Towards Clinical Translation of Microbeam Radiation Therapy (MRT) with a Compact Source

PURPOSE/OBJECTIVE(S)

MRT is an innovative concept of spatially fractionated radiation therapy that has demonstrated substantially improved normal tissue tolerance while achieving local tumor control in a wealth of preclinical studies. In MRT a collimator shapes a few micrometers wide planar x-ray beams with a spacing of a few 100 µm. MRT has the potential to improve cancer treatment substantially. However, until now, only a few large 3rd generation synchrotrons provide beam parameters that would allow patient treatments and therefore, MRT has not yet become clinically available. For a clinical translation, compact x-ray sources are required, that produce high dose rate orthovoltage x-rays from a micrometer sized emitter.

MATERIALS/METHODS

We developed and built a first prototype of a line focus x-ray tube (LFxT) dedicated to preclinical MRT research. By exploiting the heat capacity limit, the LFxT can deliver dose rates above 100 Gy/s from a just 50 µm-wide focal spot without destroying the rapidly (>200 Hz) rotating x-ray target. A bespoke collimator splits the homogeneous x-ray field into 50 µm wide high-dose peaks separated by 350 µm wide low-dose troughs (valleys). While the prototype in our lab is restricted to a power of 90 kW and 10 Gy/s at 300 kVp, we have started the development of the first clinically usable LFxT-2 at 1.5 MW power and >100 Gy/s at 600 kVp beam quality. We investigated the clinical applicability of the LFxT-2 by performing retrospective treatment planning studies. In particular, we were examining, whether 600 kVp photons would suffice to meet clinical dose constraints in MRT treatments treatment scenarios for first clinical use of MRT. We coupled the open source platform 3D Slicer with an in-house developed dose calculation algorithm for MRT treatment planning. For comparability of spatially fractionated MRT doses with conventional broad beam treatments, the MRT dose was converted to equivalent uniform dose (EUD) and equivalent doses in 2-Gy-fractions (EQD2). The 3D Slicer RT toolkit enabled the dosimetric analysis based on dose volume histograms (DVHs).

RESULTS

We installed a preclinical prototype of the LFxT that is currently put into operation and commissioned. Simulations show the feasibility of the next generation LFxT-2 with more than 100 Gy/s peak dose rate. Planned MRT dose distributions with the LFxT-2 meet established radiotherapy dose constraints in many of the investigated clinical cases. However, treatment planning procedures are not yet optimal and require improvement.

CONCLUSION

In a next step, we will build the LFxT-2 and aim for first clinical MRT trials at this source. In order to further improve calculated MRT dose distributions, we will implement inverse treatment planning techniques.

Heat management of a compact x-ray source for microbeam radiotherapy and FLASH treatments

BACKGROUND

Microbeam and x-ray FLASH radiation therapy are innovative concepts that promise reduced normal tissue toxicity in radiation oncology without compromising tumor control. However, currently only large third-generation synchrotrons deliver acceptable x-ray beam qualities and there is a need for compact, hospital-based radiation sources to facilitate clinical translation of these novel treatment strategies.

PURPOSE

We are currently setting up the first prototype of a line-focus x-ray tube (LFxT), a promising technology that may deliver ultra-high dose rates (UHDR) of more than 100Gy/s from a table-top source. The operation of the source in the heat capacity limit allows very high dose rates with micrometer-sized focal spot widths. Here, we investigate concepts of effective heat management for the LFxT, a prerequisite for the performance of the source.

METHODS

For different focal spot widths, we investigated the temperature increase numerically with Monte Carlo simulations and finite element analysis (FEA). We benchmarked the temperature and thermal stresses at the focal spot against a commercial x-ray tube with similar power characteristics. We assessed thermal loads at the vacuum chamber housing caused by scattering electrons in Monte Carlo simulations and FEA. Further, we discuss active cooling strategies and present a design of the rotating target.

RESULTS

Conventional focal spot widths led to a temperature increase dominated by heat conduction, while very narrow focal spots led to a temperature increase dominated by the heat capacity of the target material. Due to operation in the heat capacity limit, the temperature increase at the focal spot was lower than for the investigated commercial x-ray tube. Hence, the thermal stress at the focal spot of the LFxT was considered uncritical. The target shaft and the vacuum chamber housing require active cooling to withstand the high heat loads.

CONCLUSIONS

The heat capacity limit allows very high power densities at the focal spot of the LFxT and thus facilitates very high dose rates. Numerical simulations demonstrated that the heat load imparted by scattering electrons requires active cooling. This article is protected by copyright. All rights reserved.

High-resolution and sensitivity bi-directional x-ray phase contrast imaging using 2D Talbot array illuminators

Two-dimensional (2D) Talbot array illuminators (TAIs) were designed, fabricated, and evaluated for high-resolution high-contrast x-ray phase imaging of soft tissue at 10-20 keV. The TAIs create intensity modulations with a high compression ratio on the micrometer scale at short propagation distances. Their performance was compared with various other wavefront markers in terms of period, visibility, flux efficiency, and flexibility to be adapted for limited beam coherence and detector resolution. Differential x-ray phase contrast and dark-field imaging were demonstrated with a one-dimensional, linear phase stepping approach yielding 2D phase sensitivity using unified modulated pattern analysis (UMPA) for phase retrieval. The method was employed for x-ray phase computed tomography reaching a resolution of 3 µm on an unstained murine artery. It opens new possibilities for three-dimensional, non-destructive, and quantitative imaging of soft matter such as virtual histology. The phase modulators can also be used for various other x-ray applications such as dynamic phase imaging, super-resolution structured illumination microscopy, or wavefront sensing.

X-ray dark-field radiography for in situ gout diagnosis by means of an ex vivo animal study

Gout is the most common form of inflammatory arthritis, caused by the deposition of monosodium urate (MSU) crystals in peripheral joints and tissue. Detection of MSU crystals is essential for definitive diagnosis, however the gold standard is an invasive process which is rarely utilized. In fact, most patients are diagnosed or even misdiagnosed based on manifested clinical signs, as indicated by the unchanged premature mortality among gout patients over the past decade, although effective treatment is now available. An alternative, non-invasive approach for the detection of MSU crystals is X-ray dark-field radiography. In our work, we demonstrate that dark-field X-ray radiography can detect naturally developed gout in animals with high diagnostic sensitivity and specificity based on the in situ measurement of MSU crystals. With the results of this study as a potential basis for further research, we believe that X-ray dark-field radiography has the potential to substantially improve gout diagnostics.

Single spectrum three-material decomposition with grating-based x-ray phase-contrast CT

Grating-based x-ray phase-contrast imaging provides three simultaneous image channels originating from a single image acquisition. While the phase signal provides direct access to the electron density in tomography, there is additional information on sub-resolutional structural information which is called dark-field signal in analogy to optical microscopy. The additional availability of the conventional attenuation image qualifies the method for implementation into existing diagnostic routines. The simultaneous access to the attenuation coefficient and the electron density allows for quantitative two-material discrimination as demonstrated lately for measurements at a quasi-monochromatic compact synchrotron source. Here, we investigate the transfer of the method to conventional polychromatic x-ray sources and the additional inclusion of the dark-field signal for three-material decomposition. We evaluate the future potential of grating-based x-ray phase-contrast CT for quantitative three-material discrimination for the specific case of early stroke diagnosis at conventional polychromatic x-ray sources. Compared to conventional CT, the method has the potential to discriminate coagulated blood directly from contrast agent extravasation within a single CT acquisition. Additionally, the dark-field information allows for the clear identification of hydroxyapatite clusters due to their micro-structure despite a similar attenuation as the applied contrast agent. This information on materials with sub-resolutional microstructures is considered to comprise advantages relevant for various pathologies.

A Haematocrit Corrected Micro Determination of the P&P-Test and Blood Clotting Factors in Capillary Blood

A new micro test for the determination of the P &P-test, and the factors II, V, and VII is described. The advantage of the new test is the possibility to discontinue the separation of the erythrocytes and the plasma. It only presumes the determination of the patient’s haematocrit, which is considered in the dilution of the blood sample. The results are not influenced by different haematocrits. They give excellent information on normal and pathologic coagulation activities, what is shown in three different groups of patients varying with respect to their age and partially receiving phenprocoumarol.

[Basic considerations for increasing flexibility of services in medical rehabilitation]

Medical rehabilitation measures continue to be delivered nearly exclusively on an inpatient basis. A graded treatment concept comparable to those in place for instance in the acute or long-term care fields, is non-existent, while the medical need for a community-based ambulatory rehabilitation system is uncontested. Not least before a background of ever scacer financial resources among the rehabilitation agencies involved, non-inpatient rehabilitation has been gaining significance as it is generally hoped to achieve greater economy of service delivery. As a logical consequence, the demand for greater flexibility in delivering medical rehabilitation services and benefits is a focus of attention in the current rehabilitation policy debate. Greater flexibility in medical rehabilitation delivery means replacing portions of rehabilitation measures currently provided on an inpatient basis by partial-hospitalization or ambulatory service delivery; or continuing and complementing inpatient rehabilitation measures by non-inpatient ones; or using non-inpatient measures to provide aftercare post-discharge from inpatient rehabilitation. Moreover, ambulatory rehabilitation is intended to reach the population unamenable to attending far-away inpatient programmes. It is of utmost significance for the future evolution of ambulatory rehabilitation that the various financially responsible agencies involved in rehabilitation take a joint position on the subject of non-inpatient rehabilitation. Several proposals are submitted in this respect; for indications in the fields of neurology, orthopedics, cardiology, and geriatrics, catalogues of degrees of severity considered suitable for ambulatory rehabilitation are first presented.

Efficiency of heparin in the treatment of newborn infants with respiratory distress syndrome and disseminated intravascular coagulation

Forty newborns with severe shock and disseminated intravascular coagulation were randomized for treatment with heparin or placebo. Mortality was equal in both groups. The heparin group required significantly shorter periods of artificial ventilation. The coagulation system improved faster, and the coagulation pattern showed normal values in the treatment group. Due to the low number of cases, these differences could not be statistically confirmed.

[Supplementary intravenous nutrition in term and preterm neonates (author's transl)]

16 term and preterm neonates received intravenous nutriton for at least three days. The dosage was 1--2 g amino acids, 1 g of fat, and 8--10 g glucose per kg body weight and day. Compatibility was investigated by daily determinations of the amino acid pattern in the serum and measurement of free fatty acids and triglycerides. All results were compared to five neonates who were fed completely orally from the first day of life. Leucine, methionine, proline, and valine levels were elevated during intravenous nutrition, but only the high methionine levels were regarded as a nutrional imbalance. Free fatty acids and triglycerides showed no significant differences as compared to the control group.

Etiopathology and classification of acquired coagulation disorders in the newborn infant

In the newborn period low vitamin K dependent coagulation factors are frequently found in connection with normal global tests. To investigate this peculiar coagulation status studies were performed in 54 newborns who were divided into three groups according to their clinical course and the existence of bleeding. The results are compared to coagulation tests used for the diagnosis of disseminated intravascular coagulation (DIC). An early sign of an increased turnover of coagulation factors is a difference in the fibrinogen concentration determined by an immunological technique and a coagulation test which is sensible to fibrin(ogen)-degradation-products (FDP'S). At this stage factor II, V and VII levels are still within the normal range suggesting an increased production. In a more severe disturbance of the clotting system the increased turnover is no longer compensated by an increased production, and platelets and later on factor II and VII levels are lowered. At this early stage of DIC the vitamin K dependent factors are correlated to the factors I and V. Finally factors I and V drop as well. This stage in most infants is accompanied by the clinical symptom of bleeding. The clotting tests results are well correlated to the severity of the disease.

Pharmacokinetic investigations in adult humans after parenteral administration of the lysine salt of acetyl-salicylic acid

The lysine salt of acetylsalicylic acid was administered intravenously to four volunteers and intramuscularly to three of them. The drug was tolerated without any observed side effects. Immediately after intravenous application most of the plasma salicylate was acetylsalicylic acid. The highest concentration of acetylsalicylic acid was found after 2 minutes, highest levels of salicylic acid after 60 minutes. Elimination of acetylsalicylic acid was relatively quick within the first period after intravenous administration according to a half-life of 8 minutes. Half-life of salicylic acid was determined to be 3 hours. Intramuscular application results in a constant blood level for a longer period. Bioavailability of acetylsalicylic acid was slightly lower after intramuscular application than after intravenous administration.

alpha1-Antitrypsin and alpha2-macroglobulin in newborn infants. I. The influence of perinatal complications

The levels of alpha1-antitrypsin and alpha2-macroglobulin in the plasma of 129 newborns were determined. The infants were divided into 3 groups according to their perinatal history. In healthy newborns with an uneventful perinatal history the normal values for alpha1-antitrypsin were 1.97 +/- 0.44 g/l, and for alpha2-macroglobulin 3.11 +/- 0.69 g/l. No changes in these levels were found during the first week of life. The levels of alpha1-antitrypsin and alpha2-macroglobulin showed significant correlation to each other. In healthy newborns with different complications in the obstetric history the levels of alpha1-antitrypsin were not influenced, whereas alpha2-macroglobulin decreased slightly during the first week of life. The levels of alpha1-antitrypsin and of alpha2-macroglobulin showed no further correlation to each other. In sick term and preterm newborns (n = 18) alpha1-antitrypsin was increased in 5 of 7 babies suffering from bacterial infections and lowered in 4 of 9 cases with respiratory disturbances. Alpha2-macroglobulin was lowered in 15 babies. These results indicate different kinetics of the two antiproteases in vivo.

[The etiology of transitory hyperbilirubinemia in newborn infants]

Recent investigations have shown that haemolysis plays a major role in the etiology of transitory hyperbilirubinaemia of the newborn. Our studies indicate that unconjugated bilirubin itself is in part the causative agent for this haemolysis. In vitro bilirubin causes damage of red cells which finally results in haemolysis. Newborns suffering from transitory hyperbilirubinaemia have a red cell population which is especially sensitive to the haemolytic effects of bilirubin. The initial bilirubin increase after birth is caused by relative dysfunction of the liver, causing further haemolysis of bilirubin sensitive red cells. Hyperbilirubinaemia decreases when all sensible red cells are destroyed and liver function improves.

[Problems of conductor demonstration in haemophilia A: error possibilities in the determination of factor-VIII-associated antigen]

Difficulties in the detection of haemophilia A carriers by the determination of the ratio factor VII coagulation activity to factor VII antigen concentration are shown in part one of our investigations. The second part evaluates methodical parameters of the quantitative immunoelectrophoretic technique. According to our results reliable data can only be obtained under the following conditions: 1. At least three determinations of each sample are required and the mean value should be used as the final result. 2. Each gel plate should be calibrated separately 3. The calibration line should include values less than 100%. Factor VIII concentrates are not suitable for determination of the calibration curve, as higer dilution results in lower calculated concentration of the undiluted concentrate. Storage of pooled normal plasma at--25 degrees C is possible without significant loss of antigen concentration over 5 months. However, plasma samples of a single person show an unpredictable variation in the antigen concentration during storage over the same time.

Effects of bilirubin on red cell metabolism

Blirubin causes certain defects in erythrocyte metabolism, mainly in glycolysis. These effects of bilirubin were studied in vitro using a relatively physiological assay medium, which consisted of heparinized whole blood. Bilirubin was added in a small quantity of NaOH solution. In the presence of bilirubin a reduced glucose consumption of red cells and an accelerated depletion in the ATP and glycerate-2,3-bisphosphate concentration was found. Bilirubin levels lower than 50 mumol/l did not influence the glucose consumption. In agreement to other investigations it was established that bilirubin causes haemolysis of red cells. ATP-deficient cells are more sensitive to this effect.

[Retention of platelets in newborns (author's transl)]

In healthy, 24-72 hour-old newborns, platelet retention is significantly elevated compared to adults. A relationship could not be established between the retention and the erythrocyte count, bilirubin in the serum or the content of energy-rich phosphates in the erythrocytes. The above results indicate that the platelet function in newborns is elevated and/or comparable with the adult norm. The basic cause of the frequent symptoms of hemorrhage during the newborn period cannot be traced back to disturbed thrombocyte function.

[Heroin withdrawal syndrome in newborns (author's transl]

A case of a severe heroin withdrawal syndrom in a newborn infant is reported. Diagnostic and therapeutic aspects of the disease are reviewed.

[Standardization of ADP-induced thrombocyte aggregation]

It is the purpose of this study to standardize platelet aggregation according to the method of Born. It was found that aggregation is influenced by the time of storage, the pH and temperature of plasma. However, there is no significant correlation between platelet number versus aggregation in healthy subjects. To get reproducible results, the plasma samples should be investigated within 2 hours after venipuncture. During storage temperature of all samples should be constant.

Letter: Sodium valproate and platelet function

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Vitamin E concentrations in term and preterm newborns and their clinical course

Vitamin E deficiency in premature infants has been described as being associated with low hemoglobin levels in the 2nd month of life. Recently, low vitamin E concentrations were suspected as being associated with sudden death in infancy. As vitamin E is absorbed incompletely from the premature's intestine, vitamin E levels in the serum were determined in 80 prematures on the 10th day of life. The result was correlated to the clinical course of the infants and to the hemoglobin levels up to the 30th day. Low concentrations of vitamin E and lower hemoglobin levels were found more frequently in new borns, whose clinical course was characterized by additional complications and who received parenteral nutrition. A group of uncomplicated newborns showed no correlation of vitamin E to hemoglobin values. Thus early diagnosis of vitamin E-dependent anemia is not possible and the usefulness of vitamin E should be investigated only in newborns with an uneventful clinical course.

[A comparison of different methods of measuring bleeding time (author's transl)]

Two methods of determining bleeding time (Ivy's and Duke's) were compared using a standardized method. Skin cuts were made with either a disposable scalpel or a precision plunger. Ivy's method gave results which were markedly superior to those with Duke's. It was, furthermore, shown that reproducibility of two successive determinations in the same person largely depended on the experience of the investigator. Best results were obtained using the precision plunger and automatic collection of blood. But even when these were used, there were frequent deviations of more than 20% in duplicate samples.

[Rhesus incompatibility and anti-D prevention in the Düsseldorf region (a ten-year survey) (author's transl)]

Among 116 120 children born between 1964 and 1973, 512 (0.44%) required treatment for haemolytic disease of the newborn caused by the presence of irregular antibodies. While the incidence between 1964 to 1970 ranged between 0.42 to 0.56%, it fell from 1971 to 1973 to 0.28%, evidence for effective anti-D prophylaxis since 1971. Those cases still occurring after 1971 were largely due to pregnancies which had started before 1971. In addition there were abortions, sensitizations during the first pregnancy, but also blood transfusions as cause for new sensitizations. Sensitization after pregnancy despite anti-D prophylaxis was observed twice. In the last few years there has been a relative increase of rare antibodies, increasing the complexities of serological diagnosis. Safety and speed of treatment can be further improved by more frequent identification of irregular antibodies in the mother and regular reports to the paediatrician.

[Enterobacter-osteomyelitis in two neonates (author's transl)]

Two boys aged up to 2 weeks suffered from enterobacter-sepsis. In both cases osteomyelitis developed in spite of treatment with Gentamycin or Gentamycin combined with Chepazolin. Both children were, taking accont of the risks, then treated with Chloramphenicol (100 mg/kg body weight/24 hours) and the first patient also, for a short time, with tetracyclin. In the second patient we saw a marrow depression dependent on Chloramphenicol and its dosage which disappeared rapidly, when the drug was withheld.

[Influence of ribose on 2,3-diphosphoglycerate concentrations in human erythrocytes]

The effect of ribose on the 2,3-diphosphoglycerate concentration (2,3-DPG) of human red blood cells was investigated and compared to the effect of inosine. Ribose as well as inosine increases 2,3-DPG. Most impressing effects can be demonstrated on stored blood, which is poor in 2,3-DPG concentration. Physiologic 2,3-DPG-concentrations, however, may be increased too. Generally the effect of inosine is greater than the effect of ribose. When ribose is applicated intravenously a slight increase in 2,3-DPG is found. Both compounds own characteristic side-effects, which diminish their value for therapeutical purposes.

Position of the oxygen dissociation curve in newborns with transitory hyperbilirubinaemia

In newborns, suffering from transitory hyperbilirubinaemia, oxygen partial pressure of blood was measured at 50% oxygen saturation (p50). The p50 shows a decline with rising serum bilirubin on the 98-percent confidence level. The statistic values were 20.7 mm Hg at 0 and 19.6 mm Hg at 10 mg bilirubin/100 ml serum. The consequences for the icteric child are discussed.