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Lech Papiez

Publications and source records attributed to Lech Papiez.

16 recordsLinked to original sources
PubMed2006

High density dental materials and radiotherapy planning: comparison of the dose predictions using superposition algorithm and fluence map Monte Carlo method with radiochromic film measurements.

BACKGROUND AND PURPOSE: During radiotherapy planning high density dental materials create a major challenge in determining correct dose distribution inside patients with head-and-neck tumors. PATIENTS AND METHODS: In this work we investigated the absorbed dose distribution inside a solid water slab phantom with embedded high density material irradiated by a 6MV photon beam of field size 10x10cm. We evaluated the absorbed dose distribution with three different techniques: superposition algorithm, radiochromic film, and the fluence map Monte Carlo (FMMC) method. RESULTS: The results obtained with radiochromic film and FMMC were in good agreement (within +/-5% of the dose) with one another. The superposition algorithm, which is often considered superior to other commercially available dose calculation algorithms, produced appreciably less accurate results than FMMC. In particular, downstream from the high density cerrobend inhomogeneity the superposition algorithm predicts a higher dose than the measurement does by at least 10-16% depending upon the size of the inhomogeneity and the distance from it. Upstream of the high density inhomogeneities the superposition algorithm predicts a lower than measured dose due to its failure to predict the dose enhancement close to the inhomogeneity interface. CONCLUSIONS: The delivered dose downstream from a high density inhomogeneity would be significantly less than the prescribed dose calculated by the superposition algorithm. The FMMC method which is based on a hybrid of the superposition algorithm input fluence data and Monte Carlo can be a useful tool in predicting dose in the presence of high density (e.g. dental) materials.

Algorithms↗
PubMed2006

Excessive toxicity when treating central tumors in a phase II study of stereotactic body radiation therapy for medically inoperable early-stage lung cancer.

PURPOSE: Surgical resection is standard therapy in stage I non-small-cell lung cancer (NSCLC); however, many patients are inoperable due to comorbid diseases. Building on a previously reported phase I trial, we carried out a prospective phase II trial using stereotactic body radiation therapy (SBRT) in this population. PATIENTS AND METHODS: Eligible patients included clinically staged T1 or T2 (< or = 7 cm), N0, M0, biopsy-confirmed NSCLC. All patients had comorbid medical problems that precluded lobectomy. SBRT treatment dose was 60 to 66 Gy total in three fractions during 1 to 2 weeks. RESULTS: All 70 patients enrolled completed therapy as planned and median follow-up was 17.5 months. The 3-month major response rate was 60%. Kaplan-Meier local control at 2 years was 95%. Altogether, 28 patients have died as a result of cancer (n = 5), treatment (n = 6), or comorbid illnesses (n = 17). Median overall survival was 32.6 months and 2-year overall survival was 54.7%. Grade 3 to 5 toxicity occurred in a total of 14 patients. Among patients experiencing toxicity, the median time to observation was 10.5 months. Patients treated for tumors in the peripheral lung had 2-year freedom from severe toxicity of 83% compared with only 54% for patients with central tumors. CONCLUSION: High rates of local control are achieved with this SBRT regimen in medically inoperable patients with stage I NSCLC. Both local recurrence and toxicity occur late after this treatment. This regimen should not be used for patients with tumors near the central airways due to excessive toxicity.

Aged↗
PubMed2006

On probabilistically defined margins in radiation therapy.

Margins about a target volume subject to external beam radiation therapy are designed to assure that the target volume of tissue to be sterilized by treatment is adequately covered by a lethal dose. Thus, margins are meant to guarantee that all potential variation in tumour position relative to beams allows the tumour to stay within the margin. Variation in tumour position can be broken into two types of dislocations, reducible and irreducible. Reducible variations in tumour position are those that can be accommodated with the use of modern image-guided techniques that derive parameters for compensating motions of patient bodies and/or motions of beams relative to patient bodies. Irreducible variations in tumour position are those random dislocations of a target that are related to errors intrinsic in the design and performance limitations of the software and hardware, as well as limitations of human perception and decision making. Thus, margins in the era of image-guided treatments will need to accommodate only random errors residual in patient setup accuracy (after image-guided setup corrections) and in the accuracy of systems designed to track moving and deforming tissues of the targeted regions of the patient's body. Therefore, construction of these margins will have to be based on purely statistical data. The characteristics of these data have to be determined through the central limit theorem and Gaussian properties of limiting error distributions. In this paper, we show how statistically determined margins are to be designed in the general case of correlated distributions of position errors in three-dimensional space. In particular, we show how the minimal margins for a given level of statistical confidence are found. Then, how they are to be used to determine geometrically minimal PTV that provides coverage of GTV at the assumed level of statistical confidence. Our results generalize earlier recommendations for statistical, central limit theorem-based recommendations for margin construction that were derived for uncorrelated distributions of errors (van Herk, Remeijer, Rasch and Lebesque 2000 Int. J. Radiat. Oncol. Biol. Phys. 47 1121-35; Stroom, De Boer, Huizenga and Visser 1999 Int. J. Radiat. Oncol. Biol. Phys. 43 905-19).

Artifacts↗
PubMed2005

Evaluation of underdosage in the external photon beam radiotherapy of glottic carcinoma: Monte Carlo study.

PURPOSE: Underdosage in the human larynx may be the true factor behind the decrease in local control rates. PATIENTS AND METHODS: To evaluate underdosage with Monte Carlo a CT-based geometrical model of the patient's neck (mathematical neck) was created. Dose was calculated for a pair of 6 Me V parallel-opposed photon beams modulated with 15 degree steel wedges. RESULTS: At least 5% of volume of 3.5 cm(3) hypothetical tumor near the air wall of the larynx receives less than 86% of the maximum tumor dose. The same volume received less than 91% of the maximum tumor dose when the mathematical neck had no air cavities. CONCLUSIONS: We conclude the significant underdosage at the air-tissue interface in the larynx occurs in traditional radiotherapy treatments, especially in the glottic part of the larynx.

Benchmarking↗
PubMed2005

The need for rotational margins in intensity-modulated radiotherapy and a new method for planning target volume design.

PURPOSE: The effect of rotational errors on the coverage of clinical target volumes (CTVs) is examined. A new planning target volume (PTV) construction that considers the individual paths traced by movements of the target boundary points is developed. METHODS AND MATERIALS: A standard uniform margin expansion was compared with a PTV constructed from the space swept out by a concave moving target. A new method formed the PTV by aggregating the separate convex hulls taken of the positions of the individual target boundary points in a sampling of CTV displacements. RESULTS: A 0.5-cm uniform margin adequate for translations was inadequate given CTV rotation about a fixed off-center axis. A PTV formed of the target's swept-out area was 22% smaller than needed for coverage by a uniform margin, but computationally is not readily extended to translations combined with rotations about a shifting axis. Forming instead the union of convex hulls of the boundary points in a sampling of CTV displacements represented these movements in the PTV design and retained the target's concave shape. CONCLUSIONS: Planning target volumes should accommodate target rotation. The union of convex hulls of the boundary point positions in a sampling of displacements can effectively represent multiple sources of deviations while preserving target concavities.

Radiotherapy Planning, Computer-Assisted↗
PubMed2005

Stereotactic body radiation therapy of early-stage non-small-cell lung carcinoma: phase I study.

PURPOSE: A Phase I dose escalation study of stereotactic body radiation therapy to assess toxicity and local control rates for patients with medically inoperable Stage I lung cancer. METHODS AND MATERIALS: All patients had non-small-cell lung carcinoma, Stage T1a or T1b N0, M0. Patients were immobilized in a stereotactic body frame and treated in escalating doses of radiotherapy beginning at 24 Gy total (3 x 8 Gy fractions) using 7-10 beams. Cohorts were dose escalated by 6.0 Gy total with appropriate observation periods. RESULTS: The maximum tolerated dose was not achieved in the T1 stratum (maximum dose = 60 Gy), but within the T2 stratum, the maximum tolerated dose was realized at 72 Gy for tumors larger than 5 cm. Dose-limiting toxicity included predominantly bronchitis, pericardial effusion, hypoxia, and pneumonitis. Local failure occurred in 4/19 T1 and 6/28 T2 patients. Nine local failures occurred at doses < or =16 Gy and only 1 at higher doses. Local failures occurred between 3 and 31 months from treatment. Within the T1 group, 5 patients had distant or regional recurrence as an isolated event, whereas 3 patients had both distant and regional recurrence. Within the T2 group, 2 patients had solitary regional recurrences, and the 4 patients who failed distantly also failed regionally. CONCLUSIONS: Stereotactic body radiation therapy seems to be a safe, effective means of treating early-stage lung cancer in medically inoperable patients. Excellent local control was achieved at higher dose cohorts with apparent dose-limiting toxicities in patients with larger tumors.

Aged↗
PubMed2005

DMLC leaf-pair optimal control for mobile, deforming target.

Existing algorithms of dynamic control of independent pairs of leaves allow optimal DMLC delivery of IMRT to rigid targets translating parallel to leaf trajectories. However, in numerous cases of radiotherapy treatments simplifying assumptions of rigid-like motions of targets and surrounding tissues are clearly not satisfied. Therefore algorithms have to be developed that allow one to control MLC so that predetermined intensities are delivered to various points in targets that experience compression and expansion at the time of irradiation. Moreover, it is desirable for such algorithms to ensure that delivery of modulated intensity map will be done with minimal expense of monitor units. Derivation of the algorithm that optimizes the DMLC IMRT to mobile, deforming target is presented in this paper. [To illustrate the general algorithm two representative examples of DMLC IMRT delivery to deforming targets are presented in full detail.] Finally, similarities and differences between solutions for immobile targets, for moving, rigid targets and for moving, deforming targets are discussed.

Algorithms↗
PubMed2005

Synchronized delivery of DMLC intensity modulated radiation therapy for stationary and moving targets.

When delivering intensity modulated treatments the "tongue-and-groove" underdosage effect is a concern that should not be ignored. Algorithms aimed at removing the tongue-and-groove underdosage have been investigated in the past for irradiation of stationary targets. This paper is devoted to algorithms that remove tongue and grove effect for stationary and moving targets. To this end this paper develops original mid-time based algorithms for leaf synchronization. These algorithms exhibit a few additional advantageous properties for DMLC IMRT delivery beyond the removal of tongue-and-grove underdosage. In particular, they safeguard the minimization of time of delivery (for mid-time synchronized algorithms). Moreover, they avoid iterative procedures for synchronization of delivery for multiple pairs of leaves.

Algorithms↗
PubMed2005

Real-time DMLC IMRT delivery for mobile and deforming targets.

In numerous cases of radiotherapy delivery to moving targets, simplifying assumptions of identical pattern of motions of tissue for each fraction are not satisfied. Therefore, algorithms capable to respond in real time to motions of target registered at treatment should be developed to improve the precision of radiation intensity delivery. The DMLC delivery of predetermined intensity maps to moving and deforming targets in real time is developed in this paper. Algorithms are constructed so that constraints on maximum admissible speed of leaves are preserved during delivery. A sequence of examples is presented to illustrate behavior of leaf trajectories for representative cases of [dynamic multileaf collimator] (DMLC) [intensity modulated radiation therapy] (IMRT) real-time delivery. The examples presented show real-time deliveries to targets moving as rigid bodies and targets deforming uniformly over their volumes. Examples are admitting random perturbations of predefined target motions that are time dependent only, i.e., target motion perturbations are identical for all target points.

Algorithms↗
PubMed2004

Monte carlo simulation of the Leksell Gamma Knife: II. Effects of heterogeneous versus homogeneous media for stereotactic radiosurgery.

The absence of electronic equilibrium in the vicinity of bone-tissue or air-tissue heterogeneity in the head can misrepresent deposited dose with treatment planning algorithms that assume all treatment volume as homogeneous media. In this paper, Monte Carlo simulation (PENELOPE) and measurements with a specially designed heterogeneous phantom were applied to investigate the effect of air-tissue and bone-tissue heterogeneity on dose perturbation with the Leksell Gamma Knife. The dose fall-off near the air-tissue interface caused by secondary electron disequilibrium leads to overestimation of dose by the vendor supplied treatment planning software (GammaPlan) at up to 4 mm from an interface. The dose delivered to the target area away from an air-tissue interface may be underestimated by up to 7% by GammaPlan due to overestimation of attenuation of photon beams passing through air cavities. While the underdosing near the air-tissue interface cannot be eliminated with any plug pattern, the overdosage due to under-attenuation of the photon beams in air cavities can be eliminated by plugging the sources whose beams intersect the air cavity. Little perturbation was observed next to bone-tissue interfaces. Monte Carlo results were confirmed by measurements. This study shows that the employed Monte Carlo treatment planning is more accurate for precise dosimetry of stereotactic radiosurgery with the Leksell Gamma Knife for targets in the vicinity of air-filled cavities.

Algorithms↗
PubMed2003

Extracranial stereotactic radioablation: physical principles.

Extracranial stereotactic radioablation (ESR) involves treating well-demarcated targeted tissues (e.g. tumor with minimal margin for set-up uncertainties) with very large doses of radiation in single or a few fractions with the intent of causing profound late tissue damage within the targeted volume. In such circumstances, considerable effort must be taken to reduce non-target tissue exposure to the high dose levels in order to prevent late complications to involved organs. Consequently, the following conditions for effective delivery of the ESR techniques have to be satisfied: 1) delivery of a high dose per fraction, i.e. 10-24 Gy; 2) delivery of only a few fractions per course of treatment (e.g. 1-4); 3) shaping of the prescription isodose surface conformally to the target surface; 4) delivery of a non-uniform dose distribution within the target with the highest dose in centrally located regions of hypoxia; 5) rapid fall-off of dose from the target volume to healthy tissue in all directions. In this paper it is shown that high doses per fraction in few fractions can be delivered to a variety of locations with both efficacy and acceptable toxicity (conditions 1 and 2). Conformal shaping of the high isodose surfaces is best accomplished by employing many beams (5-10) each with carefully milled apertures precisely coincident with the target projection (condition 3). Beam intensity modulation creating parabolic beam entrance fluence profiles both concentrates the highest dose in central regions of tumor hypoxia and increases fall-off gradients outside of the target (conditions 4 and 5). It is also shown that isotropic, highly non-coplanar beam arrangements avoiding oppositional fields allow more optimal fall-off gradients to normal tissue as opposed to coplanar treatments (condition 5).

Feasibility Studies↗
PubMed2003

Extracranial stereotactic radiation delivery: expansion of technology beyond the brain.

The development of improved immobilization systems, and a greater understanding of the radiobiologic considerations associated with stereotactic radiotherapy has recently led to the clinical implementation of this technology to extracranial sites. The shared principles of targeting and treatment delivery has led to a greater understanding of the potential role this therapy may have in the management of extracranial disease. This article will review, the radiobiologic considerations and the basic principles of physics and dosimetry that help govern the utilization of extracranial stereotactic radiotherapy. In addition, this article will summarize the data that exists in the literature to date, that has documented the rationale, and efficacy of this novel therapeutic approach.

Adrenal Gland Neoplasms↗
PubMed2003

Extracranial stereotactic radioablation: results of a phase I study in medically inoperable stage I non-small cell lung cancer.

INTRODUCTION: Surgical resection is standard therapy for patients with stage I non-small cell lung cancer (NSCLC), however, many patients are medically inoperable. We set out to investigate a new therapy akin to brain radiosurgery called extracranial stereotactic radioablation (ESR) in a phase I trial. PATIENTS AND METHODS: Eligible patients included those with clinically staged T1 or T2 (tumor size, < or = 7 cm) N0M0 biopsy confirmed NSCLC. All patients had comorbid medical problems that precluded thoracotomy. The median age was 75 years, and the median Karnofsky performance status was 80. ESR was administered in three separate fractions over 2 weeks. Three to five patients were treated within each dose cohort starting at 800 cGy per fraction (total, 2,400 cGy) followed by successive dose escalations of 200 cGy per fraction (total increase per cohort, 600 cGy). Waiting periods occurred between dose cohorts to observe toxicity. Patients with T1 vs T2 tumors underwent separate independent dose escalations. RESULTS: A total of 37 patients were enrolled since February 2000. One patient experienced grade 3 pneumonitis, and another patient had grade 3 hypoxia. For the entire population, there was no appreciable decline in cardiopulmonary function as measured by symptoms, physical examination, need for oxygen supplementation, pulmonary function testing, arterial blood gas determinations, or regular chest imaging. Both T-stage groups ultimately reached and tolerated 2,000 cGy per fraction for three fractions (total, 6,000 cGy). The maximum tolerated dose for this therapy in either T-stage group has yet to be reached. Tumors responded to treatment in 87% of patients (complete response, 27%). After a median follow-up period of 15.2 months, six patients experienced local failure, all of whom had received doses of < 1,800 cGy per fraction. CONCLUSIONS: Very high radiation dose treatments were tolerated in this population of medically inoperable patients with stage I NSCLC using ESR techniques.

Aged↗
PubMed2002

Monte Carlo simulation of the Leksell Gamma Knife: I. Source modelling and calculations in homogeneous media.

The Monte Carlo code PENELOPE has been used to simulate photon flux from the Leksell Gamma Knife, a precision method for treating intracranial lesions. Radiation from a single 6OCo assembly traversing the collimator system was simulated, and phase space distributions at the output surface of the helmet for photons and electrons were calculated. The characteristics describing the emitted final beam were used to build a two-stage Monte Carlo simulation of irradiation of a target. A dose field inside a standard spherical polystyrene phantom, usually used for Gamma Knife dosimetry, has been computed and compared with experimental results, with calculations performed by other authors with the use of the EGS4 Monte Carlo code, and data provided by the treatment planning system Gamma Plan. Good agreement was found between these data and results of simulations in homogeneous media. Owing to this established accuracy, PENELOPE is suitable for simulating problems relevant to stereotactic radiosurgery.

Computer Simulation↗
PubMed2002

Very high energy electrons (50-250 MeV) and radiation therapy.

High energy electron beams in the range 150-250 MeV are investigated to evaluate their feasibility for radiotherapy. Monte Carlo simulation results from PENELOPE code are used to determine lateral spread and penetration of these beams. It is shown that dose distribution of electron beams compare favorably with photon beams. Electromagnetic control of electron beams enables scanned intensity modulation not possible with photon beams.

Electrons↗