Dosimetric properties of a novel brachytherapy balloon applicator for the treatment of malignant brain-tumor resection-cavity margins

Feasibility of intratumoral 165Holmium siloxane delivery to induced U87 glioblastoma in a large animal model, the Yucatan minipig

Glioblastoma is the most aggressive primary brain tumor leading to death in most of patients. It comprises almost 50-55% of all gliomas with an incidence rate of 2-3 per 100,000. Despite its rarity, overall mortality of glioblastoma is comparable to the most frequent tumors. The current standard treatment combines surgical resection, radiotherapy and chemotherapy with temozolomide. In spite of this aggressive multimodality protocol, prognosis of glioblastoma is poor and the median survival remains about 12-14.5 months. In this regard, new therapeutic approaches should be developed to improve the life quality and survival time of the patient after the initial diagnosis. Before switching to clinical trials in humans, all innovative therapeutic methods must be studied first on a relevant animal model in preclinical settings. In this regard, we validated the feasibility of intratumoral delivery of a holmium (Ho) microparticle suspension to an induced U87 glioblastoma model. Among the different radioactive beta emitters, 166Ho emits high-energy β(-) radiation and low-energy γ radiation. β(-) radiation is an effective means for tumor destruction and γ rays are well suited for imaging (SPECT) and consequent dosimetry. In addition, the paramagnetic Ho nucleus is a good asset to perform MRI imaging. In this study, five minipigs, implanted with our glioblastoma model were used to test the injectability of 165Ho (stable) using a bespoke injector and needle. The suspension was produced in the form of Ho microparticles and injected inside the tumor by a technique known as microbrachytherapy using a stereotactic system. At the end of this trial, it was found that the 165Ho suspension can be injected successfully inside the tumor with absence or minimal traces of Ho reflux after the injections. This injection technique and the use of the 165Ho suspension needs to be further assessed with radioactive 166Ho in future studies.

Feasibility of removable balloon implant for simultaneous magnetic nanoparticle heating and HDR brachytherapy of brain tumor resection cavities

AIM

Hyperthermia (HT) has been shown to improve clinical response to radiation therapy (RT) for cancer. Synergism is dramatically enhanced if HT and RT are combined simultaneously, but appropriate technology to apply treatments together does not exist. This study investigates the feasibility of delivering HT with RT to a 5-10mm annular rim of at-risk tissue around a tumor resection cavity using a temporary thermobrachytherapy (TBT) balloon implant.

METHODS

A balloon catheter was designed to deliver radiation from High Dose Rate (HDR) brachytherapy concurrent with HT delivered by filling the balloon with magnetic nanoparticles (MNP) and immersing it in a radiofrequency magnetic field. Temperature distributions in brain around the TBT balloon were simulated with temperature dependent brain blood perfusion using numerical modeling. A magnetic induction system was constructed and used to produce rapid heating (>0.2°C/s) of MNP-filled balloons in brain tissue-equivalent phantoms by absorbing 0.5 W/ml from a 5.7 kA/m field at 133 kHz.

RESULTS

Simulated treatment plans demonstrate the ability to heat at-risk tissue around a brain tumor resection cavity between 40-48°C for 2-5cm diameter balloons. Experimental thermal dosimetry verifies the expected rapid and spherically symmetric heating of brain phantom around the MNP-filled balloon at a magnetic field strength that has proven safe in previous clinical studies.

CONCLUSIONS

These preclinical results demonstrate the feasibility of using a TBT balloon to deliver heat simultaneously with HDR brachytherapy to tumor bed around a brain tumor resection cavity, with significantly improved uniformity of heating over previous multi-catheter interstitial approaches. Considered along with results of previous clinical thermobrachytherapy trials, this new capability is expected to improve both survival and quality of life in patients with glioblastoma multiforme.

Remote afterloading patient-specific brachytherapy with liquid radioisotope for irradiation of extensive scalp lesions: A Monte Carlo study

PURPOSE

The aim of this study is to propose a remote afterloading patient-specific brachytherapy technique for total scalp irradiation by utilizing liquid radioisotope as well as a three-dimensional (3D) printer and to find an optimal radioisotope for the suggested technique.

METHODS

We designed a brachytherapy device composed of liquid radioisotope tank, tube, patient-specific applicator, and a thin flexible pouch. The liquid radioisotope tank, tube, and the flexible pouch are interconnected one another to constitute a closed loop system. The pouch is located inside the solid patient-specific applicator; therefore, when the liquid radioisotope is injected into the pouch, the pouch is inflated and fills the space inside the applicator. The 3D-printed patient-specific applicator keeps the uniform thickness of the liquid radioisotope conforming patient's contour. To investigate an optimum condition for the suggested system, we performed Monte Carlo simulation with the GEANT4 simulation toolkit. To find the optimal radioisotope, percent depth doses (PDDs) of P-32, Sr-89, Y-90, and I-125 solutions were acquired in a rectangular parallelepiped phantom. For the selected radiation source, PDDs as well as dose rates in spherical phantoms with radii of 7.7 cm (infant head size) and 9.1 cm (adult head size) were acquired.

RESULTS

To deliver prescription doses at 4-mm depth regions (scalp region), 1-mm-thick Y-90 and 5-mm-thick I-125 in liquid form were found to be feasible for the suggested technique. For both spherical phantoms with radii of 7.7 and 9.1 cm, when delivering 2 Gy at the 4-mm depth region with the 1-mm-thick Y-90 and 5-mm-thick I-125 sources, 53.3 and 3.8 Gy were delivered at the surface regions, respectively (delivery time = 111.1 and 3.5 min with 1 GBq/ml solutions). The PDDs of Y-90 and I-125 became less than 1% at depths greater than 8 and 50 mm, respectively.

CONCLUSIONS

The remote afterloading patient-patient specific brachytherapy with I-125 or Y-90 in liquid form seems feasible for total scalp irradiation.

Injectable Hydrogels for Localized Chemotherapy and Radiotherapy in Brain Tumors

Overall survival of patients with newly diagnosed glioblastoma (GBM) remains dismal at 16 months with state-of-the-art treatment that includes surgical resection, radiation, and chemotherapy. GBM tumors are highly heterogeneous, and mechanisms for overcoming tumor resistance have not yet fully been elucidated. An injectable chitosan hydrogel capable of releasing chemotherapy (temozolomide [TMZ]) while retaining radioactive isotopes agents (iodine, [¹³¹I]) was used as a vehicle for localized radiation and chemotherapy, within the surgical cavity. Release from hydrogels loaded with TMZ or ¹³¹I was characterized in vitro and in vivo and their efficacy on tumor progression and survival on GBM tumors was also measured. The in vitro release of ¹³¹I was negligible over 42 days, whereas the TMZ was completely released over the first 48 h. ¹³¹I was completely retained in the tumor bed with negligible distribution in other tissues and that when delivered locally, the chemotherapy accumulated in the tumor at 10-fold higher concentrations than when delivered systemically. We found that the tumors were significantly decreased, and survival was improved in both treatment groups compared to the control group. Novel injectable chemo-radio-hydrogel implants may potentially improve the local control and overall outcome of aggressive, poor prognosis brain tumors.

Guidelines by the AAPM and GEC-ESTRO on the use of innovative brachytherapy devices and applications: Report of Task Group 167

Although a multicenter, Phase III, prospective, randomized trial is the gold standard for evidence-based medicine, it is rarely used in the evaluation of innovative devices because of many practical and ethical reasons. It is usually sufficient to compare the dose distributions and dose rates for determining the equivalence of the innovative treatment modality to an existing one. Thus, quantitative evaluation of the dosimetric characteristics of innovative radiotherapy devices or applications is a critical part in which physicists should be actively involved. The physicist's role, along with physician colleagues, in this process is highlighted for innovative brachytherapy devices and applications and includes evaluation of (1) dosimetric considerations for clinical implementation (including calibrations, dose calculations, and radiobiological aspects) to comply with existing societal dosimetric prerequisites for sources in routine clinical use, (2) risks and benefits from a regulatory and safety perspective, and (3) resource assessment and preparedness. Further, it is suggested that any developed calibration methods be traceable to a primary standards dosimetry laboratory (PSDL) such as the National Institute of Standards and Technology in the U.S. or to other PSDLs located elsewhere such as in Europe. Clinical users should follow standards as approved by their country's regulatory agencies that approved such a brachytherapy device. Integration of this system into the medical source calibration infrastructure of secondary standard dosimetry laboratories such as the Accredited Dosimetry Calibration Laboratories in the U.S. is encouraged before a source is introduced into widespread routine clinical use. The American Association of Physicists in Medicine and the Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) have developed guidelines for the safe and consistent application of brachytherapy using innovative devices and applications. The current report covers regulatory approvals, calibration, dose calculations, radiobiological issues, and overall safety concerns that should be addressed during the commissioning stage preceding clinical use. These guidelines are based on review of requirements of the U.S. Nuclear Regulatory Commission, U.S. Department of Transportation, International Electrotechnical Commission Medical Electrical Equipment Standard 60601, U.S. Food and Drug Administration, European Commission for CE Marking (Conformité Européenne), and institutional review boards and radiation safety committees.

Smart Radiation Therapy Biomaterials

Radiation therapy (RT) is a crucial component of cancer care, used in the treatment of over 50% of cancer patients. Patients undergoing image guided RT or brachytherapy routinely have inert RT biomaterials implanted into their tumors. The single function of these RT biomaterials is to ensure geometric accuracy during treatment. Recent studies have proposed that the inert biomaterials could be upgraded to "smart" RT biomaterials, designed to do more than 1 function. Such smart biomaterials include next-generation fiducial markers, brachytherapy spacers, and balloon applicators, designed to respond to stimuli and perform additional desirable functions like controlled delivery of therapy-enhancing payloads directly into the tumor subvolume while minimizing normal tissue toxicities. More broadly, smart RT biomaterials may include functionalized nanoparticles that can be activated to boost RT efficacy. This work reviews the rationale for smart RT biomaterials, the state of the art in this emerging cross-disciplinary research area, challenges and opportunities for further research and development, and a purview of potential clinical applications. Applications covered include using smart RT biomaterials for boosting cancer therapy with minimal side effects, combining RT with immunotherapy or chemotherapy, reducing treatment time or health care costs, and other incipient applications.

Outcome of Adult Brain Tumor Consortium (ABTC) prospective dose-finding trials of I-125 balloon brachytherapy in high-grade gliomas: challenges in clinical trial design and technology development when MRI treatment effect and recurrence appear similar

OBJECTIVES

The aim of this study is to define the maximal safe radiation dose to guide further study of the GliaSite balloon brachytherapy (GSBT) system in untreated newly diagnosed glioblastoma (NEW-GBM) and recurrent high-grade glioma (REC-HGG). GBST is a balloon placed in the resection cavity and later filled through a subcutaneous port with liquid I-125 Iotrex, providing radiation doses that diminish uniformly with distance from the balloon surface.

METHODS

The Adult Brain Tumor Consortium initiated prospective dose-finding studies to determine maximum tolerated dose in NEW-GBM treated before standard RT or after surgery for REC-HGG. Patients were inevaluable if there was progression before the 90-day posttreatment toxicity evaluation point.

RESULTS

Ten NEW-GBM patients had the balloon placed, and 2/10 reached the 90 day timepoint. Five REC-HGG enrolled and two were assessable at the 90-day evaluation endpoint. Imaging progression occurred before 90-day evaluation in 7/12 treated patients. The trials were closed as too few patients were assessable to allow dose escalation, although no dose-limiting toxicities (DLTs) were observed. Median survival from treatment was 15.3 months (95 % CI 7.1-23.6) for NEW-GBM and 12.8 months (95 % CI 4.2-20.9) for REC-HGG.

CONCLUSION

These trials failed to determine a maximum tolerated dose (MTD) for further testing as early imaging changes, presumed to be progression, were common and interfered with the assessment of treatment-related toxicity. The survival outcomes in these and other related studies, although based on small populations, suggest that GSBT may be worthy of further study using clinical and survival endpoints, rather than standard imaging results. The implications for local therapy development are discussed.

Immediate post-operative brachytherapy prior to irradiation and temozolomide for newly diagnosed glioblastoma

To determine whether immediate post-operative brachytherapy can be safely applied to newly diagnosed glioblastomas to retard tumor progression prior to initiation of external beam radiation therapy (EBRT) and temozolomide. Between 1996 and 2011, eleven patients underwent implantation of GliaSite (n = 9) or MammoSite (n = 2) at the time of surgical resection. Brachytherapy was carried out on post-operative day 2-3, with 45-60 Gy delivered to a 1 cm margin. All patients underwent subsequent standard radiation/temozolomide treatment 4-5 weeks post-irradiation. There were no wound related complications. Toxicity was observed in two patients (2/11 or 18 %), including one post-operative seizure and one case of cerebral edema that resolved after a course of steroid treatment. Immediate post-operative and pre-irradiation/temozolomide magnetic resonance imaging assessment was available for 9 of the 11 patients. Two of these nine patients (22 %) developed new regions of contrast enhancement prior to irradiation/temozolomide. This compares favorably to historical data where 53 % of patient suffer such tumor progression. While there was a trend toward improved 6 month progression free survival in the brachytherapy/temozolomide/radiation treated patients, the overall survival of these patients were comparable to historical controls. This case series demonstrates the safety of immediate post-operative brachytherapy when applied prior to EBRT and temozolomide in the treatment of newly diagnosed glioblastomas.

Evaluation of minimally invasive excisional brain biopsy and intracranial brachytherapy catheter placement in dogs

OBJECTIVE

To evaluate a technique for minimally invasive excisional brain biopsy and intracranial brachytherapy catheter placement in dogs.

ANIMALS

5 healthy adult female dogs.

PROCEDURES

Computed tomographic guidance was used to plan a biopsy trajectory to a selected area of brain with reference to a localizer grid. The procedure was performed through a 1-cm skin incision and 6-mm burr hole by use of a 9-gauge biopsy device. Five cylindrical samples (3 to 4 mm in diameter and 7 to 12 mm in length) were removed over 5 cycles of the vacuum-assisted tissue excision system, leaving approximately a 2-cm³ resection cavity. A balloon-tipped intracranial brachytherapy catheter was placed through the burr hole into the resection cavity, expanded with saline (0.9% NaCl) solution, and explanted 7 days later.

RESULTS

4 of 5 dogs survived the procedure. The fifth died because of iatrogenic brain damage. Neurologic deficits were unilateral and focal. Twenty-four hours after surgery, all surviving dogs were ambulatory, 2 dogs exhibited ipsiversive circling, 4 had contralateral proprioceptive deficits, 3 had contralateral menace response deficits, 2 had a reduced contralateral response to noxious nasal stimulation, and 1 had dull mentation with intermittent horizontal nystagmus and ventrolateral strabismus. Neurologic status improved throughout the study period. Histologic quality of biopsy specimens was excellent.

CONCLUSIONS AND CLINICAL RELEVANCE

This technique enabled histologic diagnosis from high-quality biopsy specimens obtained through a minimally invasive technique and has potential applications for multimodal treatment of deep brain tumors in dogs.

Technological advances in radiation oncology for central nervous system tumors

Advances in computer software technology have led to enormous progress that has enabled increasing levels of complexity to be incorporated into radiotherapy treatment planning systems. Because of these changes, the delivery of radiotherapy evolved from therapy designed primarily on plain 2-dimensional X-ray images and hand calculations to therapy based on 3-dimensional images incorporating increasingly complex computer algorithms in the planning process. In addition, challenges in treatment planning and radiation delivery, such as problems with setup error and organ movement, have begun to be systematically addressed, ushering in an era of so-called 4-dimensional radiotherapy. This review article discusses how these advances have changed the way in which many common neoplasms of the central nervous system are being treated at present.

Surgical Therapies in Brain Metastasis

Brain metastases are the most common intracranial tumors in adults and source of the most common neurological complications of systemic cancer. The treatment approach to brain metastases differs essentially from treatment of systemic metastases due to the unique anatomical and physiological characteristics of the brain. Surgery and radiosurgery are important components in the complex treatment of brain metastases and can prolong survival and improve the quality of life (QOL). Aggressive intervention may be indicated for selected patients with well-controlled systemic cancer and good performance status in whom central nervous system (CNS) disease poses the greatest threat to functionality and survival. In this review the respective roles of surgery and radiosurgery, patient selection, general prognostic factors and tailoring of optimal surgical management strategies for cerebral metastases are discussed.

Brachytherapy for brain tumors

Over the past several decades neurooncologists have attempted to find an adjuvant treatment that prolongs survival for patients with malignant brain tumors. Brachytherapy, radiotherapy delivered by placing radioactive sources directly into the tumor, was initially thought to be the solution to this problem. Initial single institution studies showed very promising results; however, this technique has failed to show a significant survival advantage in two randomized studies. Despite this, brachytherapy continues to be used in a number of centers throughout the world for the treatment of various types of brain tumors including low-grade gliomas, anaplastic astrocytomas, glioblastomas, meningiomas and metastases. This article reviews brachytherapy's rationale, radiobiology, complications, indications, and results from numerous studies that have focused on its application for brain tumors with emphasis on its application for glial tumors.

Treatment of recurrent glioblastoma multiforme with GliaSite brachytherapy

PURPOSE

In this study, we assess the efficacy of GliaSite brachytherapy in the treatment of patients with recurrent glioblastoma multiforme (GBM).

METHODS AND MATERIALS

Between 1999 and 2004, 24 patients with recurrent glioblastoma multiforme were treated with the GliaSite Radiation Therapy System (RTS). The GliaSite is an inflatable balloon catheter that is placed in the resection cavity at the time of surgical resection. Low-dose-rate radiation is then delivered locally by temporarily inflating the balloon with an aqueous solution of organically bound (125)I (Iotrex [sodium 3-((125)I)-iodo-4-hydroxybenzenesulfonate]). Patients at the Johns Hopkins Hospital with recurrent GBM, who were previously treated with surgery and external beam radiotherapy, underwent surgical resection followed by GliaSite balloon implantation. Subsequently, the patients received radiation therapy using the GliaSite to a mean dose of 53.1 Gy. Ten patients were male, and 14 patients were female. The mean age was 48.1 years. All patients had pathologically confirmed recurrent GBM. The median Karnofsky performance status (KPS) was 80. Median follow-up time was 21.8 months.

RESULTS

At the time of analysis, 18 patients (75%) had died; 6 patients (25%) were alive. Median survival from diagnosis for all patients was 23.3 months. Median survival after GliaSite brachytherapy was 9.1 months. Patients with a KPS > or =70 had a median survival of 9.3 months, whereas patients with a KPS <70 had a median survival of 3.1 months (p < 0.003). Survival was not significantly different between patients receiving 45 Gy and patients receiving a dose greater than 45 Gy. Acute side effects were minor, consisting of mild nausea and/or headache. One patient developed a wound infection. No incidents of meningitis were observed. Late sequelae were rare, but 2 incidents of symptomatic radiation necrosis were observed. One patient developed transient expressive aphasia.

CONCLUSIONS

GliaSite radiotherapy confers a prolongation of survival in patients with recurrent glioblastoma multiforme compared to historical controls with recurrent GBM. GliaSite therapy leads to a favorable survival outcome of 9.3 months in patients with KPS > or =70, but only 3.1 months in patients with KPS <70. Favorable survival is observed for patients within each recursive partitioning analysis class. Treatment with GliaSite is safe and generally well tolerated. Additional data are needed to fully assess the therapeutic benefit of GliaSite brachytherapy for recurrent GBM.

(125)I liquid in an intracranial balloon: TG-43 formalism for an extended source

PURPOSE

To present a calculation formalism for spherical homogeneous liquid brachytherapy sources and to analyze the difficulties encountered in numerical integration over non-spherical source volumes.

METHODS AND MATERIALS

TG-43 formalism provides a general definition of the geometric factor for distributed source distributions. Here the geometric factor and dose for a spherical source are computed for an (125)I balloon. The errors in numerical summation of dose from point sources are assessed by computing ratios of the geometric factors of point-source and extended-source voxel volumes.

RESULTS

This sphere calculation agrees well with measured dose values, showing maximum and average differences of 4.8% and 0.5% at the balloon surface. Numerical integration gives errors greater than 1% within five voxel radii of a voxel source.

CONCLUSIONS

A new spherical dose calculation technique is proposed for brachytherapy treatment planning systems. Numerical integration over point source voxels is not accurate near the balloon surface.

Medical Devices of the Head, Neck, and Spine

There are many medical devices used for head, neck, and spinal diseases and injuries, and new devices are constantly being introduced. Many of the newest devices are variations on a previous theme. Knowing the specific name of a device is not important. It is important to recognize the presence of a device and to have an understanding of its function as well as to be able to recognize the complications associated with its use. The article discusses the most common and important devices of the head, neck, and spine, including cerebrospinal fluid shunts and the Codman Hakim programmable valve; subdural drainage catheters, subdural electrodes, intracranial electrodes, deep brain stimulators, and cerebellar electrodes; coils, balloons, adhesives, particles, and aneurysm clips; radiation therapy catheters, intracranial balloons for drug installation, and carmustine wafers; hearing aids, cochlear implants, and ossicular reconstruction prostheses; orbital prostheses, intraocular silicone oil, and lacrimal duct stents; anterior and posterior cervical plates, posterior cervical spine wiring, odontoid fracture fixation devices, cervical collars and halo vests; thoracic and lumbar spine implants, anterior and posterior instrumentation for the thoracic and lumbar spine, vertebroplasty, and artificial disks; spinal column stimulators, bone stimulators, intrathecal drug delivery pumps, and sacral stimulators; dental and facial implant devices; gastric and tracheal tubes; vagus nerve stimulators; lumboperitoneal shunts; and temperature- and oxygen-sensing probes.

An inflatable balloon catheter and liquid 125I radiation source (GliaSite Radiation Therapy System) for treatment of recurrent malignant glioma: multicenter safety and feasibility trial

OBJECT

In this study the authors evaluated the safety and performance of the GliaSite Radiation Therapy System (RTS) in patients with recurrent malignant brain tumors who were undergoing tumor resection.

METHODS

The GliaSite is an inflatable balloon catheter that is placed in the resection cavity at the time of tumor debulking. Low-dose-rate radiation is delivered with an aqueous solution of organically bound iodine-125 (lotrex [sodium 3-(125I)-iodo-4-hydroxybenzenesulfonate]), which are temporarily introduced into the balloon portion of the device via a subcutaneous port. Adults with recurrent malignant glioma underwent resection and GliaSite implantation. One to 2 weeks later, the device was filled with Iotrex for 3 to 6 days, following which the device was explanted. Twenty-one patients with recurrent high-grade astrocytomas were enrolled in the study and received radiation therapy. There were two end points: 1) successful implantation and delivery of brachytherapy; and 2) safety of the device. Implantation of the device, delivery of radiation, and the explantation procedure were well tolerated. At least 40 to 60 Gy was delivered to all tissues within the target volume. There were no serious adverse device-related events during brachytherapy. One patient had a pseudomeningocele, one patient had a wound infection, and three patients had meningitis (one bacterial, one chemical, and one aseptic). No symptomatic radiation necrosis was identified during 21.8 patient-years of follow up. The median survival of previously treated patients was 12.7 months (95% confidence interval 6.9-15.3 months).

CONCLUSIONS

The GliaSite RTS performs safely and efficiently. It delivers a readily quantifiable dose of radiation to tissue at the highest risk for tumor recurrence.

The Brain Tumor Cooperative Group NIH Trial 87-01: A Randomized Comparison of Surgery, External Radiotherapy, and Carmustine versus Surgery, Interstitial Radiotherapy Boost, External Radiation Therapy, and Carmustine

OBJECTIVE

The objective of the Brain Tumor Cooperative Group NIH Trial 87-01 trial was to investigate the effect of additional implanted radiation therapy in newly diagnosed patients with pathologically confirmed malignant gliomas.

METHODS

The study involved a randomized comparison of surgery, external beam radiotherapy, and carmustine (BCNU) versus surgery, external beam therapy, interstitial radiotherapy boost, and BCNU in newly diagnosed malignant gliomas. 125I was chosen as best suited for this effort because it allowed preimplantation planning and postimplantation quality assurance review. Two hundred ninety-nine patients met the eligibility criteria and were randomized into the two arms of the study between December 1987 and April 1994. Follow-up continued for an additional 3 years. Twenty-nine patients were identified as having committed protocol violations and were excluded, resulting in 270 subjects in the Valid Study Group. One hundred thirty-seven patients received external beam radiation and BCNU, and 133 underwent the 125I implantation plus external beam radiation and BCNU therapy.

RESULTS

The overall median survival for the Valid Study Group was 64.3 weeks. The median survival for patients receiving additional therapy of 125I was 68.1 weeks, and median survival for those receiving only external beam radiation and BCNU was 58.8 weeks. The cumulative proportion surviving between the two treatment groups was not statistically significantly different (log-rank test, P = 0.101). As in other studies in the literature, age, Karnofsky score, and pathology were predictors of mortality. Additional analyses incorporating an adjustment for these prognostic variables, either in a stratified analysis or Cox proportional hazards model, did not result in statistically significant differences in the cumulative proportion of patients surviving between the two treatment groups.

CONCLUSION

We conclude that there is no long-term survival advantage of increased radiation dose with 125I seeds in newly diagnosed glioma patients.

Experimental investigation of dose calibrator response for 125I brachytherapy solutions contained in 5 mL plastic syringes and 2 mL conical glass v-vials as a function of filling mass

The effect of measurement geometry on the determination of the activity of solutions containing 125I for use in brachytherapy applications has been investigated for 5 mL plastic syringes and 2 mL conical glass dose vials as a function of filling mass. New dial settings for the syringes over a filling mass range of 1 to 3 g have been determined to be 497+/-8 and 469+/-8 (expanded, k = 2, uncertainties) for the NIST Capintec CRC- 12 and Capintec CRC-35R, respectively, with any effect due to the filling mass lying within the uncertainty in the activity calibration. A filling mass effect was observed in the dose vials, causing a 10.5% reduction in the chamber response from a 2 g filling mass to 1 g. Dial settings at 2 g were experimentally found to be 143+/-2 and 135+/-2 (expanded uncertainties) for the NIST Capintec CRC-12 and Capintec CRC-35R, respectively. The appropriate dial settings for the same vials with a 1 g filling mass were found to be 120+/-2 and 114+/-2 for CRC-12 and CRC-35R, respectively. Differences of up to +/-45% in the activity determination were observed between values obtained with the manufacturer's recommended setting and the settings obtained experimentally for each specific geometry. Calibration factors were also determined for a Vinten 671 Radionuclide Calibrator, giving values of 0.226+/-0.009 pA x MBq(-1) and 0.231+/-0.004 pA x MBq(-1) (expanded uncertainties), respectively, for the 1 and 2 g dispensings. This study demonstrates that experimentally determined calibration factors for the exact measurement geometry are necessary when measuring radionuclides in configurations other than the manufacturer's standard geometry, especially when nuclides that emit low-energy radiations are involved.

Preclinical evaluation of a novel device for delivering brachytherapy to the margins of resected brain tumor cavities

OBJECT

The objectives of this study were to evaluate the safety and performance of a new brachytherapy applicator in the treatment of resected brain tumors in a canine model.

METHODS

The brachytherapy applicator is an inflatable balloon catheter that is implanted in the resection cavity remaining after a brain tumor has been debulked. After implantation the balloon is inflated with Iotrex, a sterile solution containing organically bound iodine-125. The low-energy photons emitted by the iodine-125 deposit a therapeutic radiation dose across short distances from the surface of the balloon. After delivery of a prescribed radiation dose to the targeted volume, the radioactive fluid is retrieved and the catheter removed. Small resections of the right frontal lobe were performed in large dogs. Magnetic resonance (MR) images were obtained and used to assess tissue response and to measure the conformance between the resection cavity wall and the balloon surface. In four animals a dose ranging from 36 to 59 Gy was delivered. Neurological status and histological characteristics of the brain were assessed in all dogs. Implantation and explantation as well as inflation and deflation of the device were easily accomplished and well tolerated. The device was easily visualized on MR images, which demonstrated the expected postsurgical changes. The resection cavity and the balloon were highly conformal (range 93-100%). Histological changes to the cavity margin were consistent with those associated with surgical trauma. Additionally, radiation-related changes were observed at the margins of the resection cavity in dogs in which the brain was irradiated.

CONCLUSIONS

This balloon catheter and 125I radiotherapy solution system can safely and reliably deliver radiation to the margins of brain cavities created by tumor resection. Results of this study showed that intracranial pressure changes due to balloon inflation and deflation were unremarkable and characteristic of the imaging properties and radiation safety profile of the device prior to its clinical evaluation. Clinically relevant brachytherapy (adequate target volume and total dose) was accomplished in all four animals subjected to treatment.

A cost-minimising analysis of standard radiotherapy and two experimental therapies in glioblastoma

BACKGROUND AND PURPOSE

Accelerated radiotherapy (ART) and intracavity brachytherapy (ICBT) have been introduced in the primary treatment of glioblastoma. Our objective was to determine total treatment costs, hospitalisation time, and treatment outcome in these two experimental therapies compared to standard treatment.

MATERIALS AND METHODS

In the time period 1985 to 1st May 1999, a total of 174 patients with histologically confirmed glioblastoma multiforme were given postoperative radiotherapy according to three different treatment schedules at three different time intervals. A conventional regime of external radiotherapy (54Gy/30 fractions) was given to 58 patients (group I), 75 patients were treated with ART (48Gy/twice daily 30 fractions) (group II), and 41 patients were given ICBT (60Gy/ten fractions) (group III). Treatment costs including surgery, hospital stay, hospital hotel stay, and radiotherapy were calculated.

RESULTS

The total mean costs employing the three treatment alternatives were calculated to $25,618 (group I), $23,442 (group II), and $14,534 (group III). Total mean stay in hospital for the whole primary treatment was 48.8, 41.6, and 19 days for groups I, II, and III respectively. Median survival figures were 16, 14, and 13 months for groups I, II, and III, respectively.

CONCLUSIONS

The total cost of postoperative radiotherapy in glioblastoma is comparable to other health care services. ART did not improve the total treatment cost or influence the need for hospitalisation compared to standard treatment. ICBT seemed to have economic benefits with less need for hospitalisation.

Pre-targeted locoregional radioimmunotherapy with 90Y-biotin in glioma patients: phase I study and preliminary therapeutic results

The aim of this study was to determine the maximum-tolerated dose, of a pre-targeting three-step (3-S) method employing 90Y-biotin in the locoregional radioimmunotherapy (RIT) of recurrent high grade glioma, and to investigate the antitumor efficacy of this new treatment. Twenty-four patients with recurrent glioma underwent second surgical debulking and implantation of a catheter into the surgical resection cavity (SRC), in order to introduce the radioimmunotherapeutic agents [biotinylated monoclonal antibody (MoAb), avidin and 90Y-biotin]. Eight patients with anaplastic astrocytoma (AA) and 16 patients with glioblastoma (GBM) were injected with biotinylated anti-tenascin MoAb (2 mg), then with avidin (10 mg; 24 h later) and finally 90Y-biotin (18 h later). Each patient received two of these treatments 8-10 weeks apart. The injected activity ranged from 0.555 to 1.110 GBq (15-30 mCi). Dosage was escalated by 0.185 GBq (5 mCi) in four consecutive groups. The treatment was well tolerated without acute side effects up to 0.740 GBq (20 mCi). The maximum tolerated activity was 1.110 GBq (30 mCi) limited by neurological toxicity. None of the patients developed hematologic toxicity. In three patients infection occurred around the catheter. The average absorbed dose to the normal brain was minimal compared with that received at the SRC interface. At first control (after 2 months), partial (PR) and minor (MR) responses were observed in three GBM (1 PR; 2 MR) and three AA patients (1 PR; 2 MR) with an overall objective response rate of 25%. Stable disease (SD) was achieved in seven GBM and five AA patients (50%). There was disease progression in six GBM patients (25%), but in none of the AA patients. At the dosage of 0.7-0.9 GBq per cycle, locoregional 3-S-RIT was safe and produced an objective response in 25% of patients. Based on these encouraging results, phase II studies employing 3-S-RIT soon after first debulking are justified.

Experimental validation of dose calculation algorithms for the GliaSite RTS, a novel 125I liquid-filled balloon brachytherapy applicator

This paper compares experimentally measured and calculated dose-rate distributions for a novel 125I liquid-filled brachytherapy balloon applicator (the GliaSite RTS), designed for the treatment of malignant brain-tumor resection-cavity margins. This work is intended to comply with the American Association of Physicists in Medicine (AAPM) Radiation Therapy Committee's recommendations [Med. Phys. 25, 2269-2270 (1998)] for dosimetric characterization of low-energy photon interstitial brachytherapy sources. Absolute low dose-rate radiochromic film (RCF) dosimetry measurements were performed in coronal planes about the applicator. The applicator was placed in a solid water phantom, machined to conform to the inflated applicator's surface. The results were used to validate the accuracy of Monte Carlo photon transport (MCPT) simulations and a point-source dose-kernel algorithm in predicting dose to water. The absolute activity of the 125I solution was determined by intercomparing a National Institute of Standards and Technology (NIST) 125I standard with a known mass of radiotherapy solution (Iotrex) in an identical vial and geometry. For the two films not in contact with applicator, the average agreement between RCF and MCPT (specified as the mean absolute deviation in successive 4 mm rings) was found to be within +/-5% at distances 0.2-25 mm from the film centers. For the two films touching the catheter, the mean agreement was +/-14.5% and 7.5% near the balloon surface but improving to 7.5% and 6% by 3.5 mm from the surface. These errors, as large as 20% in isolated pixels, are likely due to trim damage, 125I contamination, and poor conformance with the balloon. At larger distances where the radiation doses were very low, the observed discrepancies were significantly larger than expected. We hypothesize that they are due to a dose-rate dependence of the RCF response. A 1%-10% average difference between a simple one-dimensional path-length semiempirical dose-kernel model and the MCPT calculations was observed over clinically relevant distances.

Biodistribution and dosimetry of an aqueous solution containing sodium 3-(125I)iodo-4-hydroxybenzenesulfonate (Iotrex) for brachytherapy of resected malignant brain tumors

Iotrex is an aqueous radiotherapy solution containing sodium 3-(125I)iodo-4-hydroxybenzenesulfonate (125I-HBS), which is used as the radiation source for the brachytherapy of resected of brain tumor cavity margins with the GliaSite catheter. During routine clinical use of this brachytherapy applicator and radiation source, approximately 0.1% of the afterloaded Iotrex will diffuse through the GliaSite balloon. Our purpose was to assess the radiation doses to normal organs under routine clinical use of the GliaSite.

METHODS

Five groups of rats received intracerebral injections of an 131I-HBS solution (131I used as a surrogate for 125I in the synthesis of 125I-HBS) with one group sacrificed at 15 minutes, 30 minutes, 1 hour, 2 hours and 4 hours post-administration. Urine was collected and activity retention in numerous organs was measured. The biodistribution data were used to estimate radiation doses to normal organs of the Reference Adult Male and Female phantoms.

RESULTS

Radioactivity was rapidly and completely cleared from the brain (98% cleared by 2 hours) and total body (urinary clearance; 93%@2 hours). No organ retained > 0.7% of the radioactivity at 4 hours. For 100% loss of the radiotherapy solution from the balloon catheter (device failure), all organs would receive less than 100 mGy (10 rad), except the bladder wall (2800 mGy, 280 rad), uterus (130 mGy, 13 rad) and distal colon (270 mGy, 27 rad). Under normal conditions, all organ doses are 1000-fold lower (< 3 mGy or 0.3 rad).

CONCLUSIONS

Under routine clinical conditions, the radiation doses to normal organs are inconsequential. Should the maximum clinical load of Iotrex (16.7 GBq of 125I) be released intracerebrally, the radiation doses to all organs would be below the thresholds for deterministic effects.

Neurosurgical advances in the treatment of brain tumors

Surgery remains an important part of the treatment of primary malignant brain tumors. When surgery is utilized, care must be taken to maximize the safety of the procedures. This article emphasizes advances in lesion localization within the brain and technology used to identify the function of normal tissue around the tumor. Many of the new treatment paradigms involve a surgical procedure. For example, surgery is necessary for biodegradable treatment delivery systems, and for some focal radiation therapy. Neurosurgeons are familiar with implantable catheter systems for other types of disease such as hydrocephalus; however, there is now an opportunity to take advantage of such technology to assist in the delivery of treatment agents locally within a tumor. Although no specific surgical advance has offered cure of malignant tumors, surgery remains necessary for utilization of the treatment advances now becoming available.