدل ﻧﻮﺗﺮون رﺳﯿﺪه ﺑﻪ ﺗﯿﺮوﺋﯿﺪ ﺑﻪ ازاي دز ﺗﺠﻮﯾﺰي ﮐﻞ )54 ﮔﺮي( ﺑﻪ اﯾﺰوﺳﻨﺘﺮ، 12/366 ﻣﯿﻠﯽ ﺳﯿﻮرت ﺑﻮد ﮐﻪ ﺑﺎ ﺗﻮﺟﻪ ﺑﻪ آن، ﻣﻘﺪار ﺧﻄﺮ ﺳﺮﻃﺎن ﺛﺎﻧﻮﯾﻪ در ﺗﯿﺮوﺋﯿﺪ 0/001 درﺻﺪ ﺑﻪ دﺳﺖ آﻣﺪ. ﻧﺘﯿﺠﻪ ﮔﯿﺮي: ﻣﻘﺪار دز درﯾﺎﻓﺘﯽ ﺗﯿﺮوﺋﯿﺪ ﺣﯿﻦ ﭘﺮﺗﻮدرﻣﺎﻧﯽ ﻣﻐﺰ ﺑﺎ ﭘﺮﺗﻮي ﭘﺮاﻧﺮژي ﻧﻤﯽ ﺗﻮاﻧﺪ آﺳﯿﺐ زﯾﺴﺖ ﺷﻨﺎﺧﺘﯽ ﻗﺎﺑﻞ ﺗﻮﺟﻬﯽ را ﺣﺎﺻﻞ ﮐﻨﺪ. در ﻧﺘﯿﺠﻪ ، ﺧﻄﺮ ﺳﺮﻃﺎن ﺛﺎﻧﻮﯾﻪ ي ﺗﯿﺮوﺋﯿﺪ ﻧﺎﺷﯽ از آﻟﻮدﮔﯽ ﻧﻮﺗﺮوﻧﯽ ﺑﻪ ﻧﺴﺒﺖ ﭘﺎﯾﯿﻦ اﺳﺖ

Background: Thyroid cancer is one of the most common secondary malignancies as a result of receiving therapeutic doses to the head and neck. In this study, the probability of secondary thyroid cancer risk due to neutron contamination of 15 MV Siemens Linear Accelerator (LINAC) in brain tumor 3D-Conformal Radiation Therapy (3D-CRT) was calculated. Methods: Neutron fluence and neutron dose were measured at different points at the treatment table using an energy-independent neutron detector consisting of a sphere moderator and a Boron Trifluoride (BF3) counter, and the neutron dose equivalent to the thyroid was determined to calculate the probability of secondary cancer risk. Findings: The neutron dose equivalent was obtained at the central axis (0.304 mSv/Gy) and at 4 cm (0.285 mSv/Gy), 15 cm (0.229 mSv/Gy), 45 cm (0.125 mSv/Gy), and 150 cm (0.02 mSv/Gy) inferior. The neutron dose equivalent reaching the thyroid for the total prescribed dose was 12.366 mSv. According to that, the probability of secondary thyroid cancer risk was obtained as 0.001%. Conclusion: The thyroid dose in high-energy radiation therapy of brain tumor cannot cause significant biological damage. Therefore, the risk of secondary thyroid cancer due to neutron contamination is relatively low.