Ядерная медицина и лучевая терапия

Optimization of Treatment Planning Parameters used in Tomotherapy for Breast Cancer Patients

Abstract

Reena Devi PH, Tabassum W, Siji Nojin P, Nara M, Priyanka A and Sarin R

Aim: To study the effect of various planning parameters viz field width (FW), pitch factor (PF) on breast tumor and evaluate the relation among these parameters and their influence on the quality of plan and the treatment time.
Material and method: Nine plans for each of the ten breast cancer patients were created taking various combinations of field width (FW) and pitch keeping the Modulation factor (MF) constant 3. The reference plan selected for the study is field width of 1, pitch 0.215. Other plans were created keeping the same constraints and penalty as the reference plan and 1000 iterations. Target coverage was evaluated in terms of conformity index (CN) and homogeneity index (HI) while the sparing of organs at risk (OARs) were evaluated in terms of mean, maximum and relevant dose volumes. Low dose spillages in normal tissues were also evaluated. The plans are compared with the reference plan using the Wilcoxon Signed Ranks Test. Concept of plan Quality index is also used to evaluate the plans qualitatively.
Results: The mean treatment delivery time for 5, 2.5 and 1.0 cm FW plans were 5.04 ± 0.4, 8.51 ± 0.87 and 20.67 ± 2.02 minutes respectively. There was no significant variation in doses for OARs and COIN and HI of targets for 1 cm and 2.5 cm plans except for 5 cmplans. But the low dose spillage increased by 9-14% and 23-43% for 2.5 and 5 cm respectively.
Conclusion: Dose to the OARs was not significantly higher for 2.5_FW plans from the reference plan but, significantly higher for 5_FW. Larger the FW and higher the pitch, spillage were more. On the basis of our analysis, 2.5_0.215 plan with MF=3, can be considered as the optimum plan for unilateral breast treatment using Tomotherapy.