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Techniki dynamiczne generujące zróżnicowany rozkład dawki promieniowania w radioterapii
... The two dosimetric parameters describing a therapeutic beam of radiation generated by a conventional medical accelerator are uniformity and flatness. These factors characterize the intensity (dose) of radiation in the plane perpendicular to the beam axis (CAX) [1][2][3][4][5][6]. ...
... The aforementioned results with γ-rays irradiation by 60 Co source ( Figure 12) and 15 MV X-ray irradiation ( Figure 13) mean that YAG:Ce crystals are not so convenient materials for investigation of beam uniformity at therapeutic radiation treatment by X-rays with high energies (above 6 MV) in the open field mode and can be substituted or combined with a heavy analogue of such material as LuAG:Ce garnet with ρ = 6.73 g/cm 3 and Z eff = 62 [2]. Currently, such research is in progress, and preliminary results are very encouraging ( Figure 15). ...
Thermostimulated luminescence (TSL) dosimetry is a versatile tool for the assessment of dose from ionizing radiation. In this work, the Ce3+ doped Y3Al5O12 garnet (YAG:Ce) with a density ρ = 4.56 g/cm3 and effective atomic number Zeff = 35 emerged as a prospective TSL material in radiotherapy applications due to its excellent radiation stability, uniformity of structural and optical properties, high yield of TSL, and good position of main glow peak around 290–300 °C. Namely, the set of TSL detectors produced from the YAG:Ce single crystal is used for identification of the uniformity of dose and energy spectra of X-ray radiation generated by the clinical accelerator with 6 MV and 15 MV beams located in Radiotherapy Department at the Oncology Center in Bydgoszcz, Poland. We have found that the YAG:Ce crystal detects shows very promising results for registration of X-ray radiation generated by the accelerator with 6 MV beam. The next step in the research is connected with application of TSL detectors based on the crystals of much heavier garnets than YAG. It is estimated that the LuAG:Ce garnet crystals with high density ρ = 6.0 g/cm3 and Zeff = 62 can be used to evaluate the X-rays produced by the accelerator with the 15 MV beam.
A water beam imaging system (WBIS) was developed and used to verify dose distributions for intensity modulated radiotherapy (IMRT) using dynamic multileaf collimator (MLC). The WBIS consists of a water container, a scintillator screen, a charge-coupled device (CCD) camera, and a portable personal computer (Wellhöfer Dosimetrie, Schwarzenbruck, Germany). The scintillation image is captured by the CCD camera. The pixel value in this image indicates the dose value in the scintillation screen. The verification is performed by comparing the WBIS image achieved from the measurement with dose distribution from the IMRT plan. Because of light scattering in the WBIS the image is blurred. An iterative reconstruction algorithm is proposed to remove the blurring effect of light scattering. From the measured image of a 10 cm × 10 cm x-ray beam and the simulation result of the dose distribution using the Monte Carlo method, the blur function can be achieved. Based on this function, the proposed algorithm is applied to reconstruct the true dose distribution for an IMRT plan from the measured WBIS image. The reconstruction dose distributions are compared with Monte Carlo simulation results. Reasonable agreement can be observed from the comparison. The proposed approach makes it possible to carry out real-time quality assurance tasks for IMRT dose verification.
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A very flexible iterative method for simultaneous optimization of dynamic multileaf collimation, scanning patterns and compensation filters has been developed. The algorithm can account for and optimize almost all the degrees of freedom available in a modern radiation therapy clinic. The method has been implemented for three dimensional treatment planning. The algorithm has been tested for a number of cases where both traditional wedge filters and block collimators, and modern equipment such as scanned beams and multileaf collimators are available. It is shown that the algorithm can improve heavily on traditional uniform dose plans with respect to the probability of achieving tumor control without causing severe complications (P +) simply by finding the optimal beam weights and block collimator settings. By allowing more complex equipment to deliver the dose and by accounting for their increased flexibility during the optimization, the dose plan can be substantially improved with respect to the applied objective functions. It is demonstrated that flexible lateral collimation combined with compensators or scanned beams in most cases allow close to optimal dose delivery. Here both the calculation time and the amount of primary computer memory needed has been reduced by performing the dose calculations in a cone beam coordinate system allowing the use of approximately spatially invariant energy deposition kernels. A typical calculation time for optimization of a two‐field technique in a three dimensional volume is about 20 s per iteration step on a Hewlett‐Packard 735 workstation. A well converged solution is normally obtained within about 50–100 iterations or within 15–30 min.
Aim
The evaluation what kind of statistical informations concomitant with DVH are essential in estimations of dose distribution in conformal planning of radiotherapy.
Method
Un the base of test case – cancer of the base of tongue, irradiation plans for different sizes of irradiation boost field margins were analysed. DVHs-differential and cumulative for selected critical organs and target volume have been accounted. On base of standard deviation and minimal doses in select volumes target and critical tissues have been estimated. Then probability of local control the risk of complications have been expected.
Results and discussion
The modelled results show, that graphic representation of DVH is not sufficient information itself in estimation of dose distribution. Statistical parameters like modal dole, standard deviation determine essential supplement of graphic dose distribution. Especially standard deviation contains indispensable information. The histogram differential and cumulative should be used together for estimations of dose distribution. It appears that estimation of dose distribution in target volume should be based on cumulative histogram and estimation of dose distribution in critical organs – on differential histogram.
Purpose: Intensity modulated radiation therapy (IMRT) has been shown to provide highly conformal dose to the target while significantly sparing the normal tissues. IMRT plans have been routinely delivered via multileaf collimators (MLC) using either dynamic or step-and-shoot mode. The effect of organ motion is usually considered by applying a 1-2 cm margin around the target. The actually delivered target dose distribution is different from the ideal dose distribution and the normal tissues in the margin area receive much higher doses, which may yield higher complications later on. The purpose of this work is to incorporate organ motion into MLC leaf sequencing for IMRT treatments. Our objective is to study the feasibility of this approach and the clinical advantages in terms of dose coverage and normal tissue sparing.
Dose distributions can often be significantly improved by modulating the two-dimensional intensity profile of the individual x-ray beams. One technique for delivering intensity modulated beams is dynamic multileaf collimation (DMLC). However, DMLC is complex and requires extensive quality assurance. In this paper a new method is presented for a pretreatment dosimetric verification of these intensity modulated beams utilizing a charge-coupled device camera based fluoroscopic electronic portal imaging device (EPID). In the absence of the patient, EPID images are acquired for all beams produced with DMLC. These images are then converted into two-dimensional dose distributions and compared with the calculated dose distributions. The calculations are performed with a pencil beam algorithm as implemented in a commercially available treatment planning system using the same absolute beam fluence profiles as used for calculation of the patient dose distribution. The method allows an overall verification of (i) the leaf trajectory calculation (including the models to incorporate collimator scatter and leaf transmission), (ii) the correct transfer of the leaf sequencing file to the treatment machine, and (iii) the mechanical and dosimetrical performance of the treatment unit. The method was tested for intensity modulated 10 and 25 MV photon beams; both model cases and real clinical cases were studied. Dose profiles measured with the EPID were also compared with ionization chamber measurements. In all cases both predictions and EPID measurements and EPID and ionization chamber measurements agreed within 2% (1 sigma). The study has demonstrated that the proposed method allows fast and accurate pretreatment verification of DMLC. (C) 1999 American Association of Physicists in Medicine. [S0093-2405(99)01411-X].
Purpose: Compare dose distributions of traditional versus conformal beam orientations in paranasal sinus malignancies.Materials and methods: Maximum normal tissue doses, dose volume histograms (DVH), normal tissue complication probabilities (NTCP), and the percentage of each normal tissue receiving >80% of the average target dose (V80) were calculated.Results/Conclusions: Conformal planning reduced the V80 to the optic nerves and chiasm as well as the normal tissue maximum doses to the ipsilateral and contralateral optic nerves and chiasm, and mean NTCPs.
Purpose: Brenner and Hall’s 1999 paper estimating an α/β value of 1.5 Gy for prostate tumors has stimulated much interest in the question of whether this ratio (of intrinsic radiosensitivity to repair capacity) is much lower in prostate tumors than in other types of tumors that proliferate faster. The implications for possibly treating prostatic cancer using fewer and larger fractions are important. In this paper we review updated clinical data and present somewhat different calculations to estimate α/β.
Introduction . Definitive radiation therapy has been established as an effective treatment in patients with advanced cervical cancer. The aim of the study is to evaluate the results of MDR brachytherapy and external beam radiation in patients with cervical cancer in stages II b and III. Material and methods . Between 1981 and 1986 161 patients with advanced cervical cancer (34 – stage II b; 127 – stage III acc. to FIGO scale) were treated in the Institute of Oncology in Gliwice. The treatment was one of combined radiotherapy: external beam radiation (60Co photons) and original MDR brachytherapy 137Cs based on individually selected applicators and fractionation schedule. Results . The 5-year disease-free survival rate for patients with stage II b tumours was 60%, with stage III – 41%. In 54 patients (33,5%) clinical examination after the completion of treatment revealed persistent disease, 26 patients (16%) developed local recurrences, 11 patients (7%) – distant metastases. Treatment tolerance in the analysed group was good. Severe postradiation complications were noted in 2 cases (1%). Conclusion . The efficiency and tolerance of cervical cancer treatment combined with MDR brachytherapy was good and comparable with data reported in literature.
D A Wigg
Madison, WI: Medical Physics Publishing (2001)
488pp, price: $180.00, ISBN: 1-930524-05-6
Working on the basis that treatment planning algorithms will in future need to be more biologically based, the author of this book has spent several years researching this area and has developed an interactive bioeffect planning system at his own Centre in Adelaide. A clinical oncologist by profession, Dr Wigg discusses the clinical and physiological considerations which determine biological response to radiation but at the same time has not held back from using copious mathematics to put the ideas into a quantitative context. Overall there is a heavy reliance on elaborate equations and the book reads very much as though it has been prepared for physicists.
The text is written in a generally clear style and, along with the extensive literature and parameter review, the work comes across as being one of considerable scholarship. Some readers might quibble about the order in which the more basic ideas are introduced but, for those patient enough to seek out the details they are looking for, the book will be found useful. One feature is that it does not simply discuss the various models used to quantify fractionation and dose-rate effects, but also examines their parameter sensitivity and how they might need to be `tweaked' in order for them to better fit the clinical data. Indeed, the author's emphasis on the need for clinical credibility before models can be used widely in bioeffect planning comes across in many places. The chapters discussing the radiobiology of arteriovenous malformations (AVMs), combined radiotherapy and chemotherapy, radiation volume effects and radiobiological parameter values stand out as being particularly useful.
Unfortunately, the book is quite badly let down by the graphs; for one reason or another many have little or no value. In nearly all of the figures the formula used to develop the data points is printed in its entirety next to the graph. Whilst some may consider this laudable, the inclusion of (often complex) formulae in the axis captions requires a lot of space, as a result of which many of the graphs are excessively contracted in one direction, rendering them of next to no value. A further irritation is that many of the axis scales extend far beyond the range of the plotted data, an elementary point which should have been picked up by the publisher. Finally, some of the graphs purporting to demonstrate the different predictions of alternative models appear to be identical while others (e.g. those on pages 106 and 107) contain no data points at all. The likely explanation for these shortcomings is that the graphs are taken directly from laptop computers used in teaching workshops to illustrate how biological effects are altered when the assumed models (or parameters) are varied. In an interactive forum this approach probably works well but the inclusion of the un-edited graphs as static entities within the book makes them much less effective.
Despite these criticisms the author has produced something that contains enough solid discussion on bioeffect planning to warrant a place in departments with an interest in this field. It does fall short of being an ideal teaching text and those approaching this subject from a cold-start may find that they need to additionally refer to some of the referenced papers in order to glean the most benefit from the book. However, with the subject still in an embryonic stage it will be some time before things become set in stone and this book does manage to provide the most comprehensive overview of models and data currently available.
An introductory chapter reviews basic principles of treatment planning, including field arrangements, type and energy of radiation, shielding, and beam modification. The sections which follow consider tumors at specific sites. Each section contains a brief overview of the role of radiation therapy, the pertinent regional anatomy, methods of assessing the extent of tumor, and how to define treatment volume. There are practical instructions for patient positioning, choice of field arrangements, and implementation of the final plan. Separate chapters on pediatric tumors and systemic and palliative radiation complete the work. The text is supplemented by anatomic drawings and radiographs.
Total skin low energy electron irradiation (TSEI) remains one of the most effective modes of treatment for generalized superficial lesions. After a brief review of the irradiation beam requirements (treatment of the first few milimeters of skin, uniformity of dose distribution in spite of variations in the shape and size of patients) and the different irradiation methods, the autors present the technique used at Henri Mondor hospital and some other french centers. It consist of 3 vertical adjacent fields with patient lying alternatively in prone then supine position. An custome-made lucite scattering screen used together with incident electran beams of 7–9 MeV provides an homogenous dose distribution in patient's parts of large radius of curvature.The dosimetric study performed essentially with TLD dosimeters and films has shown that the lucite screen was the best choice because its transparency makes easier patient positionning and it induces a very low X-ray contamination. It also shown that the screen has to be set close to the patient both to increase the skin dose and to keep an acceptable dose-rate at the patient's level.Besides experiments performed with a semi-infinite fiat phantom made of equivalent-tissue material and an Alderson Rando phantom simulating the human body, experiments were carried out with layered flat phantoms of small thicknesses and cylindrical phantoms (radii varying from 1 to 9 cm) simulating hand and lower limb cross sections. Results obtained at 4 MeV (mean energy at the patient's surface) have shown that the overdosage in anatomical structure of large radius of curvature but small thickness (palme of hands) is 200% of the prescribed dose for 1 cm thickness, 160% for 2 cm and becomes normal for thicknesses ≥3 cm. Large variations of dose have also been measured in cylindical phantoms simulating fingers, ankle or wrist. They depend on both the radius of the structure and the incidence angle of the beam at the skin surface. Some examples are presented.Such results confirmed by in vivo measurements can explain the complications in anatomical regions of small radii of curvature and/or small thickness (erythematous skin, swelling of feet, ankles and hands) reported by different authors. It is the reason why shields for the hands or feet have to be provided well before the full course of therapy is completed, and thus irrespective of the irradiation technique used.
Purpose:
To implement intensity-modulated radiation therapy (IMRT) for primary nasopharynx cancer and to compare this technique with conventional treatment methods.
Methods and materials:
Between May 1998 and June 2000, 23 patients with primary nasopharynx cancer were treated with IMRT delivered with dynamic multileaf collimation. Treatments were designed using an inverse planning algorithm, which accepts dose and dose-volume constraints for targets and normal structures. The IMRT plan was compared with a traditional plan consisting of phased lateral fields and a three-dimensional (3D) plan consisting of a combination of lateral fields and a 3D conformal plan.
Results:
Mean planning target volume (PTV) dose increased from 67.9 Gy with the traditional plan, to 74.6 Gy and 77.3 Gy with the 3D and IMRT plans, respectively. PTV coverage improved in the parapharyngeal region, the skull base, and the medial aspects of the nodal volumes using IMRT and doses to all normal structures decreased compared to the other treatment approaches. Average maximum cord dose decreased from 49 Gy with the traditional plan, to 44 Gy with the 3D plan and 34.5 Gy with IMRT. With the IMRT plan, the volume of mandible and temporal lobes receiving more than 60 Gy decreased by 10-15% compared to the traditional and 3D plans. The mean parotid gland dose decreased with IMRT, although it was not low enough to preserve salivary function.
Conclusion:
Lower normal tissue doses and improved target coverage, primarily in the retropharynx, skull base, and nodal regions, were achieved using IMRT. IMRT could potentially improve locoregional control and toxicity at current dose levels or facilitate dose escalation to further enhance locoregional control.
Purpose:
Radiation therapy is the treatment of choice for early glottic squamous cell cancer in many institutions over the world. Despite a relatively homogenous clinical model of T1 glottic tumors for the fractionation studies, the relationships between dose-time parameters remain unclear. To analyze the influence of fractionation parameters and hemoglobin level on tumor cure, this study has been performed.
Materials and methods:
This is a retrospective review of 235 patients with T1N0M0 glottic cancer treated by radiation therapy alone given in a conventional schedule with 5 fractions each week. The individual total dose, dose per fraction, and overall treatment time (OTT) ranged from 51-70 Gy, 1.5-3.0 Gy, and 24-79 days, respectively. The median follow-up was 48 months. Patient data--total dose, dose per fraction, OTT, and hemoglobin level (Hb) measured before the radiation treatment--were fitted by the mixed LQ/log-logistic model.
Results:
The 5-year local relapse-free survival rate was 84%. All parameters included in the mixed LQ/log-logistic model improved the fit significantly. The dose-response curve for 235 patients with T1 glottic cancer was well defined and steep, and showed significant decrease in tumor control probability (TCP) when total doses were below 61 Gy. The 10-day prolongation of OTT, from 45 to 55 days, decreased the TCP by 13%. The dose of 0.35 Gy/day, compensated repopulation during the 1 day of prolongation, which indicates a potential doubling time (Tpot) for glottic T1 tumor clonogens of 5.5 days. The drop of Hb level of 1 g/dl (from 13.8 g/dl to 12.8 g/dl) gave a 6% decrease of TCP, provided that OTT was 45 days.
Conclusion:
The significant correlation between the total dose, overall treatment time, hemoglobin concentration, and tumor control probability has been found for T1 glottic cancer.
To use the time-dependent linear-quadratic model, both in the standard form and in a form modified to incorporate intertumor heterogeneity, in a reanalysis of 4 datasets for larynx tumor control, to provide more representative and direct estimates of the lag period, the time factor (lambda/alpha), and the clonogen population inactivation dose ([lnk]/alpha).
The data comprised 2,225 patients treated in Edinburgh (UK), Glasgow (UK), Manchester (UK), or Toronto (Canada), with tumor control assessed after at least 2 years. Heterogeneity in each series was taken into account using the coefficient of variation (CV) of the clonogen radiosensitivity (alpha). Maximum likelihood techniques were used to provide best estimates of the parameters, and also direct estimation of the more stable parameter ratios of interest.
The use of different heterogeneity factors for the different series allowed common dose/time parameters to be fitted across all four series in a way not possible using the standard model, enabling the inherent effect of heterogeneity in flattening dose-response curves and in reducing time factors to be separated from the underlying more-representative values. Radiosensitivity CVs were calculated to be 30% (Edinburgh), 36% (Glasgow), 40% (Manchester), and 71% (Toronto). The lag phase was 32 days (95% CL 20-38 days) which was longer than the value of 23 days (11-36 days) deduced using the standard model without the heterogeneity parameter. The time factor was 1.2 (0.8-2.2) Gy/day, again greater than the value of 0.80 (0.54-1.41) Gy/day derived using the standard model. Similar larger time factors and longer lag periods could be reproduced using the standard model either by using a parameterization based on parameter ratios, or by omitting the discordant Toronto data and refitting just the data from the three UK centers.
It was concluded that the heterogeneity model provides a better representation of the time factor for tumor control when data are analyzed comprising different stages of disease treated at different centers. The model allows different amounts of heterogeneity in different series, which tend to flatten dose-responses curves and reduce time factors, to be taken in to account. Also, direct maximum likelihood estimates can be made of the lag period, the time factor (lambda/alpha), and the fractionation sensitivity (beta/alpha), as well as the clonogen population inactivation dose (lnk)/alpha. Values of these parameter ratios are more robust and stable than the individual parameter values. The results of the present analysis using a total of 2,225 patients from four centers indicate that the average lag period may be somewhat longer and the average time factor somewhat greater (and the 95% confidence limits of the time factor exclude previous estimates), than the values deduced previously using simpler models and more diverse multi-center datasets.