Radiation exposure of the glandular mammary tissue in women patients with mediastinal Hodgkin lymphoma treated with protons

Purpose

Secondary breast cancer is a frequent late adverse event of mediastinal Hodgkin lymphoma radiotherapy. Secondary breast cancers overwhelmingly correspond to ductal carcinoma and develop from the glandular mammary tissue. In addition, during childhood, radiation overexposure of the glandular tissue may lead to a late breast hypotrophy at adult age. The aim of this study was to evaluate the radiation exposure to the glandular tissue in patients treated for mediastinal Hodgkin lymphoma with intensity-modulated proton therapy, in order to evaluate the potential dosimetric usefulness of its delineation for breast sparing.

Materials and methods

Sixteen consecutive intermediate-risk mediastinal female patients with Hodgkin lymphoma treated with consolidation radiation with deep inspiration breath hold intensity-modulated proton therapy to the total dose of 30 Gy were included. Breasts were delineated according to the European Society for Radiotherapy and Oncology guidelines for treatment optimization (“clinical organ at risk”). The glandular tissue (“glandular organ at risk”) was retrospectively contoured on the initial simulation CT scans based on Hounsfield unit (HU) values, using a range between −80 HU and 500 HU.

Results

The mean and maximum doses delivered to the glandular organ at risk were significantly lower than the mean and maximum doses delivered to the clinical organ at risk, but were statistically correlated. Glandular organ at risk volumes were significantly smaller.

Conclusion

Optimizing the treatment plans on the clinical breast contours will systematically lead to overestimation of the dose received to the glandular tissue and, consequently, to an indistinct and involuntary improved glandular tissue sparing. As such, our findings do not support the consideration of the glandular tissue as an additional organ at risk when planning intensity-modulated proton therapy for mediastinal Hodgkin lymphoma in female patients.