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Biomedical subjects

V Moiseenko

Publications and source records attributed to V Moiseenko.

7 recordsLinked to original sources
PubMed2004

Radiation quality of a tomotherapy photon fan beam.

Tomotherapy, a novel radiotherapy technique, uses narrow fan beams for cancer patient treatment. Photon energy spectra for a rectangular 10 x 1 cm2 photon beam were analyzed in central axis and penumbra regions at depths of 3 to 10 cm in a water phantom. A 6 MV beam of a Varian 2100C/D Linear Accelerator was modeled using BEAM99 Monte Carlo calculations to simulate energy transport in a water phantom. Arrays of 4 x 2 mm2 scoring regions were arranged to cover the central axis and penumbra areas. Radiation quality factors were calculated based on dose-mean linear energy transfer. Although there appears to be a trend towards higher quality factor values in the penumbra area, this change is fairly small, at most 3% in penumbra region. We conclude that change in radiation quality is not likely to be an issue in a tomotherapeutic approach when 6 MV x rays are used.

Dose-Response Relationship, Radiation↗
PubMed2001

Considerations for the implementation of target volume protocols in radiation therapy.

PURPOSE: Uncertainties in patient repositioning and organ motion are accounted for by defining a planning target volume (PTV). We make recommendations on issues not explicitly discussed in existing protocols for PTV design. METHODS: A quantity called "coverage" is defined to quantify how effectively a PTV encompasses the clinical target volume, and is applied to examine the impact of several factors. A stochastic simulation is used to determine the coverage required for a desirable balance between tumor control probability (TCP) and the irradiated volume. Using a sample anatomy, we assess the importance of the method used to add uncertainties, the shape of the uncertainty distribution, the effect of systematic uncertainties, and the use of nonuniform margins. Additionally, we examine the benefit of patient immobilization techniques. RESULTS: Our example indicates that 95% coverage is a reasonable goal for treatment planning. Using this as a comparison value, our example indicates quadrature addition of uncertainties predicts smaller margins (7 mm) than linear addition (11 mm), Gaussian distribution of uncertainties (7 mm) require the same margin as a uniform distribution (7 mm), systematic uncertainties have a small effect on TCP below a threshold value (4 mm), and nonuniform margins allow only a slight reduction of irradiated volume. CONCLUSION: We recommend that uncertainties should generally be added in quadrature, the exact shape of the uncertainty distribution is not critical, systematic uncertainties should be maintained below some threshold value, and nonuniform margins may be effective when uncertainties are anisotropic.

Clinical Protocols↗
PubMed2000

Normal tissue complication probabilities: dependence on choice of biological model and dose-volume histogram reduction scheme.

PURPOSE: To evaluate the impact of dose-volume histogram (DVH) reduction schemes and models of normal tissue complication probability (NTCP) on ranking of radiation treatment plans. METHODS AND MATERIALS: Data for liver complications in humans and for spinal cord in rats were used to derive input parameters of four different NTCP models. DVH reduction was performed using two schemes: "effective volume" and "preferred Lyman". DVHs for competing treatment plans were derived from a sample DVH by varying dose uniformity in a high dose region so that the obtained cumulative DVHs intersected. Treatment plans were ranked according to the calculated NTCP values. RESULTS: Whenever the preferred Lyman scheme was used to reduce the DVH, competing plans were indistinguishable as long as the mean dose was constant. The effective volume DVH reduction scheme did allow us to distinguish between these competing treatment plans. However, plan ranking depended on the radiobiological model used and its input parameters. CONCLUSIONS: Dose escalation will be a significant part of radiation treatment planning using new technologies, such as 3-D conformal radiotherapy and tomotherapy. Such dose escalation will depend on how the dose distributions in organs at risk are interpreted in terms of expected complication probabilities. The present study indicates considerable variability in predicted NTCP values because of the methods used for DVH reduction and radiobiological models and their input parameters. Animal studies and collection of standardized clinical data are needed to ascertain the effects of non-uniform dose distributions and to test the validity of the models currently in use.

Animals↗