A joint physics and radiobiology DREAM team vision - Towards better response prediction models to advance radiotherapy

Radiotherapy developed empirically through experience balancing tumour control and normal tissue toxicities. Early simple mathematical models formalized this practical knowledge and enabled effective cancer treatment to date. Remarkable advances in technology, computing, and experimental biology now create opportunities to incorporate this knowledge into enhanced computational models. The ESTRO DREAM (Dose Response, Experiment, Analysis, Modelling) workshop brought together experts across disciplines to pursue the vision of personalized radiotherapy for optimal outcomes through advanced modelling. The ultimate vision is leveraging quantitative models dynamically during therapy to ultimately achieve truly adaptive and biologically guided radiotherapy at the population as well as individual patient-based levels. This requires the generation of models that inform response-based adaptations, individually optimized delivery and enable biological monitoring to provide decision support to clinicians. The goal is expanding to models that can drive the realization of personalized therapy for optimal outcomes. This position paper provides their propositions that describe how innovations in biology, physics, mathematics, and data science including AI could inform models and improve predictions. It consolidates the DREAM team's consensus on scientific priorities and organizational requirements. Scientifically, it stresses the need for rigorous, multifaceted model development, comprehensive validation and clinical applicability and significance. Organizationally, it reinforces the prerequisites of interdisciplinary research and collaboration between physicians, medical physicists, radiobiologists, and computational scientists throughout model development. Solely by a shared understanding of clinical needs, biological mechanisms, and computational methods, more informed models can be created. Future research environment and support must facilitate this integrative method of operation across multiple disciplines.

Single photon detection and signal analysis for high sensitivity dosimetry based on optically stimulated luminescence with beryllium oxide

Single photon detection applied to optically stimulated luminescence (OSL) dosimetry is a promising approach due to the low level of luminescence light and the known statistical behavior of single photon events. Time resolved detection allows to apply a variety of different and independent data analysis methods. Furthermore, using amplitude modulated stimulation impresses time- and frequency information into the OSL light and therefore allows for additional means of analysis. Considering the impressed frequency information, data analysis by using Fourier transform algorithms or other digital filters can be used for separating the OSL signal from unwanted light or events generated by other phenomena. This potentially lowers the detection limits of low dose measurements and might improve the reproducibility and stability of obtained data. In this work, an OSL system based on a single photon detector, a fast and accurate stimulation unit and an FPGA is presented. Different analysis algorithms which are applied to the single photon data are discussed.

Verteilung und Wanderung von Phosphoglycerat zwischen den Chloroplasten und dem Cytoplasma während der Photosynthese

The distribution of phosphoglyceric acid (PGA) * between chloroplasts and cytoplasm of leaf cells during transients from dark to light and vice versa has been investigated. The data indicate that pools of PGA in the chloroplasts and cytoplasm are interchangeable and that PGA may function as a transport metabolite in actively metabolising leaf cells. These views are supported by the following results:

1. In the presence of 14CO2 and light, labelled PGA rapidly appears in the cytoplasm, even though the carboxydismutase reaction, in which 14C enters into PGA, proceeds in the chloroplasts.

2. After less than 1 min. illumination in the presence of 14CO2, the distribution of labelled PGA between chloroplasts and cytoplasm reaches an equilibrium, which is then maintained. The same distribution is to be found by enzymatic analyses of the total pools of PGA in chloroplasts and cytoplasm. When equilibrium is reached, the percentages of both 14C labelled and of total PGA to be found in the chloroplasts of Spinach and Elodea are approximately 75% and 35 —40% respectively.

3. In both the chloroplasts and the cytoplasm, the levels of PGA first decrease after illumination to a fraction of the original dark levels and then show a concomitant slow increase. On darkening a further very rapid increase in PGA occurs in chloroplasts and cytoplasm.

4. In photosynthetically active leaf material the rate of decrease in the level of cytoplasmic PGA, as observed after 12 —15 secs. illumination, is higher than the turnover rate of PGA in respiration.

5. Upon illumination, aqueously isolated chloroplasts, suspended in isotonic sucrose buffer, reduce added PGA to dihydroxyacetone phosphate and other products far faster than they reduce added NADP. Whereas PGA reduction is not increased by ultrasonic disintegration of the chloroplasts, the reduction of NADP is stimulated. This indicates that whereas the movement of NADP is prevented by a permeability barrier, the transferance of PGA across the chloroplast membrane occurs easily.

6. In illuminated Elodea shoots the inhibition of metabolism by cyanide after 15 secs. photosynthesis in the presence of Η14CO3 ⊖ leads to a rapid decrease in PGA. This applies to both the 14C labelled PGA and the total PGA to a similar extent. The decrease in PGA amounts from 70 — 85% of the original dark levels. Since the chloroplasts of Elodea contain only 35—40% of the total PGA of the cell, a fall in the level of PGA as a result of the cyanide poisoning obviously occurs not only in the chloroplasts, but also in the cytoplasm. Since cyanide effectively inhibits cytochrome oxidase, while PGA reduction in the chloroplasts is relatively resistant, the large decrease in PGA suggests that part of the cytoplasmic PGA is transferred into the chloroplasts and reduced there.

Die Verteilung des Orthophosphates auf Plastiden, Cytoplasma und Vacuole in der Blattzelle und ihre Veränderung im Licht-Dunkel-Wedisel

The distribution of orthophosphate between chloroplasts and the nonchloroplast parts of leaf cells has been investigated. Upon illumination, the percentage of the total orthophosphate located in the chloroplasts decreases rapidly, while darkening results in a slow increase of that percentage to the original dark value. If, in the dark, comparable concentrations of orthophosphate in the chloroplasts and in the cytoplasm are assumed, the concentration of orthophosphate in the vacuole can be calculated from the available data. Values are then obtained, which are considerably lower than the corresponding values in the protoplasm; this indicates that a concentration gradient for orthophosphate is maintained between the cytoplasm and the vacuole.

Leaves of spinach and Elodea, which were fed 32P for 2 to 4 hours and then left to stand for two or three days, showed higher specific activities of orthophosphate in the chloroplasts than in the nonchloroplast parts of the cells. Since there is reasn to assume a fairly rapid exchange of orthophosphate between chloroplasts and cytoplasm, the differences in the specific activities which were observed several days after feeding with 32P, point to a very slow exchange of orthophosphate across the tonoplast membrane.

Transportable frontal chromatographic unit for decontamination purposes based on the twin column concept

The design and operation of a separation unit based on frontal chromatography is described. The important feature of the design is the array column --> detector --> column which allows process monitoring below the detection limits of the monitor. By using "fraternal twin columns" an in-process calibration of the detector is achieved reducing the waste production. The design contains provisions for on-line destructive and non-destructive monitoring. Tests of the unit prove its versatility with respect to decontamination processes. Due to its compactness, the unit is transportable, if not portable, and the module construction allows easy posting and set-up in areas with restricted access. The unit is capable of processing up to 5 m3 solution per year depending on the chemical system used.

Twin column chromatography for industrial-scale decontamination processes

A frontal chromatographic unit was devised consisting of a column-detector-column array. The unit is either equipped with identical columns (identical twins) or with columns of varying length (fraternal twins). Due to the finite nature of the columns, a prerun is formed at the column walls following the same regularities as the main stream. These regularities are used for the identification of the process termination below the detection limits of the monitor. For the implementation, a clear preference is given to the employment of fraternal twins, as the feed assay can be integrated into the separation process.

On-line monitoring of a frontal chromatographic separation using inductively coupled plasma atomic emission spectroscopy

A test array is described employing a destructive analytical technique for the long-term monitoring of an industrial-scale separation process. As an example, we chose frontal chromatography as the separation and ICP/AES as the analytical method. The feed solution of the process was conveyed by a process pump via the separation unit to a sample station, where a small portion was diverted and transported by a roller pump into the spectrometer. We equipped our array with different loops for operating the process, calibrating the instrument and verifying the calibration. We obtained identical results for the different loops by absorbing the pulsation of the process pump and arranging for identical suction lines of the spectrometer pump. Based on the results, we redesigned the sample station for a technical application using only commercially available parts.

Long-term stabilization in patients with malignant glioma after treatment with liposomal doxorubicin

BACKGROUND

Resistance to chemotherapeutic agents and poor blood-brain barrier penetration are major limitations in the treatment of malignant glioma. To improve drug delivery across the blood-brain barrier, the authors used doxorubicin as liposomal encapsulated formulation (Caelyx, Scheringh-Plough, Munich, Germany) in therapy of recurrent malignant glioma.

METHODS

Fifteen patients with recurrent high-grade gliomas were included in the study. Of these, 13 patients could be evaluated, including 6 patients with glioblastoma, 1 patient with gliosarcoma and 6 patients with anaplastic astrocytoma. The treatment consisted of liposomal doxorubicin (20 mg/m(2)), applied intravenously every 2 weeks.

RESULTS

Stabilization of the disease was observed in 54% (7 of 13) of patients. Partial response and complete response (CR) were not observed. Median time-to-progression was 11 weeks. Progression free survival at 12 months was 15%. Median overall survival (OS) after doxorubicin therapy was 40.0 weeks, whereas the median OS after diagnosis reached 20.0 months (87.0 weeks). Doxorubicin was well tolerated, with main side effects being palmoplantar erythrodysesthesia occurring in 38% and myelotoxicity (World Health Organization Grade 3-4) in 31% of the patients.

CONCLUSIONS

Doxorubicin has been shown to be a safe treatment with moderate activity that may lead to long-term stabilization in recurrent high-grade glioma patients. Of note, median OS after all and after initiation of recurrence therapy was prolonged in comparison with the OS in other Phase II studies, as recently described by Wong et al. (Wong ET, Hess KR, Gleason MJ, Jaeckle KA, Kyritsis AP, Prados MD, et al. Outcomes and prognostic factors in recurrent glioma patients enrolled onto phase II clinical trials. J Clin Oncol 1999;17:2572.).

[Osteochondroplastic tracheobronchopathy]

The words tracheobronchopathia osteochondroplastica (TO) were coined by Aschoff in 1910, defining a rare disease of the tracheobronchial system which most often is only "accidentally" discovered in the course of examinations, a bronchoscopy or computerized tomography, which are undertaken for other reasons. A characteristic sign for this disease are multiple cobblestone-like protrusions in the trachea and bronchus which are caused by calcifications, chondrifications and ossifications of the upper layer of the mucous membrane. We report on a 81-year old patient who was diagnosed with the disease while undergoing a fiberoptic bronchoscopy during a prolonged weaning phase. In the beginning we discussed the possibility of a neoplasia or a chronic inflammatory process as differential diagnosis and based on that we considered a dilatative tracheotomy for the weaning period. After histological confirmation of a TO we refrained from the measure, the reason being that in our opinion the patient would not profit from it. To reach a correct diagnosis a good interdisciplinarian cooperation is essential. The patient was successfully extubated on the 11th post-operative day after a patient conventional weaning which was supported by accompanying symptomatic measures. Apart from the case report we present a summary of the literature on TO concerning epidemiology, pathology, diagnosis and therapeutical measures.

[Positioning trauma in anesthesia and surgical intensive care medicine (2)]

Specific modes of positioning are essential for successful surgery. These are again critically assessed in this final part of our review. Technically correct execution can minimize the risk of damage caused by positioning, although the possibility of damage still exists. First of all, the position on the fracture table is discussed. Great care must be taken concerning the perineal post and leg holder. In the lateral decubitus position, the correct positioning of head and spine as well as that of the lower arm are of great importance. When using the Trendelenburg and reverse Trendelenburg position, the effect on the cardiopulmonary system and the intracranial pressure must to be taken into consideration. Prone position and its modifications (i.e. tuck position) demand diligent care concerning the positioning of the head. There must be absolutely no bulbus compression and the abdominal wall should not be under pressure. While employing the sitting position, the patient should be adequately monitored so that venous air embolism can be recognized and treated as soon as possible. Because of the increased occurrence of grave complications, the sitting position should be used only if this is absolutely necessary.

[Damage due to patient positioning in anesthesia and surgical medicine (1)]

Positioning a patient for surgery requires great care and caution. Correct positioning provides the surgeon with good access to the site, minimizes blood loss and reduces the risk of damage to nerves, soft tissue, compartments and the cardio-pulmonary system. Each position has its specific risks. These have to be evalued against the benefits. Extreme positions of the joints should be avoided whenever possible. The ulnar nerve or the plexus brachialis are at highest risk in the positioning of extremities. Good anatomical comprehension makes it possible to take effective counter-measures. In the case of damage to the ulnar nerve in spite of optimal positioning, some authors found pre-existent non-symptomatic dysfunction in up to 30% of the cases. Patients suffering from peripheral vascular disease are usually at higher risk to suffer acute ischaemia, or, in the extreme, rhabdomyolysis with compartment syndrome, when positioned with elevated extremities (as in lithotomy position) or when a tourniquet is applied. Next to other factors, the duration of surgery seems to be of some importance. Operation sites above the heart carry a higher risk of venous air embolism unrelated to the positioning. In these cases adequate monitoring should be generously applied. Loss of visus is a rare but very severe complication most often seen in connection with the prone position. Still, postoperative blindness has occurred in all positions. It is absolutely imperative to avoid all pressure to the bulbus. The same law applies to surgery and positioning: indicated and correctly executed positioning, to which the patient has effectively consented, is legal, even if damage should occur. If the plaintiff demands compensation for damage, the distribution of onus of proof depends essentially on the accuracy of documentation. If documentation is faulty, the plaintiff may be granted relief or even shift of the onus of proof. This does not apply to a criminal lawsuit; in that case, culpable medical fallibility must be proven, since otherwise, the principle of "in dubio pro reo" applies. The interdisciplinary responsibilities concerning the positioning must be clearly defined and it is essential that the documentation of positioning as well as the documentation of positioning control is carried out as accurately as possible. Correct positioning can effectively aid surgery. Slovenly positioning should not be accepted, as there is a high probability of ill effects, possibly of permanent damage.

Persistence of complexed acidic phospholipids in rapidly mineralizing tissues is due to affinity for mineral and resistance to hydrolytic attack: in vitro data

Acidic phospholipids, complexed with calcium and inorganic phosphate, are components of extracellular matrix vesicles. Both the complexed acidic phospholipids and matrix vesicles have previously been shown to serve as hydroxyapatite (HA) nucleators in solution and when implanted in a muscle pouch. The present study supplies evidence that complexed acidic phospholipids can persist in mineralizing tissues both because of their affinity for HA and because of their resistance to hydrolysis by phospholipase A2. Calcium-phosphatidylserine-phosphate complex (CPLX-PS) synthesized with 14C-labeled phosphatidylserine (PS) was used to measure CPLX-PS affinity for HA using a Langmuir adsorption isotherm model. The affinity was shown to be higher and more specific than that of PS itself (K = 8.66 ml/mumol; N, the number of binding sites = 20.4 mumol/m2 as compared with previously reported values for PS of K = 3.33 ml/mumol, and N = 4.87 mumol/m2). Incorporated into synthetic liposomes and incubated in a calcium phosphate solution in which mineralization is induced by an ionophore, CPLX-PS showed behavior distinct from free PS. As previously reported, PS in these liposomes totally blocked HA formation. On the other hand, CPLX-PS in similar concentrations had a varied response, having no effect, slightly inhibiting, or actually promoting HA formation. CPLX-PS was also shown to be a poorer substrate for phospholipase A2 than PS, with Km = 4.63 mM for CPLX-PS and Km = 0.27 mM for PS; and Vmax = 0.029 ml/minute for CPLX-PS and Vmax = 0.066 ml/minute for PS. These data explain how complexed acidic phospholipids may persist in the growth plate and facilitate initial mineral deposition.

[Total hip endoprostheses--characteristic aspects from the anesthesiologic viewpoint]

Total hip replacement is a frequently practised operation. Depending on age, circumstances and individual assessment, cemented, non-cemented and hybrid forms are used. Apart from general risks, such as vascular and/or neural injuries, thrombosis and infections, there are specific risks, depending on the surgical technique. If cemented systems are used, the anesthesiologist must be on the alert in respect of a possible multi-causal cardiopulmonary depression during the implantation of the prosthesis. Incidents may be reduced or moderated by measures such as reduction of pressure from the femoral cavity or anesthetic measures such as avoidance of N2O during or after cementation, use of anti-histamines, etc., but there is no absolute protection from severe reactions by the cardiopulmonary system. In these cases it is imperative to recognise and treat hypoxic conditions immediately, whatever the cause, such as cardiac or pulmonary depression. If a non-cemented hip replacement is used or a revision is necessary the main problem is usually a higher blood loss. Especially in such cases it is necessary to apply a well-organised sequence of blood-saving methods to protect patients from the general risks of homologous blood transfusion. Even though the main concern of the public is the possibility of contamination of donor blood with the AIDS virus, transmission of hepatitis C virus is a much more common problem. Depending on the diagnostic methods the occurrence of thrombosis after total hip replacement has been reported to be as much as 55%. To minimise this high incidence, sufficient prophylaxis, adequate fluid therapy, suitable anesthetic techniques and cutting down on the duration of the operation should be taken into account. The use of low molecular weight heparins has certain advantages. If deep vein thrombosis has occurred, therapy consists of anticoagulation with intravenous heparin and immobilisation. A rare but severe complication is a deep hip prosthetic infection. More than 50% of infections are caused by coagulase-negative staphylococci and anaerobic bacteria. To avoid sepsis it is imperative to employ adequate high-dosage antibiotics, revisional surgery and, if necessary, even excision arthroplasty. There is no "ideal" anesthesiological method for total hip replacement. Regional techniques as well as general anesthesia have their specific pros and cons which are controversially discussed in respect of their priority. To achieve early diagnosis of embolism, especially in the case of high risk patients, the exigency of extensive haemodynamic monitoring as well as Doppler-ultrasound is discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

Osteopontin-hydroxyapatite interactions in vitro: inhibition of hydroxyapatite formation and growth in a gelatin-gel

Osteopontin is a phosphorylated bone matrix sialoprotein, postulated to play a regulatory role in biomineralization. The effects of a crude preparation of rat bone osteopontin and a more highly purified bovine bone osteopontin were evaluated using a gel diffusion system to measure effects of 0.1-100 micrograms/ml of this matrix protein on hydroxyapatite formation and crystal proliferation. Bovine osteopontin at concentrations greater than 25 micrograms/ml inhibited both hydroxyapatite formation and growth in a dose-dependent manner. Osteopontin at concentrations lower than 25 micrograms/ml had no detectable effect on the amount of mineral accumulated in experiments with and without pre-formed hydroxyapatite seed crystals either when initial mineral deposition was assessed at 3.5 days, or when mineral formation and growth were assessed at 5 days. There was a statistically significant dose-dependent decrease in crystal length at all concentrations tested. The rat osteopontin preparation had similar inhibitory abilities. Partial dephosphorylation of bovine osteopontin with alkaline phosphatase removed its inhibitory ability, and reduced its ability to bind calcium. The affinity of bovine osteopontin for hydroxyapatite was determined based on a Langmuir adsorption isotherm, with values of K (binding affinity) and N (number of binding sites) being 0.026 ml/microgram and 1084 micrograms/m2, respectively. The data suggest that, in this system, osteopontin is an effective inhibitor of hydroxyapatite formation and growth due to its affinity for the hydroxyapatite crystals. In this system, osteopontin, distinct from other phosphoproteins which both promote and inhibit hydroxyapatite deposition, did not enhance mineral formation at any concentration tested.

Extracorporeal shock wave lithotripsy in symptomatic cholesterol gallbladder stone patients with a second generation electrohydraulic lithotripter (MPL-9000): experiences with 106 patients over 15 months

One hundred and six patients were treated with a second generation underwater spark discharge lithotripter (Dornier MPL-9000). During the 15-month study period, Kaplan-Meier analysis predicted a stone clearance rate of 16.5% after 4 months, 37% (7 months), 71% (10 months), and 81% (15 months), respectively. Patients with multiple stones had a 5% probability to be free of stones after 13 months of treatment, when compared to 100% in patients with solitary stones smaller than 2 cm (p less than 0.001). Stones with densities below 100 Hounsfield units (HU) on computed tomography disappeared in 75% of the cases within 13 months. Rim calcified stones were cleared in 100% after 10 months of treatment. Fragmentation efficacy proved to be an essential predictive parameter for stone clearance: a fragment size below 5 mm after extracorporeal shock wave lithotripsy resulted in a 100% stone clearance within 13 months regardless of the initial stone number, size, and density. None of the stones fragmented to pieces of more than 10 mm in diameter could be dissolved within the observation period. Obviously, modern generation electrohydraulic lithotripters are effective in stone fragmentation, thus providing the basis for successful bile acid therapy provided the patients are properly selected.

Cerebral blood flow and cerebrovascular reserve 5 years after EC-IC bypass

CBF-studies using the Xenon-133-inhalation technique were performed in 18 patients with a unilateral carotid artery occlusion, 5.4 years after a STA-MCA procedure. For comparison we used the CBF data of 29 patients with the same diseases who had had conservative treatment for a variable period of time. CBF was measured during rest and after the intravenous administration of 1 g acetazolamide. During rest we found a significant interhemispheric difference in both groups. After activation with acetazolamide this difference disappeared in the bypass group, but not in the conservatively treated patients. Our data show that the bypass procedure obviously affects the vascular reserve capacity in a positive way over a long period of time. One criteria for success of STA-MCA procedures might be the cerebral reserve capacity tested with CBF-studies under activation.

Photoorientation, motility and pigmentation in a freshwater peridinium affected by ultraviolet radiation

The effects of ultraviolet radiation on orientation, motility and pigmentation were measured in the freshwater dinoflagellate, Peridinium gatunense. Histograms of the positive phototactically oriented cells showed a decrease in the degree of orientation even after short exposure times. Quantification of the orientation revealed a significant inhibition after 2 h exposure. Similarly, the percentages of motile cells and the mean linear velocity of the cells was strongly affected. UV radiation also caused a massive bleaching of the cellular pigments as shown by absorption spectra determined after increasing exposure times. The ecological consequences of these effects are discussed.

[Procurement of organ donors--initial results of the Berlin-Potsdam-Frankfurt model]

The shortage of donor kidneys is the main cause of the even insufficient supply of patients suffering from end stage renal disease. In 1987 a transplant coordinator to the districts Berlin, Frankfurt and Potsdam with 3.1 Mio inhabitants was introduced. The functions of the coordinator and the approach to organ procurement are described in detail. In comparison with 1986 the number of explanted kidneys could doubled in 1988 (68 vs 143). The number of 46.3 explanted kidneys per million inhabitants is comparable with other areas or countries with excellent organ procurement system.

Effects of solar radiation on photoorientation, motility and pigmentation in a freshwater Peridinium

Solar radiation has a pronounced effect on photoorientation, motility and pigmentation in the freshwater dinoflagellate, Peridinium gatunense. Photoorientation (positive phototaxis) is impaired even after short exposure times and is totally inhibited after about 2.5 h. The percentage of motile cells decreases after short exposure times and after 4 h most cells are immotile. Likewise, the mean velocity decreases after an initial light-induced increase (photokinesis) under solar radiation. Solar UV-B (280-320 nm) radiation seems to be the major cause for the effects, since cutting off shorter wavelength by an ozone cuvette or WG filters prolongs the tolerated exposure times. Possible UV-B targets are the photoreceptor pigments since solar radiation causes a massive bleaching of the cells within a few hours.

Hemispheric CBF-alterations in the time course of focal and diffuse brain injury

Hemispheric CBF-alterations were studied in the time course of focal and diffuse-brain injury in a series of 25 head injured patients. Repeated 133 Xe CBF measurements with a mobile 10 detector system were performed in order to evaluate hemispheric CBF and cerebral vasoreactivity after change of PaCO2. Focal brain injury influenced hemispheric CBF varying in the time course: A hyperperfusion could be found within the first seven days after injury in 55 percent, whereas a hypoperfusion could be detected during the whole examination period in 18 percent. In diffuse injury we never saw such CBF abnormalities. On the other hand hemispheric CO2-reactivity was disturbed in focal and diffuse lesions, whereas a correlation between altered CBF at rest and CO2-reactivity could be only detected in 40% in focal injury. This investigations demonstrates no significant general, however, a partial influence of morphological damage upon cerebral microcirculation.

[The formation of polyphosphates in ankistrodesmus braunii by photophosphorylation in red and in far-red light under nitrogen]

A simplified extraction procedure was used to study the effect of red and far-red light (683 and 712 nm) on the incorporation of (32)P and on the distribution pattern of various phosphate fractions in 8 min-experiments under nitrogen. Nitrogen was used to avoid competition for energy-rich phosphate bonds between CO2-fixation and the formation of polyphosphates. The total incorporation of (32)P was higher in red than in far-red light, and so was the percentage of the acidsoluble organic phosphate. In the absence of oxygen the incorporation in the dark was rather low and mainly confined to orthophosphate. The ratio between the amount of labelling of polyphosphates and that of acid-soluble organic phosphates was higher in far-red light and in the dark than in red light.DCMU, even in a nitrogen atmosphere, produced a servre inhibition in red light. This inhibition increased with increasing light intensity. The labelling of organic phosphates was more affected than that of polyphosphates, while orthophosphate incorporation was least inhibited. In far-red light, DCMU exerted little influence except at a rather high light intensity, showing that cyclic photophosphorylation was proceeding alone.Antimycin A, on the other hand, was almost ineffective in strong red light, but produced a serious inhibition in far-red light. In red light of medium intensity, antimycin effected some inhibition, although much less than DCMU. Under these conditions the effect of the two inhibitors was additive when they were applied together. Labelling of polyphosphates was more sensitive to antimycin A than labelling of acid-soluble organic phosphates.It may be concluded from the data presented that far-red light produces conditions for pure cyclic photophosphorylation, whereas a large proportion of the photophosphorylation taking place in red light in the absence of CO2 and exogenous oxygen might be regarded as "pseudocyclic". The distribution pattern of the phosphorylated fractions under the different conditions suggests that polyphosphate formation in the light is favoured but not exclusively effected by cyclic photophosphorylation.