Conceptus dose from involved-field radiotherapy for Hodgkin's lymphoma on a linear accelerator equipped with MLCs

To estimate the scattered dose to conceptus from involved-field radiotherapy for Hodgkin's lymphoma on a linear accelerator equipped with multileaf collimators.

Anthropomorphic phantoms were used to simulate an average pregnant woman at the 1st, 2nd and 3rd trimesters of gestation. Conceptus dose was measured using thermoluminescent dosimeters. Phantom measurements were performed for the minimum, medium and maximum field dimensions that may be employed during radiation therapy to lymph nodes in the neck, axilla, mediastinum and neck-mediastinum. The components of the scattered dose to conceptus were determined. Phantom exposures were generated with a 6-MV photon beam.

Neck irradiation with a tumor dose of 35 Gy resulted in a conceptus dose of 1.1-8.7 cGy depending upon the stage of pregnancy, the distance from treatment volume, and the field size applied. The corresponding conceptus dose ranges from radiotherapy in the regions of axilla, mediastinum and neck-mediastinum was 1.2-14.3 cGy, 3.7-57.7 cGy, and 5.1-91.8 cGy, respectively. The contribution of collimator scatter and head leakage to the total conceptus dose varied from 21% to 80% depending upon the irradiation site and gestational age.

The conceptus dose associated with cervical node irradiation is below the threshold value of 10 cGy during the entire pregnancy. Radiation therapy to lymph nodes in the axilla, mediastinum and neck-mediastinum may possibly lead to a conceptus dose of > 10 cGy and, therefore, informed decisions about the pregnancy termination should be made.