Dosimetric Verification of Hybrid Treatment Plan by TLD in the Treatment of Nasopharyngeal Cancer Radiotherapy

Abstract

Traditional treatment planning in nasopharyngeal cancer is now replaced by reverse planning using optimization techniques Intensity Modulated Radiotherapy-Intensity Modulated Arc Therapy (IMRT-IMAT) and Hybrid therapy planning using both. Hybrid plans are needed especially for critical organ doses that cannot be reduced in IMAT or IMRT treatment plans, or for PTV volumes that are not well covered. The dose calculations of the Treatment Planning Systems (TPS) that make these complex calculations need to be verified by dosimetric methods. In this study, TPS accuracy was tested by Thermoluminescence dosimeter (TLD). Computed tomography images of the Alderson® Rando Phantom for treatment planning in nasopharyngeal cancer were scanned. Planned Target Volume 70 Gy (PTV70) and critical organs (right parotid, left parotid, medulla and brain stem) were detected while computed tomography sections of a standard nasopharyngeal tumor patient were utilized by fusion. IMRT, IMAT and Hybrid treatment plans were created with the same dose prescription on the phantom using Eclipse (version 8.9.17) TPS. In Alderson® Rando Phantom, TLDs placed in the right and left parotid, medulla spinalis and brain stem were converted to cumulative doses and compared with the dose values on the treatment planning computer. The highest difference between Eclipse TPS and TLD mean reading values was found to be 3.5 % in the left parotid IMRT plan, 2.78 % in the brain stem in the IMAT plan and 3.16 % in the brain stem in the hybrid plan. In this study, we determined dosimetric accuracy of the Hybrid treatment plan for nasopharynx is less than 4 % in TPS.

Keywords

• Nasopharynx,Eclipse TPS,Hybrid Plan,TLD

Nazofarenks Kanseri Radyoterapi Tedavisinde Hibrit Tedavi Planının TLD ile Dozimetrik Doğrulanması

Abstract

Nazofarenks kanserinde geleneksel tedavi planlama, günümüzde yerini optimizasyon tekniklerinin kullanıldığı tersten planlamaya Yoğunluk Ayarlı Radyoterapi – Yoğunluk Ayarlı Arc Terapi (IMRT-IMAT) ve ikisinin birlikte kullanıldığı Hibrit tedavi planlamalara bırakmıştır. Özellikle IMAT veya IMRT tedavi planlarında düşürülemeyen kritik organ dozları veya iyi kapsanamayan PTV hacimleri için Hibrit planlara ihtiyaç duyulmaktadır.  Bu karmaşık hesaplamaları yapan Tedavi Planlama Sistemlerinin (TPS) doz hesaplarının dozimetrik yöntemlerle doğrulanması gerekmektedir. Bu çalışmada Termolüminesans dozimetre (TLD) yöntemi ile TPS doğruluğu test edilmiştir. Alderson® Rando Fantom’un nazofarenks kanseri tedavi planlaması için tedavi şartlarında bilgisayarlı tomografi görüntüleri çekilmiştir. Planlanan Hedef Hacim 70 Gy (PTV70) ve kritik organlar (sağ parotis, sol parotis, medulla ve beyin sapı) tespit edilirken standart bir nazofarenks tümörlü hastanın Bilgisayarlı tomografi kesitlerinden füzyon yapılarak yararlanılmıştır. IMRT, IMAT ve Hibrit tedavi planları Eclipse (version 8.9.17) TPS kullanılarak fantom üzerinde aynı doz reçetesi ile oluşturulmuştur. Alderson® Rando Fantomda sağ ve sol parotise, medulla spinalise ve beyin sapına denk gelecek şekilde yerleştirilen TLD’lerin okuma değerleri toplam doza dönüştürülerek tedavi planlama bilgisayarındaki doz değerleriyle karşılaştırılmıştır. Eclipse TPS ile TLD ortalama okuma değerleri arasında en fazla fark IMRT planında Sol Parotiste % 3.5, IMAT planında Beyin Sapında % 2.78, Hibrit planda Beyin Sapında % 3.16 olarak bulunmuştur. Bu çalışma ile Nazofarenks için yapılan Hibrit tedavi planının TPS de doğruluğunun % 4 ten az olduğunu dozimetrik olarak tespit ettik.

Keywords

• Nazofarenks,Eclips TPS,Hibrit plan,TLD

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