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Assessment of Radiation Induced Second Cancer Risks in Proton Therapy and IMRT for Organs Inside the Main Radiation Field

H Paganetti

H Paganetti1*, M Moteabbed1, B Athar1,2, J Adams1, U Schneider3, T Yock1, (1) Massachusetts General Hospital, Boston, MA, (2) Hampton University, Hampton, VA, (3) Radio-Onkologie Hirslanden, Aarau, Switzerland

SU-E-T-258 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: Radiation therapy can potentially cause a second malignancy. There is clinical evidence that those occur typically within the beam path in the medium/high dose region. The purpose of this study was to assess the risk for developing a radiation induced tumor within the treated volume and to compare this risk for proton therapy and IMRT.

Methods: Fully contoured age and gender specific whole body phantoms (4-year and 14-year old) were uploaded into a treatment planning system and typical tumor volumes were contoured based on patients treated for optic glioma and vertebral body Ewing's sarcoma. Lifetime attributable risks (LARs) for developing a second malignancy were calculated using a risk model incorporating factors for cell kill, mutations, repopulation, and inhomogeneous organ doses.

Results: For standard fractionation schemes, the LAR for developing a second malignancy from radiation therapy alone were found to be up to 2.7% for a 4-year old optic glioma patient treated with IMRT considering a soft tissue carcinoma risk model only. Sarcoma risks were found to be below 1% in all cases. For the 14-year old, risks were found to be about a factor of 2 lower. For the Ewing's sarcoma cases the risks based on the sarcoma model were typically higher than the carcinoma risks, i.e. up to 1.3% LAR for soft tissue sarcoma. Generally, the risk from proton therapy turned out to be lower by a factor of 2 to 10. However, comparison of a 3-field and 4-field proton plan shows that the distribution of the dose, i.e., the particular treatment plan, plays a role as well.

Conclusions: In general, proton therapy can significantly reduce the risk for developing an in-field second malignancy. Risk analysis based on our formalism could be applied within treatment planning programs to guide treatment plans for pediatric patients.

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