Transient genome-wide transcriptional response to low-dose ionizing radiation in vivo in humans.

PURPOSE: The in vivo effects of low-dose low linear energy transfer ionizing radiation on healthy human skin are largely unknown. Using a patient-based tissue acquisition protocol, we have performed a series of genomic analyses on the temporal dynamics over a 24-hour period to determine the radiation response after a single exposure of 10 cGy. METHODS AND MATERIALS: RNA from each patient tissue sample was hybridized to an Affymetrix Human Genome U133 Plus 2.0 array. Data analysis was performed on selected gene groups and pathways. RESULTS: Nineteen gene groups and seven gene pathways that had been shown to be radiation responsive were analyzed. Of these, nine gene groups showed significant transient transcriptional changes in the human tissue samples, which returned to baseline by 24 hours postexposure. CONCLUSIONS: Low doses of ionizing radiation on full-thickness human skin produce a definable temporal response out to 24 hours postexposure. Genes involved in DNA and tissue remodeling, cell cycle transition, and inflammation show statistically significant changes in expression, despite variability between patients. These data serve as a reference for the temporal dynamics of ionizing radiation response following low-dose exposure in healthy full-thickness human skin.

Impact of nodal regression on radiation dose for lymphoma patients after radioimmunotherapy.

UNLABELLED: Radioimmunotherapy for non-Hodgkin's lymphoma often results in surprisingly high response rates compared with those expected from estimated absorbed radiation doses. Several factors, including radiobiologic response, selective targeting, and heterogeneous absorbed radiation within the lymphoma, are likely to contribute to the lack of a dose-response relationship. This article investigates the impact of nodal regression on absorbed radiation dose and applies a correction factor to account for its effect. METHODS: The radioactivity in and regression of 37 superficial lymph nodes were measured in 7 non-Hodgkin's lymphoma patients treated with 775-3,450 MBq/m(2) of (131)I-Lym-1 monoclonal antibody. Nodal dimensions were measured with calipers and radioactivity was quantitated using gamma-camera imaging on multiple days after (131)I-Lym-1 injection. Both nodal regression and radioactivity were fit with monoexponential functions. Formulas were developed to account for simultaneous change in nodal mass and radioactivity. All lymph nodes with size and radioactivity measurements, and exponential-fit coefficients of determination of >0.8, were included in the analysis. RESULTS: A 3 orders-of-magnitude node-to-node variation in initial radiopharmaceutical concentration (MBq/g) was observed, with the highest concentrations in the smallest nodes. Reduction in radioactivity as a function of time (biologic half-life) varied by about a factor of 2. In contrast, the rate of nodal regression varied by orders of magnitude, from a 14-h half-time to no regression at all. Five nodes regressed with a half-time that was shorter than their observed effective radiopharmaceutical half-life. Accounting for the effect of nodal regression resulted in dose corrections ranging from 1 (no correction) to a factor of >10, with 70% of nodes requiring a correction factor of at least 20% and >50% of nodes requiring a correction factor of >2. Corrected for nodal regression, 46% of nodes analyzed had absorbed radiation doses of >10 Gy and 32% had doses of >20 Gy. CONCLUSION: These results highlight the importance of accounting for change in mass, particularly tumor regression, when assessing absorbed radiation dose for tissues whose mass changes during the time the radiation dose is being absorbed. The increase in calculated absorbed dose when this change is considered provides better insight into the high nodal response rates observed in non-Hodgkin's lymphoma patients.

Application of MINERVA Monte Carlo simulations to targeted radionuclide therapy.

Recent clinical results have demonstrated the promise of targeted radionuclide therapy for advanced cancer. As the success of this emerging form of radiation therapy grows, accurate treatment planning and radiation dose simulations are likely to become increasingly important. To address this need, we have initiated the development of a new, Monte Carlo transport-based treatment planning system for molecular targeted radiation therapy as part of the MINERVA system. The goal of the MINERVA dose calculation system is to provide 3-D Monte Carlo simulation-based dosimetry for radiation therapy, focusing on experimental and emerging applications. For molecular targeted radionuclide therapy applications, MINERVA calculates patient-specific radiation dose estimates using computed tomography to describe the patient anatomy, combined with a user-defined 3-D radiation source. This paper describes the validation of the 3-D Monte Carlo transport methods to be used in MINERVA for molecular targeted radionuclide dosimetry. It reports comparisons of MINERVA dose simulations with published absorbed fraction data for distributed, monoenergetic photon and electron sources, and for radioisotope photon emission. MINERVA simulations are generally within 2% of EGS4 results and 10% of MCNP results, but differ by up to 40% from the recommendations given in MIRD Pamphlets 3 and 8 for identical medium composition and density. For several representative source and target organs in the abdomen and thorax, specific absorbed fractions calculated with the MINERVA system are generally within 5% of those published in the revised MIRD Pamphlet 5 for 100 keV photons. However, results differ by up to 23% for the adrenal glands, the smallest of our target organs. Finally, we show examples of Monte Carlo simulations in a patient-like geometry for a source of uniform activity located in the kidney.