Biomedical subjects

A Montelius

Publications and source records attributed to A Montelius.

At least 19 recordsLinked to original sources

PubMed1998

Comparative treatment planning between proton and x-ray therapy in esophageal cancer.

PURPOSE: Conformal treatment planning with megavoltage x-rays and protons for five patients with esophageal cancer has been studied in an attempt to determine if there are advantages of using protons instead of x-rays. METHODS AND MATERIALS: For each of the five patients, two different proton plans, one x-ray plan, and one mixed plan with x-rays and protons were made. A three-dimensional treatment planning system, TMS, was used. The evaluation of the different plans was made by applying the tumor control probability (TCP) model proposed by Nahum and Webb and the normal tissue complication (NTCP) model proposed by Lyman on the dose distributions in terms of dose-volume histograms (DVHs). RESULTS: The comparison shows advantages of using protons instead of x-rays for all five patients. The dose-limiting organs at risk are the spinal cord, the lungs, and the heart, but the proton plans also spare the kidneys better than the x-ray plan does. At 5% NTCP in any risk organ, the calculated mean TCP value for the five patients is increased by an average of 20%-units (from 2 to 23%-units) with the best proton plan compared with x-rays only. However, if we assume maximally a 1% risk in the spinal cord and a total NTCP for the two lungs of 100%, the mean TCP value for the five patients is increased from 6 to 49% with the best proton plan compared with x-rays only. The corresponding figure for the mixed plan is 27%. These gains are relatively insensitive to variations within reasonable limits in the biological parameters. CONCLUSIONS: Protons appear to have clear therapeutic advantages over conventional external radiotherapy when treating esophageal carcinoma.

Aged↗

PubMed1998

Radiotherapy of breast cancer after breast-conserving surgery: an improved technique using mixed electron-photon beams with a multileaf collimator.

BACKGROUND AND PURPOSE: Loco-regional radiotherapy after breast cancer surgery significantly reduces the risk of recurrences. An increase of cardiac deaths for irradiated breast cancer patients has been reported in some studies, especially for women with tumours in the left breast. The aim of this study was to compare retrospectively the conventionally used technique using two opposed tangential photon beams with a modified technique using a combination of photon and electron beams to find an optimal technique with respect to dose homogeneity in the breast and surrounding regional lymph nodes and a minimal dose in the organs at risk. MATERIALS AND METHODS: Thirty patients with stage II breast cancer who received different types of adjuvant systemic therapy were included in the investigation. Comparative dose planning of two techniques was performed, i.e. an isocentric technique with two photon beams with coplanar medial beam edges and a technique with one electron and three photon beams with a common isocentre for all beams aided by a multileaf collimator. RESULTS: The mixed technique was selected for eight of 12 patients with left-sided breast cancers because of significantly lower doses to the heart. However, the decision-making was influenced by many factors such as dose coverage of the target volume combined with minimizing of the doses to the organs at risk and the contralateral breast. CONCLUSION: The use of the mixed technique will optimize the loco-regional radiotherapy after breast-conserving surgery for many left-sided breast cancers.

Adult↗

PubMed1998

Improvements in absorbed dose measurements for external radiation therapy using ferrous dosimeter gel and MR imaging (FeMRI).

A ferrous gel, based on ferrous (Fe) sulphate and agarose, was used with a clinical magnetic resonance imaging (MRI) scanner to obtain relative dose distribution data from therapeutic photon and electron beams. The FeMRI gel was scanned using a new MRI acquisition protocol optimized for T1 measurements. Thorough comparisons with silicon semiconductor detector and ionization chamber measurements, as well as with Monte Carlo calculations, were performed in order to quantify the improvements obtained using FeMRI for dose estimations. Most of the relative doses measured with FeMRI were within 2% of the doses measured with other methods. The larger discrepancies (2-4%) found at shallow depths are discussed. The uncertainty in relative dose measurements using FeMRI was significantly improved compared with previously reported results (5-10%, one standard deviation, 1 SD), and is today between 1.6% and 3.3% (depending on dose level, 2 SD). This corresponds to an improvement in the minimum detectable dose (3 SD above background) from approximately 2 Gy to better than 0.6 Gy. The results obtained in this study emphasize the importance of obtaining basic FeMRI dose data before the method is extended to complicated treatment regimes.

Electrons↗

PubMed1997

Potential advantages of protons over conventional radiation beams for paraspinal tumours.

BACKGROUND AND PURPOSE: Conformal treatment planning with megavoltage X-rays and protons was studied in an attempt to determine if there are advantage of boost therapy with protons instead of X-rays for a patient with a tumour growing around the cervical spinal cord. MATERIALS AND METHODS: A patient with a Ewing sarcoma was selected for the model study. The proton boost plan was realised with a six beam patched technique. Several X-ray boost techniques were planned, some not yet practically realisable. The techniques giving the best dose distributions and the best tumour control probabilities in the absence of significant late toxicity were looked for. The boost techniques were added to two large lateral X-ray beams covering the planning target volume (PTV) and the main risk organ, the spinal cord. The evaluation was made with two biological models, i.e. the tumour control probability (TCP) model, proposed by Webb and Nahum (Webb, S. and Nahum, A.E. A model for calculating tumour control probability in radiotherapy including the effect of inhomogeneous distributions of dose and clonogenic cell density. Phys. Med. Biol. 38: 653-666, 1993), and the normal tissue complication probability (NTCP) model, first derived by Lyman (Lyman, J.T. Complication probability as assessed from dose-volume histograms. Radiat. Res. 104: s13-s19, 1985). RESULTS: The comparison showed small but clear advantages of protons for the boost. At 1% NTCP in the spinal cord, the calculated TCP was on average 5% higher. However, depending on the values of the parameters chosen in the biological models, the gain for protons varied from 0-10%. The smallest gains were seen in radiosensitive tumours for which the TCP was close to 100% with any of the techniques and in radioresistant tumours for which neither technique resulted in any appreciable probability of local cure. CONCLUSION: Protons appear to have therapeutic advantages over conventional radiotherapy in tumours with relatively high radiosensitivity situated close to the spinal cord.

Adult↗

PubMed1997

The conceptual design of a radiation oncology planning system.

The conceptual design of a three-dimensional, radiation oncology planning system is described. To assure that clinical needs were met, the working routines in two major Swedish radiation oncology departments were analysed in detail. Generic work flow was identified and mapped and compared to those in other institutions. The flow was partitioned into a number of nodes that together formed a basis for the design of the system handling logistics. The design criteria of this system emphasised accommodation of current clinical practice and traditional treatment modalities, and facilitated means to validate the computational techniques. The system should also allow for new procedures and was based on the analysis of current practice and a synthetic idea of how 3D treatment planning should be done. The final product supports the treatment planning work in its entirety. It is believed that the techniques followed are of interest to those engaged in computer systems of similar purposes and complexities.

Computer Systems↗

PubMed1997

Correction factors for parallel-plate chambers used in plastic phantoms in electron dosimetry.

In electron beam dosimetry using parallel-plate chambers solid phantoms are sometimes necessary. To obtain the dose to water from the ionization obtained in the solid phantom, fluence correction factors and perturbation factors have to be applied. In this study fluence factors in a perturbation free geometry have been determined experimentally for common phantom materials. Wall perturbation factors for simulated Attix, NACP, and Roos chambers have also been determined for the same materials. Comparative Monte Carlo calculations have been performed using the EGS4 Monte Carlo code. Comparison with data in newly published protocols such as IAEA and IPEMB shows an agreement with the results obtained in this paper to within 1%, demonstrating that the data published in these protocols may be used with reasonable accuracy if recommended phantoms are used. The results also show that if unsuitable phantom materials are used, the wall perturbation factors may differ for different chambers and for different phantom materials by more than 3% and perturbation factors have to be considered in order to obtain a high accuracy in the dose determination.

Dose-Response Relationship, Radiation↗

PubMed1997

Dosimeter gel and MR imaging for verification of calculated dose distributions in clinical radiation therapy.

A dosimeter gel, based on an agarose gel infused with a ferrous sulphate solution and evaluated in a magnetic resonance scanner, was used for complete verification of calculated dose distributions. Two standard treatment procedures, treatment of cancer in the urinary bladder and treatment of breast cancer after modified radical mastectomy, were examined using pixel-by-pixel and dose volume histogram comparison. The dose distributions calculated with the dose planning system was in very good agreement with the measured ones. However, in the case of the more complicated breast cancer treatment, some discrepancies were found, mainly at the beam abutment region. This may be explained by field displacements errors and by a small limitation of the dose planning utilising small electron beams in this region. The dosimeter gel system have proven to be a useful tool for dosimetry in clinical radiation therapy applications.

Breast Neoplasms↗

PubMed1996

Preoperative radiotherapy in rectal carcinoma--aspects of acute adverse effects and radiation technique.

PURPOSE: To explain a possible association between treatment technique and postoperative mortality after preoperative radiotherapy of rectal carcinoma, the dose distributions were compared in model experiments. METHODS AND MATERIALS: Preoperative radiotherapy with a three-beam technique delivered in five fractions to 25 Gy (5 Gy/daily for 5 or 7 days) was given to patients with primary resectable rectal carcinoma. The adverse effects of this treatment, both acute and late, have been low. In a parallel trial using an identical fractionation schedule and total dose but with a two-beam technique, the postoperative mortality was higher. Two-, three-, and four-beam techniques were analyzed in 20 patients with computed tomography based, three-dimensional dose planning. Dose distributions and dose-volume histograms in the planning target volume (PTV) and in the organs at risk were considered. A numerical "biological" model was used to compare the techniques. RESULTS: The two-beam and the four-beam box techniques give the most homogeneous dose distributions in the PTV, although all techniques result in dose distributions that would be considered adequate, provided 16 MV or higher photon energies are used. Three- and four-beam techniques show advantages over the two-beam technique with respect to organs at risk, particularly the small bowel. With the two-beam technique and the upper beam limit at mid-L4, the volume of the bowel that receives > 95% of the prescribed dose, and hence, is included in the treated volume (TV), is more than twice as large as that with three- and four-beam techniques, and that of the total body between 1.5 and 2 times as large. The results of the analyses using the biological model indicate that the three- and four-beam techniques result in less small bowel complication rates than the two-beam technique. The integral energy to the total body is similar for all treatment modalities compared. CONCLUSIONS: The volume of bowel included in the TV, rather than the energy imparted to the body, influences postoperative mortality, and emphasizes the importance of precise radiotherapy planning to minimize normal tissue toxicity.

Aged↗

PubMed1996

Acute lumbosacral plexopathy during and after preoperative radiotherapy of rectal adenocarcinoma.

The benefit of preoperative radiotherapy of adenocarcinoma of the rectum with respect to a reduced local recurrence rate and an improved survival should be weighed against adverse effects. For 14 years a three-beam, isocentric technique was employed at our hospital to deliver five fractions (5.0 or 5.1 Gy), over 5 or 7 days preoperatively, to patients with rectal cancer which was considered primarily resectable. The adverse effects of the radiotherapy were few, but acute pain and subacute neurological symptoms and signs did occur. An apparent increase in the frequency of these symptoms/signs was noted during 1993. The pain and neurological symptoms are described in case reports and the individual treatments are reviewed. The three-beam technique was analyzed in detail with individual, CT-based, three-dimensional dose-planning and dose distributions in the vicinity of the lumbar nerve plexus are presented. The major result of this analysis showed that technical errors could be excluded, that human errors were unlikely, and that the culprit probably was an unexpected sensitivity to marginal changes in the daily dose and unknown or unexpected radiosensitizing effects of concurrent diseases or medication.

Acute Disease↗

PubMed1996

Comparative treatment planning between proton and X-ray therapy in locally advanced rectal cancer.

BACKGROUND AND PURPOSE: Conformal treatment planning with megavoltage X-rays and protons for medically inoperable patients with a large rectal cancer has been studied in an attempt to determine if there are advantages of using protons instead of X-rays. MATERIAL AND METHODS: Three dose plans were made for each of the six patients: one proton plan, including three beams covering the primary tumour and adjacent lymph nodes and three boost beams covering the primary tumour: one X-ray plan, eight beams including a boost with four beams and one mixed plan with four X-ray beams and a boost with three proton beams. A three dimensional treatment-planning systems, TMS, was used. The evaluation of the different plans was made by applying the biological models TCP and NTCP on the dose distributions in terms of dose-volume histograms. RESULTS: The comparison shows advantages of using protons instead of X-rays for all six patients, but in three of them, the advantage is only marginal. The dose-limiting organ at risk is the small bowel, but the proton plan and the mixed plan also spare the bladder and the femoral heads better. At 5% NTCP in any risk organ, the calculated mean TCP value for the six patients is increased by 14%-units with the proton plan and 8%-units with the mixed plan compared to X-rays only. CONCLUSIONS: Proton beam therapy has potential advantages when treating medically inoperable patients with a large rectal cancer over conventional X-ray therapy. Since the benefits are comparatively small, although clinically worthwhile, large randomised studies are needed.

Aged↗

PubMed1996

Wall effects in plane-parallel ionization chambers.

All dosimetry protocols recommend the use of plane-parallel chambers for dose determination in electron beams with energies below 10-15 MeV. The protocols have assumed chamber perturbation effects to be negligible. The new AAPM Protocol (TG39) includes a cavity replacement factor prepl that differs from unity for some chambers, but assumes that the wall perturbation factor, pwall, may be taken as unity. In this paper the perturbation of the wall has been determined, using a large plane-parallel ionization chamber with exchangeable front and back walls. The results show that in many commercial chambers there is an energy dependent pwall factor, mainly due to differences in backscatter from the often thick chamber body as compared to the phantom material. Backscatter in common phantom and chamber materials may differ by as much as 2% at low electron energies (Plastic Water as compared to polystyrene). The front walls are often thin, resulting in negligible perturbation, but the 0.5 mm front wall of graphite in the NACP chamber was found to increase the response by 0.7% in a PMMA phantom. The experimental results have been compared with EGS4 Monte Carlo calculations using the DOSRZ code. There is an agreement within statistical and experimental uncertainties (0.5%) indicating that it is possible to use Monte Carlo calculations to calculate perturbation factors with good accuracy.

Graphite↗

PubMed1995

Faraday cup dosimetry in a proton therapy beam without collimation.

A Faraday cup in a proton beam can give an accurate measurement of the number of protons collected by the cup. It is shown that the collection efficiency with a proper design can be close to unity. To be able to calibrate an ionization chamber from such a measurement, as is recommended in some dosimetry protocols, the energy spectrum of the proton beam must be accurately known. This is normally not the case when the lateral beam extension is defined by collimators. Therefore a method for relating an ionization chamber measurement in an uncollimated beam to the total number of protons in the beam has been developed and is described together with experimental results from calibrating an ionization chamber using this method in the therapeutic beam in Uppsala. This method is applicable to ionization chambers of any shape and the accuracy is estimated to be 1.6% (1 SD).

Biophysical Phenomena↗

PubMed1995

Dose calculations in proton beams: range straggling corrections and energy scaling.

Three-dimensional dose planning systems employing accurate proton transport algorithms are essential for calculating absorbed dose distributions in proton therapy. In this paper, a pencil beam algorithm for the transport of protons in materials of interest for radiation therapy is developed. The Fermi-Eyges multiple-scattering theory is used to derive transport equations for calculating proton fluence and absorbed dose distributions. The multiple-scattering theory of Molière is used to predict mean square scattering angles and to develop an expression for calculating the root mean square (RMS) radial spread of a proton pencil beam, as a function of depth, in an arbitrary scattering material. A correction factor is suggested to account for the decrease in the radial spread at the end of the range due to range straggling. The effects of neglecting large-angle scattering events and the possibility of incorporating such events into the pencil beam algorithm are discussed. An energy scaling technique for determining the water-equivalent surface energy at a given depth in a heterogeneous scattering medium is developed. The water-equivalent energy, giving the same Molière scattering parameter B in water, is determined and the 1/e angle in water is scaled to the appropriate width in the scattering material. By using stored analytically or Monte Carlo calculated pencil beam distributions in water, the large-angle single-scattering events may be incorporated by approximating the scattering in an arbitrary material by the scattering in water for protons of the appropriate water-equivalent surface energy.

Algorithms↗

PubMed1995

Ionization chamber dosimetry of proton beams using cylindrical and plane parallel chambers. Nw versus Nk ion chamber calibrations.

Determinations of the absorbed dose in a 170 MeV proton beam have been performed using seven ionization chambers of different types: five cylindrical (two FWT IC-18 and three NE-2571, of which one was modified to have the central electrode made of graphite) and two plane parallel (NACP-02 and Roos FK-6). The ionization was converted into absorbed dose in the proton beam according to the generalization of the formalism provided by the IAEA Code of Practice (TRS 277), which enables the use of the same equations for all kinds of beam used in radiotherapy. The absorbed dose obtained with the two IC-18 chambers, a chamber type commonly used as a reference in proton beams, was up to 1.5% lower than that obtained with the Farmer NE-2571 chamber, which was used as the reference in this work when calibration factors in terms of NK were used. To investigate this difference, experimental ND factors for six chambers (the two IC-18 chambers, the NACP-02, the FK-6 and two of the NE-2571 chambers) were determined in a high-energy electron beam. The procedure commonly recommended for plane parallel ion chambers was used for all the chambers, using the same reference chamber, a Farmer NE-2571. In the 170 MeV proton beam all the ND factors yielded consistent absorbed dose determinations within the estimated experimental uncertainties. This finding calls into question the value of the product kattkm for the IC-18 chamber given by the IAEA Code of Practice used in this comparison, and points at possible chamber to chamber variations that theoretical kattkm factors cannot predict. The investigations enabled the determination of the Pwall(60Co) factor of the Roos FK-6 plane parallel chamber, yielding 1.003 +/- 0.5%, and a correction for the effect of the aluminium central electrode of NE-2571 chambers in proton beams, equal to 1.003 +/- 0.4%. Two of the chambers (the plane parallel FK-6 and the modified cylindrical NE-2571) were provided with calibration factors in terms of absorbed dose to water, Nw, at the quality of 60Co by the Primary Standard Dosimetry Laboratory in Germany (PTB). Using the Nw formalism excellent agreement was found with the determination based on the experimental ND, giving support to the implementation of the NW procedure in therapeutic proton beams.

Humans↗

PubMed1994

Patient positioning for fractionated precision radiation treatment of targets in the head using fiducial markers.

When irradiating targets in the brain, an accurately localised dose is often needed. One crucial moment to achieve this is the positioning of the patient. We have developed a positioning method where the patient is immobilised with a bite block and a head mould, and where the position of the target is determined by X-ray imaging of fiducial markers that are placed in the patient's skull. A method for computing the transformation needed to move the target from the observed to the prescribed position and orientation is described. This method uses the information from two orthogonal X-ray images and takes measurement errors and data from three or more markers into account. Results from using the method clinically in proton beam therapy are given.

Algorithms↗

PubMed1993

Relative biological effectiveness of intermediate energy protons. Comparisons with 60Co gamma-radiation using two cell lines.

Range modulated proton beams are used for radiotherapy of malignant tumours at several accelerator laboratories with the aim of introducing proton therapy as a clinical hospital-based therapy modality. Due to the finite range and the sharpness of the dose gradients, the dose to well defined target volumes can be raised without excessive irradiation of non-target tissue. The prescribed proton doses are determined in part on the basis of the relative biological effectiveness (RBE) of the particular radiation quality. In this study, RBE values were determined for a proton beam with a maximal range of 33 mm, which corresponds to an energy of approximately 67 MeV. The range modulated depth-dose distribution, with a 20 mm extended Bragg peak, was mainly designed for high precision treatment of small targets such as uveal melanomas. The tested cell lines, LS-174T and V79-379A, were chosen because of their suitability for clonogenic assays. The cells were irradiated with single doses in the range 2-10 Gy at different depths in the extended peak region of the range modulated proton beam. RBE values were determined by comparing the doses needed to obtain the same reduction in colony formation (0.5, 0.1 and 0.01) as with the reference 60Co gamma source. The mean RBE value was 1.22 with a standard deviation of 0.08. The variations depended on both cell type and on the survival levels considered.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1993

Backscatter radiation at tissue-titanium interfaces. Biological effects from diagnostic 65 kVp x-rays.

The induced secondary electrons from a metal surface by diagnostic x-rays are thought to contribute to cell damage near the tissue-metal boundaries of metal implants. Titanium implants are becoming increasingly more popular for tissue reconstructions and it is rather often desirable to take radiographs of the operated area. In this study we compared the biological effects of radiation on cultured mammalian test cells grown on titanium plates with the radiation effects on cells that were grown on plastic control plates. In order to study the acute radiation effects on cell growth it was necessary to work with rather high radiation doses (0.7-5 Gy). Photon energies, suitable for diagnostic radiography in odontology, 65 kV, were applied. We found that the cells grown on titanium plates were, in terms of the applied dose in the surrounding culture medium, more sensitive to the irradiations than the cells growing on plastic plates. The survival curve for the cells on titanium had a steeper slope, showed no shoulder in the low-dose region and looked like curves normally obtained for high LET radiation. It was not possible to resolve to what degree the titanium-dependent changes were due to an increased dose near the titanium surface or to a change in the radiobiological effectiveness. Although there was a significant decrease in cellular survival near the metal, postoperative intraoral radiography after titanium implantations need not be excluded. The maximal doses given in odontological x-ray examinations are less than 1 mGy and, if the results in this study are applied, the biological effects near the titanium implant will correspond to biological effects in soft tissue of doses less than 20 mGy which is lower than the doses that give acute effects. The risk of acute healing disturbances are significant only at much higher radiation doses.

Animals↗

PubMed1991

Backscatter radiation at tissue-titanium interfaces. Analyses of biological effects from 60Co and protons.

It has been claimed that implanted metals can cause backscatter radiation in radiation therapy with a dose enhancement at the bone-metal and tissue-metal interfaces on the beam entrance side. Theoretical calculations and experimental measurements with ionization chambers have indicated that such effects might be significant. Titanium implants are increasingly used in oral and maxillo-facial surgery for reconstruction purposes. A more detailed knowledge of backscatter-induced effects is therefore desired when head and neck cancers in patients with implants are treated with radiotherapy. We have made comparisons of cell survival after irradiation of two types of cultured cells grown directly on titanium metal and on plastic control supports. The cell cultures were irradiated with either 60Co photons or range modulated protons. No significant differences in the colony-forming capacity were found between the irradiated cells grown on titanium and those grown on plastic control supports. This was the case for both radiation types and the results were also observed to be dose-independent. The only observed phenomena were that the two cell-lines differed in radiosensitivity and that protons gave higher biological effects than gamma radiation. The results show that there were no significant changes in cell survival at the interface between the tissue equivalent medium and titanium support indicating that a dose increase induced by backscatter radiation, which possibly could demolish the osseointegration or induce osteoradionecrosis, are minimal when high energy photons or range modulated protons are applied.

Animals↗