Detection of radiation-induced lung injury using hyperpolarized (13)C magnetic resonance spectroscopy and imaging.

Radiation-induced lung injury limits radiotherapy of thoracic cancers. Detection of radiation pneumonitis associated with early radiation-induced lung injury (2-4 weeks postirradiation) may provide an opportunity to adjust treatment, before the onset of acute pneumonitis and/or irreversible fibrosis. In this study, localized magnetic resonance (MR) spectroscopy and imaging of hyperpolarized (13)C-pyruvate (pyruvate) and (13)C-lactate (lactate) were performed in the thorax and kidney regions of rats 2 weeks following whole-thorax irradiation (14 Gy). Lactate-to-pyruvate signal ratio was observed to increase by 110% (P < 0.01), 57% (P < 0.02), and 107% (P < 0.01), respectively, in the thorax, lung, and heart tissues of the radiated rats compared with healthy age-matched rats. This was consistent with lung inflammation confirmed using cell micrographs of bronchioalveolar lavage specimens and decreases in arterial oxygen partial pressure (paO2), indicative of hypoxia. No statistically significant difference was observed in either lactate-to-pyruvate signal ratios in the kidney region (P = 0.50) between the healthy (0.215 ± 0.100) and radiated cohorts (0.215 ± 0.054) or in blood lactate levels (P = 0.69) in the healthy (1.255 ± 0.247 mmol/L) and the radiated cohorts (1.325 ± 0.214 mmol/L), confirming that the injury is localized to the thorax. This work demonstrates the feasibility of hyperpolarized (13)C metabolic MR spectroscopy and imaging for detection of early radiation-induced lung injury.

Sci-Fri PM: Delivery - 02: CT image guidance strategies for dose-adaptive IMRT of the prostate.

On-line CT imaging in the radiotherapy room has become the norm for targeted intensity-modulated radiotherapy (IMRT), enabling precise adjustments of the daily patient setup based on soft tissue visualization. Corrections for plasticity of the anatomy and dose deformation are within technological reach but will require more on-line resources. We have developed a computer model that allows exploration of "what if" scenarios for assessing the benefits of Image Guidance strategies in terms of the multi-fraction dose distribution and DVH metrics (Target D95 and rectum V70). In this work we report on changes in anatomy and resultant dose distribution as observed in 35 daily megavoltage CT (MVCT) scans of the pelvis during prostate therapy for 13 patients. Our goal is to assess the effectiveness and efficiency of various adaptive strategies involving imaging schedule with and without dose re-planning of 5-field IMRT with 18 MV x-rays. Our research questions are: To what extent do radiation dose distributions delivered to individual patients (in vivo) diverge from the planned dose distributions (in silico)? Is there a robust schedule of CT image guidance, with or without dose re-planning that will mitigate discrepancies? For prostate IMRT, we conclude that image guidance schedule can be relaxed when generous GTV margins (10/7mm) are used. Tighter margins (isotropic 5 mm) reduce the dose to the rectum as expected. However, daily re-planning may be required to maintain adequate target coverage as planned when tighter margins are used.

A two-source model for electron beams: calculation of relative output factors.

A two-source model for the calculation of relative output factors (ROF) for clinical applications of electron beams has been developed. The model consists of (1) an effective extended source above the final field-defining aperture (cutout) plane and (2) a source due to scattering from the aperture. Calculations are based on Fermi-Eyges theory and a pencil beam algorithm with parameters determined independently for each major scattering component. The model predicts a modified inverse square law for determining the dose rate for the electron beams. It also generalizes the "square-root method" and "one-dimensional method" that are often used clinically for ROF calculations. A computer program based on the model has been developed to calculate ROF for irregular fields. The predictions of ROF values have been compared with measurements on a Varian CLINAC 2100C/D accelerator for different cutout size, energies, applicators, and SSDs for square fields, rectangular fields, circular fields, and irregular fields. The agreement between prediction and measurement of the ROF for these wide range of conditions is generally within 1% for energies from 6 to 20 MeV. This two-source model can be used for clinical applications and it requires a minimal set of measured input data.

Survival of Ixodes scapularis (Acari: Ixodidae) exposed to cold.

The cold hardiness of Ixodes scapularis Say unengorged larvae, engorged larvae, unengorged nymphs, engorged nymphs, and unengorged adults was evaluated. Ticks were exposed to cold for 2 or 8 h at a range of temperatures. Likelihood ratio tests and LT50 estimates were used to evaluate cold hardiness. Likelihood ratio tests indicated that stage and engorgement effects were significant with the exception of the stage effect between engorged larvae and engorged nymphs. LT50 estimates indicated that unengorged nymphs were the most cold-hardy, followed by engorged nymphs, unengorged adults, and both unengorged and engorged larvae. Sex of adult ticks had no statistically significant effect on cold hardiness. Unengorged larvae and unengorged nymphs were tested for evidence of a cold-hardening response. No larvae or nymphs exposed to a cold pretreatment and subsequent cold treatment displayed rapid cold-hardening.

Arbovirus surveillance in Iowa, USA, during the flood of 1993.

During the summer of 1993, mosquitoes were collected by dry ice-baited CDC light traps from July through September in 12 different cities in Iowa. In all, 169,907 mosquitoes belonging to 17 different species were collected. A total of 2,013 pools were processed for arbovirus isolation, from which 59 arbovirus isolates were obtained: 41 Flanders (FLA), 16 trivittatus (TVT), one Cache Valley (CV), and one Turlock (TUR). Supplementary sentinel chicken and human data are also included. In spite of the increase in larval habitats and elevated mosquito populations, there was not an increase in virus transmission.

Response of Iowa mosquito populations to unusual precipitation patterns as measured by New Jersey light trap collections.

New Jersey light trap data from 1993, a year with unusually high amounts of precipitation, and 1994 were compared with mean light trap counts for the previous 8-10 years in each of 6 locations. The study took place in Iowa. In 1993, Aedes trivittatus and Culex tarsalis populations were unchanged. Anopheles punctipennis and Culex pipiens complex populations were significantly higher, and Aedes vexans populations increased in all 6 sites, significantly so in 2 sites. Species composition was unchanged. In 1994, populations of each of these species were not significantly different from the long-term means. Aedes vexans populations were above average in all sites and populations of the remaining species were below average.

Utilization of a high energy photon beam for whole body irradiation.

Use of a high energy linear accelerator (giving high dose rates) for whole body irradiation is recommended because (a) there is a shorter treatment time compared with other techniques using orthovoltage or 60Co irradiation; and (b) there is more comfort for the patient, who does not have to turn over to receive an acceptably uniform dose. Dosimetry indicates that the usual data is not applicable for such treatments given at large distances from the source. A method of dosage calculation at large distances was checked by using TLD dosimetry in a Rando phantom.