Abstract
BackgroundWe explore the use of a clinical orthovoltage X-ray treatment unit as a small-animal radiation therapy system in a tumoral model of cervical cancer.MethodsNude mice were subcutaneously inoculated with 5 × 106 HeLa cells in both lower limbs. When tumor volume approximated 200 mm3 treatment was initiated. Animals received four 2 mg/kg intraperitoneal cycles (1/week) of cisplatin and/or 6.25 mg/kg of gemcitabine, concomitant with radiotherapy. Tumors were exposed to 2.5 Gy/day nominal surface doses (20 days) of 150 kV X-rays. Lead collimators with circular apertures (0.5 to 1.5 cm diameter) were manufactured and mounted on the applicator cone to restrict the X-ray beam onto tumors. X-ray penetration and conformality were evaluated by measuring dose at the surface and behind the tumor lobe by using HS GafChromic film. Relative changes in tumor volume (RTV) and a clonogenic assay were used to evaluate the therapeutic response of the tumor, and relative weight loss was used to assess toxicity of the treatments.ResultsNo measurable dose was delivered outside of the collimator apertures. The analysis suggests that dose inhomogeneities in the tumor reach up to ± 11.5% around the mean tumor dose value, which was estimated as 2.2 Gy/day. Evaluation of the RTV showed a significant reduction of the tumor volume as consequence of the chemoradiotherapy treatment; results also show that toxicity was well tolerated by the animals.ConclusionResults and procedures described in the present work have shown the usefulness and convenience of the orthovoltage X-ray system for animal model radiotherapy protocols.
Highlights
Introduction to Radiological Physics and RadiationDosimetry John Wiley and Sons, Inc; 1986.20
Systemic secondary effects related with nonconformal irradiations, such as immune response, bone marrow depletion, etc., may mask the effect of interest in tumor, or in the evaluation of chemotherapy agents combined with radiotherapy
Dose rate measurements were performed by the Medical Physics personnel from the Radiotherapy Department at Instituto Nacional de Cancerología (INCan) using a calibrated end-window parallel-plate ionization chamber (Marcus Advance, PTW, Germany)
Summary
Introduction to Radiological Physics and RadiationDosimetry John Wiley and Sons, Inc; 1986.20. Research groups have been working in the development of dedicated small-animal irradiation systems that potentially will delivery conformal doses to chosen targets, either tumors or normal tissues [5,6,7,8]. These systems are still in the process of prototype design or in validation studies, and their availability and cost will possibly limit the access to this technology. This might be important in small research centers or developing countries, not able to afford the acquisition of a small animal irradiator immediately
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