Adequate target volume in total-body irradiation by intensity-modulated radiation therapy using helical tomotherapy: A simulation study

Recently,intensity-modulated radiation therapy (imrt) has been used for total-body irradiation (tbi). since the planning target volume (ptv) for tbi includes the surrounding air,a dose prescription to the ptv provides high fluence to the body surface. thus with just a small set-up error,the body might be exposed to a highfluence beam. this study aims to assess which target volume should be prescribed the dose,such as a clinical target volume (ctv) with a margin,or a ctv that excludes the surface area of the skin. three treatment plans were created for each patient: the 5-mm clipped plan (plan a),the 0-mm margin plan (plan b) and the 5-mm margin plan (plan c). the ctv was the whole body. ptvs were the ctv with the exception of 5 mm from the skin surface in plan a,equal to the ctv in plan b,and the ctv with a 5 mm margin in plan c. the prescribed dose was 12 gy in six fractions. to assess the influence of the set-up error,dose distributions were simulated on computed tomography (ct) images shifted 2 pixels (= 4.296 mm),5 pixels (= 10.74 mm) and 10 pixels (= 21.48 mm) in the lateral direction from the original ct. with a set-up error of 10.74 mm,v110% was 8.8%,11.1% and 23.3% in plans a,b and c,respectively. the prescription to the ptv containing the surrounding air can be paradoxically vulnerable to a high-dose as a consequence of a small set-up error. © the author 2016.