The relationship between the technical accuracy of stereotactic interstitial implantation for high grade gliomas and the pattern of tumor recurrence

A novel three-dimensional template combined with MR-guided 125I brachytherapy for recurrent glioblastoma

Background

At present, the treatment of recurrent glioblastoma is extremely challenging. In this study, we used a novel three-dimensional non-coplanar template (3DNPT) combined with open MR to guide ¹²⁵I seed implantation for recurrent glioblastoma. The aim of this study was to evaluate the feasibility, accuracy, and effectiveness of this technique.

Methods

Twenty-four patients of recurrent glioblastoma underwent 3DNPT with open MR-guided ¹²⁵I brachytherapy from August 2017 to January 2019. Preoperative treatment plan and 3DNPT were made according to enhanced isovoxel T1-weighted MR images. ¹²⁵I seeds were implanted using 3DNPT and 1.0-T open MR imaging guidance. Dosimetry verification was performed after brachytherapy based on postoperative CT/MR fusion images. Preoperative and postoperative dosimetry parameters of D90, V100, V200, conformity index (CI), external index (EI) were compared. The objective response rate (ORR) at 6 months and 1-year survival rate were calculated. Median overall survival (OS) measured from the date of brachytherapy was estimated by Kaplan-Meier method.

Results

There were no significant differences between preoperative and postoperative dosimetry parameters of D90, V100, V200, CI, EI (P > 0.05). The ORR at 6 months was 75.0%. The 1-year survival rate was 58.3%. Median OS was 12.9 months. One case of small amount of epidural hemorrhage occurred during the procedure. There were 3 cases of symptomatic brain edema after brachytherapy treatment, including grade three toxicity in 1 case and grade two toxicity in 2 cases. The three patients were treated with corticosteroid for 2 to 4 weeks. The clinical symptoms related to brain edema were significantly alleviated thereafter.

Conclusions

3DNPT combined with open MR-guided ¹²⁵I brachytherapy for circumscribed recurrent glioblastoma is feasible, effective, and with low risk of complications. Postoperative dosimetry matched the preoperative treatment plan. The described method can be used as a novel implantation technique for ¹²⁵I brachytherapy in the treatment of recurrent gliomas.

Trial registration

The study was approved by the Institutional Review Board of Shandong Provincial Hospital Affiliated to Shandong University (NSFC:NO.2017–058), registered 1st July 2017.

Neuroimaging classification of progression patterns in glioblastoma: a systematic review

BACKGROUND

Our primary objective was to report the current neuroimaging classification systems of spatial patterns of progression in glioblastoma. In addition, we aimed to report the terminology used to describe 'progression' and to assess the compliance with the Response Assessment in Neuro-Oncology (RANO) Criteria.

METHODS

We conducted a systematic review to identify all neuroimaging studies of glioblastoma that have employed a categorical classification system of spatial progression patterns. Our review was registered with Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) registry.

RESULTS

From the included 157 results, we identified 129 studies that used labels of spatial progression patterns that were not based on radiation volumes (Group 1) and 50 studies that used labels that were based on radiation volumes (Group 2). In Group 1, we found 113 individual labels and the most frequent were: local/localised (58%), distant/distal (51%), diffuse (20%), multifocal (15%) and subependymal/subventricular zone (15%). We identified 13 different labels used to refer to 'progression', of which the most frequent were 'recurrence' (99%) and 'progression' (92%). We identified that 37% (n = 33/90) of the studies published following the release of the RANO classification were adherent compliant with the RANO criteria.

CONCLUSIONS

Our review reports significant heterogeneity in the published systems used to classify glioblastoma spatial progression patterns. Standardization of terminology and classification systems used in studying progression would increase the efficiency of our research in our attempts to more successfully treat glioblastoma.

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.

Controversies concerning the application of brachytherapy in central nervous system tumors

INTRODUCTION

Brachytherapy (BRT) is defined as a therapy technique where a radioactive source is placed a short distance from or within the tumor being treated. Much expectation has been placed on its efficacy to improve the outcome for patients with central nervous system (CNS) tumors due to the initial promising results from single institution retrospective studies. However, these optimistic findings have been highly debated since the selection criteria itself is preferable to other therapeutic modalities. The fact that BRT demonstrated no significant survival advantage in two prospective studies, together with the emerging role of stereotactic convergence therapy as a promising alternative, has further decreased the enthusiasm for BRT. Despite all the negative aspects, BRT continues to be conducted for the management of CNS tumors including gliomas, meningiomas and brain metastases.

MATERIAL AND METHODS

As many controversies have been aroused concerning the experience and future application of BRT, this article reviews the existing heterogeneities in terms of implants choice, optimal dose rate, targeting volume, timing of BRT, patients selection, substantial efficacy, BRT in comparison with stereotactic convergence therapy techniques and BRT in combination with other treatment modalities (data were identified by Pubmed searches).

RESULTS AND CONCLUSION

Though it is inconvincible to argue for the routine use of BRT, BRT may provide a choice for patients with large recurrent or inoperable deep-seated tumors, especially with the Glia-site technique. Radiotherapies including BRT may hold more promise if biologic mechanisms of radiation could be better understand and biologic modifications could be added in clinical trials.

Open low-field magnetic resonance imaging for target definition, dose calculations and set-up verification during three-dimensional CRT for glioblastoma multiforme

AIMS

To assess the effect on target delineation of using magnetic resonance simulation for planning of glioblastoma multiforme (GBM). Dose calculations derived from computed tomography- and magnetic resonance-derived plans were computed. The accuracy of set-up verification using magnetic resonance imaging (MRI)-based digital reconstructed radiographs (DRRs) was assessed.

MATERIALS AND METHODS

Ten patients with GBM were simulated using computed tomography and MRI. MRI was acquired with a low-field (0.23 T) MRI unit (SimMRI). Gross tumour volumes (GTVs) were delineated by two radiation oncologists on computed tomography and MRI. In total, 30 plans were generated using both the computed tomography, with (planbathoCT) and without (planCT) heterogeneity correction, and MRI data sets (planSimMRI). The minimum dose delivered (Dmin) to the GTV between computed tomography- and MRI-based plans was compared. The accuracy of set-up positioning using MRI DRRs was assessed by four radiation oncologists.

RESULTS

The mean GTVs delineated on computed tomography were significantly (P<0.001) larger than those contoured on MRI. The mean (+/-standard deviation) Dmin difference percentage was 0.3+/-0.8, 0.1+/-0.6 and -0.2+/-1.0% for the planCT/planbathoCT-, planCT/planSimMRI- and planbathoCT/planSimMRI-derived plans, respectively. The set-up differences observed with the computed tomography and MRI DRRs ranged from 1.0 to 4.0 mm (mean 1.5 mm; standard deviation+/-1.4).

CONCLUSIONS

GTVs defined on computed tomography were significantly larger than those delineated on MRI. Compared with computed tomography-derived plans, MRI-based dose calculations were accurate. The precision of set-up verifications based on computed tomography- and MRI-derived DRRs seemed similar. The use of MRI only for the planning of GBM should be further assessed.

Phase I trial of gross total resection, permanent iodine-125 brachytherapy, and hyperfractionated radiotherapy for newly diagnosed glioblastoma multiforme

PURPOSE

To evaluate the feasibility of gross total resection and permanent I-125 brachytherapy followed by hyperfractionated radiotherapy for patients with newly diagnosed glioblastoma.

METHODS AND MATERIALS

From April 1999 to May 2002, 21 patients with glioblastoma multiforme were enrolled on a Phase I protocol investigating planned gross total resection and immediate placement of permanent I-125 seeds, followed by postoperative hyperfractionated radiotherapy to a dose of 60 Gy at 100 cGy b.i.d., 5 days per week. Median age and Karnofsky performance status were 50 years (range, 32-65 years) and 90 (range, 70-100), respectively. Toxicity was assessed according to Radiation Therapy Oncology Group criteria.

RESULTS

Eighteen patients completed treatment according to protocol. The median preoperative tumor volume on magnetic resonance imaging was 18.6 cm(3) (range, 4.4-41.2 cm(3)). The median brachytherapy dose measured 5 mm radially outward from the resection cavity was 400 Gy (range, 200-600 Gy). Ten patients underwent 12 reoperations, with 11 of 12 reoperations demonstrating necrosis without evidence of tumor. Because of high toxicity, the study was terminated early. Median progression-free survival and overall survival were 57 and 114 weeks, respectively, but not significantly improved compared with historical patients treated at University of California, San Francisco, with gross total resection and radiotherapy without brachytherapy.

CONCLUSIONS

Treatment with gross total resection and permanent I-125 brachytherapy followed by hyperfractionated radiotherapy as performed in this study results in high toxicity and reoperation rates, without demonstrated improvement in survival.

Image fusion analysis of volumetric changes after interstitial low-dose-rate iodine-125 irradiation of supratentorial low-grade gliomas

The aim of this study was to compare the volumes of tumor necrosis, reactive zone and edema with the three-dimensional dose distributions after brachytherapy treatments of gliomas. The investigation was performed an average of 14.2 months after low-dose-rate (125)I interstitial irradiation of 25 inoperable low-grade gliomas. The prescribed dose was 50-60 Gy to the tumor surface. Dose planning and image fusion were performed with the BrainLab-Target 1.19 software. In the CT/ MRI images, the "triple ring" (tumor necrosis, reactive ring and edema) developing after the interstitial irradiation of the brain tumors was examined. The images with the triple ring were fused with the planning images, and the isodose curves were superimposed on them. The volumes of the three regions were measured. The average dose at the necrosis border was determined from the isodose distribution. For quantitative assessment of the dose distributions, the dose nonuniformity ratio (DNR), homogeneity index (HI), coverage index (CI) and conformal index (COIN) were calculated. The relative volumes of the different parts of the triple ring after the interstitial irradiation compared to the reference dose volume were the following: necrosis, 40.9%, reactive zone, 47.1%, and edema, 367%. The tumor necrosis developed at 79.1 Gy on average. The average DNR, HI, CI and COIN were 0.45, 0.24, 0.94 and 0.57, respectively. The image fusion analysis of the volume of tumor necrosis, reactive ring and edema caused by interstitial irradiation and their correlation with the dose distribution provide valuable information for patient follow-up, treatment options, and effects and side effects of radio therapy.

Accuracy and conformity of stereotactically guided interstitial brain tumour therapy using I-125 seeds

OBJECTIVE

To assess the accuracy of the stereotactic implantation procedure of catheters containing I-125 seeds in brain tumours and investigate the effect of catheter deviations on the dose distribution in patients.

METHODS

A randomised sample (n = 37) of all patients treated with I-125 seeds in our department between 6/1994 and 2/2002 was examined. Intraoperative X-ray images were used to measure deviations of implanted I-125 seed catheters from their planned positions and the influence on dose conformity, tumour surface dose and dose burden of surrounding healthy brain tissue was determined.

RESULTS

The mean spatial target point deviation was 2.0 mm (maximum 4.1 mm, SD 0.9 mm) and in 54.1% of the cases, reduction of the planned dose was greater than 5%. Target point deviations less than 1.5 mm have only minor influence on surface dose and conformity. Results indicated that in 10.8% of the cases the realized dose distribution showed a 'slight deviation', according to the guideline criteria for external radiosurgery of the Radiation Therapy Oncology Group. In 89.2% of the patients the applied dose conformed to the target volume.

CONCLUSIONS

Stereotactically guided interstitial irradiation with I-125 seeds can be used to treat brain tumours and metastases with high conformity comparable to radiosurgery. The observed deviations of the stereotactically implanted I-125 seed catheters from their planned target points were smaller when compared to frameless procedures. In order to maintain the required spatial accuracy of 1.5 mm in interstitial therapy using I-125 seeds, it appears necessary to optimise stereotactic instruments further.

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.

A feasibility study of interstitial hyperthermia plus external beam radiotherapy in glioblastoma multiforme using the Multi ELectrode Current Source (MECS) system

PURPOSE

Thermoradiotherapy has been shown in several randomized trials to increase local control compared to radiotherapy alone. The first randomized study of interstitial hyperthermia in glioblastoma multiforme showed a survival benefit for hyperthermia, though small. Improvement of the heating technique could lead to improved results. The purpose of this feasibility study is to present the clinical and thermal data of application of an improved interstitial hyperthermia system.

METHODS AND MATERIALS

Six patients with a glioblastoma multiforme were treated with interstitial hyperthermia using the Multi Electrode Current Source Interstitial Hyperthermia (MECS-IHT) system. The MECS-IHT system has the capability of spatial monitoring of temperature and individually steering of heating electrodes. Three sessions were given aiming at a steady state temperature of 42 degrees C for 1 h, with an interval of 3-4 days, during an external irradiation scheme of 60 Gy in 6 weeks. Hyperthermia was delivered with a mean of 10 catheters, 18 heating electrodes and 38 thermal probes per patient.

RESULTS

Sub-optimal temperatures were encountered in the first two patients leading to adjustments in technique thereafter with subsequent improvement of thermal data. With a catheter spacing of 11-12 mm, measurements yielded a mean T(90), T(50) and T(10) of 39.9, 43.7 and 45.2 degrees C, respectively, over three sessions in the last patient. The power per electrode to reach this temperature distribution varied from 25-100% of full power in each of the last four patients. Thermal data were reproducible over the three sessions. Acute toxicity was minimal.

CONCLUSIONS

Despite the spatial steering capabilities of the MECS-IHT system, a large temperature heterogeneity was encountered. The heterogeneity was the reason to limit the catheter spacing to 11-12 mm, thus making only small tumour volumes feasible for interstitial heating.

Permanent iodine 125 brachytherapy in patients with progressive or recurrent glioblastoma multiforme

This study reports the initial experience at the University of California San Francisco (UCSF) with tumor resection and permanent, low-activity iodine 125 (125I) brachytherapy in patients with progressive or recurrent glioblastoma multiforme (GM) and compares these results to those of similar patients treated previously at UCSF with temporary brachytherapy without tumor resection. Thirty-eight patients with progressive or recurrent GM were treated at UCSF with repeat craniotomy, tumor resection, and permanent, low-activity 125I brachytherapy between June 1997 and May 1998. Selection criteria were Karnofsky performance score > or =60, unifocal, contrast-enhancing, well-circumscribed progressive or recurrent GM that was judged to be completely resectable, and no evidence of leptomeningeal or subependymal spread. The median brachytherapy dose 5 mm exterior to the resection cavity was 300 Gy (range, 150-500 Gy). One patient was excluded from analysis. Median survival was 52 weeks from the date of brachytherapy. Age, Karnofsky performance score, and preimplant tumor volume were all statistically significant on univariate analyses. Multivariate analysis for survival showed only age to be significant. Median time to progression was 16 weeks. Both univariate and multivariate analysis of freedom from progression showed only preoperative tumor volume to be significant. Comparison to temporary brachytherapy patients showed no apparent difference in survival time. Chronic steroid requirements were low in patients with minimal postoperative residual tumor. We conclude that permanent 125I brachytherapy for recurrent or progressive GM is well tolerated. Survival time was comparable to that of a similar group of patients treated with temporary brachytherapy.

Role of radiation therapy and radiosurgery in glioblastoma multiforme

Randomized trials have supported a role for radiation therapy in the initial management of Glioblastoma Multiforme (GBM) for over twenty-five years. Although technological advances in imaging and three-dimensional treatment planning have reduced the toxicity for patients and have allowed safe radiation dose escalation, unfortunately they have not produced a correspondingly dramatic improvement in overall survival. The dose of 60 Gy partial brain RT remains the standard of care for patients with newly diagnosed GBM. Recently completed randomized trials of brachytherapy and radiosurgery do not support these modalities in the initial management of GBM, but these and other focal RT techniques such as intensity modulated radiation therapy enable safe retreatment in selected patients. Future studies will need to explore radiation biologic response modification and radiosensitization through targeted therapies.

Phase II study of high central dose Gamma Knife radiosurgery and marimastat in patients with recurrent malignant glioma

PURPOSE

To assess the outcome of high central dose Gamma Knife radiosurgery plus marimastat in patients with recurrent malignant glioma.

METHODS AND MATERIALS

Twenty-six patients with recurrent malignant glioma were enrolled in a prospective Phase II study between November 1996 and January 1999. The radiosurgery dose was prescribed at the 25-30% isodose surface to increase the dose substantially within the tumor's presumably hypoxic core. Marimastat was administered after radiosurgery to restrict regional tumor progression. Survival was compared with that of historical patients treated at our institution with standard radiosurgery.

RESULTS

The median times to progression after radiosurgery for Grade 3 and 4 patients was 31 and 15 weeks, respectively. The corresponding median survival time after radiosurgery was 68 and 38 weeks. The median survival time after radiosurgery in the historical patients was 59 and 44 weeks.

CONCLUSION

The dual strategies of using high central dose radiosurgery to overcome tumor hypoxia together with marimastat to inhibit local tumor invasion may offer a small survival advantage for recurrent Grade 3 tumors; they do not offer an advantage for recurrent Grade 4 tumors.

Brachytherapy of glioblastoma recurring in previously irradiated territory: predictive value of tumor volume

PURPOSE

To evaluate the impact of tumor volume on survival of patients reirradiated with (192)Ir for recurrent glioblastoma.

METHODS AND MATERIALS

Between 1993 and 1997, 42 patients with recurrent glioblastomas (29 males and 13 females, age 18-69 years, median age 49) were treated with (192)Ir implantation. Previous treatments included surgery, external beam radiotherapy, and chemotherapy. Maximum diameter of the recurrent tumor was 1.2-10.1 cm (median: 5.7 cm) and tumor volume was 1.6-122 cm(3) (median: 23 cm(3)). Karnofsky performance status score was 50-100 (median: 80). Brachytherapy dose was 40-60 Gy.

RESULTS

Probability of overall survival was 80% at 6 months, 48% at 1 year, and 11% at 2 years. Median survival was 50 weeks. Univariate analysis showed that both tumor volume (T < or T > or = 30 cm(3)) and Karnofsky performance status score were significant predictors of survival. Multivariate analysis showed that smaller tumor volumes were associated with a higher probability of survival (p < 0.001).

CONCLUSION

Tumor volume less than 30 cm(3) was associated with a higher probability of, and quality of, survival than larger lesions for patients reirradiated by brachytherapy for recurrent glioblastoma.

Extraneural metastatic glioblastoma after interstitial brachytherapy

PURPOSE

This is a report of 3 cases of extraneural metastasis of glioblastoma after interstitial radiation and assessment of pertinent literature addressing concern over an increased risk of these events with this therapy.

METHODS AND MATERIALS

In a series of 82 patients treated with (125)I brachytherapy for primary malignant brain tumors over a 7-year interval, 3 cases of extraneural glioblastoma were identified. The multicatheter technique for delivery of (125)I sources was utilized in all. Extraneural metastases were documented by imaging studies or biopsy. Over the same period, 310 patients with primary malignant brain tumors were treated without brachytherapy.

RESULTS

Biopsy-proven scalp and skull metastases occurred in 2 patients, at 3 and 8 months following brachytherapy. Each developed radiographic evidence of systemic metastases at 7 and 14 months postbrachytherapy, respectively. The third patient developed biopsy-proven cervical node involvement 4 months after brachytherapy. No patients with malignant gliomas undergoing craniotomy or stereotactic biopsy, but not brachytherapy, during the same time period developed extraneural metastases. Incidence in previously reported series commenting on this otherwise rare process range from 0% to 4.3%. The incidence of extraneural metastases in this series is 3.7% (3/82) and is comparable to those reports.

CONCLUSIONS

Percutaneous catheter-delivered brachytherapy may be associated with an increased incidence of extraneural metastatic glioma.

The role of brachytherapy for palliation

The goal of palliative radiation is to alleviate symptoms in a short amount of time and maintain an optimal functional and quality-of-life level while minimizing toxicity and patient inconvenience. Despite advances in multimodality antineoplastic therapies, failure to control the tumor at its primary site frustratingly remains the predominant source of morbidity and mortality in many patients with cancer. Escalation of doses of radiation using external beam irradiation has been shown to improve local tumor control, but limits are imposed by the tolerance of normal surrounding structures. The highly conformal nature of brachytherapy enables the radiation oncologist to accomplish safe escalation of radiation doses to the tumor while minimizing doses to normal surrounding structures. Thus, by enhancing the potential for local control, brachytherapy used alone or as a supplement to external beam radiation therapy retains a significant and important role in achieving the goals of palliation. Proper patient selection, excellent technique, and adherence to implant rules will minimize the risk of complications. The advantages realized with the use of brachytherapy include good patient tolerance, short treatment time, and high rates of sustained palliation. This article reviews various aspects of palliative brachytherapy, including patient selection criteria, implant techniques, treatment planning, dose and fractionation schedules, results, and complications of treatment. Tumors of the head and neck, trachea and bronchi, esophagus, biliary tract, and brain, all in which local failure represents the predominant cause of morbidity and mortality, are highlighted.

Interstitial brachytherapy for malignant brain tumors

For nearly 20 years, interstitial brachytherapy has been used as adjuvant treatment for malignant brain tumors in both prospective clinical trials and as part of standard therapy. Numerous publications analyzing the results of this treatment seem to indicate an improvement in median survival for highly selected patients. Some newly diagnosed glioblastoma multiforme, recurrent malignant glioma, brain metastases and possibly low grade gliomas seem to benefit. While Iodine-125 (I-125) remains the most popular radionuclide for brachytherapy, there is a recent move away from temporary high-activity implants to permanent low-activity implants. This review article will concentrate on the results from the University of California, San Francisco, as well as recent series published since 1990. In spite of the increased availability of radiosurgery, interstitial brachytherapy still has a place in the management of these difficult tumors.

A technique for accurate planning of stereotactic brain implants prior to head ring fixation

PURPOSE

A two-step procedure is described for accurate planning of stereotactic brain implants prior to head-ring fixation.

METHODS AND MATERIALS

Approximately 2 weeks prior to implant a CT scan without the head ring is performed for treatment-planning purposes. An entry point and a reference point, both marked with barium and later tattooed, facilitate planning and permit correlation of the images with a later CT scan. A plan is generated using a conventional treatment-planning system to determine the number and activity of I-125 seeds required and the position of each catheter. I-125 seed anisotropy is taken into account by means of a modification to the treatment planning program. On the day of the implant a second CT scan is performed with the head ring affixed to the skull and with the same points marked as in the previous scan. The planned catheter coordinates are then mapped into the coordinate system of the second CT scan by means of a manual translational correction and a computer-calculated rotational correction derived from the reference point coordinates in the two scans.

RESULTS

The rotational correction algorithm was verified experimentally in a Rando phantom before it was used clinically. For analysis of the results with individual patients a third CT scan is performed 1 day following the implant and is used for calculating the final dosimetry.

CONCLUSION

The technique that is described has two important advantages: 1) the number and activity of seeds required can be accurately determined in advance; and 2) sufficient time is allowed to derive the best possible plan.

[Radiotherapy of glioblastoma]

Glioblastoma cells appear to be inherently radioresistant and to present a significant fraction of hypoxic cells. The most significant prognostic factors to compare results achieved in several series of patients are the age, performance status and quality of surgical resection. Several randomized trials have provided evidence supporting the efficacy of radiation therapy in the treatment of glioblastoma. Prescription of a 60-Gy dose delivered according to a conventional dose-fractionation scheme (single daily fractions of 1.7 to 2 Gy five times per week) in a target volume with a 2-3 cm margin of tissue surrounding the perimeter of the contrast enhancing lesion on computerized tomography and magnetic resonance imaging is derived from observations made in several retrospective and prospective studies. Evidence of improvement in survival was observed neither in patients receiving hyperfractioned and accelerated radiotherapy, nor in patients for whom radiation sensitizers such as nitroimidazole compounds or halogenated pyrimidine analogs were associated to radiation therapy. The addition of nitrosourea to radiotherapy increases the 2-year survival rate by about 10%. Combination of full-dose external beam radiotherapy and brachytherapy or radiosurgery boost in selected patients with glioblastoma leads to an increase in the median survival, while external beam radiation alone in patients with similar prognosis does not.

Demonstration of brachytherapy boost dose-response relationships in glioblastoma multiforme

PURPOSE

To evaluate brachytherapy dose-response relationships in adults with glioblastoma undergoing temporary 125I implant boost after external beam radiotherapy.

METHODS AND MATERIALS

Since June 1987, orthogonal radiographs using a fiducial marker box have been used to verify brain implant source positions and generate dose-volume histograms at the University of California, San Francisco. For adults who underwent brachytherapy boost for glioblastoma from June 1987 through December 1992, tumor volumes were reoutlined to ensure consistency and dose-volume histograms were recalculated. Univariate and multivariate analysis of various patient and treatment parameters were performed evaluating for influence of dose on freedom from local failure (FFLF) and actuarial survival.

RESULTS

Of 102 implant boosts, 5 were excluded because computer plans were unavailable. For the remaining 97 patients, analyses with adjustment for known prognostic factors (age, KPS, extent of initial surgical resection) and prognostic factors identified on univariate testing (adjuvant chemotherapy) showed that higher minimum brachytherapy tumor dose was strongly associated with improved FFLF (p = 0.001). A quadratic relationship was found between total biological effective dose and survival, with a trend toward optimal survival probability at 47 Gy minimum brachytherapy tumor dose (corresponding to about 65 Gy to 95% of the tumor volume); survival decreased with lower or higher doses. Two patients expired and one requires hospice care because of brain necrosis after brachytherapy doses > 63 Gy to 95% of the tumor volume with 60 Gy to > 18 cm3 of normal brain.

CONCLUSION

Although higher minimum tumor dose was strongly associated with better local control, a brachytherapy boost dose > 50-60 Gy may result in life-threatening necrosis. We recommend careful conformation of the prescription isodose line to the contrast enhancing tumor volume, delivery of a minimum brachytherapy boost dose of 45-50 Gy in conjunction with conventional external beam radiotherapy, and reoperation for symptomatic necrosis.