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.

Dosimetric feasibility of sparing the primary site for oropharyngeal squamous cell carcinoma after transoral laser microsurgery in patients with unilateral positive neck nodes.

PURPOSE: To quantify the effect of sparing the primary site after transoral laser microsurgery (TLM) for oropharyngeal squamous cell carcinoma (OPSCC). METHODS AND MATERIALS: We reviewed 4 patients with OPSCC who were treated with TLM and postoperative radiation. All patients had T1 base of tongue primaries with the following N stages: 1 N1; 2 N2a; and 1 N2b. Three were lateralized to the right and 1 lateralized to the left. The primary site was not spared initially. We created new intensity modulated radiation treatment (IMRT) plans that spared the primary site. The prescribed dose to the high-risk (HR) and standard-risk (SR) planning target volumes (PTVs) was 60 Gy and 46 Gy at 2 Gy/fraction. PTV-SR and PTV-HR were adjusted to exclude the primary site. The primary site was maximally spared while maintaining similar PTV coverage and normal tissue avoidance as the initial plan. Dosimetric comparisons were made between the initial and primary-site sparing IMRT plans. RESULTS: Dosimetric coverage of the PTVs and normal tissues (pharyngeal constrictors, contralateral parotid, etc) were comparable. The mean dose to the primary site was reduced by 20 Gy. The mean dose to the oral cavity was reduced by 25 Gy. CONCLUSIONS: This study suggests that omitting the primary site from the radiation therapy target volume is unlikely to reduce long-term swallowing function to a meaningful degree in patients who receive radiation therapy following TLM for base of tongue cancer.