Estimating the risk of secondary lung cancer from radiotherapy for pediatric Hodgkin’s lymphoma patients using a mechanistic model

Purpose
This study aims to estimate the risk of secondary lung cancer, expressed as the excess absolute risk (EAR), in pediatric patients treated with radiotherapy for Hodgkin’s lymphoma. The project was approved by the INCA Ethics Committee under CAAE 55933222.4.0000.5274.

Methods
The mechanistic and the OED (Organ Equivalent Dose) models were applied for this estimate. Two cases were included in this study, the bell-shaped and the plateau dose–response relationships obtained from the full mechanistic model. OED results were slightly lower using the full mechanistic and plateau models compared with the bell-shaped model.

Results
For an attained age 45 years after exposure, taking into account the three models, the EAR (cases per 104 person-years) values ranged from 19.71 to 25.07 for patients with age at exposure of 15 and 16 years; from 6.98 to 7.22 for patient with age at exposure of 12 years; from 9.73 to 11.29 for patients with age at exposure of 5 and 6 years; and from 16.05 to 16.84 for patient with age at exposure of 13 years. Inadequate coverage and lack of conformity of the treatment target reflect high-dose-volume parameters and finally the estimated risk.

Conclusion
The mechanistic model makes it possible to estimate the secondary cancer risk and compare it with regard to dose distributions, without having to wait for several years to observe the actual risk.