High Dose Rate Unit Research Articles

Quality of life and sexual functioning among endometrial cancer patients treated with one week adjuvant high-dose-rate vaginal brachytherapy schedule.

PurposeTo examine quality of life (QOL) and sexual functioning in a series of patients with intermediate- and high-intermediate risk endometrial cancer, treated with exclusive adjuvant one week high-dose-rate (HDR) vaginal brachytherapy (VBT) schedule.Material and methodsBetween July 2008 and October 2013, 55 patients with diagnosis of endometrial cancer were treated with adjuvant exclusive VBT. All patients had undergone surgical treatment with a laparotomy approach before VBT. Post-operative VBT was administered 6-8 weeks after surgery. Treatment was delivered to vaginal vault using Nucletron HDR unit with iridium-192 source at a dose of 21 Gy/3 fractions of 7 Gy each, three times a week, every other day, prescribed at 0.5 cm depth of vaginal wall, and 3 cm in length from the apex. QOL was assessed using European Organization for Research and Treatment of Cancer (EORTC) quality of life questionnaire Core-30 (QLQ-C30), and EORTC cancer-specific quality of life questionnaire (QLQ-CX24).ResultsMedian follow-up time was 92 months (range, 42-162 months). Questionnaires were carried out respectively at 1, 3, 6, 12, 24, 36, 48, and 60 months after the end of BT. Response rate to questionnaires was 100% (n = 55). Nineteen patients (35%) answered all the questions of surveys, while 36 patients (65%) completed the surveys, except for questions on sex activity, vaginal function, and sex enjoyment. Longitudinal analysis during 5-year follow-up period showed a statistically significant trend towards worsening of fatigue, constipation, and diarrhea. Overall physical functioning and role functioning was not impaired after VBT. Over the time, sex enjoyment improved, except for elderly patients. For emotional functioning, sex worry and social functioning presented no significant time-related effect.ConclusionsOne week brachytherapy schedule to vaginal cuff is generally well-tolerated. QOL does not worsen after applying vaginal brachytherapy.

Gamma-ray dose rate surveys help investigating century-scale beach ridge progradation in the wave-dominated Catumbela delta (Angola)

A strandplain at the downdrift side of the wave-dominated Catumbela delta (Angola) includes distinguishable deposits with very high natural radioactivity (up to 0.44 microSv/hour). In order to establish the geometry of these sedimentary units and understand their genetic processes, dose rate surveys were performed with the portable equipment Rados RDS-40WE. In addition, grain-size distribution, heavy-mineral composition and gamma-ray mass spectra of the high dose rate deposits were analysed. High dose rate values are found in ribbon units aligned parallel to the shoreline, which are a few tens of meters wide and up to approximately 3 km long. These units reflect the concentration of Th-bearing grains in coastal deposits enriched in heavy minerals. An integrated analysis of the high dose rate ribbons in GIS environment with aerial photography and topographic maps suggests that parts of the high dose rate units formed during the last two centuries may be related with the erosion of older shoreline deposits, due to updrift displacements of the Catumbela river outlet and recycling of shoreline accumulations with downdrift deposition. Simple gamma-ray surveys carried out with a portable detector can unravel depositional units characterised by significant enrichment in heavy-mineral grains that are likely to correspond to key events in the evolution of wave-dominated accumulations. The location of such deposits should be taken into account when planning future work using more expensive or time-consuming techniques.

TU‐D‐201‐07: Severity Indication in High Dose Rate Brachytherapy Emergency Response Procedure

Purpose:Understanding the corresponding dose to different staff during the High Dose Rate (HDR) Brachytherapy emergency response procedure could help to develop a strategy in efficiency and effective action. In this study, the variation and risk analysis methodology was developed to simulation the HDR emergency response procedure based on severity indicator.Methods:A GammaMedplus iX HDR unit from Varian Medical System was used for this simulation. The emergency response procedure was decomposed based on risk management methods. Severity indexes were used to identify the impact of a risk occurrence on the step including dose to patient and dose to operation staff by varying the time, HDR source activity, distance from the source to patient and staff and the actions. These actions in 7 steps were to press the interrupt button, press emergency shutoff switch, press emergency button on the afterloader keypad, turn emergency hand‐crank, remove applicator from the patient, disconnect transfer tube and move afterloader from the patient, and execute emergency surgical recovery.Results:Given the accumulated time in second at the assumed 7 steps were 15, 5, 30, 15, 180, 120, 1800, and the dose rate of HDR source is 10 Ci, the accumulated dose in cGy to patient at 1cm distance were 188, 250, 625, 813, 3063, 4563 and 27063, and the accumulated exposure in rem to operator at outside the vault, 1m and 10cm distance were 0.0, 0.0, 0.1, 0.1, 22.6, 37.6 and 262.6. The variation was determined by the operators in action at different time and distance from the HDR source.Conclusion:The time and dose were estimated for a HDR unit emergency response procedure. It provided information in making optimal decision during the emergency procedure. Further investigation would be to optimize and standardize the responses for other emergency procedure by time‐spatial‐dose severity function.

Dosimetric analysis of Co-60 source based high dose rate (HDR) brachytherapy: A case series of ten patients with carcinoma of the uterine cervix

AimTo analyse the dosimetric parameters of Co-60 based high dose rate (HDR) brachytherapy plans for patients of carcinoma uterine cervix. BackgroundCo-60 high dose rate (HDR) brachytherapy unit has been introduced in past few years and is gaining importance owing to its long half life, economical benefits and comparable clinical outcome compared to Ir-192 HDR brachytherapy. Materials and methodsA study was conducted on ten patients with locally advanced carcinoma of the uterine cervix (Ca Cx). Computed tomography (CT) images were taken after three channel applicator insertions. The planning for 7 Gray per fraction (7Gy/#) was done for Co-60 HDR brachytherapy unit following the American Brachytherapy Society (ABS) guidelines. All the patients were treated with 3# with one week interval between fractions. ResultsThe mean dose to high risk clinical target volumes (HRCTV) for D90 (dose to 90% volume) was found to be 102.05% (Standard Deviation (SD): 3.07). The mean D2cc (dose to 2 cubic centimeter volume) of the bladder, rectum and sigmoid were found to be 15.9Gy (SD: 0.58), 11.5Gy (SD: 0.91) and 4.1Gy (SD: 1.52), respectively. ConclusionThe target coverage and doses to organs at risk (OARs) were achieved as per the ABS guidelines. Hence, it can be concluded that the Co-60 HDR brachytherapy unit is a good choice especially for the centers with a small number of brachytherapy procedures as no frequent source replacement is required like in an Ir-192 HDR unit.

Mammosite Brachytherapy Dosimetry-Effect of Contrast and Air Interface on Skin Dose

High-dose-rate (HDR) brachytherapy is an effective internal radiation therapy procedure for treating malignant neoplasms. This technique is widely used in breast cancer treatments to destroy residual cancer cells surrounding the lumpectomy cavity following surgery. This is done by inserting a balloon catheter into the cavity that is inflated with saline as well as a medium of radiographic contrast. Then the radioactive isotope is positioned into the center of the balloon using an HDR unit to deliver the prescribed dose to a volume surrounding the balloon. Most of the currently available treatment planning systems (TPS) for brachytherapy, including Nucletron Oncentra, estimate dose using proprietary algorithms which use a pre-calculated dose metric derived from Ir-192 placed in a water phantom. However, they do not take into account variations in attenuation due to inhomogeneities in different tissues. This may lead to several questions: do these TPS estimate absorbed dose correctly within the target tissue? What are the effects on breast-air interface within the target volume? Does a radiographic contrast medium in the balloon alter the dose distribution calculated by TPS? These uncertainties and doses can be quantified by using the data recorded in a tissueequivalent patient phantom which is aided by a PN junction commercial diode detector and an electrometer. During this investigation, we used a cubical water phantom and Mammosite® single lumen balloon system to measure effects on breast-air interface, the diode detector was placed on the phantom wall to simulate the tissue air interface. Measured data were compared with predictions from the Oncentra TPS for the same geometry. These results may help quantify uncertainties in the predicted versus actual skin doses used during the treatments. This in turn could increase the clinicians’ predictive power regarding potential excessive skin dose that could cause toxicity in patients.

Determination of transit dose profile for a 192Ir HDR source

Several studies have reported methodologies to calculate and correct the transit dose component of the moving radiation source for high dose rate (HDR) brachytherapy planning systems. However, most of these works employ the average source speed, which varies significantly with the measurement technique used, and does not represent a realistic speed profile, therefore, providing an inaccurate dose determination. In this work, the authors quantified the transit dose component of a HDR unit based on the measurement of the instantaneous source speed to produce more accurate dose values. The Nucletron microSelectron-HDR Ir-192 source was characterized considering the Task Group 43 (TG-43U1) specifications. The transit dose component was considered through the calculation of the dose distribution using a Monte Carlo particle transport code, MCNP5, for each source position and correcting it by the source speed. The instantaneous source speed measurements were performed in a previous work using two optical fibers connected to a photomultiplier and an oscilloscope. Calculated doses were validated by comparing relative dose profiles with those obtained experimentally using radiochromic films. TG-43U1 source parameters were calculated to validate the Monte Carlo simulations. These agreed with the literature, with differences below 1% for the majority of the points. Calculated dose profiles without transit dose were also validated by comparison with ONCENTRA(®) Brachy v. 3.3 dose values, yielding differences within 1.5%. Dose profiles obtained with MCNP5 corrected using the instantaneous source speed profile showed differences near dwell positions of up to 800% in comparison to values corrected using the average source speed, but they are in good agreement with the experimental data, showing a maximum discrepancy of approximately 3% of the maximum dose. Near a dwell position the transit dose is about 22% of the dwell dose delivered by the source dwelling 1 s and reached 104.0 cGy per irradiation in a hypothetical clinical case studied in this work. The present work demonstrated that the transit dose correction based on average source speed fails to accurately correct the dose, indicating that the correct speed profile should be considered. The impact on total dose due to the transit dose correction near the dwell positions is significant and should be considered more carefully in treatments with high dose rate, several catheters, multiple dwell positions, small dwell times, and several fractions.

SU-E-T-132: Commissioning Integrated System in High-Dose-Rate (HDR) Brachytherapy

Purpose: Because of the delivery of large doses in a few fractions, any deviation generally results in a medical event for HDR brachytherapy. NRC Section §35.633 on full calibration measurements requires among others, the determination of (a) source positioning accuracy, (b) length of transfer tubes, (c) length of applicators, and (d) function of the transfer tubes, applicators, and transfer tube ‐ applicator interface. While the determination of the individual parameters may be acceptable, the use as an integrated system may fail resulting in medical events reported to NRC. Methods: A treatment plan was designed to check the integrity of the integrated system consisting of the applicator connected to the HDR remote afterloader unit via designated transfer tubes. In this fashion, data entry of both the length of the applicator and the dwell positions must be entered into the treatment planning system. The first dwell position was set at the extreme end of the applicator. A series of dwell positions of equal or unequal spacing was set to track the pathway of the applicator. During dose delivery, the applicator was placed over a film or digital radiograph. Results: The successful completion of the dose delivery assures that there are no obstructions and confirms the integrity of the interconnectivity of the HDR unit, transfer tubes, and applicator. The radiograph allowed an evaluation of the maximum extent of the travel of the source relative to the applicator and thereby validating the data entry on the length of the applicator, dwell positions, and dwell spacing. In addition, the radiograph also revealed the travel of the source within the applicator. Conclusions: Commissioning using end‐to‐end testing of an integrated system should be applied to HDR brachytherapy. This process would have eliminated a number of medical events recently reported.

Measurements of dose discrepancies due to inhomogeneities and radiographic contrast in balloon catheter brachytherapy

Recently, a device called MammoSite, consisting of a balloon and a catheter, was developed to perform partial-breast irradiation using a high-dose-rate (HDR) brachytherapy unit with ease and reproducibility. However, the actual dose to the skin does not agree well with the calculated dose by the treatment planning system because of the difference between the calculation condition and the real treatment condition (i.e., homogeneous water and full scatter condition vs contrast solution and lack of full scatter condition). In this study, the authors experimentally estimated dose discrepancies due to contrast and lack of full scatter in breast HDR brachytherapy with MammoSite. Using metal-oxide-semiconductor field-effect transistor detectors and a breast phantom, the dose discrepancies between the calculation and the treatment conditions were measured according to contrast concentration (10% and 20% volume ratios), balloon size (35 and 60 cm3), and source to detector distance ranging from 25 to 50 mm. The source was an Ir-192 isotope from Nucletron HDR unit. The dose discrepancies from the calculation condition due to both contrast and lack of full scatter combined ranged from about -1.4 +/- 2.5% to -18.2 +/- 2.0% in the studied cases (error bound is in two sided confidence interval of 80% based on Student's t distribution). In all cases, the effect of lack of full scatter was dominant to that of contrast and significant dose discrepancies existed between the calculation and the real treatment conditions, indicating that the actual skin dose is less than that which is currently calculated.

SU-FF-T-11: Measurements of Dose Discrepancies Due to Inhomogenieties and Radiographic Contrast in Balloon Catheter Brachytherpay

Purpose: Recently, a device called MammoSite consisting of balloon and catheter was developed to perform partial breast irradiation using high‐dose‐rate (HDR) brachytherapy unit with ease and reproducibility. However, the actual dose to the skin does not agree well with the calculated dose by the treatment planning system because of the difference between the calculation condition and the real treatment condition (i.e., homogeneous water and full scatter condition vs. contrast existing and lack of full scatter condition). In this study, we experimentally estimated dose discrepancies due to contrast and lack of full scatter in breast HDR brachytherapy with MammoSite. Method and Materials: Using MOSFET detectors and a breast simulating phantom, the dose discrepancies between calculation and treatment condition were measured according to contrast concentration (10 and 20% volume ratio), balloon size (35 cc and 60 cc), and source to detector distance (SDD) ranging from 25 to 50 mm. The source was Ir‐192 isotope from Nucletron HDR unit. To correct the energy dependency of MOSFET detectors, the mean energy of each measured condition was obtained using Monte Carlo simulation with simplified geometry. For uncertainty analysis, the 80% confidence level of measurements was assessed by Student's t distribution. Results: The dose discrepancies from calculation condition due to both contrast and lack of full scatter combined ranged from about −1.4% to −18.2% in studied cases. Conclusion: In all cases, the effect of lack of full scatter was dominant to that of contrast. Significant dose discrepancies existed between the calculation and the real treatment condition due to contrast and lack of full scatter. Therefore, actual skindose is expected to be less than calculated.

Tracking brachytherapy sources using emission imaging with one flat panel detector

This work proposes to use the radiation from brachytherapy sources to track their dwell positions in three-dimensional (3D) space. The prototype device uses a single flat panel detector and a BB tray. The BBs are arranged in a defined pattern. The shadow of the BBs on the flat panel is analyzed to derive the 3D coordinates of the illumination source, i.e., the dwell position of the brachytherapy source. A kilovoltage x-ray source located 3.3 m away was used to align the center BB with the center pixel on the flat panel detector. For a test plan of 11 dwell positions, with an Ir-192 high dose rate unit, one projection was taken for each dwell point, and locations of the BB shadows were manually identified on the projection images. The 3D coordinates for the 11 dwell positions were reconstructed based on two BBs. The distances between dwell points were compared with the expected values. The average difference was 0.07 cm with a standard deviation of 0.15 cm. With automated BB shadow recognition in the future, this technique possesses the potential of tracking the 3D trajectory and the dwell times of a brachytherapy source in real time, enabling real time source position verification.

Determination of absorbed dose in water at the reference point for an HDR brachytherapy source using a Fricke system

A ring‐shaped Fricke device was developed to measure the absolute dose on the transverse bisector of a high dose rate (HDR) source at from its center in water, . It consists of a polymethylmethacrylate (PMMA) rod (axial axis) with a cylindrical cavity at its center to insert the radioactive source. A ring cavity around the source with thickness and height is centered at from the central axis of the source. This ring cavity is etched in a disk shaped base with diameter and thickness. The cavity has a wall around it thick. This ring is filled with Fricke solution, sealed, and the whole assembly is immersed in water during irradiations. The device takes advantage of the cylindrical geometry to measure . Irradiations were performed with a Nucletron microselectron HDR unit loaded with an Alpha Omega radioactive source. A Spectronic® 1001 spectrophotometer was used to measure the optical absorbance using a quartz cuvette with light pathlength. The PENELOPE Monte Carlo code (MC) was utilized to simulate the Fricke device and the Alpha Omega source in detail to calculate the perturbation introduced by the PMMA material. A NIST traceable calibrated well type ionization chamber was used to determine the air‐kerma strength, and a published dose‐rate constant was used to determine the dose rate at the reference point. The time to deliver to the reference point was calculated. This absorbed dose was then compared to the absorbed dose measured by the Fricke solution. Based on MC simulation, the PMMA of the Fricke device increases the by 2.0%. Applying the corresponding correction factor, the value assessed with the Fricke device agrees within 2.0% with the expected value with a total combined uncertainty of 3.43% . The Fricke device provides a promising method towards calibration of brachytherapy radiation sources in terms of and audit HDR source calibrations.

TH‐C‐352‐02: From Licensing to QA, How to Implement HDR Brachytherapy Into Your Clinic

Brachytherapy has been utilized as a modality for treating cancer since shortly after the discovery of radium by Madame Curie in the early 1900's. Although radium was the workhorse for brachytherapy treatments in the first half of the 21st century, alternative sources began to emerge in the 1950's as mechanisms to produce radioactive isotopes were discovered. Cesium‐137, and a number of other low dose rate (LDR) sources were soon utilized clinically. However, it was not until the 1980's that high dose rate (HDR) brachytherapy emerged as a possible alterative to LDR treatments. Although HDR had the advantage of delivering dose in a shorter time frame, there were several concerns regarding this transition, such as the radiological response of HDR versus LDR treatments, and staff safety. Prior to the era of HDR units, most sources were loaded manually resulting in occupational dose to staff participating in LDR procedures. However, before HDR programs could be utilized clinically, alternatives for manual loading were necessary as the resulting exposure to staff would be prohibitively high. In response, remote afterloading HDR units emerged, allowing sources to be delivered to patients remotely. However, along with this advancement in technology came increasing regulatory and quality assurance requirements.Although there are a number of similarities between LDR and HDR treatments, there are substantial differences in the clinical implementations of these treatment programs. During this presentation, we will discuss relevant federal regulatory requirements, NRC licensing, AAPM recommendations and task group reports, available HDR equipment, and logistical planning in order to develop a successful HDR program.Educational Objectives:1. Discuss the necessary steps to prepare for the clinical implementation of a HDR brachytherapy program.a. NRC licensingb. Equipment purchasec. Room design and shieldingd. Acceptance testing and commissioninge. Quality assurance2. Discuss logistics for HDR workflow.

A dose verification method for high-dose-rate brachytherapy treatment plans

To evolve a fast dose verification method for high-dose-rate (HDR) brachytherapy treatment plans and to demonstrate its applicability in different clinical cases. We developed a software tool in VC++ for the Varisource HDR unit for HDR dosimetry plan verification using TG-43 parameters. HDR treatment dosimetry of a number clinical cases using Varisource was verified by comparison with the treatment planning system (TPS). A number of different types of clinical cases treated by Varisource were evaluated. TPS calculated dose values and verification code calculated dose values were found to agree to within 3% for most of the dose calculation points. We have validated with clinical cases a fast and independent dose verification method of the dosimetry at selected points for HDR brachytherapy treatments plan using TG-43 parameters. This can be used for the verification of the TPS calculated dose at various points. The code is written to work with Varisource, but it can conceivably be modified for other sources also by using the fitted constant of the respective source.

Energy and integrated dose dependence of MOSFET dosimeter sensitivity for irradiation energies between and

Since metal-oxide-semiconductor field effect transistors (MOSFETs) medical applications in radiotherapy and radiology are gaining popularity, evaluating them under radiation of different energies is of major interest. This study aims at a characterization of MOSFET sensitivity with regard to total integrated dose. Sensitivity is expressed by the water calibration factor (CFw) and allows the user to associate the voltage difference reading displayed by the device to a dose value in water at the MOSFET location. The CFw of seven p-type dual-bias MOSFETs were measured for several accumulated doses. The radiation sources used were a 60Co unit ((E)gamma: 1.25 MeV), an 192Ir high dose rate unit ((E)gamma: 380 keV), and an orthovoltage unit providing two x-ray energy spectra for tube voltages of 30 kV((E)gamma:14.8 KeV) and 150 kV((E)gamma:70.1 keV). The CFw value diminishes with increasing threshold voltage, especially for low-energy radiation. It was stable for 60Co irradiations, while it decreased 6%, 5%, and 15% for beam energies of 192Ir, 150 kV, and 30 kV, respectively. The decrease rate is higher for the first half of the device lifetime. This behavior is explained by an alteration of the effective electric field applied to the MOSFET during irradiation, caused by the accumulation of holes at the Si-SiO2 interface. It is strongly dependent on the nature of the radiation, and particularly affects low x-ray energies. A frequent calibration of the device for this radiation type is essential in order to achieve adequate measurement accuracy, especially in low-energy applications, such as superficial therapy, brachytherapy, and diagnostic and interventional radiology.

Preliminary experience of high dose rate (HDR) brachytherapy following video assisted thoracoscopic surgery (VATS) based sublobar resection in patients with peripheral non-small cell lung cancer and poor pulmonary functions

7269 Background: To describe the initial experience of delivering adjuvant radiotherapy following sublobar resection using HDR brachytherapy after VATS resection of lung lesions. Methods: Between March and November 2004, 14 patients were treated with VATS sublobar resection and HDR brachytherapy to 16 peripheral lung lesions that were pathologically proven to be non-small cell lung carcinoma. Intraoperatively, brachytherapy catheters were sutured and anchored over the stapled line and to the chest wall. Brachytherapy planning was done using a CT-based planning system. A remote afterloading HDR unit was used for treatment. A median dose of 2,450 cGy was given at 350 cGy per fraction over 7 fractions twice a day, 6 hours apart, over 4 days as inpatient. Dose was prescribed to 1 cm deep to the stapled line. Biologically, this dose is approximately 5,000 cGy and above (180 cGy per fraction equivalent) at the depth of 5 mm in reference to the resection margin. Results: At median and average followup times of 3 months and 4 months respectively, patients tolerated the postoperative brachytherapy well with no pneumonitis or excess complication. Average hospital stay was one week. There was one case of empyema which may or may not be related to radiation treatment. There were 2 incidents of catheter migration due to inadvertent catheter movement during wound care. Consequently, re-planning was needed in order to continue accurate radiation delivery for these patients. Conclusions: Low dose rate brachytherapy has been described in literature for this subgroup of patients for improving local control rate. This is a first report of using HDR brachytherapy with VATS. In our initial experience, patients tolerate this method of brachytherapy well with no significant acute side effect. HDR technique complements with VATS efficiently and does not prolong hospital stay. Remote afterloading technique allows no radiation exposure to staff members or others. Further data are needed to determine the clinical impact of HDR brachytherapy in this subgroup of patients. No significant financial relationships to disclose.

SU‐FF‐T‐32: Imaged‐Based Simulation Technique To Determine Stepping Source Dwell Position For MammoSite(r) Brachytherapy Procedures

Purpose: Incorrect dwell position for the stepping source in MammoSite® radiation therapy system would result in severe dose error to the treated volume. In many centers, CT‐simulators have replaced the fluoroscopic simulators. An alternative method must be developed for this purpose. This project evaluates the feasibility of CT‐based simulation to determine the dwell position for the stepping source of the Nucletron® High‐Dose Rate (HDR) unit. Method and Materials: A MammoSite® balloon applicator is placed in the surgical cavity intraoperatively at the time of segmented mastectomy for breast cancer. The balloon is inflated to near spherical shape with saline solution mixed with a small amount of radiographic contrast to aid in visualization. After recovery, the patient is brought to the radiation oncology facility to determine the quality of the implant and also to determine the stepping source dwell position. A dummy source train is initially inserted in the applicator and pushed to the distal end. The distance is measured using the Nucletron® measuring tool. CT scans of the breast was taken with 1 mm slice thickness. After the images have been acquired, a virtual 3‐dimensional breast is generated. Based on the virtual breast, the path of the dummy source train inside the applicator is assessed. Results: A digitally reconstructed radiography (DRR) that maximizes the projection of the pathway is created. A method is formulated to determine the center of the sphere and marks on the source pathway. The dwell position is determined by subtracting the difference of distance between the distal seed and center of the sphere from the maximum source distance as set on the HDR unit. Conclusion: For institutions where the fluoroscopic simulator has been replaced by a CT‐simulator, imaged‐based simulation allows an effective method of determining the stepping source dwell position for MammoSite® brachytherapy procedures.

High-Dose-Rate Brachytherapy in Combination with Stenting Offers a Rapid and Statistically Significant Improvement in Quality of Life for Patients with Endobronchial Recurrence

Symptomatic endobronchial recurrence after treatment failure is common in advanced non-small cell lung cancer. Optimal palliation has yet to be defined. We examined the combination of near-simultaneous, high-dose-rate (HDR) brachytherapy with stenting in this cohort of patients. Informed consent for intervention was obtained for 10 patients experiencing severely symptomatic (hemoptysis and oxygen-dependent shortness of breath), biopsy-proven endobronchial recurrence. All patients (eight men, two women, aged 52-77 years) had failed to respond to chemoradiotherapy for stage IIIB non-small cell lung cancer. Intervention consisted of placement of a self-expanding metallic stent (Nitinol/Ultraflex stent, Boston Scientific Co., Natick, MA) into the obstructing region. During that same bronchoscopy, HDR catheters were introduced. A dose of 6 Gy at 0.5 cm from the catheter was then delivered via an HDR unit. Two additional HDR sessions followed at weekly intervals for a total dose of 18 Gy. Patients under went follow-up bronchoscopes 1 month after the last HDR and when clinically indicated. All patients completed the prescribed therapy. No morbidity was noted from bronchoscopy, HDR, or stenting. All patients had rapid relief of signs and symptoms. At 1 week after stenting/first HDR, a statistically significant improvement in Karnofsky status was noted. Pulmonary palliation was maintained for the duration of their survival. The radio-opaque stent also offered significant advantages for catheter placement and verification during the HDR procedure. Although this series is small, the beneficial outcome obtained deserves further evaluation.

Accuracy of Dose Delivery in Gynecological Brachytherapy

Mailed thermoluminescence dosimetry (TLD) has been used in many dosimetry intercomparisons and quality assurance procedures, however mainly in external beam therapy (1 6). For brachytherapy, 19% source calibration intercomparison with mailed TLD has also been performed (4). With careful in vivo TL dosimetry it is possible to determine the overall accuracy of the treatment procedure and find weak points in the chain of external radiotherapy (5). Since the similar principle should also be valid for brachytherapy, we have performed in vivo rectal measurements with TLD during gynecological intracavitary treatments and the results have been compared with the corresponding dose calculations, source strength measurements and specifications. Material and Methods. With mailed TLD it is possible to omit the calibration intercomparison of TLD chains of each centre, once the calibration of the TLD for the reference centre has been checked. Although easily performed, rectal in vivo TLD has not been found very useful in routine patient dosimetry with single measurements, as in the estimation of rectal maximum dose, due to the problems with probe localization (7). Instead, the technique has been used for testing the agreement between actual and calculated dose in intracavitary radiotherapy (8) where the results of multiple measurements have been used in the statistical analysis. A flexible probe has been used widely for in vivo rectal dosimetry (7-9). We constructed a flexible silicon tube which was filled with 4 TLD pellets (lithium borate), lead markers and water equivalent spacers (8). The calibration of the TL probe was checked in water for Iq7Cs and 'Wo and the intrinsic accuracy was better than *2'% Six gynecological afterloading units in Finland were included in the study: three Selectron (Nucletron) high dose rate (HDR) units (labelled afterwards with Nos. I , 2 and 3) with V o sources, two Selectron medium dose rate (MDR) units (Nos. 4 and 5 ) with 7Cs sources and an old non-commercial HDR unit with one '37Cs source (No. 6) . In MDR treatments the probe was irradiated for one hour (8) and in HDR treatments for the whole treatment time. Ten successive patients were investigated. Thus, the maximum number of the measurement points was 40 in each institute. The accurate localization of the flexible probe close to any anatomic structure or reference point, like the ICRU reference points (10) or the point of rectal maximum dose, is difficult and it was not objected. Instead, the aim of the present study was to investigate the general accuracy of the dose calculation and delivery in gynecological intracavitary radiotherapy. The stated dose for each site of the TL dosimeters was calculated by the treatment planning system routinely used in each institute. The source configuration data were based on the anterior-posterior and lateral radiographs. Due to the lead markers inside the probe the sites of the TLD pellets could easily be determined on the radiographs (8). The dose delivered by the radiographs was considered negligible. Because of a few poor quality radiographs some distant calculation points had to be omitted. In addition, a comparison between dose calculation programs was performed. The Theraplan V05 (Theratronics) system was selected as a reference (units Nos. 5 and 6 ) and the stated doses of the unit No. 4 (dose calculation with non-commercial Finnish software called SisDos) and No. 2 (dose calculation with Cadplan by Varian-Dosetek) were recalculated from the original radiographs by the reference system using the same input data. Because the stated doses of the units Nos. 1, 2 and 3 were calculated with the Cadplan system, only the data of unit No. 2 was selected for recalculation with Theraplan. The reference treatment planning system had been checked against measurements both in reference conditions and in vivo (8). In addition to the spatial information of the sources essential physical parameters affecting the dose delivery are the source strength specified either by activity or air-kerma rate and the treatment time. Since errors in source strength and timer contribute directly to the delivered dose, both parameters were determined independently. In Finland the source specification data of the manufacturer is used in treatment planning if the difference between the commissioning measurements and the manufacturer's data is below 5% We extracted the measured source strength from the commissioning documents for the units Nos. 1, 2, 3, and 4, but a new measurement was made in air with the calibrated ionization chamber for the units Nos. 5 and 6. The results were presented as a ratio of the measured to stated source strength as follows

Clinical use of a digital simulator for rapid setup verification in high dose rate brachytherapy

Fractionated high dose rate (HDR) brachytherapy provides a number of technical advantages over conventional implant therapy in that (a) it can be carried out on an outpatient basis, (b) personnel exposure is reduced to insignificant levels, and (c) patient motion during irradiation is minimized, resulting in a more accurate delivery of the planned radiation dose distribution to the target and critical structures. The patient discomfort associated with the repeated applicator insertions and/or treatment setups can be alleviated to the extent that the setup time is held to a minimum. This work describes the use of a prototype digital simulator to obtain fast, high-quality digital images for rapid setup verification. The digital imaging system of the prototype simulator consists of a charge-coupled device (CCD) camera, which views the x-ray image optically transmitted from a conventional phosphor screen. Treatment is carried out with a remote afterloading HDR unit immediately after setup verification with the patient on the simulator stretcher. The high-resolution digital images are processed and displayed in about 5 s, as opposed to a minimum of approximately 2 min for film. The imaging system has been evaluated for a variety of implant types, both intracavitary and interstitial. The digital radiographs provided permanent high-resolution images as required in most cases for precise applicator positioning. The gray scale manipulation capabilities were found to be useful for imaging in regions of different density, such as lung and soft tissue, in the same radiograph. The advantages of short image acquisition and display times were observed in all cases, but were most evident in the intraluminal procedures, which sometimes involved several pretreatment applicator adjustments at a time of considerable patient discomfort. Pretreatment imaging is necessary to fully exploit the technical advantages of HDR brachytherapy. High-quality digital radiography offers unique advantages in HDR setup and verification by providing fast high-resolution, undistorted images with software manipulation capabilities and permanent storage of images.

High dose endobronchial irradiation in recurrent bronchogenic carcinoma

Between November 1988 and March 1990, 24 patients with endobronchial tumors that had recurred after external beam radiation therapy were treated with high dose rate intraluminal irradiation. A remote afterloading high dose rate unit was used, and most patients received two endobronchial treatments, separated by a two week interval. All patients were given the same dose and dose specification to assess the feasibility and complications of the therapy. At each treatment, 15 Gy were delivered with dose specified at a radius of 6 mm from the center of the source, which corresponds to a dose of 9 Gy at a radius of 1 cm. Overall, 21 of 24 patients (88%) showed good symptomatic improvement. Of 18 patients whose chest x-ray showed evidence of collapse or atelectasis caused by tumor obstruction, 15 (83%) had evidence of reaeration. The median duration of palliation, marked by symptoms or a chest x-ray that worsened, was 26 weeks, the range varying from seven to 40 weeks. No patient died as a result of therapy and only one had a complication, bronchospasm, which responded well to bronchodilators. One patient died of hemoptysis approximately three months after treatment. Five additional patients, who were treated off protocol because they had an Eastern Cooperative Oncology Group performance status of greater than two, also received endobronchial irradiation. All five died within one month from worsening pulmonary disease, and we do not recommend endobronchial irradiation for patients with an Eastern Cooperative Oncology Group performance status of greater than two. We conclude that high dose rate endobronchial brachytherapy effectively relieves the symptoms of endobronchial obstruction due to recurrent lung cancer and can be given safely as an outpatient procedure. As the complications were minimal in this series treated with a uniform dose of 15 Gy per treatment, future studies should aim at determining the maximum tolerated dose. This technique may also be helpful as a boost after maximal external beam irradiation or to open up areas of atelectasis prior to external beam irradiation.