Risk of developing second cancer from neutron dose in proton therapy as function of field characteristics, organ, and patient age.
OBJECTIVE
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
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 approximately 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.


CONCLUSIONS
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.
Zacharatou Jarlskog
Christina
C
Department of Radiation Oncology, Copenhagen University Hospital, Copenhagen, Denmark.
Paganetti
Harald
H
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000465:Algorithms; D001932:Brain Neoplasms / Q000532:radiotherapy*; D001943:Breast Neoplasms / Q000209:etiology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007953:Leukemia, Radiation-Induced / Q000209:etiology; D008175:Lung Neoplasms / Q000209:etiology; D008297:Male; D009010:Monte Carlo Method; D009381:Neoplasms, Radiation-Induced / Q000209:etiology*; D016609:Neoplasms, Second Primary / Q000209:etiology*; D009502:Neutrons / Q000009:adverse effects*; D009928:Organ Specificity; D019047:Phantoms, Imaging; D061766:Proton Therapy; D018570:Risk Assessment; D012737:Sex Factors; D013964:Thyroid Neoplasms / Q000209:etiology; D035501:Uncertainty; D011522:Protons
D011522:Protons