Preparation of tissue compensator and investigation of resultant dose distribution effects on treatments performed with Co-60 teletherapy machine

Abstract

OBJECTIVES In this study, it was purposed to design an aluminium material using compensator in order to obtain homogeneous dose distribution in irradiated volume on an irregular treatment field. METHODS For preparation of the compensator for large body curve, the anterior supra field of 25x26 cm and the lateral field of the face of 13x12 cm were selected. For the selected fields, the compensators were prepared using a man-shaped special phantom. The selected lateral face and anterior supra field without using the compensator and on Co-60 apparatus, dose distribution was obtained by film dosimetry method from man- shaped sagittal two-segmented special phantom. Findings were controlled using another measuring system thermoluminescent dosimeter. The experimental studies made without using the compensator were repeated with the compensator. The dose distributions obtained with and without compensator were compared and any positive contribution to dose distribution was investigated. RESULTS The data obtained from this study using compensator on the treatment field with excess surface irregularity, on lateral face, medial line and vertical axis, showed 5% more homogeneous dose distribution, and for supra field, parallel axis to radiation field to isodose distribution was 11.1% more homogeneous. CONCLUSION Consequently, in the case of curved or irregular treatment surfaces, a more homogeneous dose distribution can be produced using tissue compensators prepared for each patient separately. This will increase treatment quality in clinical use.

Keywords

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Co-60 teleterapi cihazı ile yapılan tedavilerde doku kompansatörü tasarlanması ve buna bağlı doz dağılımı etkisinin araştırılması

Öz

AMAÇ Bu çalışmada, tedavi yüzeyinin eğri ya da düzensiz olması halinde ışınlanan volüm içindeki doz dağılımının homojen olmasını sağlamak amacıyla, alüminyum materyali kullanarak kompansatör dizayn edilmesi amaçlandı. GEREÇ VE YÖNTEM Kompansatör hazırlanması için vücut eğriliğinin fazla olduğu 13x12 cm büyüklüğünde yan yüz alanı, 25x26 cm büyüklüğünde ön supra alanı seçildi. Seçilen alanlar için insan şeklinde özel hazırlanmış fantom kullanılarak kompansatörler hazırlandı. Seçilen yan yüz, ön supra alanı için kompansatör kullanılmadan Co-60 cihazında, insan benzeri sagital iki simetrik parça halinde olan özel fantomda film dozimetri yöntemiyle doz dağılımları elde edildi ve bu doz dağılımlarının doğruluğu, bir başka doz ölçüm yöntemi olan termoluminesans dozimetre yöntemi ile kontrol edildi. Kompansatör kullanılmadan yapılan deneysel çalışmalar, kompansatör kullanılarak tekrar edildi. Kompansatör kullanılmadan ve kullanılarak elde edilen doz dağılımları karşılaştırıldı; kompansatör kullanımının doz dağılımına olumlu katkısı araştırıldı. BULGULAR Bu çalışmanın sonunda elde edilen veriler, yüzey eğriliği fazla olan tedavi alanlarında kompansatör kullanılması ile yan yüz alanlarda, orta hatta ışına dik eksende izodoz dağılımını %5 oranında daha homojen hale getirdiği, supra alanında radyasyon alanına paraleleksende izodoz dağılımını %11, 1 oranında daha homojen hale getirdiğini göstermektedir. SONUÇ Tedavi yüzeyinin eğri ya da düzensiz olması halinde hastaya özel hazırlanan kompansatörün, ışınlanan volüm içindeki doz dağılımını daha düzgün bir hale getirdiği, buna bağlı olarak klinik kullanımında tedavi kalitesini arttıracağı görülmüştür.

Anahtar Kelimeler

• Doz dağılımı, kompansatör, radyoterapi

Kaynakça

1. 1) Ansbacher W, Robinson DM, Scrimger JW. Missing tissue compensators: evaluation and optimization of a commercial system. Med Phys 1992;19(5):1267 72
2. 2) Bagne FR, Samsami N, Hoke SW, Bronn DG. A study of effective attenuation coefficient for calculating tissue compensator thickness. Med Phys 1990;17(1):117-21
3. 3) Basran PS, Ansbacher W, Field GC, Murray BR. Evaluation of optimized compensators on a 3D planning system. Med Phys 1998;25(10):1837-44
4. 4) Beddar AS, Thomason C, Leung PM. Description and evaluation of a new 3-D computerized treatment planning dose compensator system. Med Dosim 1994;19(4):227-35
5. 5) Ellis F, Feldman A, Oliver R. Compensation for tissue inhomogeneity in cobalt 60 therapy. Br J Radiol 1964;37:798-80
6. 6) Evans MD, Schreiner LJ. A simple technique for film dosimetry. Radiother Oncol 1992;23(4):265-7
7. 7) Fletcher GH. Textbook of radiotherapy. 3rd. ed. Lea and Febiger; 1980. p. 20-4
8. 8) Hall EJ, Oliver R. The use of standard isodose distributions with high energy radiation beams-the accuracy of a compensator technique in correcting for body contours. Br J Radiol 1961;34:43-52

9. 9) Johns HE, Cunningham JR. The physics of radiology. 4th. ed. Charles, C. Thomas, Springfleld; 1983. p. 389-90
10. 10) Khan FM. The physics of radiation therapy. 2nd ed. Williams and Wilkins; 1992. p. 299-307
11. 11) Paliwal BR, Podgorsak MB, Harari PM, Haney P, Jursinic PA. Evaluation and quality control of a commercial 3-D dose compensator system. Med Dosim 1994;19(3):179-85
12. 12) Park HC, Almond PR. Tissue compensation and verification of dose uniformity. Med Dosim 1993;18(4):193-6
13. 13) Perez CA, Brady LW. Principles and Practice of Radiation Oncology. 3rd ed. Lippincott-Raven; 1998. p. 300-3
14. 14) Shahabi S. Blackburn's Introduction to Clinical Radiation Therapy Physics. Med. Phys. Publishing Co; 1989. p. 185-92
15. 15) Mayles WP, Yarnold JR, Webb S. Improved dose homogeneity in the breast using tissue compensators. Radiother Oncol 1991;22(4):248-51
16. 16) Cardarelli GA, Rao SN, Cail D. Investigation of the relative surface dose from Lipowitz-metal tissue compensators for 24- and 6-MV photon beams. Med Phys 1991;18(2):282-7
17. 17) Yin FF, Schell MC, Rubin P. A technique of automating compensator design for lung inhomogeneity correction using an electron portal imaging device. Med Phys 1994;21(11):1729-32
18. 18) Constantinou C, Harrington JC. Tissue compensators made of solid water or lead for megavoltage X-ray radiotherapy. Med Dosim 1989;14(1):41-7
19. 19) Jani SK, Pennington EC. Tissue compensators with use of vinyl lead sheets for head and neck portals on 4-MV x rays. Med Phys 1990;17(3):481-2
20. 20) Thomas SJ, Bruce G. Skin dose near compensating filters in radiotherapy. Phys Med Biol 1988;33(6):703-10
21. 21) Thomas SJ. A computer-calculated difference tissue compensator system. Br J Radiol 1985;58(691):665-8
22. 22) Mageras GS, Mohan R, Burman C, Barest GD, Kutcher GJ. Compensators for three-dimensional treatment planning. Med Phys 1991;18(2):133-40
23. 23) Robinson DM, Scrimger JW. An analytic approach to optimized retracted missing tissue compensators. Med Dosim 1990;15(2):51-9
24. 24) Robinson DM, Scrimger JW. Optimized tissue compensators. Med Phys 1990;17(3):391-6
25. 25) Chu T, Lee K, Dunscombe P. A technique for the evaluation of a missing tissue compensator system. Med Phys 1993;20(3):713-6
26. 26) Henderson SD, Purdy JA, Gerber RL, Mestman SJ. Dosimetry considerations for a Lipowitz metal tissue compensator system. Int J Radiat Oncol Biol Phys 1987;13(7):1107-12
27. 27) Jones D, Christopherson D, Judd D, Esagui L, Hafermann MD, Rieke JW. The incorporation of partial shielding of the spinal cord in a tissue deficit compensator in radiotherapy of the thorax. Med Dosim 1995;20(1):1-5
28. 28) Weeks KJ, Arora VR, Leopold KA, Light KL, King SC, Ray SK, et al. Clinical use of a concomitant boost technique using a gypsum compensator. Int J Radiat Oncol Biol Phys 1994;30(3):693-8
29. 29) Baker CM, Filimonov A, Conine F, Coughlin CT. Treatment of the intact breast using tangent split beam fields and half 15 degree wedges as tissue compensators. Radiol Technol 1986;58(2):135-8
30. 30) Williamson JF, Khan FM, Sharma SC. Film dosimetry of megavoltage photon beams: a practical method of isodensity-to-isodose curve conversion. Med Phys 1981;8(1):94-8
31. 31) Söderström S, Brahme A. Which is the most suitable number of photon beam portals in coplanar radiation therapy? Int J Radiat Oncol Biol Phys 1995;33(1):151-9
32. 32) Kutcher GJ, Coia L, Gillin M, Hanson WF, Leibel S, Morton RJ, et al. Comprehensive QA for radiation oncology: report of AAPM Radiation Therapy Committee Task Group 40. Med Phys 1994;21(4):581-618