Estimating the excess lifetime risk of radiation induced secondary malignancy (SMN) in pediatric patients treated with craniospinal irradiation (CSI): Conventional radiation therapy versus helical intensity modulated radiation therapy.

PURPOSE To quantify the risk of radiation-induced second malignancies (SMN) in pediatric patients receiving craniospinal irradiation (CSI) either with 3-dimensional conformal radiation therapy (Conv CSI) or tomotherapy helical intensity modulated radiation therapy (Tomo CSI). METHODS AND MATERIALS A novel predictive model that accounts for short- and long-term carcinogenesis was incorporated into our institutional treatment planning system to quantify the lifetime risk of SMN in incidentally irradiated organs. Five pediatric patients previously treated with CSI were studied. For each case, Conv CSI and Tomo CSI plans were computed. The excess absolute number of SMN was computed for each plan for each patient. For female patients, age was varied to assess its impact. RESULTS Tomo CSI has a much higher risk than Conv CSI for breast cancer. Tomo has a slightly increased risk for the lung, and conventional has a slightly higher risk for the thyroid. Both techniques have intermediate risks to the pancreas and stomach, and lesser risks to the bladder and rectum. For the breast, the magnitude of the absolute risks varied with age: 14.2% versus 7.4% (Tomo vs Conv) age 5; 16.9% versus 7.6% age 10, and 18.6% versus 8.0% age 15. CONCLUSIONS Tomo has a higher risk for inducing breast and lung second cancers, and when using Tomo-based intensity modulated radiation therapy, care should be taken to avoid incidental radiation to the breast. When planning CSI, one needs to balance these cancer risks against other normal tissue effects.