Second cancer risk assessments after involved-site radiotherapy for mediastinal Hodgkin lymphoma

This study was conducted to provide second cancer risk assessments attributable to involved-site radiotherapy (ISRT) of mediastinal Hodgkin lymphoma (HL) and to compare these risks with those from the conventional involved-field radiation therapy (IFRT).

Both ISRT and IFRT plans were made for 11 patients (six females, five males) with HL in the region of mediastinum. All three-dimensional plans involved 6 MV photon beams and delivered 30 Gy to the target site. Differential dose-volume histograms were defined for the lung, female breast, and esophagus which were partly included within the planned treatment fields. The patient-specific organ equivalent dose (OED) and the relevant lifetime attributable risk (LAR) of developing malignancies in each of the above critical organs were determined with the aid of a mechanistic, plateau and bell-shaped models. The LAR estimates were compared with the baseline risks for unexposed people.

The OED range of lung, breast, and esophagus calculated by the ISRT plans was 176.1-360.2, 19.5-124.1, and 42.6-157.7 cGy, respectively. The resultant LARs of developing lung and breast cancer as estimated by the three different models were at least 1.8 and 5.3 times lower than the baseline risks, respectively. The probability for the appearance of radiation-induced esophageal malignancies from ISRT in males was also up to 3.8 times smaller than the nominal incidence cancer rates. The corresponding probability in irradiated females exceeded the baseline risks. The estimated lifetime risks for lung and breast cancer induction due to ISRT were systematically and significantly lower than those from the IFRT irrespective of the model used for analysis (P < 0.05). No significant difference was found between the LARs for esophageal cancer development estimated by the ISRT and IFRT plans (P = 0.63).

The presented second cancer risk data may be of value in the selection of the optimal radiotherapy technique for the management of mediastinal HL and in the subsequent follow-up of irradiated patients.