A comparison of selected dosimetric parameters of two Hodgkin Lymphoma radiotherapy techniques with reference to potential risk of radiation induced heart disease

Purpose: Hodgkin lymphoma (HL) is one of the most frequent malignancies among pediatric patients. One of the common causes of death in HL survivors after radiation therapy (RT), is radiation-induced heart disease (RIHD). The aim of this study was to compare several dosimetric parameters for two methods of early stage Hodgkin lymphoma radiotherapy with reference to potential risk of RIHD.

Materials and Methods: Using a series of computed tomography slices of 40 young patients, treatment planning was done in two methods of HL RT, including involved field (IFRT) and involved site (ISRT) in doses of 20, 30, and 35 Gy. Contouring of clinical target volume as well as the organs at risk, including the heart, was performed by a radiation oncologist. The mean and maximum dose of heart (D_heart-mean and D_heart-max), the volume of heart receiving a dose more than 25 Gy (V25), and the standard deviation of dose as a dose homogeneity index in heart, were used to compare the RIHD risk.

Results: The mean value for D_heart-mean in ISRT method in all doses was less compare to IFRT. Maximum reduction in mean value of D_heart-mean occurred at moving from 30 Gy IFRT to ISRT by 9.53 Gy (p < 0.001) and minimum was between 35 Gy IFRT and ISRT. The mean value for D_heart-max was fewer in IFRT rather than ISRT and the maximum difference was between 35 Gy IFRT and ISRT (1.35 Gy). The mean of V25 of heart was 26.66% and 23.74% in 35 Gy IFRT and ISRT, respectively, and dose distribution was more homogeneous in IFRT.

Conclusions: If D_heart-max and V25 of heart or homogeneity of dose distribution in heart are considered as determining factors in RIHD, then IFRT can be considered optimum, especially in 35 Gy IFRT; while, assuming the D_heart-mean as the most important factor in RIHD, superiority of ISRT over IFRT is observed.