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

Year 2008, Volume: 23 Issue: 4, 182 - 188, 01.05.2008

Evren Ozan Göksel Murat Okutan Aydın Çakır Hatice Bilge

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

References

• 1. Klevenhagen SC. Physics of electron beam therapy. In collaboration with the hospital physicist association. Bristol: Adam Hilger Ltd.; 1985.7
• 2. Günhan B, Kemikler G, Koca A. Determination of surface dose and the effect of bolus to surface dose in electron beams. Med Dosim 2003;28(3):193-8.
• 3. Khan FM. The Physics of radiation therapy. 3rd ed. Baltimore, MD: Lippincot Williams and Wi l k i n s; 2003.
• 4. Parida DK, Verma KK, Chander S, Joshi RC, Rath GK. Total skin electron irradiation therapy in mycosis fungoides using high-dose rate mode: a preliminary experience. Int J Dermatol 2005;44(10):828-30.
• 5. Amin-Zimmerman F, Paris K, Minor GI, Spanos W. Postmastectomy chest wall radiation with electronbeam therapy: outcomes and complications at the University of Louisville. Cancer J 2005;11(3):204-8.
• 6. Hurkmans CW, Saarnak AE, Pieters BR, Borger JH, Bruinvis IA. An improved technique for breast cancer irradiation including the locoregional lymph nodes. Int J Radiat Oncol Biol Phys 2000;47(5):1421-9.
• 7. Yaparpalvi R, Fontenla DP, Beitler JJ. Improved dose homogeneity in scalp irradiation using a single set-up point and different energy electron beams. Br J Radiol 2002;75(896):670-7.
• 8. Tapley N. High-energy photon and electron beam. Cancer 1977;39(2 Suppl):788-801.
• 9. Karzmark CJ. Advances in linear accelerator design for radiotherapy. Med Phys 1984;11(2):105-28.
• 10. Mills MD, Hogstrom KR, Almond PR. Prediction of electron beam output factors. Med Phys 1982;9(1):60-8.
• 11. The use of plane-paralel ionization chambers in highenergy electron and photon beams. An International Code of Practice for Dosimetry. Thecnical Report Series No.381, IAEA. Vienna; 1997.
• 12. Mills MD, Hogstrom KR, Fields RS. Determination of electron beam output factors for a 20-MeV linear accelerator. Med Phys 1985;12(4):473-6.
• 13. Kirby TH, Gastorf RJ, Hanson WF, Berkley LW, Gagnon WF, Hazle JD, et al. Electron beam central axis depth dose measurements. Med Phys 1985;12(3):357-61.
• 14. Schlegel W, Mahr A. 3D conformal radiation therapy. A Multimedia introduction to methods and thecn i q u e s . Berlin, Heidelberg, New Yo r k: S p r i n g e r Verlag; 2007