Ion recombination correction in carbon ion beams.

PURPOSE: In this work, ion recombination is studied as a function of energy and depth in carbon ion beams. METHODS: Measurements were performed in three different passively scattered carbon ion beams with energies of 62 MeV/n, 135 MeV/n, and 290 MeV/n using various types of plane-parallel ionization chambers. Experimental results were compared with two analytical models for initial recombination. One model is generally used for photon beams and the other model, developed by Jaffé, takes into account the ionization density along the ion track. An investigation was carried out to ascertain the effect on the ion recombination correction with varying ionization chamber orientation with respect to the direction of the ion tracks. The variation of the ion recombination correction factors as a function of depth was studied for a Markus ionization chamber in the 62 MeV/n nonmodulated carbon ion beam. This variation can be related to the depth distribution of linear energy transfer. RESULTS: Results show that the theory for photon beams is not applicable to carbon ion beams. On the other hand, by optimizing the value of the ionization density and the initial mean-square radius, good agreement is found between Jaffé's theory and the experimental results. As predicted by Jaffé's theory, the results confirm that ion recombination corrections strongly decrease with an increasing angle between the ion tracks and the electric field lines. For the Markus ionization chamber, the variation of the ion recombination correction factor with depth was modeled adequately by a sigmoid function, which is approximately constant in the plateau and strongly increasing in the Bragg peak region to values of up to 1.06. Except in the distal edge region, all experimental results are accurately described by Jaffé's theory. CONCLUSIONS: Experimental results confirm that ion recombination in the investigated carbon ion beams is dominated by initial recombination. Ion recombination corrections are found to be significant and cannot be neglected for reference dosimetry and for the determination of depth dose curves in carbon ion beams.

Radiation protection system at the RIKEN RI beam factory.

The RIKEN RI (radioactive isotope) Beam Factory is scheduled to commence operations in 2006, and its maximum energy will be 400 MeV u(-1) for ions lighter than Ar and 350 MeV u(-1) for uranium. The beam intensity will be 1 pmicroA (6 x 10(12) particles s(-1)) for any element at the goal. For the hands-on-maintenance and the rational shield thickness of the building, the beam loss must be controlled with several kinds of monitors. Three types of radiation monitors will be installed. The first one consists of a neutron dose equivalent monitor and an ionisation chamber, which are commercially available area monitors. The second one is a conventional hand-held dose equivalent monitor wherein the logarithmic signal is read by a programmable logic controller based on the radiation safety interlock system (HIS). The third one is a simple plastic scintillator called a beam loss monitor. All the monitors have threshold levels for alarm and beam stop, and HIS reads all these signals.

Biophysical characteristics of HIMAC clinical irradiation system for heavy-ion radiation therapy.

PURPOSE: The irradiation system and biophysical characteristics of carbon beams are examined regarding radiation therapy. METHODS AND MATERIALS: An irradiation system was developed for heavy-ion radiotherapy. Wobbler magnets and a scatterer were used for flattening the radiation field. A patient-positioning system using X ray and image intensifiers was also installed in the irradiation system. The depth-dose distributions of the carbon beams were modified to make a spread-out Bragg peak, which was designed based on the biophysical characteristics of monoenergetic beams. A dosimetry system for heavy-ion radiotherapy was established to deliver heavy-ion doses safely to the patients according to the treatment planning. A carbon beam of 80 keV/microm in the spread-out Bragg peak was found to be equivalent in biological responses to the neutron beam that is produced at cyclotron facility in National Institute Radiological Sciences (NIRS) by bombarding 30-MeV deuteron beam on beryllium target. The fractionation schedule of the NIRS neutron therapy was adapted for the first clinical trials using carbon beams. RESULTS: Carbon beams, 290, 350, and 400 MeV/u, were used for a clinical trial from June of 1994. Over 300 patients have already been treated by this irradiation system by the end of 1997.

Proton dosimetry intercomparison based on the ICRU report 59 protocol.

BACKGROUND AND PURPOSE: A new protocol for calibration of proton beams was established by the ICRU in report 59 on proton dosimetry. In this paper we report the results of an international proton dosimetry intercomparison, which was held at Loma Linda University Medical Center. The goals of the intercomparison were, first, to estimate the level of consistency in absorbed dose delivered to patients if proton beams at various clinics were calibrated with the new ICRU protocol, and second, to evaluate the differences in absorbed dose determination due to differences in 60Co-based ionization chamber calibration factors. MATERIALS AND METHODS: Eleven institutions participated in the intercomparison. Measurements were performed in a polystyrene phantom at a depth of 10.27 cm water equivalent thickness in a 6-cm modulated proton beam with an accelerator energy of 155 MeV and an incident energy of approximately 135 MeV. Most participants used ionization chambers calibrated in terms of exposure or air kerma. Four ionization chambers had 60Co-based calibration in terms of absorbed dose-to-water. Two chambers were calibrated in a 60Co beam at the NIST both in terms of air kerma and absorbed dose-to-water to provide a comparison of ionization chambers with different calibrations. RESULTS: The intercomparison showed that use of the ICRU report 59 protocol would result in absorbed doses being delivered to patients at their participating institutions to within +/-0.9% (one standard deviation). The maximum difference between doses determined by the participants was found to be 2.9%. Differences between proton doses derived from the measurements with ionization chambers with N(K)-, or N(W) - calibration type depended on chamber type. CONCLUSIONS: Using ionization chambers with 60Co calibration factors traceable to standard laboratories and the ICRU report 59 protocol, a distribution of stated proton absorbed dose is achieved with a difference less than 3%. The ICRU protocol should be adopted for clinical proton beam calibration. A comparison of proton doses derived from measurements with different chambers indicates that the difference in results cannot be explained only by differences in 60Co calibration factors.

Hemangioblastoma of the central nervous system: nature of the stromal cells as studied by the immunoperoxidase technique.

Ten hemangioblastomas of the central nervous system were examined by an immunoperoxidase technique for glial fibrillary acidic protein (GFAP), S-100 protein, and Factor VIII-related antigen to determine the origin of the stromal cells. In seven cases scattered stromal cells were positive for GFAP, and eight cases showed variable numbers of S-100 protein-positive cells. These positive cells were present throughout the tumors. S-100 protein-positive stromal cells corresponded to GFAP-positive cells, but the former were more numerous than the latter. Staining for Factor VIII-related antigen was negative in stromal cells, except in endothelial cells lining capillaries. It was suggested that stromal cells of capillary hemangioblastomas are composed by heterogeneous cell populations.

Dosimetry and measured differential W values of air for heavy ions.

Heavy-ion irradiation systems were designed and constructed at two cyclotron facilities in Japan for use in various fields of radiation physics and radiation biology. A 135 MeV/u carbon beam as well as 12 MeV/u carbon and helium-3 beams were first used in experiments. We have established a systematic method for heavy-ion dosimetry at both high and low incident energies involving measurements of fluences. We also obtained differential W values (w) of air for those beams by comparing the results of fluence measurement dosimetry with ionization chamber dosimetry. The differential W values of air were found to be 36.2 +/- 1.0, 34.5 +/- 1.0, and 33.7 +/- 0.9 eV for 6.7 MeV/u carbon ions, 10.3 MeV/u 3He ions, and 129.4 MeV/u carbon ions, respectively. The w value for high-energy heavy ions approaches the W value for high-energy electron or photon beams. In ionization chamber dosimetry for a heavy-ion beam, we found a track-size effect. A difference in the track sizes of heavy ions in the gas and solid phases affected the output current of the ion chamber in the case of high-energy heavy ions.

Skin and epidural recording of spinal somatosensory evoked potentials following median nerve stimulation: correlation between the absence of spinal N13 and impaired pain sense.

A clinical lesion study and intraoperative epidural recordings were made to test the origin and clinical significance of the spinal N13 and P13 of somatosensory evoked potentials (SEP) that follow median nerve stimulation. Intraoperatively, the respective peak latencies of spinal P13 and N13 coincided with those of the N1 component of the dorsal cord potential and its phase reversed positivity. On both the ventral and dorsal sides of the cervical epidural space, maximal amplitude was at the C5 vertebral level to which nerve input from the C6 dermatome is the main contributor. The modality of sensory impairment in the hand dermatome was examined in selected patients with cervical lesions, who showed such normal conventional SEP components as Erb N9, far-field P9, P11, P14, N18 and cortical N20, with or without loss of spinal N13. Statistically, the loss of spinal N13 was associated with decrease of pain sensation in the C6 dermatome. This was interpreted as being due to damage to the central grey matter of the cord, including the dorsal horn. Our results suggest the spinal N13 and P13 originate from the same source in the C6 spinal cord segment and that they are good indicators for the detection of centromedullary cervical cord damage.

High-risk dural arteriovenous fistulae of the transverse and sigmoid sinuses.

Dural arteriovenous fistulae of the transverse and sigmoid sinuses are highly variable in symptomatology and prognosis. However, we have identified a subgroup of patients who have a high risk of hemorrhage and dementia due to severe venous overload caused by high arterial flow into the fistulae and by occlusive changes of the transverse and sigmoid sinuses. Three representative cases selected from 31 patients with dural arteriovenous fistulae of the transverse and sigmoid sinuses are presented, and 45 reported similar cases are reviewed to discuss pathophysiology and problems encountered during treatment.

Energy loss of 70 MeV protons in organic polymers.

Using Bragg ionization curves, measurements of the average stopping power of organic polymers relative to that of water have been made for 70 MeV protons losing about 30 MeV in the absorbers. By comparing calculated curves to experimental ones, I-values for the polymers were obtained, relative to the I-value for A1. For repeated measurements with A-150 tissue equivalent plastic, the standard deviation of the ratio of the average stopping powers q was +/- 0.06%. It was found that q depends on the year of production of A-150. For other absorbers, the uncertainty of q is estimated to be +/- 0.2%, with a corresponding uncertainty of the I-values of +/- 1.5%. Most measured I-values exceed values calculated with the additivity rule by about 10%. During the course of the measurements, fluctuations of the proton energy from the cyclotron of up to 0.8% were found.

Natural course of unoperated intracranial arteriovenous malformations: study of 50 cases.

The clinical course of 50 patients with conservatively treated intracranial arteriovenous malformations (AVM's) was followed, most of them for more than 5 years. The average follow-up period was 13.4 years. The initial symptom was intracranial bleeding in 29 patients (58%) and seizure in 15 patients (30%). Small and deep-seated AVM's were associated with a high incidence of bleeding; however, repeated hemorrhages were not necessarily indicative of a poor prognosis. Children younger than 15 years had a better prognosis than adults. There was no correlation between pregnancy and bleeding. In the hemorrhage group, the incidence of rebleeding was 6.9% in the 1st year after initial rupture, 1.91% per year after 5 years, and 0.92% per year after 15 years. The overall incidence of rebleeding was 34.5% in the hemorrhage group. Of the 50 patients, 37 (74%) had a good clinical outcome, four (8%) had a fair outcome, and four (8%) had a poor outcome; five patients died.

Carbon beam dosimetry intercomparison at HIMAC.

To verify international uniformity in carbon beam dosimetry, an intercomparison programme was carried out at the heavy ion medical accelerator (HIMAC). Dose measurements with ionization chambers were performed for both unmodulated and 6 cm modulated 290 MeV/nucleon carbon beams. Although two different dosimetry procedures were employed, the evaluated values of absorbed dose were in good agreement. This comparison established a common framework for ionization chamber dosimetry between two different carbon beam therapy facilities.

Acute epidural hematoma complicating Paget's disease of the skull.

Although among Anglo-Saxons Paget's disease is relatively common, it is very rare in Japan. The incidence of Paget's disease increases as age advances, and in elderly people over 90 years of age it can be seen in as many as 10%. On the other hand, acute epidural hematoma seldom occurs in the older generation, because dural adhesion to the internal table of the skull becomes more intense. We have encountered an 86-year old woman with advanced Paget's disease who developed an acute epidural hematoma after trivial head trauma. Acute epidural hematoma complicating Paget's disease has been reported only twice before and this case is the first report in Japan. The literature on the pathogenesis of the acute epidural hematoma complicating Paget's disease is reviewed.

Invasive character of malignant endothelial cells in vinyl-chloride-induced liver angiosarcoma.

Two cases of vinyl-chloride-induced angiosarcoma of the liver were investigated with special reference to the invasive character of malignant endothelial cells. Histological findings of the liver were similar in both cases. The liver angiosarcoma was multicentric and consisted of three portions: a peripheral parenchymal area, an intermediate mottled area, and a central cavernous area. Microscopically the intermediate area showed a mixture of fibrosis and cell infiltration of various patterns. At the periphery, yellowish brown parenchymal tissues remained and were always associated with sinusoidal changes, from non-cellular dilatation to trabecular growth of the small round cells. Under electron microscope, the small round cells showed direct contact with red blood cells and hepatocytes. Thus, the sinusoidal small cell infiltration is thought to be an initial lesion of angiosarcomatous transformation. Because none of the liver is free from these sinusoidal changes, partial hepatectomy would not be indicated even in a patient with few cavernous lesions.

Conservative management of cerebellar hemorrhage in pregnancy.

A case of cerebellar arteriovenous malformation (AVM) during pregnancy is reported. A 26-year-old primigravida had cerebellar hemorrhage at 32 weeks of gestation. She was conservatively controlled until term with a good outcome accomplished by elective cesarean section. AVM in the left cerebellar hemisphere was confirmed by angiography after delivery and successfully removed. Here we present a review of AVM during pregnancy and a few case reports of cerebellar AVM-complicated pregnancy published in available literatures.

Dosimetry of 70 MeV proton beams from the NIRS cyclotron.

Dosimetry of 70 MeV proton beams for radiotherapy was carried out using various ionization chambers. The beam irradiation conditions, dose estimation with an ionization chamber, measurement of dose distributions, and calculation of isodose curves for the proton beams will be discussed.

Determination of ion recombination loss by two-voltage method for pulsed radiation beams.

The ion recombination loss is one of the most important correction factors for dosimetry using ionization chamber especially for the measurement of high-intensity pulsed radiation beam. The two-voltage method has been used frequently for the correction of ion recombination loss. Several ways to approximate the method are presented. Comparisons were carried out to check the validity of the approximation. Using four ionization chambers of different types and shapes, measurements were made to obtain the optimal value of the ratio for the two voltages.

Choroidal epithelial cyst in the cerebellopontine angle associated with trigeminal neuralgia--case report.

The authors describe the case of a 37-year-old female with a symptomatic epithelial cyst in the cerebellopontine angle, which is extremely rare. The cyst caused trigeminal neuralgia, which completely disappeared following its removal. The histological diagnosis was choroidal epithelial fluid-filled cyst. The wall of the cyst consisted of a single layer of epithelial cells with microvilli and a basement membrane.

Shielding experiment of heavy-ion produced neutrons using a tissue-equivalent proportional counter.

A shielding experiment was performed at the HIMAC (Heavy Ion Medical Accelerator in Chiba), of National Institute of Radiological Sciences (NIRS), to measure neutron dose using a spherical TEPC (tissue-equivalent proportional counter) of 12.55 cm inner diameter. Neutrons are produced from a 5 cm thick stopping length Cu target bombarded by 400 MeV/nucleon C6+ ions and penetrate concrete or iron shields of various thicknesses at 0 degree to the beam direction. From this shielding experiment. y-distribution, mean lineal energy, absorbed dose, dose equivalent and mean-quality factor were obtained behind the shield as a function of shield thickness. The neutron dose attenuation lengths were also obtained as 126 g cm(-2) for concrete and 211 g cm(-2) for iron. The measured results were compared with the calculated results using the MARS Monte Carlo code.

Induced radioactivity in CU targets produced by high-energy heavy ions and the corresponding estimated photon dose rates.

Irradiation experiments were performed at the Heavy Ion Medical Accelerator in Chiba (HIMAC) facility, National Institute of Radiological Sciences. The radioactive spallation products in a thick Cu target were obtained for Ar(230, 400 MeV per nucleon), Si(800 MeV per nucleon), Ne(100, 230, 400 MeV per nucleon), C(100, 230, 400 MeV per nucleon), He(100, 230 MeV per nucleon), p(100, 230 MeV) ions. The gamma-ray spectra from irradiated Cu samples inserted into the composite Cu target were measured with a high-purity germanium (HPGe) detector. From the gamma-ray spectra, we obtained the spatial distribution of radioactive yields of spallation products of 40 nuclides in the Cu sample in the Cu target. From the spatial distribution of radioactive yields, we estimated the residual activity and photon dose induced in the Cu target. The residual activity and photon dose become larger with the increase in projectile energy per nucleon and the range of the projectile beam for the same projectile energy per nucleon.

[A case of cavernous hemangioma with acute visual disturbance (author's transl)].

The authors report a case of parasellar cavernous hemangioma having grown to the suprasellar region within 3 year's period and showing acute visual disturbance caused by intratumoral hemorrhage. A 44-year-old woman, who had experienced spontaneous intracerebral hematoma in the left inferior frontal lobe 3 years ago and then obtained good recovery in the post-operative period had suddenly developed decreased visual acuity of the left eye without other neurological deficit. CT scan revealed an irregular mass lesion in the chiasmal region, which had a crown-like high density area over the suprasellar low density. Carotid angiogram showed a suprasellar avascular mass and the left A1 segment showed marked narrowing. Neither tumor nor venous pooling was visible in the capillary and venous phase. Surgery disclosed a reddish dark tumor with thin capsular wall, extending from the left cavernous sinus to the suprasellar region, and it was accompanied by intratumoral hemorrhage compressing the left optic nerve. The tumor was subtotally removed. High density area on the precontrast scan was confirmed to be intratumoral hemorrhage and the low density area was of organized tissue due to thrombosis. Histological finding was compatible to cavernous hemangioma. Postoperatively visual acuity of the patient was well recovered, but left 3rd and 6th cranial nerve palsy followed. The authors discussed the mechanism of acute onset and CT findings of the cavernous hemangioma arising in the chiasmal region with a review of literature.