Adaptation of stochastic microdosimetric kinetic model for charged-particle therapy treatment planning.

The microdosimetric kinetic (MK) model underestimates the cell-survival fractions for high linear energy transfer (LET) and high dose irradiations. To address the issue, some researchers previously extended the MK model to the stochastic microdosimetric kinetic (SMK) model. In the SMK model, the radiation induced cell-survival fractions were estimated from the specific energies z d and z n absorbed by a microscopic subnuclear structure domain and a cell nucleus, respectively. By taking the stochastic nature of z n as well as that of z d into account, the SMK model could reproduce the measured cell-survival fractions for radiations with wide LET and dose ranges. However, treatment planning based on the SMK model was unrealistic in clinical practice due to its long computation time and huge memory space required for the computation. In this study, we modified the SMK model to shorten the computation time and to reduce the memory space required for the computation. By using the dose-averaged cell-nucleus specific energy per event [Formula: see text] in the SMK formalism, the stochastic nature of z n was reflected onto the estimated cell-survival fractions. The accuracy of the modified SMK model was examined through the comparison between the estimated and the measured survival fractions of human salivary gland tumor cells and V79 cells. We then implemented the modified SMK model into the in-house treatment planning software for scanned charged-particle therapy to validate its applicability in clinical practice. As examples, treatment plans of helium-, carbon-, and neon-ion beams were made for an orbital tumor case. The modified SMK model could reproduce the measured cell-survival fractions more accurately compared to the MK model especially for high-LET and high-dose irradiations. In summary, the modified SMK model offers the accuracy and simplicity required in treatment planning of scanned charged-particle therapy for wide LET and dose ranges.

Optimum size of a calibration phantom for x-ray CT to convert the Hounsfield units to stopping power ratios in charged particle therapy treatment planning.

In charged-particle therapy treatment planning, the volumetric distribution of stopping power ratios (SPRs) of body tissues relative to water is used for patient dose calculation. The distribution is conventionally obtained from computed tomography (CT) images of a patient using predetermined conversion functions from the CT numbers to the SPRs. One of the biggest uncertainty sources of patient SPR estimation is insufficient correction of beam hardening arising from the mismatch between the size of the patient cross section and the calibration phantom for producing the conversion functions. The uncertainty would be minimized by selecting a suitable size for the cylindrical water calibration phantom, referred to as an 'effective size' of the patient cross section, Leffective. We investigated the Leffective for pelvis, abdomen, thorax, and head and neck regions by simulating an ideal CT system using volumetric models of the reference male and female phantoms. The Leffective values were 23.3, 20.3, 22.7 and 18.8 cm for the pelvis, abdomen, thorax, and head and neck regions, respectively, and the Leffective for whole body was 21.0 cm. Using the conversion function for a 21.0-cm-diameter cylindrical water phantom, we could reduce the root mean square deviation of the SPRs and their mean deviation to ≤0.011 and ≤0.001, respectively, in the whole body. Accordingly, for simplicity, the effective size of 21.0 cm can be used for the whole body, irrespective of body-part regions for treatment planning in clinical practice.

Effective particle energies for stopping power calculation in radiotherapy treatment planning with protons and helium, carbon, and oxygen ions.

The stopping power ratio (SPR) of body tissues relative to water depends on the particle energy. For simplicity, however, most analytical dose planning systems do not account for SPR variation with particle energy along the beam's path, but rather assume a constant energy for SPR estimation. The range error due to this simplification could be indispensable depending on the particle species and the assumed energy. This error can be minimized by assuming a suitable energy referred to as an 'effective energy' in SPR estimation. To date, however, the effective energy has never been investigated for realistic patient geometries. We investigated the effective energies for proton, helium-, carbon-, and oxygen-ion radiotherapy using volumetric models of the reference male and female phantoms provided by the International Commission on Radiological Protection (ICRP). The range errors were estimated by comparing the particle ranges calculated when particle energy variations were and were not considered. The effective energies per nucleon for protons and helium, carbon, and oxygen ions were 70 MeV, 70 MeV, 131 MeV, and 156 MeV, respectively. Using the determined effective energies, the range errors were reduced to ⩽0.3 mm for respective particle species. For SPR estimation of multiple particle species, an effective energy of 100 MeV is recommended, with which the range error is ⩽0.5 mm for all particle species.

A dose calculation algorithm with correction for proton-nucleus interactions in non-water materials for proton radiotherapy treatment planning.

In treatment planning for proton radiotherapy, the dose measured in water is applied to the patient dose calculation with density scaling by stopping power ratio [Formula: see text]. Since the body tissues are chemically different from water, this approximation may cause dose calculation errors, especially due to differences in nuclear interactions. We proposed and validated an algorithm for correcting these errors. The dose in water is decomposed into three constituents according to the physical interactions of protons in water: the dose from primary protons continuously slowing down by electromagnetic interactions, the dose from protons scattered by elastic and/or inelastic interactions, and the dose resulting from nonelastic interactions. The proportions of the three dose constituents differ between body tissues and water. We determine correction factors for the proportion of dose constituents with Monte Carlo simulations in various standard body tissues, and formulated them as functions of their [Formula: see text] for patient dose calculation. The influence of nuclear interactions on dose was assessed by comparing the Monte Carlo simulated dose and the uncorrected dose in common phantom materials. The influence around the Bragg peak amounted to -6% for polytetrafluoroethylene and 0.3% for polyethylene. The validity of the correction method was confirmed by comparing the simulated and corrected doses in the materials. The deviation was below 0.8% for all materials. The accuracy of the correction factors derived with Monte Carlo simulations was separately verified through irradiation experiments with a 235 MeV proton beam using common phantom materials. The corrected doses agreed with the measurements within 0.4% for all materials except graphite. The influence on tumor dose was assessed in a prostate case. The dose reduction in the tumor was below 0.5%. Our results verify that this algorithm is practical and accurate for proton radiotherapy treatment planning, and will also be useful in rapidly determining fluence correction factors for non-water phantom dosimetry.

Influence of nuclear interactions in body tissues on tumor dose in carbon-ion radiotherapy.

PURPOSE: In carbon-ion radiotherapy treatment planning, the planar integrated dose (PID) measured in water is applied to the patient dose calculation with density scaling using the stopping power ratio. Since body tissues are chemically different from water, this dose calculation can be subject to errors, particularly due to differences in inelastic nuclear interactions. In recent studies, the authors proposed and validated a PID correction method for these errors. In the present study, the authors used this correction method to assess the influence of these nuclear interactions in body tissues on tumor dose in various clinical cases. METHODS: Using 10-20 cases each of prostate, head and neck (HN), bone and soft tissue (BS), lung, liver, pancreas, and uterine neoplasms, the authors first used treatment plans for carbon-ion radiotherapy without nuclear interaction correction to derive uncorrected dose distributions. The authors then compared these distributions with recalculated distributions using the nuclear interaction correction (corrected dose distributions). RESULTS: Median (25%/75% quartiles) differences between the target mean uncorrected doses and corrected doses were 0.2% (0.1%/0.2%), 0.0% (0.0%/0.0%), -0.3% (-0.4%/-0.2%), -0.1% (-0.2%/-0.1%), -0.1% (-0.2%/0.0%), -0.4% (-0.5%/-0.1%), and -0.3% (-0.4%/0.0%) for the prostate, HN, BS, lung, liver, pancreas, and uterine cases, respectively. The largest difference of -1.6% in target mean and -2.5% at maximum were observed in a uterine case. CONCLUSIONS: For most clinical cases, dose calculation errors due to the water nonequivalence of the tissues in nuclear interactions would be marginal compared to intrinsic uncertainties in treatment planning, patient setup, beam delivery, and clinical response. In some extreme cases, however, these errors can be substantial. Accordingly, this correction method should be routinely applied to treatment planning in clinical practice.

Effects of beam interruption time on tumor control probability in single-fractionated carbon-ion radiotherapy for non-small cell lung cancer.

Carbon-ion radiotherapy treatment plans are designed on the assumption that the beams are delivered instantaneously, irrespective of actual dose-delivery time structure in a treatment session. As the beam lines are fixed in the vertical and horizontal directions at our facility, beam delivery is interrupted in multi-field treatment due to the necessity of patient repositioning within the fields. Single-fractionated treatment for non-small cell lung cancer (NSCLC) is such a case, in which four treatment fields in multiple directions are delivered in one session with patient repositioning during the session. The purpose of this study was to investigate the effects of the period of dose delivery, including interruptions due to patient repositioning, on tumor control probability (TCP) of NSCLC. All clinical doses were weighted by relative biological effectiveness (RBE) evaluated for instantaneous irradiation. The rate equations defined in the microdosimetric kinetic model (MKM) for primary lesions induced in DNA were applied to the single-fractionated treatment of NSCLC. Treatment plans were made for an NSCLC case for various prescribed doses ranging from 25 to 50 Gy (RBE), on the assumption of instantaneous beam delivery. These plans were recalculated by varying the interruption time τ ranging from 0 to 120 min between the second and third fields for continuous irradiations of 3 min per field based on the MKM. The curative doses that would result in a TCP of 90% were deduced for the respective interruption times. The curative dose was 34.5 Gy (RBE) for instantaneous irradiation and 36.6 Gy (RBE), 39.2 Gy (RBE), 41.2 Gy (RBE), 43.3 Gy (RBE) and 44.4 Gy (RBE) for τ = 0 min, 15 min, 30 min, 60 min and 120 min, respectively. The realistic biological effectiveness of therapeutic carbon-ion beam decreased with increasing interruption time. These data suggest that the curative dose can increase by 20% or more compared to the planned dose if the interruption time extends to 30 min or longer. These effects should be considered in carbon-ion radiotherapy treatment planning if a longer dose-delivery procedure time is anticipated.

Nuclear-interaction correction of integrated depth dose in carbon-ion radiotherapy treatment planning.

In treatment planning of charged-particle therapy, tissue heterogeneity is conventionally modeled as water with various densities, i.e. stopping effective densities ρ(S), and the integrated depth dose measured in water (IDD) is applied accordingly for the patient dose calculation. Since the chemical composition of body tissues is different from that of water, this approximation causes dose calculation errors, especially due to difference in nuclear interactions. Here, we propose and validate an IDD correction method for these errors in patient dose calculations. For accurate handling of nuclear interactions, ρ(S) of the patient is converted to nuclear effective density ρ(N), defined as the ratio of the probability of nuclear interactions in the tissue to that in water using a recently formulated semi-empirical relationship between the two. The attenuation correction factor Φ(w)(p), defined as the ratio of the attenuation of primary carbon ions in a patient to that in water, is calculated from a linear integration of ρ(N) along the beam path. In our treatment planning system, a carbon-ion beam is modeled to be composed of three components according to their transverse beam sizes: primary carbon ions, heavier fragments, and lighter fragments. We corrected the dose contribution from primary carbon ions to IDD as proportional to Φ(w)(p), and corrected that from lighter fragments as inversely proportional to Φ(w)(p). We tested the correction method for some non-water materials, e.g. milk, lard, ethanol and water solution of potassium phosphate (K2HPO4), with un-scanned and scanned carbon-ion beams. In un-scanned beams, the difference in IDD between a beam penetrating a 150 mm-thick layer of lard and a beam penetrating water of the corresponding thickness amounted to -4%, while it was +6% for a 150 mm-thick layer of 40% K2HPO4. The observed differences were accurately predicted by the correction method. The corrected IDDs agreed with the measurements within ±1% for all materials and combinations of them. In scanned beams, the dose estimation error in target dose amounted to 4% for a 150 mm-thick layer of 40% K2HPO4. The error is significantly reduced with the correction method. The planned dose distributions with the method agreed with the measurements within ±1.5% of target dose for all materials not only in the target region but also in the plateau and fragment-tail regions. We tested the correction method of IDD in some non-water materials to verify that this method would offer the accuracy and simplicity required in carbon-ion radiotherapy treatment planning.

A trichrome beam model for biological dose calculation in scanned carbon-ion radiotherapy treatment planning.

In scanned carbon-ion (C-ion) radiotherapy, some primary C-ions undergo nuclear reactions before reaching the target and the resulting particles deliver doses to regions at a significant distance from the central axis of the beam. The effects of these particles on physical dose distribution are accounted for in treatment planning by representing the transverse profile of the scanned C-ion beam as the superposition of three Gaussian distributions. In the calculation of biological dose distribution, however, the radiation quality of the scanned C-ion beam has been assumed to be uniform over its cross-section, taking the average value over the plane at a given depth (monochrome model). Since these particles, which have relatively low radiation quality, spread widely compared to the primary C-ions, the radiation quality of the beam should vary with radial distance from the central beam axis. To represent its transverse distribution, we propose a trichrome beam model in which primary C-ions, heavy fragments with atomic number Z ≥ 3, and light fragments with Z ≤ 2 are assigned to the first, second, and third Gaussian components, respectively. Assuming a realistic beam-delivery system, we performed computer simulations using Geant4 Monte Carlo code for analytical beam modeling of the monochrome and trichrome models. The analytical beam models were integrated into a treatment planning system for scanned C-ion radiotherapy. A target volume of 20 × 20 × 40 mm(3) was defined within a water phantom. A uniform biological dose of 2.65 Gy (RBE) was planned for the target with the two beam models based on the microdosimetric kinetic model (MKM). The plans were recalculated with Geant4, and the recalculated biological dose distributions were compared with the planned distributions. The mean target dose of the recalculated distribution with the monochrome model was 2.72 Gy (RBE), while the dose with the trichrome model was 2.64 Gy (RBE). The monochrome model underestimated the RBE within the target due to the assumption of no radial variations in radiation quality. Conversely, the trichrome model accurately predicted the RBE even in a small target. Our results verify the applicability of the trichrome model for clinical use in C-ion radiotherapy treatment planning.

Implementation of a triple Gaussian beam model with subdivision and redefinition against density heterogeneities in treatment planning for scanned carbon-ion radiotherapy.

Challenging issues in treatment planning for scanned carbon-ion (C-ion) therapy are (i) accurate calculation of dose distribution, including the contribution of large angle-scattered fragments, (ii) reduction in the memory space required to store the dose kernel of individual pencil beams and (iii) shortening of computation time for dose optimization and calculation. To calculate the dose contribution from fragments, we modeled the transverse dose profile of the scanned C-ion beam with the superposition of three Gaussian distributions. The development of pencil beams belonging to the first Gaussian component was calculated analytically based on the Fermi-Eyges theory, while those belonging to the second and third components were transported empirically using the measured beam widths in a water phantom. To reduce the memory space for the kernels, we stored doses only in the regions of interest considered in the dose optimization. For the final dose calculation within the patient's whole body, we applied a pencil beam redefinition algorithm. With these techniques, the triple Gaussian beam model can be applied not only to final dose calculation but also to dose optimization in treatment planning for scanned C-ion therapy. To verify the model, we made treatment plans for a homogeneous water phantom and a heterogeneous head phantom. The planned doses agreed with the measurements within ±2% of the target dose in both phantoms, except for the doses at the periphery of the target with a high dose gradient. To estimate the memory space and computation time reduction with these techniques, we made a treatment plan for a bone sarcoma case with a target volume of 1.94 l. The memory space for the kernel and the computation time for final dose calculation were reduced to 1/22 and 1/100 of those without the techniques, respectively. Computation with the triple Gaussian beam model using the proposed techniques is rapid, accurate and applicable to dose optimization and calculation in treatment planning for scanned C-ion therapy.

Carbon-ion radiotherapy: clinical aspects and related dosimetry.

The features of relativistic carbon-ion beams are attractive from the viewpoint of radiotherapy. They exhibit not only a superior physical dose distribution but also an increase in biological efficiency with depth, because energy loss of the beams increases as they penetrate the body. This paper reviews clinical aspects of carbon-beam radiotherapy using the experience at the National Institute of Radiological Sciences. The paper also outlines the dosimetry related to carbon-beam radiotherapy, including absolute dosimetry of the carbon beam, neutron measurements and radiation protection measurements.

Dosimetric evaluation of nuclear interaction models in the Geant4 Monte Carlo simulation toolkit for carbon-ion radiotherapy.

We tested the ability of two separate nuclear reaction models, the binary cascade and JQMD (Jaeri version of Quantum Molecular Dynamics), to predict the dose distribution in carbon-ion radiotherapy. This was done by use of a realistic simulation of the experimental irradiation of a water target. Comparison with measurement shows that the binary cascade model does a good job reproducing the spread-out Bragg peak in depth-dose distributions in water irradiated with a 290 MeV/u (per nucleon) beam. However, it significantly overestimates the peak dose for a 400 MeV/u beam. JQMD underestimates the overall dose because of a tendency to break a nucleus into lower-Z fragments than does the binary cascade model. As far as shape of the dose distribution is concerned, JQMD shows fairly good agreement with measurement for both beam energies of 290 and 400 MeV/u, which favors JQMD over the binary cascade model for the calculation of the relative dose distribution in treatment planning.

Scatter factors in proton therapy with a broad beam.

In the absence of a predictor of beam output in proton therapy using a broad beam, the beam output is obtained for individual treatments by calibrating the beam monitors. The calibration is carried out under conditions similar to the treatment conditions but with a phantom instead of the patient. However, the dose in the phantom a priori differs from that in the patient. In order to deliver the accurate dose, a correction factor has been introduced to correct the difference. This correction factor is referred to as a scatter factor in an analogy with photon therapy, and is defined as the ratio of the dose at the prescription point in the patient to the dose at the calibration point in the phantom. Under the calibration conditions at Hyogo Ion Beam Medical Center (HIBMC), the range compensator and the collimator, which are usually required in proton therapy with a broad beam, are not used. Therefore the scatter factor includes the effects of the devices as well as the difference between the dose in the patient and that in the phantom. We have developed an estimator using a dose calculation based on the pencil beam algorithm and implemented it in a treatment planning system (TPS) for clinical use. This estimator estimates the scatter factor by calculating the ratio of the doses under the same conditions in the TPS. In order to evaluate the performance of the estimator, demonstrations were carried out for cases with measurable outcomes using a gantry nozzle at HIBMC. We observed 2-3% differences between the measurements and the estimations. These differences were considered to result from the limitations of the dose calculation algorithm in modelling the beam and the patient.

Vesicular prurigo pigmentosa cured by minocycline.

We present a case of prurigo pigmentosa associated with vesicles that we call 'vesicular prurigo pigmentosa'. The subject was treated using minocycline with good results and no recurrence of the lesions over a 2-year period.

Improved branching ratio measurement for the decay K(0)(L) --> &mgr;(+)&mgr;(-)

We report results from Experiment 871, performed at the BNL AGS, of a measurement of the branching ratio K(0)(L)-->&mgr;(+)&mgr;(-) with respect to the CP-violating mode K(0)(L)-->pi(+)pi(-). This experiment detected over 6200 candidate &mgr;(+)&mgr;(-) events, a factor of 6 more than that seen in all previous measurements combined. The resulting branching ratio gamma(K(0)(L)-->&mgr;(+)&mgr;(-))/gamma(K(0)(L)-->pi(+)pi(-)) = (3. 474+/-0.057)x10(-6) leads to a branching fraction B(K(0)(L)-->&mgr;(+)&mgr;(-)) = (7.18+/-0.17)x10(-9), which is consistent with the current world average, and reduces the uncertainty in this decay mode by a factor of 3.

Dentinogenic ghost cell tumor: histologic aspects, immunohistochemistry, lectin binding profiles, and biophysical studies.

Dentinogenic ghost cell tumor accompanied with calcifying odontogenic cyst (COC) was described in terms of its clinical, histological, immunohistochemical, lectin binding and biophysical properties. The case was a 38-year-old Japanese female, in whom the tumor had arisen in the right mandibular premolar and molar region. Material obtained by partial mandibulectomy was used. Decalcified paraffin sections were used to detect keratins, involucrin, and lectin binding; and non-decalcified thin sections were used for biophysical analysis. The lesion comprising dentinogenic ghost cell tumor and COC contained odontogenic epithelium with ghost cells, eosinophilic amorphous materials and osteodentin. Some of the eosinophilic material had undergone transformation into osteodentin. Keratins in odontogenic epithelia showed positive PKK1 staining in peripheral tumor cells, and stainings with KL1 and involucrin were positive in centrally located cells. Lectin binding in the amorphous materials was comparatively strong for PNA, and SBA, moderate for WGA, RCA-1, and UEA-1, and slight for DBA and ConA. Lectin binding affinities were higher in the amorphous materials than in the osteodentin. Elemental analysis with an electron probe X-ray microanalysis of the amorphous materials and osteodentin showed a pattern similar to that found in the normal dentin. The biologic properties of the eosinophilic amorphous materials suggested the material to be poorly calcified osteodentin, which gradually transformed into the well-calcified type.

Persistence of circadian oscillation while locomotor activity and plasma melatonin levels became aperiodic under prolonged continuous light in the rat.

In order to examine the mechanism for a loss of circadian rhythms in several functions under prolonged continuous light (LL), rats were blinded following LL over 5 months, and the mode of reappearance of circadian rhythms were analyzed in locomotor activity and plasma melatonin levels. Locomotor activity and plasma melatonin levels in individual rats became aperiodic after the exposure to LL. On the day of blinding, plasma melatonin levels showed circadian rhythms having a peak coincided with the activity time of locomotor rhythm which was restored after blinding. The time of melatonin peak was not related to the time of blinding (onset of darkness) nor to the initial time of blood sampling. Circadian rhythm in plasma melatonin levels reappeared faster than those in locomotor activity. The findings suggest that aperiodism developed in these functions under prolonged LL is not due to disruption of the circadian oscillation but to uncoupling of overt functions from the circadian pacemaker.

Stimulation of in vivo calcification using collagen membranes cultured with osteoblastic cells in vitro: a preliminary report.

Guided tissue regeneration (GTR) is a useful modality in the management of periodontal disease and for bone augmentation around osseointegrated implants. This study evaluated the in vivo use of atelocollagen membrane (AC) on which osteoblastic cells (OBCs) were cultured in vitro, for application as a GTR membranous material. Osteoblastic cells isolated in our laboratory from mouse calvaria formed a thin film on the AC in vitro which was easily manipulated after 21 days in culture. The AC and OBCs complex material (ACOB) was subjected to freezing and thawing and implanted in mouse subcutaneous tissue for the study of histologic events surrounding the implanted ACOB. Histologic findings in the subcutaneous tissue showed calcification on the ACOB at 28 days postimplantation, while no such finding was evident at the control site, where only AC without OBCs were grafted. The present study suggests the possibility of membrane calcification for GTR through ACOB produced by OBCs on an AC in vitro.

Immediate response to light of rat pineal melatonin rhythm: analysis by in vivo microdialysis.

Melatonin in the extracellular space of the pineal gland was measured continuously for 4 consecutive days from single, freely moving rats by means of in vivo microdialysis. A robust circadian rhythm was observed in the pineal extracellular melatonin under both light-dark (LD) and continuous dark (DD) conditions, the patterns of which were almost identical for 4 days within individuals but varied substantially among individuals. The offset phase of melatonin rhythm was more stable than the onset phase. Light-induced phase shift of melatonin rhythm was measured in individual rats, which had been entrained to LD and subsequently released into DD. On the 1st day in DD, a 3-min light pulse of 200 lx was applied either at circadian time (CT) of 17 or 22 h (5 and 10 h after the dark onset, respectively). The light pulse rapidly suppressed the nocturnal melatonin level. The rate as well as the level of melatonin suppression was significantly greater by the pulse at CT22 than at CT17. A phase shift of the melatonin rhythm was calculated on the 2nd and 3rd days in DD. Significant phase delay shift was observed after the pulse at CT17 and advance shift after the pulse at CT22 of approximately 1 h in either case. Because the amount of phase shift was not different between the 2nd and 3rd days in DD, the phase shift of pineal melatonin rhythm by single light pulse seems to be completed immediately.

[Regulation mechanism of melatonin rhythm in the pineal gland by light: experimental studies by in vivo microdialysis].

Light has dual effects on the pineal melatonin; one is the entrainment of the circadian rhythm and the other is suppression of the melatonin synthesis. It is not known whether the entraining and suppressing effects of light are mediated by the same pathway or not. To elucidate the mechanism of the dual effects of light, (1) the sensitivity of the retina, (2) effects of acetylcholine agonist and, (3) the arrhythmicity induced by longterm continuous light, were studied by measuring melatonin continuously from a single rat by means of in vivo microdialysis. Pineal melatonin was suppressed by light more strongly at the late dark phase than at midnight, and by green light (520nm) than by red light (660nm). Pineal melatonin measured by microdialysis was decreased rapidly by a short light exposure and the melatonin rhythm was shifted on the following days. Microinjection of cholinergic agonist, carbachol, into the suprachiasmatic nucleus neither suppressed nor entrained the pineal melatonin rhythm. Immediately after the blinding, rats showed the circadian rhythm in pineal melatonin which had been abolished under long-term continuous light. While, it took several days for the locomotor rhythm to reappear. It is concluded that, (1) suppression of the pineal melatonin by light depends on the circadian phase and on the wavelength of light, (2) the threshold for light suppression is lower than that for phase-shift, (3) the melatonin rhythm starts to phase-shift on the following day of light pulse. (4) Acetylcholine is unlikely to be involved in the photic transmission both to the circadian clock and to the pineal, (5) arrhythmicity induced by long-term continuous light seems to be due to masking for the melatonin rhythm, and to uncoupling from the clock for the locomotor rhythm.