Involved Node, Site, Field and Residual Volume Radiotherapy for Lymphoma: A Comparison of Organ at Risk Dosimetry and...

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Recent lymphoma radiotherapy guidelines include involved site radiotherapy (ISRT), involved node radiotherapy (INRT), and irradiation of residual volume.
• Limited late toxicity data necessitates a comparison of organ at risk (OAR) dose-metrics and second malignancy risks for these techniques.

Purpose of the Study:

• To compare organ at risk (OAR) dose-metrics and calculated second malignancy risks among different radiotherapy planning techniques for lymphoma.
• To evaluate the impact of reducing treatment volumes on radiation exposure and potential secondary cancer development.

Main Methods:

• Four radiotherapy plans (IFRT, ISRT, INRT, residual volume) were generated for 15 patients receiving mediastinal radiotherapy.
• Doses to OARs (breasts, lungs, thyroid, heart, oesophagus) were evaluated, and relative/absolute second malignancy risks were estimated using organ equivalent dose.

Main Results:

• IFRT significantly increased doses to OARs compared to ISRT.
• INRT and residual volume techniques significantly reduced doses to all OARs compared to ISRT.
• IFRT showed significantly higher relative risks of second cancers (lung, breast, thyroid) than ISRT; INRT and residual volume showed lower risks.
• Median excess absolute risks were lowest for residual volume and highest for IFRT.
• Absolute second cancer risks were similar for ISRT and INRT.

Conclusions:

• Reducing treatment volumes from IFRT to ISRT, INRT, or residual volume decreases radiation exposure to OARs.
• This reduction in treatment volumes is predicted to lower the absolute excess risk of second malignancies.
• Similar second malignancy risks between ISRT and INRT support ISRT use when pre-chemotherapy PET scans are unavailable.