192Ir Wire Research Articles

The electron-dose distribution surrounding an 192Ir wire brachytherapy source investigated using EGS4 simulations and GafChromic TM film

The steep dose gradient around 192Ir brachytherapy wire implants is predicted by the EGS4 (PRESTA version) Monte Carlo simulation. When considering radiation absorbion regions close to the wire source, the accurate dose distribution cannot be calculated by the GE Target II Sun Sparc treatment-planning system. Experiments using GafChromic TM film have been performed to prove the validity of the EGS4 user code when calculating the dose close to the wire source in a low energy range.

High dose rate (HDR) and low dose rate (LDR) interstitial irradiation (IRT) of the rat spinal cord

Purpose: To describe a newly developed technique to study radiation tolerance of rat spinal cord to continuous interstitial irradiation (IRT) at different dose rates. Material and methods: Two parallel catheters are inserted just laterally on each side of the vertebral bodies from the level of Th 10 to L 4. These catheters are afterloaded with two 192Ir wires of 4 cm length each (activity 1–2.3 mCi/cm) for the low dose rate (LDR) IRT or connected to the HDR micro-Selectron for the high dose rate (HDR) IRT. Spinal cord target volume is located at the level of Th 12-L 2. Due to the rapid dose fall-off around the implanted sources, a dose inhomogeneity across the spinal cord thickness is obtained in the dorso-ventral direction. Using the 100% reference dose (rate) at the ventral side of the spinal cord to prescribe the dose, experiments have been carried out to obtain complete dose response curves at average dose rates of 0.49, 0.96 and 120 Gy/h. Paralysis of the hind-legs after 5–6 months and histopathological examination of the spinal cord of each irradiated rat are used as experimental endpoints. Results: The histopathological damage seen after irradiation is clearly reflected the inhomogeneous dose distribution around the implanted catheters, with the damage predominantly located in the dorsal tract of the cord or dorsal roots. With each reduction in average dose rate, spinal cord radiation tolerance is significantly increased. When the dose is prescribed at the 100% reference dose rate, the ED 50 (induction of paresis in 50% of the animals) for the HDR-IRT is 17.3 Gy. If the average dose rate is reduced from 120 Gy/h to 0.96 or 0.49 Gy/h, a 2.9- or 4.7-fold increase in the ED 50 values to 50.3 Gy and 80.9 Gy is observed; for the dose prescribed at the 150% reference dose rate (dorsal side of cord) ED 50 values are 26.0, 75.5 and 121.4 Gy, respectively. Using different types of analysis and in dependence of the dose prescription and reference dose rate, the α β ratio varies between 1.46 (0.06–3.08 CL) and 2.17 Gy (0.08–4.61). The half time of repair during continuous irradiation is 1.76 h (1.33–2.64), while no indication is found for a biphasic pattern of the kinetics of repair. Conclusion: The implantation technique in our study has shown to be a reliable model to compare the effectiveness of HDR- and LDR-interstitial continuous irradiation at different dose rates.

External beam and intraluminal radiotherapy for locally advanced bile duct cancer: role and tolerability

Background and purpose: Cholangiocarcinoma is rare but carries a poor prognosis. Radiotherapy has been used either as an adjuvant treatment following surgical resection of tumour or for palliation. The purpose of this study was to assess the feasibility and morbidity of accelerated external beam radiotherapy with or without intraluminal radiotherapy in the treatment of locally advanced bile duct cancer. Materials and methods: Thirty eight patients were treated. Surgical procedures performed prior to radiotherapy were extended hepatectomy (3), hepaticojejunostomy with tumour resection (6), palliative biliary-enteric bypass (6), biopsy (4), Whipple's procedure (1), gastrojejunostomy (1) and cholecystectomy (1). Twenty patients received external beam radiotherapy (ERT). Six patients received one Phase of ERT and 12 received two Phases, separated by a 2-week gap. Dose per Phase was 22.5 Gy in 10 twice daily fractions. After 1989, dose per Phase was increased to 27.5 Gy. One patient received Phase I ERT (30.0 Gy) using conventional fractionation and one patient received an uninterrupted, conventionally fractionated course of treatment (50.0 Gy). Fourteen patients received both ERT and intraluminal radiotherapy (IRT) using iridium-192 ( 192Ir) wire passed through a percutaneous, transhepatic catheter (median dose, ERT 23.8 Gy + IRT 40.0 Gy). In addition, four patients received IRT alone (median dose 45.0 Gy at 1 cm radius). Patients were followed for at least 42 months. Results: Median overall survival was 15 months. Overall survival for the whole group at 1, 2 and 3 years was 59.6%, 32.5% and 16.2%. Thirty four patients died of disease. Radiotherapy caused acute toxicity in seven patients. According to RTOG/EORTC criteria toxicity was Grade 1 in four cases, Grade 2 in two cases and Grade 3 in one case. Two patients developed gastrointestinal bleeding as a late complication of radiotherapy. Conclusions: Accelerated external beam radiotherapy with or without intraluminal radiotherapy is feasible and associated with acceptable toxicity when used in the management of advanced cholangiocarcinoma.

202Monte Carlo dose simulation of 192IR wires in some clinical situations

202Monte Carlo dose simulation of 192IR wires in some clinical situations

32 - Quality assurance for a 192Ir wire source dosimetry

32 - Quality assurance for a 192Ir wire source dosimetry

Intraluminal brachytherapy in the treatment of pancreas and bile duct carcinoma

A new method of palliation of malignant obstructive jaundice is presented. Twelve patients with carcinoma of the extrahepatic bile ducts (EHBD-five patients) or pancreatic head (PH-seven patients) received radiation therapy between 1988 and 1991. Percutaneous transhepatic biliary drainage was performed in four EHBD patients and an endoprosthesis was placed during endoscopic retrograde cholangiopancreatography (ERCP) in the other eight patients. All 12 received intraluminal brachytherapy (ILBT): 20-50 Gy calculated at 1 cm from the Iridium-192 (192Ir) wire. In four PH patients the source was placed in the duct of Wirsung; in the other eight patients ILBT was performed via the common bile duct. Five of the seven PH patients and one of the five EHBD patients received External Beam Radiation Therapy (EBRT): 26-50 Gy, alone or with concomitant 5-Fluorouracil (5-FU). Cholangitis occurred in six patients. Three PH patients treated with EBRT+ILBT developed gastrointestinal toxicities. With a minimum follow-up of 18 months, median survival times were 14 months (EHBD) and 11.5 months (PH); one of the seven PH patients is alive (29 months) and two of the EHBD patients are alive (18 and 43 months). All patients had satisfactory control of jaundice. The results in the EHBD patients suggest that the addition of ILBT after biliary drainage prolongs survival. Further experience is necessary to determine whether ILBT in the common bile duct and/or in the duct of Wirsung may be, in PH patients, an alternative boost technique to Interstitial Brachy-therapy (IBT) or Intraoperative Electron Beam Radiation Therapy (IOEBRT).

Nephrostomy track brachytherapy following percutaneous resection of transitional cell carcinoma of the renal pelvis

Percutaneous nephrostomy can be used to resect transitional cell carcinoma (TCC) from the renal pelvis, to avoid nephrectomy in selected patients. This procedure carries a potential risk of tumour seeding along the nephrostomy track, which it is our policy to irradiate prophylactically. A total of 25 procedures on 23 patients have been carried out since 1982. The 18 males and five females had a median age of 64 years (range 46-81) at the time of treatment. Of the ten patients with only one functioning kidney, nine had undergone contralateral nephroureterectomy, seven for TCC, one for a non-functioning kidney, and one for renal tuberculosis; one patient had received radical radiotherapy for an inoperable contralateral renal tumour. The other 13 patients had asked for a conservative treatment approach to be adopted. From 1982-1989, low dose rate 192Ir wire was used in 13 patients to deliver a median dose of 45 Gy (range 40-50) to the full length of the track at the surface of nephrostomy tube. Since 1989, we have used a high dose rate (HDR) 192Ir microSelectron to treat 12 patients with a single fraction of 10-12 Gy, including two who had undergone previously 192Ir wire track irradiation of the same kidney. One patient required a nephroureterectomy after developing a non-healing renal pelvis leak following combined modality treatment. Otherwise, no early or late radiation-related morbidity has been seen, and no nephrostomy track recurrences have occurred during a median follow-up of 5 years (range 1-9). The HDR microSelection has enabled us to deliver this treatment quickly and simply during the standard postoperative stay in hospital following percutaneous nephrostomy.

Dosimetric considerations of commercially fabricated esophageal applicators

Two commercially fabricated esophageal applicators for low dose rate intraluminal brachytherapy were compared using the dose non-uniformity ratio (DNR). One of the applicators has a single afterloading catheter while the other applicator has six afterloading catheters to accommodate low dose rate 192Ir ribbon or wire sources. Five sets of source configurations, each with a different ribbon length in the range of 5–17 cm were analysed using the DNR. The DNR shows the delivery of relatively higher total doses at higher dose rates to tissues closer to the applicators. The difference in the inhomogeneity of dose rates and the treatment volume exposed to higher dose rates than the prescribed dose rate between the two applicators are minimal. The dose homogeneity is better for the single-source applicator while the worst dose homogeneity for the six-source applicator is caused by the placement of each source closer to the surface of the applicator. The implications of higher dose rates were discussed using the α β model.

Radioactivity measurements of 192Ir wire sources with a microcalorimeter

Radioactivities of metallic 192Ir sources are measured with a microcalorimeter nondestructively. In order to convert the complete decay energy evolved from the source into thermal energy, a tungsten block is used as radiation absorber. The sample sources measured are four thin wires of Ir/Pt alloy with dimensions of 0.1 mm ø × 10 mm 1, each coated by 0.1 mm thick platinum, giving the final diameter of 0.3 mm ø. Overall uncertainty of the measurement for some 60 MBq activity is ±3.2%. Measurements of the wire sources with an ionisation chamber give smaller activities which are smaller by 10% than those from microcalorimetry mainly because of the autoattenuation effect.

皮膚悪性腫ように対する放射線治療

Skin cancer is the most common malignant neoplasm in the United States and Europe. However, these tumors are less common in Japan. Radiotherapy is an excellent modality for the treatment of selected basal cell and squamous cell carcinomas. Many patients in a foreign country prefer radiotherapy because of no pain with treatment, no hospitalization and good cosmetic result. On the other hand, skin cancer arising from scars is contraindicated for radiotherapy. A survey of the literature showed that the 5-year recurrence rates were 3 to 10% dependent on the tumor size. In addition, recurrenes following radiotherapy are satisfactorily managed by radical surgical treatment. Total skin electron irradiation for both mycosis fungoides and subcutaneous T cell lymphoma, at least in early stages, leads to a complete remission of long duration. However, the techniques of total skin electron irradiation are very difficult because of difficulty of homogeneous dose distribution for a large field. Malignant melanoma is one of the radioresistant tumors. The in vitro survival curve of malignant melanoma cell is characterized by a wide shoulder, indicating a large ability to repair sublethal radiation damage. The literatures showed that fraction size rather than total dose was of importance for the radiation response of malignant melanoma. Some authors have recently reported the excellent result of treatment for patients with advanced or recurrent carcinoma using 192Ir wire. We described the role of radiotherapy for malignant neoplasm of skin in detail.

The role of radiotherapy in the treatment of bile duct carcinoma

Forty-two patients with irresectable bile duct carcinoma (n = 31) or with microscopic evidence of tumor rest after aggressive surgery for bile duct carcinoma (n = 11) were given radiotherapy consisting intentionally of external-beam therapy and intraluminal 192Iridium ( 192Ir) wire application(s) following bile drainage procedures. The treatment was well tolerated; complications were mainly infectious and related to the success of the drainage. A median survival of 10 months was achieved for the group as a whole. Patients treated following microscopically incomplete resection survived longer than patients with an irresectable tumor (15 vs 8 months median survival, p = 0.06). Gross lymph node involvement also proved to be a prognostic factor.

Comparison of measured and calculated dose distributions around an iridium-192 wire.

The relative dose distribution around a 5.0-cm-long piece of 192Ir wire has been measured using LiF chips. Measurements were made at distances of 0.25 to 5.0 cm away from the source and distances of 0.0 to 4.0 cm along the source. In addition, measurements were also made at several distances along the axis of the source. Attention was paid to the errors associated with these measurements. A comparison was made between a commercial software program, ISODOS, an analytical solution to the Sievert integral, and the measurements. Good agreement was obtained at distances along and away from the source. Major disagreements were found at points along the source axis.

First clinical experience with a remote afterloading system for low dose rate interstitial breast implants

A new remote afterloading system, developed for low or medium dose rate brachytherapy has been clinically evaluated. With this apparatus, the Micro-Selectron, up to 15 192Ir wires or seeds encapsulated in a plastic tubing can be loaded simultaneously into implants. Improved radiological protection for the medical staff has now been achieved with this apparatus. One hundred and sixty patients have been treated so far with breast implants using remote afterloading. The mean error frequency over the last year was about one error every 10 treatments of which about half could be considered as machine failures. All treatments could, however, be finished by using spare channels of the afterloader. We have found that a set of 45 source assemblies is adequate for the loading of the breast-needle implants performed in our institute. Every 6 to 8 weeks a new set of 192Ir sources is prepared.

An accurate method of 192Ir wire implantation for locally advanced carcinoma of breast.

An accurate and reproducible method of 192Ir wire implantation of locally advanced breast tumour after locoregional megavoltage external radiotherapy has been described. The method includes the use of cobex cast for breast and tumour immobilization, of computed tomography for tumour localization, of computer for planning and isodose display and of specially made template to guide insertion of trocars and 192Ir wires.

An autoclavable transport container for guide-wires containing iridium 192.

The use of radioactive 192Ir wire in the treatment of high bile-duct carcinoma has been described by Fletcher et al (1981). At Sir Charles Gairdner Hospital the routine procedure involves initial placement of a nasobiliary catheter into the patient for both biliary drainage and accommodation of a flexible guide-wire containing the prescribed length of 192Ir wire. The guide-wire used is 1450 mm long and contains an inner stilette which is removed to allow a nylon spacer (normally 20 mm in length) followed by the 0.3 mm diameter 192Ir wire (typically 30–100 mm in length) to be inserted into the guide-wire. The stilette is then replaced to locate the spacer and 192Ir wire positively, at the distal end of the guide-wire. The loaded guide-wire is positioned under radiological control and left in the patient until the prescribed treatment dose has been delivered. Before use, the guide-wire containing the 192Ir wire must be autoclaved. A device to permit this and afford radiation protection for staff has been constructed, and is described below.

The use of simulator-based computed tomography in iridium-192 dosimetry.

When conventional radiography is used to determine the spatial distribution of brachytherapy sources, the interpretation of pairs of orthogonal radiographs may prove difficult, especially in the case of multiplane, or curved-plane implants. Where sources of uniform linear activity are implanted in a parallel array, as in the case of 192Ir wire implants arranged in the Paris system, and running in a superior–inferior direction, cross-sectional information can provide a useful addition to, and in many cases a substitute for, conventional radiography. A computed tomography (CT) system based on a radiotherapy simulator (Kotre et al, 1984) has been employed to provide this information.

Induction of Lung Tumors by Radioactive Isotopes Implanted in the Rat Lung<xref ref-type="fn" rid="FN1">2</xref>

Squamous cell carcinomas were induced in the lungs of male WAG/Rij inbred rats by radiation emitted from the isotopes iridium-192 or iodine-125. These isotopes were implanted by a surgical procedure in the lungs of young rats. Forty rats received implants of 192Ir wires and 20 animals, of 125I seeds. In a 14-month observation period, 30 of the 40 animals with implants of 192Ir wires developed tumors. Malignant hemangioendotheliomas occurred with the highest frequency (50%). From the lungs of 12 rats, squamous cell carcinomas were found. In the observation period of 17 months, 3 rats with implants of 125I seeds developed tumors, among which 1 squamous cell carcinoma could be identified. Tumor fragments were transplanted in syngeneic hosts for propagation of the tumors. Histologic appearances of tumors remained constant in subsequent passages. Responses of transplanted tumors growing in the flanks of syngeneic hosts to doses of radiation, methotrexate, or vinblastine were determined. Although the histologic appearances of the 5 squamous cell carcinomas were similar, tumor-doubling times and responses to irradiation and chemotherapeutic drugs were different. Small cell or large cell carcinomas were not observed.

'Paris' technique implant dosimetry tables for 0.3 and 0.6 mm diameter 192Ir wire.

Dosage and treatment volume parameters for 192Ir wire brachytherapy implants using the Paris technique (Pierquin & Dutreix, 1967; Pierquin et al, 1978) may be estimated using the “cross-line” data of Hall et al (1966) or the “escargot” curves of Schlienger et al (1970). An alternative approach using standard tables has been described for single plane and double plane (square array) implants in which absorption and scatter within the tissue and oblique absorption within the radioactive sources have been ignored (Casebow, 1984). The tables presented are therefore for general applications and are not specific to any particular source diameter, or indeed any radionuclide. This note describes a modification of the method to include oblique absorption and is therefore compartible with the “cross-line” data. Tables are given for the 0.3 mm and 0.6 mm diameter 192Ir wires currently available. In addition, two-plane triangular arrays of sources are considered and compared with square arrays. The Paris technique in...

Two simple tools for preparing iridium-192 wire for clinical use.

192Ir wire is supplied by Amersham International either as hairpins (or single pins) which are 60 mm long and 0.6 mm in diameter or as 0.5 m lengths of 0.3 mm diameter wire. One of its advantages in interstitial therapy is that it may be cut to the required length. A tool for cutting hairpins has been described by Collins (1975). This note describes a device which is perhaps simpler and has the advantage that it is easy to cut the pins to different leg lengths. Two commercial devices exist for loading the 0.3 mm wire into nylon tubing, but neither is ideal. The TEM loader (a commercial version of that described by Darby et al (1972)) is very expensive and the 192Ir wire may fail to feed correctly if the instrument is not perfectly aligned, although such occasions are now rare following a recent redesign. The Amersham loader (Amersham International—Type N.410), although inexpensive, is difficult to use (but we understand that Amersham International are currently redesigning their loader). This note describ...

Calculation of dose distributions for iridium-192 implants.

After reviewing the method of Hall et coll. (1966) for calculating dose rates from 192Ir wire, small changes and improvements were made and a computer program was written to calculate dose distributions. It was found that the wire position data obtained from films and supplied to the program was the largest source of inaccuracy but that with care the maximum error in the calculated dose rates was 3 per cent. If the original cross-line curves are still used for calculations the additional error introduced into the dose rates at distances of up to 4 cm from the wire is less than one per cent.