Lineer hızlandırıcılarda fiziksel ve sanal kama filtrelerin karşılaştırılması ve dozimetrik değerlendirilmesi
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Date
2011
Authors
Şengül, Aycan
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Publisher
Uludağ Üniversitesi
Abstract
Radyoterapide hedef volüm içindeki doz dağılımının homojenliğini sağlamak amacıyla kullanılan doz düzenleyicilerinden birisi de wedge filtrelerdir. Gelişen teknolojiyle birlikte, fiziksel wedge filtrelerin yerini sanal wedge filtreler almaya başlamıştır. Çalışmamızda fiziksel ve sanal wedge filtrelerin dozimetrik özelliklerini karşılaştırarak sanal wedge filtrelerin avantaj ve dezavantajlarını saptamayı amaçladık.Çalışmada Uludağ Üniversitesi Tıp Fakültesi Radyoterapi Merkezinde bulunan Siemens Artiste tedavi cihazında 6 ve 15 MV foton enerjilerinde, 5x5, 10x10, 15x15, 20x20 cm2 alanlarında, fiziksel ve sanal wedge filtrelerin dozimetrik özellikleri; wedge faktörleri, %dd eğrileri, doz profilleri, yüzey ve çevre dozları karşılaştırıldı.Wedge faktör ölçümleri, SSD:100 cm'de 5 cm derinlikte, Farmer iyon odası ve unidos elektrometre kullanılarak yapıldı. % dd eğrileri, MP3-M su fantomunda, Semifleks iyon odası ile, açık alan, fiziksel ve sanal wedge'li alanlarda ölçüldü. Ardından 0.5, 1, dmax, 5, 10, 15 cm derinliklerde doz profilleri alındı.Yüzey dozu ölçümlerinde, SSD:100 cm'de Markus paralel plak iyon odası kullanıldı. Ayrıca 2-D Array kullanılarak sanal ve fiziksel wedge filtreli alanlarda 0, 1, dmax, 5, 10, 15 cm derinliklerde çevre dozları ölçüldü.Ölçüm sonuçları incelendiğinde; aynı derinlikte, küçük alanlardan büyük alanlara doğru gidildikçe fiziksel WF'nün ~%3, sanal WF'lerinin ise, %0,2 arttığı görüldü. % dd eğrilerinden her alana ait dmax derinlikleri 6 ve 15 MV için sırasıyla 15 ±2 mm, 30 ±2 mm olarak bulundu. Fiziksel wedge doz profillerinde alan ve derinlik arttıkça penumbranın arttığı ancak enerji arttıkça azaldığı gözlenmektedir.Sanal wedge için; küçük alanlarda wedge açısının çevre dozlarına etkisinin olmadığı ancak büyük alanlarda açıyla birlikte etkinin arttığı görüldü. Fiziksel wedge için derinlik ve alan boyutu arttıkça çevre dozunun arttığı ve wedge açısı arttıkça özellikle 5 cm'den sonraki derinliklerde çevre dozunun azaldığını saptadık.Aldığımız ölçümlerde sanal wedge'in fiziksel wedge'ye göre dozimetrik olarak üstünlüğünün olmadığı görülmektedir. Sanal wedge filtrelerin çevre dozu fiziksel wedge filtreye göre yüksektir. Bu sanal wedge filtrenin dezavantajıdır. Sanal wedge filtreli alanlarda, açık alana benzer yüzey dozları görülürken fiziksel wedge filtreli alanlarda daha düşük dozlar görülür. Sanal wedge kullanımıyla MU değerinde açık alana göre bir değişim gözlenmezken, fiziksel wedge benzeri izodoz dağılımı elde edilir. Ayrıca MU artmadığı için tedavi süresi fiziksel wedge kullanımına göre kısa olur. Böylece tedavi esnasında hasta ve organ hareketlerinden kaynaklanan set-up hataları minimuma indirgenmiş olur. Sonuç olarak sanal wedge'ler set up kolaylığı ve tedavi süresinin kısalması sebebiyle tercih edilebilir. Ayrıca fiziksel wedge filtreye göre daha fazla açı alternatifi sunmasıyla planlamada avantaj sağlar. Bu çalışmada, sanal wedge filtrelerin uygun kalite kontrol programıyla tedavilerde güvenle kullanılabileceği görülmüştür.
In radiation therapy wedge filters are, one of the dose compensators which are used in order to provide the homogeneity of dose distribution in the target volume. With the developing technology, virtual wedge filters have been used instead of physical wedge filters. In this study we aimed to evaluate the advantages and disadvantages of virtual wedge filter by comparing dosimetric properties with physical and virtual wedge filters.In this study, we used Siemens Artiste linear accelerator in Uludağ University faculty of medicine and we compare dosimetric properties of virtual and physical wedge factors, depth doses, dose profiles, peripheral and surface doses, at the energies of 6 and 15 MV photon beams.Wedge factors was measured, with unidos electrometer and farmer ion chamber at SSD: 100 cm and 5 cm depth. % depth doses measured with MP3-M water phantom and with the semiflex ion chamber, we measured open fields and fields with physical and virtual wedges. Then we took the dose profiles at depths 0.5, 1, dmax, 5, 10, 15 cm.For the surface dose measurements at SSD: 100, markus pralel plate ion chamber was used. And also by using 2-D Array, peripheral doses of physical and virtual wedge fields were measured at the depths of 0, 1, dmax, 5, 10, 15 cmWhen the measurement results are analyzed, it has been observed that at the same depth, from large field to small field physical and virtual WFs are increased by %3 and %2 respectively. From the % dd curves, we evaluated the dmax depth of 6 and 15 MV photon energies 15 ±2 mm, 30 ±2 mm respectively. It is observed that, when field and depth increases at physical wedge dose profiles penumbra also increases however, it decreases as the energy increases. While virtual wedge profiles show higher gradient than physical wedge profiles at surface, the more the depth increases, the more increase occurs in the congruity between profiles.It is observed that, for virtual wedge, wedge angle has no effect on peripheral doses at small fields but the effect increases with an increase in angleat large fields. For physcial wedge, we evaluated that peripheral dose increases as the depth increases and field size and peripheral dose decreases when wedge angle increases at the depths after 5 cm.When we look at our measurements we can see that virtual wedge doesn't have dosimetric priority when it is compared with physical wedge. Peripheral dose of virtual wedge filters is higher than physical wedge filters. It is a disadvantage of virtual wedge filter. Virtual wedge fields have similar surface doses as the open fields while physical fields have lower surface doses. When we use virtual wedge, MU value doesn't change when it is compared with open field, suchlike physical wedge isodose distributions obtained. In addition, treatment time becomes shorter when compared with physical wedge since MU doesn't increase. So, the errors which are caused by patient and organ motions during treatment become minimum.In conclusion, it can be said that virtual wedges are preferred due to easy set-up and short treatment time. Furthermore, virtual wedges are more useful than physical wedges since they offer more angle choice at planning. In this study it is observed that virtual wedge filters with suitable quality control programme can be used safely during treatments.
In radiation therapy wedge filters are, one of the dose compensators which are used in order to provide the homogeneity of dose distribution in the target volume. With the developing technology, virtual wedge filters have been used instead of physical wedge filters. In this study we aimed to evaluate the advantages and disadvantages of virtual wedge filter by comparing dosimetric properties with physical and virtual wedge filters.In this study, we used Siemens Artiste linear accelerator in Uludağ University faculty of medicine and we compare dosimetric properties of virtual and physical wedge factors, depth doses, dose profiles, peripheral and surface doses, at the energies of 6 and 15 MV photon beams.Wedge factors was measured, with unidos electrometer and farmer ion chamber at SSD: 100 cm and 5 cm depth. % depth doses measured with MP3-M water phantom and with the semiflex ion chamber, we measured open fields and fields with physical and virtual wedges. Then we took the dose profiles at depths 0.5, 1, dmax, 5, 10, 15 cm.For the surface dose measurements at SSD: 100, markus pralel plate ion chamber was used. And also by using 2-D Array, peripheral doses of physical and virtual wedge fields were measured at the depths of 0, 1, dmax, 5, 10, 15 cmWhen the measurement results are analyzed, it has been observed that at the same depth, from large field to small field physical and virtual WFs are increased by %3 and %2 respectively. From the % dd curves, we evaluated the dmax depth of 6 and 15 MV photon energies 15 ±2 mm, 30 ±2 mm respectively. It is observed that, when field and depth increases at physical wedge dose profiles penumbra also increases however, it decreases as the energy increases. While virtual wedge profiles show higher gradient than physical wedge profiles at surface, the more the depth increases, the more increase occurs in the congruity between profiles.It is observed that, for virtual wedge, wedge angle has no effect on peripheral doses at small fields but the effect increases with an increase in angleat large fields. For physcial wedge, we evaluated that peripheral dose increases as the depth increases and field size and peripheral dose decreases when wedge angle increases at the depths after 5 cm.When we look at our measurements we can see that virtual wedge doesn't have dosimetric priority when it is compared with physical wedge. Peripheral dose of virtual wedge filters is higher than physical wedge filters. It is a disadvantage of virtual wedge filter. Virtual wedge fields have similar surface doses as the open fields while physical fields have lower surface doses. When we use virtual wedge, MU value doesn't change when it is compared with open field, suchlike physical wedge isodose distributions obtained. In addition, treatment time becomes shorter when compared with physical wedge since MU doesn't increase. So, the errors which are caused by patient and organ motions during treatment become minimum.In conclusion, it can be said that virtual wedges are preferred due to easy set-up and short treatment time. Furthermore, virtual wedges are more useful than physical wedges since they offer more angle choice at planning. In this study it is observed that virtual wedge filters with suitable quality control programme can be used safely during treatments.
Description
Keywords
Sanal wedge, Fiziksel wedge, Wedge faktörü, Radyoterapi, Dozimetre, Virtual wedge, Physical wedge, Wedge factor, Radiotherapy, Dosimeter
Citation
Şengül, A. (2011). Lineer hızlandırıcılarda fiziksel ve sanal kama filtrelerin karşılaştırılması ve dozimetrik değerlendirilmesi. Yayınlanmamış yüksek lisans tezi. Uludağ Üniversitesi Sağlık Bilimleri Enstitüsü.