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      Neutron equivalent doses and associated lifetime cancer incidence risks for head & neck and spinal proton therapy.

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      Physics in medicine and biology

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          Abstract

          In this work we have simulated the absorbed equivalent doses to various organs distant to the field edge assuming proton therapy treatments of brain or spine lesions. We have used computational whole-body (gender-specific and age-dependent) voxel phantoms and considered six treatment fields with varying treatment volumes and depths. The maximum neutron equivalent dose to organs near the field edge was found to be approximately 8 mSv Gy(-1). We were able to clearly demonstrate that organ-specific neutron equivalent doses are age (stature) dependent. For example, assuming an 8-year-old patient, the dose to brain from the spinal fields ranged from 0.04 to 0.10 mSv Gy(-1), whereas the dose to the brain assuming a 9-month-old patient ranged from 0.5 to 1.0 mSv Gy(-1). Further, as the field aperture opening increases, the secondary neutron equivalent dose caused by the treatment head decreases, while the secondary neutron equivalent dose caused by the patient itself increases. To interpret the dosimetric data, we analyzed second cancer incidence risks for various organs as a function of patient age and field size based on two risk models. The results show that, for example, in an 8-year-old female patient treated with a spinal proton therapy field, breasts, lungs and rectum have the highest radiation-induced lifetime cancer incidence risks. These are estimated to be 0.71%, 1.05% and 0.60%, respectively. For an 11-year-old male patient treated with a spinal field, bronchi and rectum show the highest risks of 0.32% and 0.43%, respectively. Risks for male and female patients increase as their age at treatment time decreases.

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          Author and article information

          Journal
          Phys Med Biol
          Physics in medicine and biology
          0031-9155
          0031-9155
          Aug 21 2009
          : 54
          : 16
          Affiliations
          [1 ] Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA 02114, USA.
          Article
          S0031-9155(09)15612-9
          10.1088/0031-9155/54/16/005
          19641238
          0bb770b5-aae2-463b-a2e4-0ceb89a58a93
          History

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