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. 2016 Apr-Jun;41(2):149-52.
doi: 10.4103/0971-6203.181632.

Build-up material requirements in clinical dosimetry during total body irradiation treatments

Martin Butson  1 , Dane Pope  2 , Mamoon Haque  1 , Tom Chen  3 , Guangli Song  2 , May Whitaker  2
Affiliations

Build-up material requirements in clinical dosimetry during total body irradiation treatments

Martin Butson et al. J Med Phys. 2016 Apr-Jun.

Abstract

Total body irradiation (TBI) treatments are mainly used in a preparative regimen for hematopoietic stem cell (or bone marrow) transplantation. Our standard clinical regimen is a 12 Gy/6 fraction bi-daily technique using 6MV X-rays at a large extended source to surface distance (SSD). This work investigates and quantifies the dose build-up characteristics and thus the requirements for bolus used for in vivo dosimetry for TBI applications. Percentage dose build-up characteristics of photon beams have been investigated at large extended SSDs using ionization chambers and Gafchromic film. Open field measurements at different field sizes and with differing scatter conditions such as the introduction of standard Perspex scattering plates at different distances to the measurement point were made in an effort to determine the required bolus/build-up material required for accurate determination of applied dose. Percentage surface dose values measured for open fields at 300 cm SSD were found to range from 20% up to 65.5% for fields 5 cm × 5 cm to 40 cm × 40 cm, respectively. With the introduction of 1 cm Perspex scattering plates used in TBI treatments, the surface dose values increased up to 83-90% (93-97% at 1 mm depth), depending on the position of the Perspex scattering plate compared to the measurement point. Our work showed that at least 5 mm water equivalent bolus/scatter material should be placed over the EBT3 film for accurate dose assessment for TBI treatments. Results also show that a small but measurable decrease in measured dose occurred with 5 mm water equivalent thick bolus material of areas '3 cm(2). As such, we recommend that 3 cm × 3 cm × 5 mm bolus build-up is the smallest size that should be placed over EBT3 Gafchromic film when used for accurate in vivo dosimetry for TBI applications.

Keywords: Bolus; build up dose; dosimetry; radiochromic; radiotherapy; total body irradiation.

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Figures

Figure 1
Figure 1
Geometry of irradiation conditions
Figure 2
Figure 2
Percentage build-up dose for 6 MV X-rays measured at 300 cm source to surface distance with different field sizes
Figure 3
Figure 3
Percentage build-up dose at 40 cm × 40 cm and the effect of a Perspex beam spoiler
Figure 4
Figure 4
Effects of bolus size on measured dose
See this image and copyright information in PMC

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