High Dose Rate Remote Afterloading Research Articles

SU‐F‐T‐633: Cyberknife Boost Versus Conventional Tandem and Ovoid Treatment for Cervical Cancer

Purpose:Brachytherapy has been the standard of care for cervical cancer for 100 years. The treatment can be administered using an HDR (high dose rate) remote afterloader with a 192Ir source in an outpatient setting, a PDR afterloader with a 192Ir source, or with LDR manually loaded or a remote afterloader utilizing 192Ir or 137Cs sources in an inpatient setting. The procedure involves the placement of a tandem and ovoid, tandem and ring, or tandem and cylinder applicator in an operating room setting with the patient under general anesthesia. Inaccuracies introduced into the process occurring between placement of the applicator and actual delivery can introduce uncertainty into the actual dose delivered to the tumor and critical organs. In this study we seek to investigate the dosimetric difference between an SBRT‐based radiotherapy boost and conventional Brachytherapy in treating cervical cancer.Methods:Five HDR tandem and ovoid patients were planned using the Brachyvision treatment planning system and treated in four fractions using the Varian Varisource afterloader (Varian Medical Systems). For the same cohort, the patient planning CTs were imported into Multiplan (Accuray Inc) and a dose/fractionation‐equivalent CyberKnife SBRT plan was retrospectively generated. Dosimetric quantities such as target/CTV D90, V90, D2cc for rectum, bladder, and bowel were measured and compared between the two modalities.Results:The CTV D90 for the tandem and ovoid was 2540cGy (90.7%) and 3009cGy (107.5%) for the CyberKnife plan. The D2cc for the rectum, bladder, and bowel were 1576cGy, 1641cGy, and 996cGy for the tandem and ovoid and 1374cGy, 1564cGy, and 1547cGy for CyberKnife.Conclusion:The D2cc doses to critical structures are comparable in both modalities. The CTV coverage is far superior for the CyberKnife plan. The dose distribution for CyberKnife has the advantage of increased conformality and lower maximum CTV dose.

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.

Measurement of dose perturbation around shielded ovoids in high-dose-rate brachytherapy

Purpose To analyze the effect of tungsten shields present in a Fletcher-Suit-Delclos ovoid by comparing the dose distribution computed by a treatment planning system (TPS) to the delivered dose distribution measured by radiochromic film dosimetry. Methods and Materials Gafchromic/EBT films were carefully wrapped around the caps (diameter 20–25 mm) of shielded as well as unshielded ovoids, including their anterior and posterior ends. The ovoids were irradiated to a dose of 300 cGy using a high–dose rate remote afterloading unit. The films were scanned using Vidar VXR-16 Scanner. The dose distribution in the planes above, below, and on the sides of the ovoid were compared with the dose distribution computed by TPS, which does not account for the presence of shields. Results The dose distributions obtained about the unshielded ovoid from film dosimetry was in order of what is computed by TPS (90% measurements ± 5%, maximum 8%). The dose reduction in the anterior part of the shielded ovoid affects maximally the dose to the bladder where a reduction up to 20% was noted. The reduction of dose in the posterior part of the ovoid, which is designed to shield rectum was as high as 23%. Where the shields are not present, insignificant difference in the measured and computed dose values was noticed. Conclusions The TPS may substantially overestimate the dose to the bladder and rectum, including regions that lie in the shadow of the solid angle subtended by the shields if it does not account for the presence of tungsten shields.

Animal model of radiogenic bone damage to study mandibular osteoradionecrosis

Objective The objective of the study was to create an animal model to study mandibular osteoradionecrosis (ORN) using high–dose rate (HDR) brachytherapy. Methods Ten Sprague-Dawley male rats were used in this study. Six rats received a single dose of 30 Gy using an HDR remote afterloading machine via a brachytherapy catheter placed along the left hemimandible. The remaining 4 rats served as controls with catheter placement without radiation (sham). On the day following irradiation or sham, all 3 left mandibular molars were atraumatically extracted. Twenty-eight days after irradiation, mandibles were examined using nondecalcified histology with sequential fluorochrome labeling, decalcified histology, and micro–computed tomography scanning. Results Irradiated rats demonstrated exposed bone at the extraction sockets, whereas the control animals had complete mucosalization. Alopecia was also seen in the irradiated group. Both histologic and radiologic analyses of the mandible specimens demonstrated a reduction in bone formation in the radiated mandibles as compared with controls. Conclusions Our HDR brachytherapy model incorporating postradiation dental extractions has successfully demonstrated reproducible radiogenic mandibular bone damage analogous to the clinical ORN. Although clinical criteria continue to be used today in describing ORN, this model can serve as a platform for future studies to define ORN and delineate its pathogenesis.

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.

Measurement of Transit Time of a Gammamed-Plus Remote Afterloading High Dose Rate Brachytherapy Source

Measurement of Transit Time of a Gammamed-Plus Remote Afterloading High Dose Rate Brachytherapy Source Accurate measurement of transit time of the HDR brachytherapy source of a remote after-loading unit is necessary to calculate the total radiation dose given to the treatment volume. Presently, most of the HDR brachytherapy treatment planning systems neglect the transit time in the computation of dose. The aim of this investigation is to use a well type ionization chamber to measure the transit time during the source movement between two dwell positions. As well type ionization chamber and a precision electrometer (manufacturer CD instruments, Bangalore) were used to measure the charge generated during the movement of the Ir-192 source of a Gammamed HDR brachytherapy unit with an interstitial needle. Effective transit time and effective speed were determined on the basis of methodology described by Sahoo [2]. Corrections were done on the basis of relative sensitivity values for varaious dwell position in the ionization chamber. In the present study the variation of effective speed with interdwell distance was minimal as compared with that of Sahoo [2]. The effective transit times were 0.129, 0.182, 0.301, 0.402, 0.701, and 0.993 seconds for 1, 2, 4, 6, 8 and 10 cm interdwell separations respectively. The effective transit times in the present study were higher than those of Sahoo [2]. Software modification accounting for the dynamic dose should be incorporated into all HDR planning systems. Such an improvement would enhance the safety and accuracy of HDR brachytherapy.

High Dose Rate Remote Afterloading Brachytherapy for Lung and Esophageal Cancer.

High dose rate brachytherapy for lung and esophageal cancer is performed by placing a high activity Iridium 192 source into the lumen of the airway of esophagus. Because of the high activity of the source it remains in place for only a matter of minutes, and fractionated treatments are feasible. Before this development, conventional dose rate brachytherapy required hospitalization with attendant patient discomfort, expense, and complicated radiation safety requirements. The development of high activity remote afterloading machines has removed these practical disadvantages and has led to a great interest in the use of this technology for radical treatment and palliation of obstructing malignancies. There are several unresolved issues concerning this modality for both lung and esophageal cancer. For both diseases, optimal dose and fractionation schemes are not well defined but the palliative benefits for recurrent lung cancer have been clearly shown. The use of a brachytherapy boost following radical external beam radiation therapy of lung cancer is not proven to be advantageous. For esophageal cancer, the value of brachytherapy for palliation is not established. However, there are preliminary data to suggest that it can improve outcome when used routinely after radical treatment with external beam radiation therapy.

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.

Pulse Dose Rate brachytherapy: optimization and place of imaging

Pulse Dose Rate (PDR) brachytherapy presents the potential radiobiological advantages of low dose rate and the technical and radiation protection advantages of high dose rate remote afterloading technology. The different algorithms provided by the treatment planning systems allow dose rate and isodose shape optimization regarding the volumes defined by the radiologist and the radiation oncologist. The contribution of imaging together with these new optimization tools should improve brachytherapy practice and the therapeutic ratio. These new evolutions of brachytherapy will be presented here.

High dose rate brachytherapy for early stage oral tongue cancer.

High dose rate (HDR) interstitial brachytherapy of the oral tongue is a new treatment modality. Our study evaluates the outcomes of patients with early stage oral tongue cancer as treated by HDR interstitial implant. We reviewed the records of 19 patients who were seen between 1994 and 2000 with carcinoma of the oral tongue and whose primary tumors were treated solely with interstitial implant using HDR remote afterloading technique. Ten patients had T1 N0 disease, and the remaining 9 had T2 N0 disease. Elective neck treatment was withheld for 12 patients. The remaining seven patients had ipsilateral elective neck dissection. The male-female ratio was 1:0.9, and the median age was 60 years (range, 32-81 years). The median follow-up time was 43 months (range, 6-78 months). The afterloading catheters were positioned by the submandibular approach with the assistance of a template set. Fifteen patients had single planar implants, and the remaining four had double planar implants. The median number of catheters inserted was 5 (range, 4-9). The median dose given was 55 Gy in 10 fractions over 6 days. The minimal interfraction interval was 7 hours for the first 7 patients and was extended to 8 hours for the other 12. Mandibular shields were inserted before treatment. The mucositis lasted for 6 to 20 weeks (median, 9 weeks). One patient had local failure, and the 4-year local failure-free survival rate was 94.7%. Three of the 12 patients without elective neck treatment had ipsilateral regional failure develop. They were salvaged by neck node dissection and regionally remained in control. One patient with multiple nodal metastases and extracapsular spread had biopsy-proven liver metastases and died 6 months after implant. One of the seven patients who were treated with elective neck dissection had multiple nodal metastases and extracapsular spread. She was treated with postoperative radiotherapy to the neck. She died 30 months after implant with evidence of regional and distant failure. One patient treated with double planar implant had grade II necrosis of the soft tissue and bone develop. The necrosis resolved with conservative treatment. Another four patients had small area of soft tissue deficit of the tongue attributed to aggressive debulking or biopsy before brachytherapy. Our experience in treating early stage tongue cancer with HDR remote afterloading technique is encouraging, because it gives a local control rate of 94.7% at 4 years with acceptable morbidity. Further studies are eagerly awaited to delineate the optimum schedule for this new treatment modality.

Fractionated high-dose-rate brachytherapy in the management of uterine cervical cancer.

It is well known that intracavitary radiotherapy (ICR), either alone or in combination with external-beam radiotherapy (EBRT) is an essential component of the radiation treatment of uterine cervical cancer. Although low-dose-rate (LDR) brachytherapy has been successfully applied to the management of such patients, several radiation oncologists have experience of using high-dose-rate (HDR) brachytherapy with promising clinical results over the past 4 decades. However, there has been a considerable reluctance by radiation oncologists and gynecologists in North America to employ the HDR remote afterloading technique instead of the more firmly established LDR treatment modality. In contrast, the HDR-ICR system is rapidly gaining acceptance in Korea since the introduction of the Ralstron, remotely controlled afterloading system using HDR Co-60 sources, at the Yonsei Cancer Center in 1979. According to brachytherapy statistics reported by the Korean Society of Therapeutic Radiology and Oncology, in 1997, brachytherapy was performed upon 1,758 Korean patients with uterine cervical cancer, of whom approximately 83% received HDR brachytherapy. In this review, we present our experiences of HDR-ICR for the treatment of uterine cervical cancer. In addition, we discuss the controversial points, which are raised by those considering the use of HDR-ICR for uterine cervical cancer; these issues include physical and radiobiological considerations, and the prospect of future technical improvements.

Measurement of transit time of a remote after-loading high dose rate brachytherapy source.

Quantification of transit time of a remote after-loading high dose rate (HDR) brachytherapy source is important both for accurate treatment planning and for quality assurance checks. In this investigation, an HDR-1000 well ionization chamber and a precision electrometer are used to measure the transit time of the Ir-192 source of a Nucletron Micro-Selectron HDR brachytherapy unit. The charge generated both during source dwelling at a selected position in an endobronchial catheter inserted into the chamber and during source travel to this position from another location at a distance of 0.5 to 10 cm from it was measured. A linear regression analysis of the measured charge as a function of dwell time was made. The interdwell position transit time was calculated from the ratio of the charge intercept and the slope of the straight line obtained from the regression analysis. The values of the effective transit time, which is a combination of interdwell position transit time and dwell time error of the after-loading unit, were found to be 0.03 and 0.45 s for 0.5 and 10 cm separation between two dwell positions, respectively. The average time for 1 cm travel of the source between two dwell positions was found to be 0.022 s, resulting in an average speed of 45.5 cm/s. This simple procedure has the potential to be utilized for routine quality assurance check of the interdwell position transit time of any remote after-loading HDR brachytherapy source.

Monte Carlo dosimetry of a new 192Ir high dose rate brachytherapy source.

This work provides full dosimetric data for a new high-strength 192Ir source currently launched by Varian Oncology Systems for use in their high dose rate remote afterloading systems. The active core length of the new source is reduced to 5 mm compared to a value of 10 mm for the existing VariSource source design, with all other geometric source and encapsulation details being similar. Dose-rate constant, radial dose functions, geometry factors, and anisotropy functions, utilized in the AAPM Task Group 43 dose calculation formalism, were calculated using Monte Carlo simulation. Results are compared with corresponding data published for the existing VariSource and microSelectron high dose rate sources. The dose-rate constant for the new Varian source was found to be equal to 1.101 +/- 0.006cGyh(-1) U(-1), compared to values of 1.043 +/- 0.005 and 1.116 +/- 0.006 cGyh(-1) U(-1) calculated for the existing VariSource and microSelectron sources, respectively. The radial dose functions between the three sources are similar with the exception of their values at radial distances very close to the source (r approximately 2 mm) where differences of approximately 3% are observed. The new Varian source demonstrates a smaller anisotropy relative to the existing VariSource source design for polar angles close to the source longitudinal axis, due to its smaller active core length.

An independent dose-to-point calculation program for the verification of high-dose-rate brachytherapy treatment planning

Purpose: We describe computer software that performs, quickly and accurately, secondary dose calculations for high-dose-rate (HDR) treatment plans, including those employed for prostate treatments. Methods: The program takes as primary input the data file used by the HDR remote afterloader console for treatment. Dosimetric calculations are performed using the Meisberger polynomial and the anisotropy table for the HDR Iridium-192 source. For standard applicators, treatment geometry is automatically reconstructed and the dose is calculated at relevant reference point(s). Template-based treatment plans (e.g., prostate) require additional user input; the dose calculation is then performed at user-selected reference points. A total dwell time calculation for volume and planar implants using the Manchester tables was also implemented. Results: For fixed-geometry HDR procedures, secondary dose calculations are within 2% of the treatment plan, and results are available for review instantly. For more general applications, the calculated and planned doses are typically within 3% at the prescription isodose line. The Manchester-based dwell time calculation is within 10% of the planned time.

High dose-rate afterloading 192iridium prostate brachytherapy: feasibility report

Background: Results from localized prostate cancer series using seed implants have been most encouraging. However, with current techniques, inadequate dosimetry sometimes occurs. Remote afterloading high dose rate 192Iridium brachytherapy (HDR-Ir192) theoretically remedies some potential inadequacies of seed implantation by performing the dosimetry after the needles are in place. This study was undertaken to determine the feasibility of incorporating multifractionated HDR-Ir192 in the brachytherapy management of prostate carcinoma. Methods: From October 1989 to August 1995, 104 patients were treated with a combination of multifractionated HDR-Ir192 and external beam. Patients ranged in age from 48–78 years, with a mean of 68.6 years. By TNM clinical stage, there were 1 T1b, 31 T1c, 28 T2a, 24 T2b, 9 T2c, 8 T3a, and 3 T3c lesions. For the group, the mean initial pretreatment PSA was 12.9 ng/ml (median 8.1), with 90% of the patients having had a pretreatment PSA greater than a normal value of 4.0 ng/ml. Patients with prostate volumes up to 105 cc were implanted. Treatment was initiated with perineal needle placement using ultrasound guidance. A postoperative CT scan was obtained to provide the basis for treatment planning. Four HDR-Ir192 treatments were given over a 40-h period, with a minimal peripheral dose (MPD) ranging from 3.00 to 4.00 Gy per fraction over the course of this study. Two weeks later, external beam radiation was added using 28 fractions of 1.80 Gy daily, to a dose of 50.40 Gy. Results: Follow-up ranged from 10 to 89 months, with a mean of 46 months and median of 45 months. At various follow-up points, the patient numbers at risk were: 1 year, 101; 3 years, 69; 5 years, 28. The technique proved to be uniformly applicable to a wide range of prostate volumes and was very well tolerated by patients. Nearly all significant late in-field treatment complications were genitourinary in nature. Of the patients, 6.7% developed urethral strictures that were readily manageable. Changes in technique implemented in 1993 appear to have significantly lessened the incidence of this complication. Two patients developed significant uropathy within the first treatment year, but both resolved; 1 of these 2 patients had a prior TURP. Other bladder or rectal complications have been minimal. Using PSA progression as a marker of tumor response, approximately 84% of patients whose initial PSA was less than 20 ng/ml were free of progression at 5 years by actuarial analysis. Conclusions: We found the use of transperineal ultrasonography, postimplant CT-based dosimetry, coupled with adjustable dose delivery inherent to remote afterloading technology, to give unparalleled control in performing this complex brachytherapy task. Thus, it may be advantageous in certain clinical situations where the resultant MPD is needed to reliably cover the target volume, such as in patients with carcinomas at base locales, when the possibility of moderate to extensive intraprostatic tumor exists, and in patients with large glands. Early PSA data suggest that it may be effective as a definitive treatment with rates of adverse late tissue effects that are acceptable using current technique and doses described herein. Longer follow-up is needed to ascertain its position among the various treatment regimens for prostate carcinoma.

Simple Look-Up Table of Optimized Dwell Time Intervals Using a High-Dose-Rate Remote Afterloader for Endovascular Irradiation

Purpose: This article’s objective is to develop a simple methodology deliver a uniform radiation dose to the wall of a narrow peripheral artery for preventing restenosis using a high-dose-rate (HDR) 192Ir remote afterloader. Methods and Materials: Based upon published two-dimensional data such as anisotropy factors of an HDR 192Ir source calculated from the Monte-Carlo method, arterial wall doses at a close range from an HDR source may be easily calculated using the special formula suggested in Task Group Report No. 43 published by the American Association of Physicists in Medicine. An optimization procedure was used to calculate the optimized dwell times for delivering a uniform dose along arterial walls for various arterial diameters and lengths of lesions. Results: Based on lengths of the stenosis and diameters of arteries or angioplasty balloons, a set of simple look-up tables for optimal dwell time intervals of endovascular radiation treatment have been developed for the MicroSelectron HDR remote afterloader. Conclusion: Doses for endovascular irradiation have been accurately calculated with anisotropy factors. For delivering uniform doses along the arterial wall, a set of look-up tables listed for optimal dwell times is available for the HDR remote afterloader.

High dose rate brachytherapy for carcinoma of the oral tongue

The purpose of this study is to assess the feasibility of treating early-staged tongue cancer with high dose rate (HDR) remote afterloading technique. Furthermore, a new figure of merit, the Geometry Index (GI), is introduced to quantify the quality of the implants. Between 1994 and 1995, eight patients with carcinoma of the oral tongue were treated solely with interstitial implant using the HDR remote afterloading technique. Five patients had T1 N0 disease and the remaining three had T2 N0 disease. Elective neck treatment was withheld. The male-to-female ratio was 1:1, and the mean age 60 years (range: 32-72 years). The median follow-up time was 26 months (range: 6-30 months). The afterloading catheters were positioned through the submandibular approach with the assistance of templates. Six patients had single planar implant and the remaining two had double planar implant. The median number of catheters inserted was 5 (range: 4-9). The median dose given was 60 Gy in 10 fractions over 6 days. The interfraction interval was 7 h. Mandibular and maxillary shields were inserted prior to treatment. Thomadsen et al. introduced the use of Implant Quality Index (QI). We introduce a new parameter, GI, which is defined as ratio of the QI of the nonoptimized executed implant to the corresponding QI value of the nonoptimized idealized implant. The mucositis lasted for 6 to 20 weeks (median: 10 weeks). There was no local failure up to a median follow-up of 26 months. Two patients developed ipsilateral neck node metastases at 2 and 4 months following implant, respectively. One patient had involvement at level II and the other failed at level I to III. Both patients were salvaged by neck node dissection and regionally remained in control. One patient with multiple nodal metastases and extracapsular spread developed biopsy-proven liver metastases and succumbed 6 months following implant. One patient treated with double planar implant developed Grade 3 necrosis of the soft tissue and bone. This complication is largely preventable now, as we have acquired more technical expertise. The mean GI values for the single and double planar implants were 0.88 (range: 0.84-0.91) and 0.8, respectively. This correlates with our practical experience that it is more difficult to maintain a good geometry as double planar implant is required. The GI gives a better view of the geometry of implant as it compares the nonoptimized QI of the executed implant with its ideal counterpart. The failure to achieve a high GI in double planar implants is presumed to relate to technical difficulties rather than variation in individual performance. Our preliminary experience in treating early-staged tongue cancer with the HDR remote afterloading technique is inspiring, as it gives a local control rate of 100% with acceptable morbidity. Further studies are eagerly awaited to delineate the optimum schedule for this modality of treatment. It is hoped that the GI values, which represents the skills of insertion, could be routinely reported so that treatment results between different centers could be compared in a more precise manner.

Surface applicators for high dose rate brachytherapy in aids-related Kaposi's sarcoma

The development of commercially available surface applicators using high dose rate remote afterloading devices has enabled radiotherapy centers to treat selected superficial lesions using a remote afterloading brachytherapy unit. The dosimetric parameters of these applicators, the clinical implementation of this technique, and a review of the initial patient treatment regimes are presented. A set of six fixed-diameter (1, 2, and 3 cm), tungsten/steel surface applicators is available for use with a single stepping-source (Ir-192, 370 GBq) high dose rate afterloader. The source can be positioned either in a parallel or perpendicular orientation to the treatment plane at the center of a conical aperture that sits at an SSD of approximately 15 mm and is used with a 1-mm thick removable plastic cap. The surface dose rates, percent depth dose, and off-axis ratios were measured. A custom-built, ceiling-mounted immobilization device secures the applicator on the surface of the patient's lesion during treatment. Between November 1994, and September 1996, 16 AIDS-related Kaposi's sarcoma patients having a total of 120 lesions have been treated with palliative intent. Treatment sites were distributed between the head and neck, extremity, and torso. Doses ranged from 8 to 20 Gy, with a median dose of 10 Gy delivered in a single fraction. Treatments were well tolerated with minimal skin reaction, except for patients with lesions treated to 20 Gy who developed moderate/severe desquamation. Radiotherapy centers equipped with a high dose rate remote afterloading unit may treat small selected surface lesions with commercially available surface applicators. These surface applicators must be used with a protective cap to eliminate electron contamination. The optimal surface dose appears to be either 10 or 15 Gy depending upon the height of the lesion.

Combined treatment with temporary short-term high dose rate Iridium-192 brachytherapy and external beam radiotherapy for irradiation of localized prostatic carcinoma

Purpose: To evaluate the treatment outcome after radical radiotherapy of localized prostate cancer in 50 patients (38 patients with stage T1–2 and 12 patients with stage T3) after a median follow-up time of 45 months (range 18–92 months). Methods: The treatment was given by combination of external beam radiotherapy (50 Gy) and brachytherapy (2 × 10 Gy). The brachytherapy was given using TRUS-guided percutaneously inserted temporary needles with a high dose rate remote afterloading technique with Ir-192 as the radionuclide source. Three target definitions and dose levels inside the prostate gland were used. Local control was evaluated by digital rectal examination, TRUS-guided biopsies and serum PSA evaluations. Results: Clinical and biopsy verified local control was achieved in 48 of the 50 (96%) patients; for stage T1–2 in 37 of 38 (97%) patients and for stage T3 in 11 of 12 (92%) patients. A posttreatment serum PSA level ≤1.0 ng/ml was seen in 42 (84%) patients, values from >1.0 to ≤2.0 ng/ml were seen in four (8%) patients and values exceeding 2.0 were seen in four (8%) patients. The late toxicity was minimal. Conclusion: The local control results and the minimal toxicity after the combined radiotherapy treatment are promising. However, long term results are necessary before general use.

Treatment of Female Urethral Carcinoma in Medically Inoperable Patients Using External Beam Irradiation and High Dose Rate Intracavitary Brachytherapy

Purpose We developed and present our experience with high dose rate brachytherapy for treatment of carcinoma of the urethra in medically inoperable women. Materials and Methods Since 1991, 4 women with localized urethral cancer, medically unable to undergo resection or interstitial implantation, were treated with external beam and high dose rate intracavitary implantation rather than external beam irradiation alone. The fractionated implants were delivered with a high dose rate remote afterloader using a shielded vaginal applicator and modified urethral catheter. The urethral catheter was inserted through the lumen of a 20F Foley tube to improve depth dose. Homogeneous dose distribution was achieved and customized to the individual patient. Results All high dose rate brachytherapy treatments were given at the clinic without use of sedation or anesthesia. Treatment was well tolerated, and all patients maintained voluntary urinary function and local control at 12 to 55 months after therapy. Chronic morbidity due to urethral, bladder, vaginal or rectal injury, including urethral stenosis, necrosis or fistula, was not noted. Isodose distributions were compared among this technique, interstitial implantation and external beam radiotherapy alone. Conclusions Although we prefer interstitial implantation as the boost technique for women with urethral cancer, high dose rate brachytherapy is a reasonable option for medically inoperable patients. This outpatient treatment is well tolerated, preserves voluntary urinary function and enhances quality of life.