Meme Kanseri Radyoterapisinde Vmat (Volumetric Modulated Arc Therapy) Tekniği ile Farklı Grid Size Değerleri ve Doz Hesaplama Algoritmalarinin Plan Doğruluğuna Etkisi

Abstract

Bu çalışmada, meme kanseri radyoterapisinde VMAT tekniğiyle oluşturulan planlarda, doz hesaplama algoritmaları (Monte Carlo ve Pencil Beam) ve grid size (1,5 mm, 3 mm, 5 mm) değerlerinin plan doğruluğu üzerindeki etkileri karşılaştırmalı olarak değerlendirilmiştir. Planlama sürecinde, her hasta için algoritma ve grid size kombinasyonlarıyla toplam 6 farklı plan oluşturulmuştur. Monte Carlo algoritması ve 1,5 mm grid size kullanılarak oluşturulan plan, referans plan olarak kabul edilmiş; diğer planlar bu referans plan ile dozimetrik olarak karşılaştırılmıştır. Elde edilen bulgular, hem hedef hacimlerde hem de riskli organlardaki doz dağılımının, kullanılan algoritma ve grid size değerlerinden etkilendiğini göstermektedir. PTVmeme D%98 değeri referans planda (Monte Carlo 1,5 mm grid size) 47,2±1,0 Gy olarak hesaplanırken, Pencil Beam algoritması ile 5 mm grid size hesaplatılan planda 44,4±1,4 Gy’ye düştüğü gözlemlenmiştir. Riskli organlar açısından ise, özellikle algoritma değişiminin doz dağılımı üzerinde belirgin etkiler oluşturduğu görülmüştür. İpsilateral akciğerin V20 değeri referans planda %24,2±0,9 iken, Pencil Beam algoritması ile 1,5 mm grid size hesaplatılan planda %20,3 ±1,2 olarak hesaplanmış; bu azalma istatistiksel olarak anlamlı bulunmuştur (p<0,05). Sonuç olarak, Monte Carlo algoritması ve 1,5 mm grid size kullanımı, hedef hacimlerde ve riskli organlarda güvenilir ve doğru doz hesaplamaları sunmuştur. Pencil Beam algoritması ve 5 mm grid size ile oluşturulan planlarda ise, dozlar referans plana kıyasla daha düşük hesaplanmış; bu durum, tedavi sırasında hedef hacimlerin yeterince ışınlanmaması ve riskli organların beklenenden daha fazla doz almasına yol açabilir. Bu nedenle, tedavi planlarının doğruluğunu artırmak amacıyla Monte Carlo algoritması ile 1,5 mm grid size kombinasyonunun kullanılması en uygun seçenektir.

Keywords

• RADYOTERAPİ
• tedavi planlama sistemi
• algoritma
• grid size
• vmat

The Impact of Different Grid Size Values and Dose Calculation Algorithms on Plan Accuracy in Vmat-Based Radiotherapy for Breast Cancer

Abstract

This study evaluated the impact of dose calculation algorithms (Monte Carlo and Pencil Beam) and grid size values (1.5 mm, 3 mm, and 5 mm) on the accuracy of VMAT-based radiotherapy plans for breast cancer. Six different treatment plans were generated for each patient using combinations of algorithm and grid size values. The plan created with the Monte Carlo algorithm and a 1.5 mm grid size was designated as the reference plan, and all other plans were compared dosimetrically to this baseline. Results showed that both the choice of algorithm and grid size significantly influenced dose distribution in target volumes (PTVs) and organs at risk (OARs). For example, the D%98 value of the PTVmeme in the reference plan was 47.2 ± 1.0 Gy, which decreased to 44.4 ± 1.4 Gy in the Pencil Beam plan with a 5 mm grid size. For OARs, algorithm selection had a more pronounced impact. The V20 of the ipsilateral lung was 24.2 ± 0.9% in the reference plan but dropped to 20.3 ± 1.2% in the Pencil Beam plan with a 1.5 mm grid size (p<0.05). In conclusion, the Monte Carlo algorithm combined with a 1.5 mm grid size provides more accurate and reliable dose calculations for both PTVs and OARs. The Pencil Beam algorithm and larger grid sizes may underestimate dose, potentially resulting in underdosing of target volumes or unexpected overdose to critical organs. Therefore, using the Monte Carlo algorithm with a 1.5 mm grid size is considered the most appropriate choice for accurate radiotherapy planning.

Keywords

• Radiotheraphy
• treatment planning
• algorithm
• grid size
• vmat

Supporting Institution

BURSA ULUDAĞ ÜNİVERSİTESİ SAĞLIK ARAŞTIRMALARI ETİK KURULU

Ethical Statement

Bu çalışma, daha önce radyoterapi uygulanmış hastalara ait arşivlenmiş bilgisayarlı tomografi (BT) görüntüleri kullanılarak yürütülen retrospektif bir analizdir. Araştırma kapsamında hastalara herhangi bir ek işlem, tedavi veya girişimsel uygulama yapılmamıştır. Çalışma için Bursa Uludağ Üniversitesi Tıp Fakültesi Sağlık Araştırmaları Etik Kurulu’ndan onay alınmıştır (Tarih: 19.02.2025, Karar No: 2025/4/22).

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