Dosimetric comparison of TomoDirect and TomoHelical plans in post-mastectomy chest wall radiation therapy

Background: The purpose of this study was to evaluate the characteristics of TomoDirect (TD) plans compared to conventional TomoHelical (TH) plans in chest wall irradiation in patients with breast cancer. Materials and Methods: TD and TH plans for only chest wall were retrospectively created for 30 patients previously treated with TH technique in our clinic. The beam angles were arranged to cover PTV chest wall and to minimize doses to OARs, ipsilateral lung and contralateral breast in TD plan. The prescribed dose was 50 Gy in 25 fractions. Results: The mean treatment times were similar in TH and TD (310.8 and 309 s, respectively, p>0.05). There was no difference between the values of CI and HI of both plans (p>0.05). The values of Dmean, V5 and V20 of the ipsilateral lung in TD plan was significantly lower than that in TH plan for all 30 patients (p<0.001, p<0.001 and p=0.001, respectively). V25 and V30 values of the heart were significantly lower in TH than those in TD plan in left-sided chest wall irradiation (p=0.006 and p<0.001, respectively). However, V5 values in TH was significantly higher than those in TD (p<0.001). In the right-sided, there was no difference between two plans for V25 and V30 values of heart (p>0.05). Conclusion: Both of TH and TD plans produce acceptable target dose coverage in chest wall RT. Considering the risk of low-dose radiation to the critical organs; TD mode improve dose distribution.