Risk of Developing Second Cancer From Neutron Dose in Proton Therapy as Function of Field Characteristics, Organ, and Patient Age
Received 28 January 2008; received in revised form 23 April 2008; accepted 25 April 2008. published online 19 June 2008.
Purpose
To estimate the risk of a second malignancy after treatment of a primary brain cancer using passive scattered proton beam therapy. The focus was on the cancer risk caused by neutrons outside the treatment volume and the dependency on the patient's age.
Methods and Materials
Organ-specific neutron-equivalent doses previously calculated for eight different proton therapy brain fields were considered. Organ-specific models were applied to assess the risk of developing solid cancers and leukemia.
Results
The main contributors (>80%) to the neutron-induced risk are neutrons generated in the treatment head. Treatment volume can influence the risk by up to a factor of ∼2. Young patients are subject to significantly greater risks than are adult patients because of the geometric differences and age dependency of the risk models. Breast cancer should be the main concern for females. For males, the risks of lung cancer, leukemia, and thyroid cancer were significant for pediatric patients. In contrast, leukemia was the leading risk for an adult. Most lifetime risks were <1% (70-Gy treatment). The only exceptions were breast, thyroid, and lung cancer for females. For female thyroid cancer, the treatment risk can exceed the baseline risk.
Conclusion
The risk of developing a second malignancy from neutrons from proton beam therapy of a brain lesion is small (i.e., presumably outweighed by the therapeutic benefit) but not negligible (i.e., potentially greater than the baseline risk). The patient's age at treatment plays a major role.
∗Department of Radiation Oncology, Copenhagen University Hospital, Copenhagen, Denmark
†Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA
Reprint requests to: Harald Paganetti, Ph.D., Department of Radiation Oncology, Massachusetts General Hospital, 30 Fruit St., Boston, MA 02114. Tel: (617) 726-5847; Fax: (617) 724-0368
Supported in part by National Cancer Institute Grant R01 CA 116743.
ABSTRACT