Effect of scattered radiation in the total body irradiation technique: evaluation of the spoiler and wall dose component in the depthdose distribution

• Autorzy: Piotrowski T. , Adamska K. , Malicki J.
• Języki publikacji: EN

Abstrakty

EN

To determine the additional dose in layers of the body close to the skin during total body irradiation (TBI), due to radiation scattered off the treatment room walls and behind plexiglass spoilers applied to improve dose uniformity within the irradiated body. Large-field 6, 15 and 25 MV photon beams were generated by a Saturn 43 medical accelerator. A solid 30 ´ 30 ´ 30 cm3 PMMA (polymethylmethacrylate) phantom was used to represent radiation scattered from the body of the patient. Dose distributions were measured by a Farmer ionization chamber. The dose component arising from the spoiler was measured 5 mm below the phantom surface, over distances of 5-100 cm between the spoiler and the phantom surface. To measure the contribution of backscattered radiation from the walls, a small lead block was placed between the source and detector. Measurements were carried out in air with the PMMA phantom removed, to eliminate radiation backscattered from the phantom. As measured behind the spoiler, attenuation of the primary photon beam by the spoiler itself was by 8, 5 and 3% for 6, 15 and 25 MV beams, respectively. The highest dose contribution from the spoiler arose at 10 cm separation between the phantom surface and the spoiler. Assessed at a depth of 5 mm in the phantom, at spoiler-phantom separation of 10 cm, relative to case without spoiler and with wall backscatter subtracted, the dose enhancement due to the spoiler was by 8, 13 and 20% at beam energies 6, 15 and 25 MV, respectively. In these measurements, the distance between the source and the phantom surface was 300 cm and that between the source and the spoiler - 290 cm. The dose contributions due to radiation backscattered from the walls, relative to the case without any wall backscatter, estimated over the distal side of the phantom at a distance of 20 cm between the wall and that side of the phantom, were 5, 6 and 8% at beam energies 6, 15 and 25 MV, respectively. The use of a spoiler enhanced the dose in regions close to the phantom surface, compensating for the dose decrease over that area due to build-up effect. Radiation backscattered from the wall enhanced the dose in regions close to the phantom surface facing the wall.

Słowa kluczowe

EN

total body irradiation (TBI); scattered radiation; leukaemia

• Wydawca: Institute of Nuclear Chemistry and Technology
• Czasopismo: Nukleonika
• Rocznik: 2007
• Tom: Vol. 52, nr 4
• Strony: 153--158
• Opis fizyczny: Bibliogr. 25 poz., rys.

Twórcy

autor

Piotrowski T.

autor

Adamska K.

autor

Malicki J.

• Medical Physics Dept, Great Poland Cancer Centre, 15 Garbary Str., 61-868 Poznań, Poland, Tel.: [phone], Fax: [phone],

Bibliografia

• 1. Almond PR, Biggs PJ, Coursey BM et al. (1999) AAPM’s TG-51 protocol for clinical reference dosimetry of highenergy photon and electron beams. Med Phys 26:1847−1870
• 2. Barret A (1999) Total body irradiation. Rep Pract Oncol Radiother 4:47−64
• 3. Engler MJ (1986) A practical approach to uniform total body photon irradiation. Int J Radiat Oncol Biol Phys 12:2033−2039
• 4. Grinsky T, Briot E, Bridier A et al. (1997) Principles of total body irradiation. Rep Pract Oncol Radiother 2:33−35
• 5. Hui SK, Das RK, Thomadsen B et al. (2004) CT-based analysis of dose homogeneity in total body irradiation using lateral beam. J Appl Clin Med Phys 5:71−79
• 6. Kassaee A, Xiao Y, Bloch P et al. (2001) Doses near the surface during total-body irradiation with 15 MV X-rays. Int J Cancer 96:125−130
• 7. Lin JP, Chu TC, Liu MT (2001) Dose compensation of the total body irradiation therapy. Appl Radiat Isot 55:623−630
• 8. Litoborski M, Zwierzchowski G, Kierkowski J et al. (2006) Dose distribution and parameters of the linear accelerators used in Great Poland Cancer. Zeszyty Naukowe Wielkopolskiego Centrum Onkologii 3:115−311 (in Polish)
• 9. Malicki J (1997) Beam filter and compensators during total body irradiation on cobalt-60. Rep Pract Oncol Radiother 2:77−81
• 10. Malicki J (1998) Homogeneity and accuracy of the dose determination during total body irradiation. J Med Phys 23:80−81
• 11. Malicki J (1999) The accuracy of dose determination during total body irradiation. Strahlenther Onkol 175:492−496
• 12. Malicki J (2005) A career pathway for radiation therapists. Does it really exist? In regard to Kresl et al. “A historical perspective of the radiation oncology workforce and ongoing initiatives to impact recruitment and retention”. Int J Rad Oncol Biol Phys 62:292−293
• 13. Malicki J, Litoborski M, Kierzkowski J et al. (2004) How the implementation of an in vivo dosimetry protocol improved the dose delivery accuracy in head and neck radiotherapy. Neoplasma 51:155−158
• 14. Malicki J, Wachowiak J, Kosicka G et al. (1996) Dose distribution and early therapeutical effects of the total body irradiation for acute leukemia patients before bone marrow transplantation. Nowotwory 46:731−736 (in Polish)
• 15. Nowak A, Malicki J, Wachowiak J et al. (2001) Comparison of doses measured by thermoluminescent and semiconductor detectors during total body irradiation at cobalt-60 and 15 MeV linear accelerator. Rep Pract Oncol Radiother 6:40
• 16. Planskoy B, Bedford AM, Davis FM, Tapper PD, Loverock LT (1996) Physical aspects of total-body irradiation at the Middlesex Hospital (UCL group of hospitals), London 1988−1993: I. Phantom measurements and planning methods. Phys Med Biol 41:2307−2326
• 17. Quast U (1997) Total body irradiation − review of treatmenttechniques in Europe. Radiother Oncol 9:91−106
• 18. Ragona R, Anglesio S, Urgesi A et al. (1987) Technics and dosimetry in total body irradiation with 18 MeV photons. Radiol Med (Torino) 73:438−442 (in Italian)
• 19. Rittmann KL (1996) Quality assurance in total body irradiation by in vivo dosimetry. Rep Pract Oncol Radiother 1:21−24
• 20. Sanchez-Nieto B, Sanchez-Doblado F, Arrans R et al. (1993) Backscatter correction algorithm for TBI treatment conditions. Med Dosim 18:107−111
• 21. Sanchez-Nieto B, Sanchez-Doblado F, Terron JA et al. (1997) Lateral scatter correction algorithm for percentage depth dose in a large-field photon beam. Med Dosim 22:121−125
• 22. Scrimger JW (1977) Radiation backscattered from high atomic number materials in high energy photon beams. Radiology 124:815−817
• 23. Van Dam J, Rijnders A, Vanuytsel L et al. (1988) Practical implications of backscatter from outside the patients on the dose distribution during total body irradiation. Radiother Oncol 13:193−201
• 24. Weeks KJ, Litvienko VN, Madey JM (1997) The Compton backscattering process and radiotherapy. Med Phys 24:417−423
• 25. Zwierzchowski G, Piotrowski T, Kosicka G et al. (2006) Dose distribution during total body irradiation. Zeszyty Naukowe Wielkopolskiego Centrum Onkologii 3:5−35 (in Polish)