Radiation Therapy Oncology Group. Research Plan 2002-2006. Medical Physics Committee.
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Brachytherapy↗
Biomedical subjects
D Fontenla
Publications and source records attributed to D Fontenla.
Three-dimensional conformal radiation therapy may improve the therapeutic ratio of high dose radiation therapy for lung cancer.
PURPOSE: The specific aim of 3-dimensional conformal radiation therapy is to improve the target dose distribution while concomitantly reducing normal tissue dose. Such an approach should permit dose escalation until the limits of acceptable normal tissue toxicity are reached. To evaluate the feasibility of tumor dose escalation for nine patients with lung cancer, we determined the dose distribution to the target and normal tissues with 3-dimensional conformal radiation therapy and conventional planning. METHODS AND MATERIALS: Plans were compared to assess adequacy of dose delivery to target volumes, dose-volume histograms for normal tissue, and normal tissue complication probabilities (NTCP) for nine patients with lung tumors. RESULTS: The mean percentage of gross disease which received < or = 70.2 Gy with 3-dimensional conformal radiation therapy (3DCRT) was 40% of the mean percentage of gross disease which received < or = 70.2 Gy with conventional treatment planning (CTP). The mean NTCP for lung parenchyma with 3DCRT was 36% of the mean NTCP with CTP. The mean esophageal NTCP with 3DCRT was 88% of the mean NTCP with CTP. CONCLUSION: This preliminary analysis suggests that three dimensional conformal radiation therapy may provide superior delivery of high dose radiation with reduced risk to normal tissue, suggesting that this approach may have the potential to improve the therapeutic ratio of high dose radiation therapy for lung cancer.
Adenocarcinoma↗
Dose computations for asymmetric fields defined by independent jaws.
Asymmetric fields defined by independent jaws can be used to split a beam or to match adjacent fields. We have extended a method originally developed for symmetric fields to calculate the dose for asymmetric fields. The dose to a point is computed as the product of the tissue maximum ratio (TMR), the off center ratio (OCR), and the inverse square factor. The TMR is computed from the measured central axis depth doses for symmetric fields. The OCR is obtained by multiplying the primary OCR (POCR) and the boundary factors (BF's) for the four jaws. The POCR's and BF's were derived from measured beam profiles, which include the effect of off-axis beam quality variations. Using this method, the beam profiles and isodose distributions for asymmetric fields of a 6-MV accelerator were calculated and compared with the measured data. The agreement is within experimental errors both in the penumbra region and along the central ray of the asymmetric field.
Humans↗
The effect of angular spread on the intensity distribution of arbitrarily shaped electron beams.
Knowledge of the relative intensity distribution at the patient's surface is essential for pencil beam calculations of three-dimensional dose distributions for arbitrarily shaped electron beams. To calculate the relative intensity distribution, the spatial spread resulting from angular spread is convolved with a two-dimensional step function whose shape corresponds to the applicator aperture. Two different approaches to obtain angular spread or the equivalent spatial spread are investigated. In the first method, the pencil beam angular spread is assumed to be Gaussian in shape. The angular spread constants (sigma theta) are then obtained from the slopes of measured intensity profiles. In the second method, the angular spread, in the form of an array of numerical values, is obtained by the deconvolution of measured intensity profiles. After obtaining the angular spread, the calculation for convolution is done in a number of parallel planes normal to the central axis at various distances from the electron collimator. Intensity at any arbitrary point in space is computed by interpolating between intensity distributions in adjacent planes on either side of the point. The effects of variations in angular spread as a function of field size for two treatment machines, one with a scanned electron beam and the other with a scattering foil, have been studied. The consequences of assuming angular spread to be of Gaussian shape are also examined. The electron intensity calculation techniques described in this paper apply primarily to methods of dose calculations that employ pencil beams generated using Monte Carlo simulations.
Electrons↗