Application of TomoDirect for craniospinal irradiation

Abstract

Objective To establish a new approach of beam arrangement with TomoDirect(TD) for craniospinal irradiation and evaluate the plan quality and treatment time. Methods Totally 7 patients were chosen for craniospinal irradiation planning in tomotherapy planning system. The 5-field TomoDirect plans, the 3-field TD plans and the Helical Tomotherapy (HT) plan were designed for each patient, respectively. Conformal index(CI), homogeneity index(HI)for PTV, dose parameters for OARs and mean dose of normal tissue were compared between these of two groups. The treatment time and monitor units were also compared. Results Except for the 3-field TD plans, all plans were able to achieve good dose conformity and dose homogeneity. The 5-field plan was superior to the 3-field plan, but a little inferior to the HT plan for the target dose. And all plans had their respective advantages for the dose of OARs. For the 5-field TD plan, the 3-field TD plan and the HT plan, the mean CI and HI were 0.79, 0.57, 0.88 and 1.06, 1.16, 1.05, respectively. The V20 of lung were 1.99%, 3.30%, 2.16%, respectively. The mean dose of heart was 6.17, 12.38 and 10.72 Gy, respectively. The mean doses of liver were 5.21, 5.14 and 4.62 Gy, respectively. The mean doses of left kidney were 4.30, 1.99 and 5.03 Gy, respectively. The mean doses of right kidney were 4.42, 2.09 and 4.91 Gy, respectively. The V5 of NT was 46.80%, 28.06% and 55.54%, respectively. The treatment time of the 5-field TD plan was the shortest one comparing with the other plans. The mean treatment time was 677, 721, and 907 s for the 5-field TD plan, the 3-field TD plan and the HT plan, respectivley. The number of MUs was 8 773, 9 657 and 12 581 for each plan. Conclusions The 5-field TD plan can decrease low dose volume in normal tissues outside the PTV and has shorter treatment time. It can be recommended for the patients like children who cannot tolerate long treatment time and need avoiding low dose to a large volume. Key words: TomoDirect; Craniospinal; Radiotherapy