Inhaled nitric oxide for primary pulmonary hypertension in pregnancy

BACKGROUND

Primary pulmonary hypertension is a rare and dangerous entity in pregnancy. Previous studies have found a 35-50% maternal mortality rate in the peripartum period. To date, most reports have described treatment of these patients with diuretics, digoxin, and calcium-channel blockers.

CASE

We describe the successful treatment of a primigravida with severe primary pulmonary hypertension. We used elective intubation before labor, inhaled nitric oxide therapy, and assisted vaginal delivery with epidural anesthesia that resulted in a viable infant and survival of the mother.

CONCLUSION

Nitric oxide can be used to successfully treat primary pulmonary hypertension in pregnancy.

Range modulation in proton therapy--an optimization technique for clinical and experimental applications

A fast optimization algorithm for range modulation in clinical and experimental applications of proton therapy is described. The method is versatile towards the number of parameters provided for range modulation, i.e. the trade-off between accuracy and simplicity of the latter can be chosen freely. The approach is, therefore, adaptable to most operating proton therapy facilities. It requires only a few basic measurements as input data and results in a depth dose uniformity of better than 2%. A typical calculation takes less than 90 s on a DEC VAXstation 3100, FORTRAN. The method has been extensively tested at the TRIUMF Proton Therapy Facility in Vancouver, BC.

The effects of nicotinamide plus carbogen or pions for microscopic SCCVII tumors

We evaluated the sensitizing effect of nicotinamide plus carbogen (N&C) and the relative biological effectiveness (RBE) of pions on microscopic tumors where necrotic tumor centers have not yet been established. Female C3H/He mice and SCCVII tumors were used. The irradiation started two days after tumor implantation. In experiment 1, the tumor beds were irradiated at various doses with 250 KVp photons in 5 fractions over 5 days. Nicotinamide (500 mg/kg/mouse/day in 0.2 ml) was injected intraperitoneally (i.p.) 60 min before irradiation, and carbogen (95% O2 + 5% CO2) was flushed at the rate of 10 l/min for 10 min before irradiation and throughout the entire irradiation procedure. In experiment 2, the tumor beds were irradiated at various doses with pions or 250 KVp photons in 10 fractions over 5 days. In both experiments, the mice were observed for 100 days. The rate of tumor appearance was evaluated and the 50% tumor control dose (TCD50) calculated. The sensitizing ratio (SR) of N&C obtained from the TCD50 assay was 1.46 and the RBE of pions was 1.24. The SR of N&C and the RBE of pions were lower for microscopic tumors than those previously reported for macroscopic tumors. These results were probably due to the absence or reduced presence of radiobiological hypoxic component in the microscopic lesion. However, N&C can be considered to provide an advantage for treatment of even clinical microscopic tumors.

The effects of seasons and light therapy on G protein levels in mononuclear leukocytes of patients with seasonal affective disorder

BACKGROUND

Information-transducing heterotrimeric G proteins have been implicated previously in the mechanism of action of mood stabilizers and in the pathophysiology of mood disorders. Mononuclear leukocytes of patients with unipolar and bipolar depression have been characterized by reduced measures of the stimulatory and inhibitory G proteins. In this study, patients with seasonal affective disorder (SAD) were measured for mononuclear leukocyte G protein levels while depressed during the winter, following light therapy, and in remission during the summer.

METHODS

Twenty-six patients with SAD and 28 healthy subjects were assessed in the study. The immunoreactivities of Gs alpha, Gi alpha, and Gbeta subunit proteins were determined by Western blot analysis of mononuclear leukocyte membranes with selective polyclonal antibodies for the various G subunit proteins, followed by densitometric quantitation using an image analysis system.

RESULTS

Untreated patients with SAD and winter, atypical-type depression showed significantly reduced mononuclear leukocyte immunoreactive levels of Gs alpha and Gi alpha proteins, similar to previous observations in patients with nonseasonal major depression. The reduced G protein levels were normalized with 2 weeks of light therapy. The same patients while in remission during the summer had G protein levels that were similar to those of healthy subjects.

CONCLUSIONS

G protein-immunoreactive measures in patients with SAD are suggested as a state marker for winter depression, which is normalized by light treatment and during the summer. We speculate that light may exert its effects via normalization of transducin (Gt protein) levels, which are thought to be reduced in winter depression.

Role of serotonin transporter promoter repeat length polymorphism (5-HTTLPR) in seasonality and seasonal affective disorder

Seasonal variations in mood and behavior (seasonality) and seasonal affective disorder (SAD) have been attributed to seasonal fluctuations in brain serotonin (5-HT). the short (s), as opposed to the long (l), allele of the 5-HT transporter linked polymorphism (5-HTTLPR) has been associated with neuroticism and depression. We hypothesized that this short allele would also be associated with SAD and with higher levels of seasonality. Ninety-seven SAD patients and 71 non-seasonal healthy controls with low seasonality levels were genotyped for 5-HTTLPR and compared statistically. Patients with SAD were less likely to have the l/l genotype (27.8% vs 47.9%; P < 0.01) and more likely to have the s allele (44.8% vs 32.4%; P < 0.02) as compared to controls. The three 5-HTTLPR genotypes were also differentially distributed in patients and controls (P < 0.03). The SAD patients with the l/l genotype had a lower mean seasonality score than did patients with the other two genotypes (mean +/- s.d. = 15.3 +/- 2.8 vs 17.1 +/- 3.4 respectively; P < 0.02). The 5-HTTLPR short allele contributes to the trait of seasonality and is a risk factor for SAD, providing further evidence for a relationship between genetic variation in the 5-HT transporter (5-HTT) and behavior.

The relative biological effectiveness of the modulated proton beam at TRIUMF

PURPOSE

The purpose of this study was to determine the relative biological effectiveness (RBE) of proton beam and to study its dependency on fraction number.

METHODS

The relative biological effectiveness (RBE) of fractionated protons compared with 60Co gamma-rays was investigated for the acute mouse skin reaction. The 80 MeV protons generated at the TRIUMF cyclotron were spread out from 7 to 25 mm to irradiate entire legs. One, two, four, and eight fractions were tested.

RESULTS

RBE values ranged from 1.15 to 1.24 for the acute skin reaction. Fraction dose dependence of RBEs was not observed.

Heterozygosity for a defective gene for CC chemokine receptor 5 is not the sole determinant for the immunologic and virologic phenotype of HIV-infected long-term nonprogressors

HIV-1-infected long-term nonprogressors are a heterogeneous group of individuals with regard to immunologic and virologic markers of HIV-1 disease. CC chemokine receptor 5 (CCR5) has recently been identified as an important coreceptor for HIV-1 entry into CD4+ T cells. A mutant allele of CCR5 confers a high degree of resistance to HIV-1 infection in homozygous individuals and partial protection against HIV disease progression in heterozygotes. The frequency of CCR5 heterozygotes is increased among HIV-1- infected long-term nonprogressors compared with progressors; however, the host defense mechanisms responsible for nonprogression in CCR5 heterozygotes are unknown. We hypothesized that nonprogressors who were heterozygous for the mutant CCR5 gene might define a subgroup of nonprogressors with higher CD4+ T cell counts and lower viral load compared with CCR5 wild-type nonprogressors. However, in a cohort of 33 HIV-1-infected long-term nonprogressors, those who were heterozygous for the mutant CCR5 gene were indistinguishable from CCR5 wild-type nonprogressors with regard to all measured immunologic and virologic parameters. Although epidemiologic data support a role for the mutant CCR5 allele in the determination of the state of long-term nonprogression in some HIV-1- infected individuals, it is not the only determinant. Furthermore, long-term nonprogressors with the wild-type CCR5 genotype are indistinguishable from heterozygotes from an immunologic and virologic standpoint.

A general cavity theory

A cavity theory is used to relate the dose deposited in the cavity (sensitive volume of the detector) to that in the surrounding medium which may be of different atomic number or composition. Burlin proposed a general cavity theory to include all cavity sizes. The Burlin theory ignores all secondary-electron scattering effects which results in large discrepancies in dose to the cavity compared with the experimental results in high atomic number media. Kearsley proposed a new general cavity theory which includes secondary-electron scattering at the cavity boundary. The Kearsley theory showed excellent agreement with experimental results for 60Co y-rays but poor correlation for 10 MV x-rays. The Kearsley theory has numerous parameters and the magnitude of the input parameters is arbitrary; therefore the dose to the cavity depends on the choice of parameters. We have developed a new cavity theory which includes secondary-electron backscattering from the medium into the cavity. The strengths of this proposed theory are that it contains few parameters and a methodical way of determining the magnitude of the parameters experimentally. the proposed theory gives better agreement with experimental results in lithium fluoride thermoluminescence dosimeters for 60Co y-rays and 10 MV x-rays in aluminium, copper and lead than do the Burlin and Kearsley cavity theories.

Studies on lymphoid tissue from HIV-infected individuals: implications for the design of therapeutic strategies

Lymphoid tissue is a major reservoir of human immunodeficiency virus (HIV) infection in vivo. In addition, the lymphoid microenvironment provides a replicative advantage to the virus in that it provides a milieu of activated target cells that allows for efficient virus spread. The process of mobilization and activation of immune competent cells directed against the virus paradoxically contributes to the propagation of virus replication. Disruption of the lymphoid microenvironment during the progression of HIV disease is a poorly understood process, which may be of considerable importance pathogenically. Studies of lymph node biopsy samples taken 8 weeks apart from individuals who did not undergo any change in their therapeutic regimen (i.e., patients who either remained untreated or remained on their ongoing nucleoside analogue reverse transcriptase inhibitor monotherapy regimen) revealed little change in histopathology or viral load over the 8-week period. These results with successive lymph node biopsy samples taken from different sites indicate that an isolated lymph node biopsy accurately reflects the pathologic process associated with HIV infection and that this process diffusely involves the lymphoid system. Treatment with reverse transcriptase inhibitor monotherapy of patients in relatively early stage HIV disease had no detectable impact on the viral load in lymphoid tissue, suggesting the need to investigate more potent antiretroviral regimens during this stage of disease. Among patients with moderately advanced HIV disease, switching to combination therapy from a monotherapy regimen resulted in decreased viral replication in lymph nodes; this effect was associated with decreases in plasma viremia. Despite the fact that measures of viral replication decreased significantly, the net frequency of HIV-infected cells in peripheral blood and lymph nodes remained unchanged. Potent antiretroviral drug combinations may be capable of profound and long-term downregulation of plasma viremia. It will be essential to monitor the status of viral trapping, viral burden, and viral replication within lymphoid tissue during treatment with such drugs to determine accurately their true potential for impact on these key features of HIV pathogenesis.

Measurements of relative biological effectiveness of the 70 MeV proton beam at TRIUMF using Chinese hamster V79 cells and the high-precision cell sorter assay

Measurements of relative biological effectiveness (RBE) have been made on the range-modulated 70 MeV proton beam at TRIUMF using a precise cell sorting survival assay. In this study, Chinese hamster V79-WNRE cells were suspended in medium containing liquid gelatin at 37 degrees C in irradiation tubes and the gel was allowed to solidify by cooling to 4 degrees C. Complete cell survival responses were measured at 11 positions with 2 mm spacing within a proton stopping peak width of approximately 2 cm. Survival responses after proton irradiation were compared with responses to 60Co gamma rays measured at the same time, and RBE values were determined as a function of both dose and depth. Above doses of 4 Gy, the average RBE for these cells throughout the modulated proton stopping distribution was 1.21 +/- 0.05, measured at a survival of 1%. However, we also observed that, within the spread-out Bragg peak, the RBE increased with increasing depth, from approximately 1.2 at the proximal part to > 1.3 at the distal part of the peak. At the distal edge of the stopping distribution, the RBE value increased significantly, to an extent that may be of concern when this region of the treatment volume is close to sensitive tissues. Below 4 Gy, the RBE value was also dependent on radiation dose, increasing significantly to values of approximately 1.37 and 1.56 at 2 and 1 Gy, respectively. Our results illustrate that the use of a single RBE value in different irradiation protocols can be an oversimplification, and argues for the use of "proton gray doses" rather than "gamma-ray equivalent grays."

Immune reaction induced by X-rays and pions and its stimulation by schizophyllan (SPG)

Female C57BL/6 mice aged 6-8 weeks with transplanted Lewis lung cancer cells were used to investigate the anti-tumour effects and immune reactions in tumour tissue induced by X-ray and pion irradiation and their modification by schizophyllan (SPG). The effect of SPG on the rate of lung metastasis and the survival time of the mice was also studied using the same tumour system. These studies showed that in this tumour system the "practical' relative biological effectiveness (RBE) of pions was 1.33 in the dose ranges used (3 Gy x 4 = P3; 6 Gy x 4 = P6). SPG increased the suppression of tumour growth associated with moderate doses of radiation: X-rays (4 Gy x 4 = X4) or P3. SPG also decreased the number of lung metastases and prolonged the life span of the mice, these effects being independent of radiation. The addition of SPG to radiation increased both the macrophage infiltration and T-lymphocyte infiltration in the local tumour and the lung nodules. There did not appear to be any major differential effect of SPG on the pion-treated mice compared with those treated with X-rays.

Early skin response to fractionated doses of pions for determining therapeutic gain factors

This study concerns the biological effectiveness of fractionated doses of pions on early skin reactions near the implanted tumor, to evaluate the therapeutic gain factors of pions. The C3H mouse limbs bearing microscopical SCCVII tumors were irradiated with pions (9.6-38.4 Gy) or x-rays (14.4-50.4 Gy) in 2-7 fractions. Nicotinamide (500 mg/kg) and carbogen (a mixture of 95% O2 + 5% CO2), as hypoxic radiosensitizers, were administered prior to the x-rays, to confirm the presence of hypoxic cells in the skin. The mean skin scores and number of damaged nails assessed. The ratios of x-ray/pion doses needed for giving comparable skin reactions were 1.3-1.5. Nicotinamide and carbogen enhanced the skin reactions. When the ratios were compared with those of tumor cure, the pions showed no therapeutic gains. One of the possible causes was that the presence of hypoxic cells in the skin may have reduced the therapeutic gain.

Proton dose monitoring with PET: quantitative studies in Lucite

The feasibility of using PET for proton dose monitoring is examined here in detail. First experimental studies in a Lucite phantom have been performed at the medical TRIUMF proton beamline for proton energies of 62 MeV and 110 MeV. The proton dose delivered to the phantom ranged from 16 Gy up to 317 Gy. The induced activity was analysed 20-40 min after the irradiation with a PET scanner. The obtained depth activity profiles were compared to our calculation based on a model using available isotope production cross-section data. Both the observed absolute count rates and the activity profiles were found to agree very well with this model. Effects such as proton range straggling, inelastic nuclear interactions and the energy spectrum of the emitted positrons were studied in detail and found to change the activities by 5-10%. The lateral deposition of dose in the phantom could be very well localized by the induced activity. However, the spatial correlation between dose depth profiles and depth activity profiles was found to be poor, hence the extraction of isodose profiles from activity profiles seems to be very difficult.

Radiosensitizing effect of nicotinamide and carbogen combined in fractionated pions or x-rays in SCCVII tumors

Well-known radiotherapeutic strategies for hypoxic cells include hypoxic radiosensitizers, heavy particles, and fractionated irradiation. This study attempted to obtain the ultimate effectiveness of these strategies by combining nicotinamide plus carbogen (N + C) as a hypoxic radiosensitizer with fractionated pions. In addition, the influence on the N + C effect of X-ray dose rate used as a reference radiation was evaluated. When SCCVII tumors in the dorsum of feet reached 50 mm3 in volume, they were irradiated with pions (0.2 Gy/min), the same dose rate (LDR; 0.2 Gy/min) X-rays, or high dose rate (HDR; 1.5 Gy/min) X-rays in 10 fractions over 11 days. Nicotinamide (0.5 mg/g) was administered i.p. one hour before irradiation, and normobaric carbogen (95% oxygen and 5% carbon dioxide) was breathed from 10 min before irradiation. The effect was evaluated by tumor growth time (TGT50) assay. The combination of N + C significantly enhanced the effect of 30 Gy LDR and 28 Gy HDR X-rays, with the effect corresponding to that of 39 Gy HDR X-rays: the enhancement ratios were 1.2 and 1.4, respectively. The effect of 20 Gy pions was equivalent to the effect of 33 Gy HDR X-rays (ratio of 1.65), or the effect of N + C combined with 28 Gy HDR X-rays. However, N + C did not enhance the effect of 20 Gy pions. This suggested that the fractionated pions had great biological effectiveness against hypoxic cells. In conclusion, N + C afforded no additional benefit with fractionated pions, but it was thought to be of value for fractionated X-rays, even in a dose rate of 0.2 Gy/min.

Biological effectiveness of fractionated dose of pions in microscopic SCCVII tumors: comparison between tumor control dose and tumor growth time assays

The relative biological effectiveness (RBE) of fractionated pions for tumor growth time (TGT) assay changes with the endpoints, so it is essential to determine the RBE for tumor control dose (TCD) assay. For this purpose, the TCD50 of fractionated pions was compared with that of photons, and the RBEs for TGT and TCD assays were concurrently compared as a function of the effect level. A "convenient" RBE (cRBE) was substituted for the RBE when the comparison was made between similar fractionation schedules with different dose per fraction. SCCVII tumors (2 x 10(4) or 2 x 10(5) cells) were implanted into the feet of C3H mice and irradiated starting from 2 days after implantation at a total dose range of either 9.6-38.4 Gy pions (2.4-6.4 Gy per fraction) or 14.4-50.4 Gy photons (3.6-7.2 Gy per fraction) in 2-10 fractions over 5-6 days. The cRBE and the RBE at the iso-effective level of 30 days TGT were 1.53-1.60 for 2.4-4.8 Gy pions and 1.50 for 4-fractionated pions, respectively: there were only small differences within these schedules used. However, the cRBE values decreased from 1.60 to 1.15 with increasing TGT from 30 to 75 days. In contrast, the cRBE values for TCD50 increased from 1.08 to 1.40 (95% confidence limits [CL]; 1.18-1.63) with increasing evaluation time from 60 to 100 days: pions significantly inhibited late tumor appearance. The TCD50 at 100 days was 28.7 Gy (CL; 25.0-32.5 Gy) for pions and 40.3 Gy (CL; 36.3-44.2 Gy) for photons. In conclusion, the RBE for TCD50 was not predictable from the RBE for TGT assay. The cRBE value of 1.4 for microscopic tumor control was in close agreement with the reported values for skin reaction.

The definition of damage interaction in International Commission of Radiation Units and Measurement Report 30

There is some clarification required in the present definition of synergism and antagonism as published in report No 30 by the International Commission on Radiation Units and Measurements for quantitative concepts in radiobiology. In the report, damage interaction appears to be defined relative to additive action rather than to independent action. While the concept of independent action is completely independent of the action mechanism of radiations, it is shown that the concept of additive action requires that isoeffective doses of two different radiations be 'mechanistically equivalent' so that one can 'switch' from one response curve to another at the corresponding effect level. This makes the meaningful use of additive action strongly dependent on a supporting model. At present, most of the current models of radiation action cannot accommodate additive action. The report also states that, due to population selection, cell killing may be greater than that due to independent action if the survivor of one radiation is sensitive to the other radiation. An in-depth study indicates that the analysis is more complicated, depending on whether or not the population is known to be mixed. Lastly, an amended definition of damage interaction for the report is proposed.

A general formulation of the concept of independent action for the combined effects of agents

Analysis schemes for the classification of synergism and antagonism for mixed agents operate on the discrepancies between observed and calculated results. As such they cannot be confirmed by experiments and therefore have to be tested in terms of mathematical and logical self-consistency. The concept of independent action is close to the literal meaning of the term "non-interaction". Since this concept does not depend on the mechanisms of actions nor on the type of effect scale used, it is suitable as one of the basic criterion for the definition of synergism and antagonism. A general mathematical framework of independent action is presented in this paper based on the concept of "relative effect" as used in the literature. The different equations for independent action currently used in various areas are shown to be manifestations of a general formula under different sets of boundary conditions, which are the natural limiting values of the effects of the corresponding system observed at low and at high doses of the agents. The framework can be generalized to the combined action of n-agents as well as to the interaction of an agent with itself. In addition, the differential form of the formula for independent action is derived. This framework of systematic definitions and derived equations enable a more in-depth study of the implications of the concept of independent action and its relation to other concepts of non-interaction.

The response of Chinese hamster V79-379A cells exposed to negative pi-mesons: evidence that increased radioresistance is dependent on linear energy transfer

Chinese hamster V79-379A cells exhibit low-dose hypersensitivity to 250 kVp X rays followed by an increased radioresistant response over the dose range 0.5-1 Gy. This phenomenon is not seen with neutrons (Marples and Joiner, Radiat. Res. 133, 41-51, 1993). It was therefore postulated the induction of radioresistance might develop as a response to a cellular event(s) which predominates after low- and not high-LET radiation. To test this hypothesis, we measured the survival response of V79-379A cells exposed to pions. Clonogenic survival was assessed for cells irradiated in the Bragg peak (35 keV/microns) and plateau region (10-20 keV/microns) of the beam, using an automated microscope (DMIPS cell analyzer). As expected, peak pions were found to be more effective per unit of dose at killing cells than plateau pions. The survival curve for cells irradiated in the plateau of the pion beam was found to incorporate a region of low-dose hypersensitivity and increased radioresistance, the effective D0 was dose-dependent, ranging from 3.5-5. This was not seen with peak pions, where the effective D0 was, on average, constant reflecting a single-exponential survival curve. Fitting the data with an induced repair model indicates that the phenomenon of increased radioresistance is almost certainly dependent on LET.

The differential aspects of the linear isobole in the study of combined action of agents

Although the isobologram is presently the most widely used method of analysis for combined effects of agents, there are several different interpretations of the linear isobole in regard to its use as a criterion of interaction. An investigation of the differential aspects of the linear isobole relation may cast some light in this regard. By conceptual extension of the present single effect level (i.e. effect-point) relation of the linear isobole to an effect-neighbourhood relation in which the linear isobole holds over a small continuous range of effect levels, the mathematical differential of the linear isobole can be developed and investigated. This differential aspect provides some useful insights into the implication and interpretation of the linear isobole relation when used as a general criterion in agent interaction studies. It can also serve as the mathematical basis for the formulation of analytic schemes in which the linear isobole relation is applicable over a continuous range of effect levels.

The study of combined action of agents using differential geometry of dose-effect surfaces

Although graphic surfaces have been used routinely in the study of combined action of agents, they are mainly used for display purposes. In this paper, it is shown that useful mechanistic information can be obtained from an analytical study of these surfaces using the tools of differential geometry. From the analysis of some simple dose-effect surfaces, it is proposed that the intrinsic curvature, referred to in differential geometry as the Gaussian curvature, of a dose-effect surface can be used as a general criterion for the classification of interaction between different agents. This is analogous to the interpretation of the line curvature of a dose-effect curve as an indication of self-interaction between doses for an agent. In this framework, the dose-effect surface would have basic uniform fabric with zero curvature in the absence of interaction, tentatively referred to as null-interaction. Pictorially speaking, this fabric is distorted locally or globally like the stretching and shrinking of a rubber sheet by the presence of interaction mechanisms between different agents. Since self-interaction with dilution dummies does not generate intrinsic curvature, this criterion of null-interaction would describe the interaction between two truly different agents. It is shown that many of the published interaction mechanisms give rise to dose-effect surfaces with characteristic curvatures. This possible correlation between the intrinsic geometric curvature of dose-effect surfaces and the biophysical mechanism of interaction presents an interesting philosophical viewpoint for the study of combined action of agents.

The response of murine B-16 melanoma to fractionated doses of pions

The relative biological effectiveness (RBE) of pions has been studied in mouse B-16 melanoma transplanted into C57BL/6 mice. To determine the RBE at both high and low doses per fraction, a range of fractionation schedules was used, with 1, 4 and 10 fractions. The reference 250 kV X ray dose rate was 1.5 Gy/min which was much higher than the dose rate of pions (0.25 Gy/min). The RBE varied depending on the number of fractions and, within the same fractionation schedule, also on the dose per fraction. The RBE ranged from 1.15 for single fractions at 12.5 days of growth delay, to 1.80 for 10 fractions at 5 days of growth delay, which was determined by the time taken for the tumors to reach 5 times the average of their original volume. RBEs at the iso-effect level of 10 days growth delay were 1.20, 1.29 and 1.62 for single, 4 fractions and 10 fractions, respectively. RBE values were influenced by both the number of fractions and the dose per fraction, that is, the larger the number of fractions and the smaller the dose per fraction, the larger the value of RBE. In comparison with RBE of normal mouse skin, it was suggested that pion therapy may provide advantage over conventional photontherapy for radioresistant tumors such as this melanoma with the maximum therapeutic gain factor of 1.2. alpha/beta ratios for B-16 melanoma were also obtained from the 10 day growth delay iso-effect curve, and were 10.5 Gy and 32.6 Gy for X ray and pions, respectively.

The response of mouse tumours to fractionated doses of pions: determination of therapeutic gain factor

Using the same experimental system which had been used to determine the pion relative biological effectiveness (RBE) for skin of mouse foot by Chaplin et al., we have determined the pion RBE for KHT sarcoma and SCCVII tumour transplanted in the foot of C3H mice. The pion RBE obtained by the tumour growth delay time method in comparison with 250 kVp X-rays at a dose rate of 150 cGy per min was determined to be 1.20, 1.28 and 1.50 with single, 4 and 10 fractions, respectively, for KHT sarcoma. As for SCCVII tumour, it was determined to be 1.17, 1.45 and 2.05 with single, 4 and 10 fractions respectively. Therefore, it has been concluded that pions have various values of RBE depending on the tumour system involved. KHT sarcoma is a tumour which grows very rapidly, on the contrary, SCCVII tumour shows somewhat slower growth characteristics. These differences of RBE between these two tumour systems possibly stem from differences in the amount of hypoxic cells and/or their rates of reoxygenation. As for therapeutic gain factor, a maximum value of 1.45 was obtained with 10 fractions using the SCCVII tumour. Pions seem to be most effective (in multiple fractions) against tumours of relatively slow growth.

Combination therapy of pions and SPG (Sonifilan, Schizophyllan), a biological response modifier for mouse tumor systems

Female C3H mice aged 8-10 weeks with transplanted KHT sarcoma or SCCVII tumor were used to investigate the antitumor effect of SPG (Sonifilan, Schizophyllan) alone and in combination with local irradiation of pions with 4 fractions of 400 cGy (total 1600 cGy). Daily doses of 10 mg/kg of SPG were given intramuscularly to the mice bearing KHT sarcoma for 14 consecutive days from day 7, and to mice bearing SCCVII tumor for 20 consecutive days from day 7 and thereafter three times a week for another 2 weeks. The antitumor effect was evaluated by the changes in tumor volume, survival curves, and the number of pulmonary metastatic nodules on the surface of the lungs. SPG failed to exert any antitumor effect and any life-prolonging effect for the KHT sarcoma. As for SCCVII tumor, in the group treated with pions and SPG, tumor growth decreased significantly (p less than 0.01) compared with the group treated with pion only, and life prolonging effect and metastasis-suppressing effect were also observed (p less than 0.04). In conditions of minimal residual disease brought about by pion irradiation, the adjuvant effect of a Biological Response Modifier (BRM) SPG may prove to be a promising method of cancer therapy for some tumors.

On the use of the pion stopping distribution and the lesion additivity concept for the calculation of effective doses in pion treatment planning

The large spatial variation in LET, and hence in RBE, is one of the main obstacles in the development of routine treatment planning of charged particle beams. Since the biological effect distribution of plans cannot be realistically measured for each patient, a simple scheme of relating effect to basic empirical physical measurement is required. For the case of a pion beam, the high LET dose distribution is correlated with that of the pion stopping density, which can be indirectly measured using several techniques. A scheme based on this spatial correlation has been developed. In this method, after partitioning the local dose into a high and a low LET fraction, the local effective dose is computed using a simple formula extracted from a recent analysis of radiobiological results for mixtures of radiations of different LET. This simple formula can also be derived from a mechanistic model of mixed radiation action developed using the hypothesis of additivity of common intermediate lesions. In this paper, the concept of spatial correlation between the high LET dose and the pion stars is merged with the concept of lesion additivity for mixed radiation, from which a simple computational scheme is formulated for the calculation of effective doses in the treatment planning of pions. Similar schemes can also be developed for other charged particle beams.

On the biophysical interpretation of the mathematical product of dose and relative biological effectiveness

The mathematical product of dose and relative biological effectiveness (DR) is commonly used empirically as the 'effective' dose of radiations. It is often interpreted as the equivalent dose of a reference radiation, such that the individual DRs of the radiation components are summed like physical doses in a mixture of radiations with different RBE values. It is shown that such a physical interpretation of DR would be both mathematically and logically inconsistent unless the action of each radiation has a constant RBE value for all end-effects. This is contrary to general experimental findings. Based on the isoeffect biological connotation in the definition of RBE, a biophysical interpretation is being introduced in this paper in which DR is always interpreted with respect to a particular end-effect on which the RBE value is evaluated, somewhat similar to having an extra biological dimension. Hence, only DRs evaluated for the same end-effect can be meaningfully computed together in a mixture. From the empirical results of radiobiological experiments using mixtures of radiations of different qualities, DRs of radiation components are shown to be additive in a mixture just like physical doses. A convenient linear computation framework is, therefore, available for the use of DRs in the empirical calculation of effect of mixtures of radiations of different qualities. The bearing of this biophysical interpretation of DR on radiation protection and treatment planning is discussed.

Pion therapy at TRIUMF. Treatment results for astrocytoma grades 3 and 4: a pilot study

At TRIUMF, (located on the University of B.C. Campus), 53 patients with supratentorial astrocytoma grades 3 and 4 were treated with pions between 1982 and 1985. A 3-dimensional spot-scanning treatment technique has proven to be practical. The accuracy of the beam alignment system used for treatment was reproducible daily within 2 mm. Low pion flux has hindered optimal beam shaping but this will soon be remedied as flux improves. The overall median survival observed (53 patients) is 262 days from date of first radiation treatment. Younger (less than 49 years) patients have significantly better survival than older (greater than 50 years) patients (p = 0.001). From a base line dose of 40 Gy photons whole brain and 17.5 Gy pion boost, doses were escalated to 33 Gy pions localised to the primary tumour and the median survival improved from 198 to 436 days. Survival curves for patients treated with localised pion techniques to doses above 30 Gy are significantly better than for those treated with schedules of pions mixed with photons (p = 0.04). It appears that optimal pion dose for brain tumours is 33 Gy minimum with a possible maximum of 36 Gy and doses delivered in 15 fractions in 3 weeks. Requirements for future trials are discussed.

Preclinical evaluation of pions in vivo: experience at TRIUMF

This paper describes the results obtained from in vivo studies of the pion beam at the TRI University Meson Facility (TRIUMF). The studies encompass work (from 1978 to 1986), designed to evaluate the RBE for early and late effects and to assess the importance of X-ray dose rate and treatment volume on these values. Results with early responding tissues, i.e. mouse and pig skin and mouse intestine indicate a pion RBE of about 1.5 in the clinically relevant dose per fraction range of 2-3 Gy. At these doses, RBE appears to be independent of the reference X-ray dose rate. However, at high doses per fraction, the RBE values become increasingly X-ray dose rate dependent. The induction of late effects by pions has been assessed by monitoring the late dermal response of pig skin; late fibrosis was not assessed in this study. The values obtained using the chosen endpoint indicate that the RBE is not significantly higher than that seen in any of the early responding tissues for pion doses as low as 2-3 Gy per fraction. The effect of increasing the treatment volume for pion therapy has been assessed using mouse intestine. The results show that for a constant field size, RBE decreases with increasing peak width. However, if peak width is held constant and field size increased, there is evidence for an increased RBE.(ABSTRACT TRUNCATED AT 250 WORDS)

On the use of effective dose in the treatment planning of high linear-energy-transfer radiation

Treatment planning for conventional radiations is based on the assumption that the effect of a combination of doses at any location in the treatment field in a multibeam plan will be equivalent to that of a single dose made up of the total sum of the doses delivered to that location. This is obviously valid for conventional low linear-energy-transfer (LET) radiations when the dose contributions from various beam components are associated with the same relative biological effectiveness (RBE) value of unity. However, this is not the case for the new generation of charged particle beams whose RBEs have been shown to vary significantly with depth. A concept of effective dose, defined as the mathematical product of physical dose and RBE value evaluated for an effect level, is developed for the treatment planning of these high-LET particle radiations. Based on radiobiological results in mixed radiation experiments, it is shown that these effective doses are linearly additive like physical doses and hence, can be used directly for general treatment planning using linear algorithms already developed for the use of physical doses. This is illustrated using examples of simplified one-dimensional plans for the TRIUMF pion beam.

An isoeffect approach to the study of combined effects of mixed radiations--the nonparametric analysis of in vivo data

The combined effects of mixed radiations can be examined using a system of simple isoeffect relations which are derived from a recent analysis of in vitro results obtained for a variety of radiation mixtures. Similar isoeffect analysis methods have been used for over two decades in studies of the combined action of toxic agents such as drugs and antibiotics. Because of the isoeffect approach, the method is particularly useful for the analysis of ordinal data for which conventional models that are based on parametric dose-effect relations may not be suitable. This is illustrated by applying the method to the analysis of a set of recently published in vivo data using the mouse foot skin reaction system for mixtures of neutrons and X rays. The good agreement between this method and the ordinal data also helps to provide further experimental support for the existence of a class of radiobiological data for which the simple isoeffect relations are valid.

Detection of pion-induced radioactivity by autoradiography and positron emission tomography

An autoradiographic technique incorporating a new imaging system was used to detect pion-induced radioactivity in Plexiglass and the results were compared with aluminium activation and PET imaging. The activity distribution in the region of the pion-stopping peak was similar in all three cases. Another large signal in the entrance region due to in-flight interactions [12C(pi-, pi- n) 11C] was detected by autoradiography and by PET but was not reflected in the aluminium activation measurements. This new technique is capable of defining the stopping region in phantoms with a better resolution than PET scanning and is useful as a complementary technique to other methods of pion dosimetry.

Analysis of interaction for mixtures of agents using the linear isobole

The linear isobole that is commonly used as a reference for the study of interaction is derived from the interaction of an agent with itself. It is shown that the general use of the linear isobole in the study of the combined effects of mixtures of agents implies interaction between the agents whether the dose-effect curves of the agents are the same or not. It is difficult to generalize the interaction between two doses of the same agent to the interaction between two doses of different agents with different action mechanisms without the use of a mechanistic model. Predictions using non-interaction defined as independent action are generally different from those using linear isobole. A simple mechanistic framework based on the concept of common intermediate lesions is introduced in this paper to relate these two methods used for the analysis of synergism and antagonism. In this framework of lesion development, two agents that have no common intermediate lesion in their action will be non-interactive (referred to as independent action). When the two agents share a common intermediate, it is shown that the combined effect will follow the linear isobole (referred to as common action). This simple framework of analysis is applicable to the general study of interaction between two agents with different types of dose-effect curves.

Effect of different stopping volumes of clinical pion beams at TRIUMF on the mouse small intestine

The survival of mouse jejunal crypt cells was measured using a microcolony assay following irradiation with one of three different pion stopping volumes. All treatments were done using the beam spot scanning system developed for clinical therapy at TRIUMF. Treatment volumes were Small, 10 ml of volume using 4 beam spots with a narrow stopping peak; Moderate, 40 ml of volume using 4 beam spots with an extended peak; Large, 1.2 liters of volume using 37 spots with an extended peak. The dose rate fluctuated considerably during treatment because of the scanning procedure. The relative biological effectiveness (RBE) values of pions were 1.11, 1.04, and 1.16 for the small, moderate, and large volumes, respectively. As the width of the stopping peak increased, from the narrow 4-cm peak of the small volume to the 12-cm peak of the moderate volume, the effectiveness of the pion beam decreased. This presumably reflects the low linear energy transfer contribution of the large number of passing pions in the wider stopping peak. The results indicate, however, a greater biological effectiveness for the large volume than for the moderate volume. Even though these fields had stopping peaks of similar width, the field size and dose rate were different. Although the increase in RBE may be partly due to an increased neutron flux from the larger volume, our results suggest that much of this apparent increase could be explained by differences in dose rate as a function of time for pions versus X rays.

The combined effects of mixtures of ionizing radiations

Ionizing radiation is a special group of toxic agents whose general interaction can be calculated. This was demonstrated using a radiation interaction model previously published. In this paper, this model is refined and mathematically reformulated using a unified set of assumptions. It postulates the existence of a common intermediate lesion and the relative action of lesions before, at and after this common stage. General quantitative dose-effect relationships of mixed radiations can be derived from the dose-effect relationships of the components in the mixture.

Phosphorylation of (Na+ + K+)-ATPase; stimulation and inhibition by substituted and unsubstituted amines

(1) In view of a previously established stimulation of steady-state phosphorylation of (Na+ + K+)-ATPase by imidazole and its inhibition by tris(hydroxymethyl)aminomethane, the effect of (structure, chemical composition and charge of) a number of primary, secondary and tertiary amines (including imidazole derivatives) has been investigated. (2) Primary amines are predominantly inhibitory and diamines are more inhibitory than monoamines. The strongest inhibition is exerted by ethylenediamine (I50 in 50 mM imidazole = 25 microM, vs. 60 mM for n-propylamine). Increasing the distance between the two amino groups from 3.7 to 8.7 A increases the I50 180-fold. The optimal distance of 3-4 A indicates a similar distance between two ligand(presumably Na+)-binding sites on the enzyme. (3) Screening or substitution of the central N-atom decreases inhibition by the nitrogen compound. Triple substitution by propyl or allyl groups leads to maximal activation, amounting to about 90% of the Na+-activation level. Triethyl substitution gives suboptimal activation and tributyl substitution leads to inhibition. Substitution by polar or negatively charged carboxyl groups diminishes or even abolishes inhibition and also diminishes or abolishes activation. (4) Although occasionally positive charge is not required for inhibition, it is prerequisite for activation. Within certain families of compounds (e.g., ethylenediamine and imidazole derivatives) inhibition or activation increases with pKa, hence with positive charge. (5) The above data are interpreted in terms of inhibition, which is competitive to Na+, being governed by Coulomb interaction. Activation, on the other hand, is predominantly determined by lipophilic (van der Waals or pi-pi electron) interactions, excluding water from the phosphorylation site, hence decreasing phosphoenzyme hydrolysis and increasing the phosphoenzyme level. The requirement of charge (though hidden by substitution) implies weak additional electrostatic interaction.

The interaction of radiations of different LET

Experimental data for mixed radiation of different LET are analysed using an isobologram approach and are shown to be consistent with the special case of 'zero interaction' in a general formulation of the effect of a combination of agents proposed by Berenbaum. This zero interaction is defined in the same sense as interaction between the lesions produced by the same radiation. This makes analysis and predictions of mixed radiation results particularly straightforward. The zero-interaction formula can be mathematically derived from a simple model of mixed radiation called the lesion additivity model using the assumption that different early lesions produced in the radiation mixture can gradually develop into an indistinguishable intermediate state and hence become additive to produce the same end point. The model is shown to be applicable to irradiation under both hypoxic and oxygenated conditions and hence is extended to the use of hypoxic cell sensitisers.

The survival response of a biological system to mixed radiations

The concept of additive radiation action is applied to the process of merging of the intermediate lesions at a common stage in the radiation inactivation pathways for lesions produced by different radiations. This gives rise to a natural nonindependent effect for combined irradiation. Even though the exact nature of this common intermediate lesion is unknown, the effect of this lesion additivity can still be formulated into a mathematical model using the assumptions: (1) there exists a stage in the chain of radiation inactivation events where different types of lesion precursors, produced by different types of radiations in a mixture, inflict lesions which become functionally indistinguishable and hence additive thereafter, to produce the same end point observed; (2) all precursors of all types are simultaneously competing for the opportunity to inflict lesions at the stage indicated in assumption 1, and each precursor has equal opportunity regardless of its origin; (3) if the radiations are delivered sequentially within a sufficiently short time, the lesion precursors of both radiations arrive at the above stage at about the same time and hence inflict lesions which are additive as described in assumptions 1 and 2. The model is quantitative but contains no free-fitting parameters. It is shown to be capable of explaining a large variety of apparently unrelated published experimental results observed for mixtures of high- and low-LET radiations.

The use of positron emission tomography in pion radiotherapy

The radioactive debris produced by pion radiotherapy can be imaged by the technique of Positron Emission Tomography (PET) as a method of non-invasive in situ verification of the pion treatment. This paper presents the first visualization of the pion stopping distribution within a tumor in a human brain using PET. Together with the tissue functional information provided by the standard PET scans using radiopharmaceuticals, the combination of pion with PET technique can provide a much better form of radiotherapy than the use of conventional radiation in both treatment planning and verification.

Pions, Vancouver

Clinical treatments at TRIUMF started in November, 1979. Ten patients with malignant subcutaneous nodules had 14 lesions treated with pions and 37 other nodules treated with 280 kV X rays. Three different fractionation regimens were used with X ray doses spanning the expected RBE range of pions. The RBE for pions for acute skin reaction for 10 fractions had a mean value about 1.5, while for 3 fractions it was 1.3 maximum. No dissociation of acute and late skin effects was seen with follow-up to 27 months after treatment. Phase 1-2 studies of Pion-Boost Therapy for patients with glioblastoma multiforme will begin in May, 1982. These will be followed in August with treatments of advanced pelvic malignancies using pions only. The existing beam line at TRIUMF will be upgraded and commitments have been given to go to higher beam currents. As a result, the dose rate should increase by a factor of at least two, allowing treatment of clinically relevant volumes in acceptable times by 1983-1984.

Radiobiology of pions at TRIUMF

Radiobiological studies at TRIUMF of the effects of pion beams have been carried out using cultured cells, mice and pigs. CHO cells in gel/medium were used for RBE determinations throughout the dose distributions. The RBE was shown to increase with depth in the stopping region, while the average RBE value decreased with increasing width of the stopping peak and also increased with increasing field size. The results suggest that the effects of peak width and field size will approximately cancel out when treatment volumes are changed, provided that all three dimensions are changed more or less proportionally. The peak center RBE values ranged from 1.2-1.3 for single doses. The oxygen enhancement ratio (OER) for pions was 2.2 compared to 2.8 for X rays. Split dose recovery was found to be somewhat reduced in the peak region. In vivo studies with mouse and pig skin have been done for 1 to 20 fractions. For mouse skin, pions showed an RBE of 1.5-1.6 for fraction numbers greater than 10. The RBE for pig skin was 1.4 for early reactions, but it may be higher for medium term reactions.

Systmatic method of formulating liquid phantoms with a given elemental composition and density

A general method of formulating tissue equivalent liquid mixtures of a given chemical composition and density using the technique of linear programming is described. It is used to generate mixtures with equivalent atomic composition as ICRP Standard Man and mammalian muscle (NBS Handbook 85) using eight compounds to cover the range of densities from 1.0 to 1.13. Use of the method to handle other parameters of a mixture is also described.

Uniform depth dose distribution for biological irradiation using negative pions

A simple, flexible technique has been developed to generate uniform depth dose profiles for the biomedical pion beam at TRIUMF using dynamic momentum control and linear programming. Either the entrance dose or the irradiation time required for a certain dose over the uniform region can be minimised. The dynamic momentum control can operate automatically under computer control even with a highly unstable beam. Cell survival profiles have been obtained for this uniform dose distribution using the gelatin technique. The RBE increases with increasing depth through the uniform dose region.

The comparative survival of clonogenic cells of a murine epithelioma irradiated in vivo with 250 kVp X rays, 60Co gamma rays, or negative pions produced by the cyclotron at TRIUMF

Squamous carcinomas in WHT/Ht mice were exposed to the biomedical pion beam at TRIUMF. The biological effects of the pion beam were compared to those of 250 kVp x rays. The dose rates were 2-3 rad/min. (.02-.03 Gy/min.) for pions and 56 rad/min. (.56 Gy) for x rays. The surviving fraction of epithelioma cells irradiated in vivo was studied using the TD50 assay. RBE values for pions were calculated from the ratio of the x-ray and pion D0 values and were found to be 1.6 +/- 0.3 for oxic cells and 2.1 +/- 0.4 for hypoxic cells. OER values were 1.8 +/- 0.5 for pions and 2.4 +/- 0.4 for 250 kVp x rays.