Clinical dosimetric study of three radiotherapy techniques for postoperative breast cancer: Helical Tomotherapy,...

This paper is to investigate the dosimetric characteristics of Helical Tomotherapy (HT), step-and-shoot intensity-modulated radiation therapy (SaS-IMRT) and three-dimensional conformal radiation therapy (3D-CRT) for the postoperative breast cancer as well as their dosimetric comparison of the normal tissues. CT images of 10 postoperative patients with early stage breast cancer were transferred into HT, SaS-IMRT and 3D-CRT planning systems respectively after the target region and normal tissues were outlined by the same physician to assure the contour consistency. Each prescribed dose for three different modalities of plans was given to a total of 50 Gy in 25 fractions. Doses and irradiated volumes in heart, lungs, as well as conformity index (CI) and homogeneity index (HI) were evaluated for detailed comparison. All three plans showed appropriate coverage for the prescribed target dose in the dosimetric comparison. The CI in HT and SaS-IMRT as well as 3D-CRT was 0.68 ± 0.12, 0.58 ± 0.08 and 0.40 ± 0.08, respectively. The HI were 1.10 ± 0.03, 1.14 ± 0.02 and 1.17 ± 0.04, which appeared intergroup significant differences (p < 0.05). V₅, V₁₀, as well as V₂₀ of the heart were smallest in 3D-CRT than HT and SaS-IMRT. V5 of the ipsilateral lung was the smallest in 3D-CRT than HT and SaS-IMRT (p < 0.05); However, V₂₀ and V₃₀ were smaller in HT and SaS-IMRT than 3D-CRT (p < 0.05). V₅ of the contralateral lung was the smallest in 3D-CRT than other groups, with V₁₀~V₃₀ were basically similar in numeric values with not obvious discrepancy. Comparing with SaS-IMRT and 3D-CRT, HT technique in treating breast cancer had the best conformity and homogeneity index as well as steepest dose gradient due to its highly modulated beamlets with rotational technique. The heart volume irradiated was the smallest in conventional 3D-CRT, with SaS-IMRT was the largest among the three techniques, as expected. The volume of the contralateral lung irradiated was the smallest in 3D-CRT than other groups. V₅ of the ipsilateral lung was the smallest in 3D-CRT than other two groups. V₁₀~V₃₀ in HT and SaS-IMRT were similar and better than 3D-CRT dosimetrically. We conclude that HT technique had advantages over SaS-IMRT and 3D-CRT based on the dosimetric comparison in this study, especially in the high dose region of ipsilateral lung, target homogeneity and dose uniformity.