Be aware of neutrons outside short mazes from 10-MV linear accelerators X-rays in radiotherapy facilities.

During the radiation survey of a reinstalled 10-MV linear accelerator in an old radiation treatment facility, high dose rates of neutrons were observed. The area outside the maze entrance is used as a waiting room where patients, their relatives and staff other than those involved in the actual treatment can freely pass. High fluence rates of neutrons would cause an unnecessary high effective dose to the staff working in the vicinity of such a system, and it can be several orders higher than the doses received due to X-rays at the same location. However, the common knowledge appears to have been that the effect of neutrons at 10-MV X-ray linear accelerator facilities is negligible and shielding calculations models seldom mention neutrons for this operating energy level. Although data are scarce, reports regarding this phenomenon are now emerging. For the future, it is advocated that contributions from neutrons are considered already during the planning stage of new or modified facilities aimed for 10 MV and that estimated dose levels are verified.

Independent checking of the delivered dose for high-energy X-rays using a hand-held PC.

BACKGROUND AND PURPOSE: The requirements on the delivered dose in radical radiation therapy are extremely high. The dose should be within a few percent and also delivered with high accuracy in space. Vendors and users have successfully managed to implement radiation therapy systems, which are able to achieve these demands with high accuracy and reproducibility. These systems include computerized tomography scanners, treatment planning systems, simulators, treatment machines, and record and verify systems. More and more common are also computer networks to assure data integrity when transferring information between the systems. Even if these systems are commissioned and kept under quality assurance programs to maintain their accuracy, errors may be introduced. Especially, the human factor is an uncontrolled parameter that may introduce errors. Thus, unintentional changes or incorrect handling of data may occur during clinical use of the equipment. Having an independent dose calculation system implemented in the daily quality assurance process may assure a high quality of treatments and avoidance of severe errors. MATERIALS AND METHODS: To accomplish this, a system of equations for calculating the absorbed dose to the prescription point from the set-up information, has been compiled into a dose-calculation engine. The model is based on data completely independent of the treatment planning system (TPS). The fundamental parameter in the dose engine is the linear attenuation coefficient for the primary photons. This parameter can readily be determined experimentally. The dose calculation engine has been programmed into a hand-held PC allowing direct calculation of the dose to the prescription point when the first treatment is delivered to the patient. RESULTS AND CONCLUSION: The model is validated with measurements and is shown to be within +/-1.0% (1 SD). Comparison against a state-of-the-art TPS shows an average difference of 0.3% with a standard deviation of +/-2.1%. An action level covering 95% of the cases has been chosen, i.e. +/-4.0%. Deviations larger than this are with a high probability due to erroneous handling of the patient set-up data. This system has been implemented into the daily clinical quality control program.

Normal tissue reactions in mice after combined treatment with metoclopramide and ionizing radiation.

We have previously shown that metoclopramide potentiates the effect of ionizing radiation and cisplatin treatment of human squamous cell carcinomas from the head and neck region xenografted to nude mice. In the present tumor study, the dose scheduling of metoclopramide in combination with radiation was evaluated, and metoclopramide was shown to be most effective in potentiating the cytotoxic effect of radiation when administered one hour before radiation. The effect of radiation in combination with metoclopramide on normal tissue was also studied in two well-established models. Acute skin reactions to radiation exposure were studied in 129-type mice, and metoclopramide did not enhance the acute skin reaction in this in vivo model. Survival after whole body irradiation was studied in heterozygote Balb/c nu/+ mice as a measure of bone marrow toxicity. Metoclopramide was not found to affect the LD50/30 in this in vivo model. The absence of potentiation of radiation damage to normal tissue in these animal studies, makes metoclopramide an interesting possibility for future clinical evaluation.