The effects of collimation designs on the depth dose distributions of electron beams

Abstract

OBJECTIVES The purpose of the present study was to investigate the effects of collimation designs on the depth dose distribution of close energy electron beams for two different linear accelerators (LINACs) with different types of secondary collimation systems. METHODS Saturne-42 (trimmer) and Oncor (cone) linear accelerators were used for the study. Depth dose measurements were done at constant SSD with solid water phantom and plane-parallel ionization chamber. RESULTS Depth dose distributions for both LINACs with the same nominal energies (9-12 MeV) and same incident mean energies (8.1-10.8 MeV) on phantom surface were found to be different. The discrepancies of the depth dose distribution curves were increased, with an increasing difference in incident mean energy. CONCLUSION The current study shows that the depth dose parameters may vary between two different LINACs for electron beams although the same nominal energy is used. If differences are not within acceptable ranges, the machines should not be used in place of each other.

Keywords

• Particle Accelerators,Equipment and Supplies,Electrons,Radiotherapy

Kolimatör dizaynlarının elektron demetlerinin derin doz dağılımlarına etkisinin araştırılması

Abstract

AMAÇ Farklı ikincil kolimatör sistemine sahip iki lineer hızlandırıcıdan, birbirlerine yakın enerji seviyelerinde elde edilen elektron ışın demetlerinin derin doz dağılımları belirlendi ve farklı kolimasyon sistemlerinin doz dağılımı üzerindeki etkisi araştırıldı. GEREÇ VE YÖNTEM Çalışma, Saturne-42 (trimmer) ve Oncor (konüs) lineer hızlandırıcılarında yapıldı. Yüzde derin doz dağılımları, paralelplan iyon odası ve katı fantom kullanılarak sabit kaynak cilt mesafesinde elde edildi. BULGULAR Her iki cihazda nominal enerjileri (9-12 MeV) ve fantom yüyeyindeki ortalama enerjileri (8,1-10,8 MeV) aynı olan, elektron ışın demetlerinin, derin doz dağılımlarının, birbiriyle aynı olmadığı görüldü. Fantom yüzeyindeki ortalama enerjiler arasındaki fark arttıkça, derin doz eğrileri arasındaki farklılıklar artmakta idi. SONUÇ Bu çalışmada, iki cihazın nominal enerjilerinin aynı olması durumunda bile derin doz parametrelerinin farklı olabileceği görülmüştür. Eğer farklar kabul edilebilir sınırlar içinde değil ise tedavide farklı cihazlar bir birlerinin yerine kullanılmamalıdır.

Keywords

• Derin doz, elektron ışınları, konüs, trimmer

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