Monte Carlo techniques should replace analytical methods for estimating dose distributions in radiotherapy treatment planning.
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Algorithms↗
Biomedical subjects
J Antolak
Publications and source records attributed to J Antolak.
Complications from radiotherapy dose escalation in prostate cancer: preliminary results of a randomized trial.
OBJECTIVE: To compare early and late side effects in prostate cancer patients with Stage T1b-T3 disease randomized to receive 70 Gy or 78 Gy. METHODS: There were 189 patients randomized with a minimum follow-up of 2 years, that were available for this analysis. All patients were initially treated with a 4-field box to an isocenter dose of 46 Gy at 2 Gy per fraction. In the 70-Gy arm, treatment was continued to a reduced volume using a 4-field box technique. In the 78-Gy arm, treatment was continued to a reduced volume using a conformal 6-field arrangement. Side effects were graded on a 1-4 scale, adapted from Radiation Therapy Oncology Group and Late Effects Normal Tissue Task Force criteria. RESULTS: No significant differences in acute rectal or bladder toxicity were seen between the two treatment techniques (p > 0.6 for all comparisons). The 5-year Kaplan-Meier risks of Grade 2 or higher late bladder toxicity were 20% and 9% for 70-Gy and 78-Gy groups, respectively (log rank, p = 0.8). The 5-year risks of Grade 2 or higher late rectal toxicity were 14% and 21% for 70 Gy and 78 Gy, respectively (p = 0.4). Dose-volume histogram analysis of the 78-Gy patients showed a significant correlation between the percentage of rectum irradiated to 70 Gy or greater and the likelihood of developing late rectal complications. Patients with more than 25% of the rectum receiving 70 Gy or greater had a 5-year risk of Grade 2 or higher complications of 37% compared to 13% for patients with 25% or less (p = 0.05). All three Grade 3 complications occurred when greater than 30% of the rectum received 70 Gy or more. CONCLUSION: The overall rate of complications was similar in both treatment arms. However, there is evidence for a significant increase in late rectal complications when more than 25% of the rectum received 70 Gy or greater. This parameter may serve as a benchmark for the design of future three-dimensional conformal trials.
Aged↗
Electron dose distributions in experimental phantoms: a comparison with 2D pencil beam calculations.
Dose distributions were measured and computed within inhomogeneous phantoms irradiated with beams of electrons having initial energies of 10 and 18 MeV. The measurements were made with a small p-type silicon diode and the calculations were performed using the pencil beam algorithm developed originally at the M D Anderson Hospital (MDAH). This algorithm, which is available commercially on many radiotherapy planning computers, is based on the Fermi-Eyges theory of electron transport. The phantoms used in this work were composed of water into which two- and three-dimensional inhomogeneities of aluminum and air (embedded in wax) were introduced. This was done in order to simulate the small bones and the air cavities encountered clinically in radiation therapy of the chest wall or neck. Our intent was to test the adequacy of the two-dimensional implementation of the pencil beam approach. The agreement between measured and computed doses is very good for inhomogeneities which are essentially two-dimensional but discrepancies as large as 40% were observed for more complex three-dimensional inhomogeneities. We can only trace the discrepancies to the complex interplay of numerous approximations in the Fermi-Eyges theory of multiple scattering and its adaptation for practical computer-aided radiotherapy planning.
Humans↗
Acquisition and display of radiation dose distributions using microcomputer technology.
In the commissioning or quality assurance of a medical linear accelerator or a computerized radiotherapy planning system, the traditional approach usually consists of acquiring and comparing one-dimensional dose profiles. This methodology is tedious and incomplete since only a portion of the radiation field can realistically be sampled. We have developed an automated measurement system which allows efficient measurement and display of complete two-dimensional dose distributions. The general purpose microcomputer used (IBM PC/XT compatible) can be interfaced economically to any water phantom dosimetry system equipped with a three axis scan controller, and can also communicate data to the treatment planning system. This allows for direct comparison of measured with computed dose distributions, thus revealing discrepancies in the dose computation algorithms used. In this paper, we describe the interface between the microcomputer, a conventional water dosimetry system (Therados RFA-3), and a treatment planning computer. We report our early experience with acquiring dose distributions and show sample comparisons with computed results for megavoltage electron beams incident on homogeneous and heterogeneous systems.
Humans↗
Evaluation of film and thermoluminescent dosimetry of high-energy electron beams in heterogeneous phantoms.
Film and thermoluminescent dosimetry (TLD) are investigated in heterogeneous phantoms irradiated by high-energy electron beams. Both film and TLD are practical dosimeters for multiple and moving beam radiotherapy. The accuracy and precision of these dosimeters for radiation dose measurements in homogeneous water-equivalent phantoms has been discussed in the literature. However, film and TLD are often used for dose measurements in heterogeneous phantoms. In those situations perturbations are produced which are related to the density and atomic number of the phantom material and the physical size and orientation of the dosimeter. In our experiments the relative dose measurements in homogeneous phantoms were the same regardless of dosimeter or dosimeter orientation. However, significant differences were observed between the dose measurements within the inhomogeneity. These differences were influenced by the type and orientation of the dosimeter in addition to the properties of the heterogeneity. These differences could be reproduced with Monte Carlo calculations and modeling of the experimental conditions.
Electrons↗