The dosimetric effect of random six-dimensional setup error in intensity-modulated radiotherapy planning for rectal cancer / 中华放射医学与防护杂志

ABSTRACT

Objective:To design a method to introduce random six-dimensional setup error (6D-SE) into the intensity-modulated radiotherapy (IMRT) planning for rectal cancer and evaluate its dosimetric effect.Methods:A total of 21 IMRT plans for patients with rectal cancer were randomly selected as reference plans [2 Gy per fraction for a total of 50 Gy; a 5 mm uniform margin around the clinical target volume (CTV) was taken as the planning target volume (PTV)]. For each fraction of the reference plan, a randomly generated 6D-SE was introduced by adjusting the geometrical parameters of the radiation field, and the dose was recalculated. The overall dose distribution with 6D-SE was obtained by adding up the dose of each fraction. A treatment simulation program that could complete the above workflow was developed using the Varian Eclipse scripting API (ESAPI). 6D-SEs that obey two preset distributions [distribution 1: translational error obey N(0, 4 2), and rotational error obey N(0, 2 2); distribution 2: translational error obey N(0, 2 2), and rotational error obey N(0, 1 2)] were introduced into the reference plans, and the dosimetric effects were assessed. Results:When the reference plans, error distribution 1, and error distribution 2 were applied, the Dmin values of the CTV were (49.4±0.41), (47.56±0.76), and (49.17±0.64) Gy, respectively; the D98% values of the CTV were (50.23±0.07), (49.98±0.10), and (50.27±0.09) Gy, respectively; the D98% values of the primary target area (the kernel part of the target area, excluding the margins) were (50.25±0.08), (50.42±0.13), and (50.33±0.10) Gy, respectively; the D98% values of the marginal area were (50.22±0.10), (49.88±0.11), and (50.26±0.10) Gy, respectively. In addition, compared with the result of the reference plans, the result of errors 1 and 2 showed no significant changes in the mean dose of the bladder and femoral heads ( P>0.05), despite slight decreases in the conformity index of the dose distribution with limited clinical significance. Conclusion:The proposed method and the treatment simulation program developed thereupon can introduce the 6D-SE obeying different distributions into the IMRT plans for rectal cancer on demand and provide overall dosimetric changes.