Amaç: Baş-boyun bölgesindeki kritik organ ve dokuların fazla sayıda olması nedeniyle reçete edilen tedavi dozlarının hastaya planlamada öngörülen yerlerinde ve hesaplanan dozda uygulanması hayati bir öneme sahiptir. Bu çalışmada, nazofarinks kanseri tanısı ile küratif radyoterapi uygulanmış 15 hastanın tedavi planları retrospektif olarak değerlendirilmiştir. Pencil Beam Konvolüsyon (PBC) ve Anizotropik Analitik Algoritması (AAA) kullanılarak yapılan 2 farklı planlamanın, normal doku dozları ve hedef hacmin almış olduğu dozlar açısından karşılaştırılması amaçlanmıştır. Gereç ve Yöntemler: Tedavi planlama sisteminde (TPS) aynı hasta için aynı dozimetrik parametreler girilerek, bu 2 ayrı doz hesaplama algoritması ile ikişer adet yoğunluk ayarlı radyoterapi [intensity-modulated radiation therapy (IMRT)] planı oluşturuldu ve elde edilen veriler, uygun istatistiksel yöntemler kullanılarak karşılaştırıldı. Bulgular: Doz-hacim histogramlarına bakıldığında, hedef hacmin hesaplanan dozimetrik değerleri açısından, AAA ile PBC arasında belirgin bir fark yoktu. Buna karşın monitör ünite sayıları arasındaki fark istatistiksel olarak anlamlı idi (p=0,001). Normal doku dozlarına bakıldığında ise spinal kord, optik sinirler, beyin sapı, parotisler ve larinks için dozimetrik veriler arasındaki farkların, istatistiksel olarak anlamlı olduğu görüldü (sırasıyla; p=0,023, p=0,001, p=0,027, p=0,001 ve p=0,001). Sonuç: Nazofarinks kanserinde olduğu gibi homojen olmayan dokuların ve hava boşluklarının bulunduğu tedavi bölgelerindeki IMRT planlamalarında, TPS'de hesaplanan normal doku doz değerleri AAA ve PBC algoritmaları arasında anlamlı farklılık göstermektedir.
Anahtar Kelimeler: Yoğunluk ayarlı radyoterapi; nazofarinks kanserleri; doz hesaplama algoritmaları; normal doku dozları
Objective: Due to the large number of critical organs and tissues in head and neck region, it is crucial to deliver the prescribed treatment doses accurately and precisely. In this study, 15 patients treated with curative radiotherapy for nasopharyngeal cancer were retrospectively assessed and compared in terms of normal tissue doses and planning target volume dose parameters, using Pencil Beam Convolution (PBC) and Anisotropic Analytical Algorithm (AAA) dose calculation algorithms. Material and Methods: For fifteen patient, two separate intensity-modulated radiation therapy (IMRT) plans were created by using these dose calculation algorithms, entering the same dosimetric parameters for the same patient at treatment planning system (TPS). The obtained data were analyzed using appropriate statistical methods. Results: When dose-volume histograms were evaluated, no significant differences were found between the AAA and PBC algorithms, in terms of calculated dosimetric values of the planning target volume. However, the difference between the calculated monitor unit values was found to be statistically significant (p=0.001). With regard to normal tissue doses, the differences between the data for spinal cord, optic nerves, brain stem, parotid and larynx were also statistically significant (p=0.023, p=0.001, p=0.027, p=0.001 and p=0.001, respectively). Conclusion: As a result, IMRT dose values calculated at TPS using AAA and PBC algorithms, differ in terms of normal tissue doses in the treatment regions that have inhomogeneous structures and air cavities, such as nasopharyngeal cancers.
Keywords: Intensity modulated radiation therapy; nasopharyngeal cancers; dose calculation algorithm; normal tissue doses
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