Incidence of late radiation necrosis with transient mass effect after interstitial low dose rate radiotherapy for cerebral gliomas

Brachytherapy in Brain Metastasis Treatment: A Scoping Review of Advances in Techniques and Clinical Outcomes

Brain metastases pose a significant therapeutic challenge in the field of oncology, necessitating treatments that effectively control disease progression while preserving neurological and cognitive functions. Among various interventions, brachytherapy, which involves the direct placement of radioactive sources into or near tumors or into the resected cavity, can play an important role in treatment. Current literature describes brachytherapy's capacity to deliver targeted, high-dose radiation while minimizing damage to adjacent healthy tissues-a crucial consideration in the choice of treatment modality. Furthermore, advancements in implantation techniques as well as in the development of different isotopes have expanded its efficacy and safety profile. This review delineates the contemporary applications of brachytherapy in managing brain metastases, examining its advantages, constraints, and associated clinical outcomes, and provides a comprehensive understanding of advances in the use of brachytherapy for brain metastasis treatment, with implications for improved patient outcomes and enhanced quality of life.

Outcome assessment of intraoperative radiotherapy for brain metastases: results of a prospective observational study with comparative matched-pair analysis

PURPOSE

Intraoperative radiation therapy (IORT) is an emerging alternative to adjuvant stereotactic external beam radiation therapy (EBRT) following resection of brain metastases (BM). Advantages of IORT include an instant prevention of tumor regrowth, optimized dose-sparing of adjacent healthy brain tissue and immediate completion of BM treatment, allowing an earlier admission to subsequent systemic treatments. However, prospective outcome data are limited. We sought to assess long-term outcome of IORT in comparison to EBRT.

METHODS

A total of 35 consecutive patients, prospectively recruited within a study registry, who received IORT following BM resection at a single neuro-oncological center were evaluated for radiation necrosis (RN) incidence rates, local control rates (LCR), distant brain progression (DBP) and overall survival (OS) as long-term outcome parameters. The 1 year-estimated OS and survival rates were compared in a balanced comparative matched-pair analysis to those of our institutional database, encompassing 388 consecutive patients who underwent adjuvant EBRT after BM resection.

RESULTS

The median IORT dose was 30 Gy prescribed to the applicator surface. A 2.9% RN rate was observed. The estimated 1 year-LCR was 97.1% and the 1 year-DBP-free survival 73.5%. Median time to DBP was 6.4 (range 1.7-24) months in the subgroup of patients experiencing intracerebral progression. The median OS was 17.5 (0.5-not reached) months with a 1 year-survival rate of 61.3%, which did not not significantly differ from the comparative cohort (p = 0.55 and p = 0.82, respectively).

CONCLUSION

IORT is a safe and effective fast-track approach following BM resection, with comparable long-term outcomes as adjuvant EBRT.

Dosimetric Impact of Source Displacement in GammaTile Surgically Targeted Radiation Therapy for Gliomas

Background This study aims to evaluate dosimetric changes that happened during the first month after GammaTile surgically targeted radiation therapy (STaRT) for gliomas due to Cesium-131 (Cs-131) seed displacement caused by cavity shrinkage in brain brachytherapy. Methodology In this study, 10 glioma patients had 4-11 GammaTiles placed along the resection bed after maximal safe resection during craniotomy. Each GammaTile is composed of four Cs-131 seeds embedded in a biodegradable collagen sponge to minimize seed movement and maintain seed-to-cavity surface distance. The Cs-131 seed positions were identified using VariSeed on day one. On day 30, post-implant computed tomography (CT) images and dosimetry parameters were calculated. An iterative closest point (ICP) algorithm was used to compute rigid transformation between the day one and day 30 seed clouds. The seed displacement was calculated after registration. The volume receiving 100% of the prescription dose (V100), the dose received by 90% of the planning target volume (D90_PTV), the planning target volume receiving 100% of the prescription dose (V100_PTV), and the dose to organs at risk (OARs) were calculated for both CT images to determine the dosimetric changes from any seed displacement. Results The mean seed displacement of 1.8 ± 1.0 mm for all patients was observed between day one and day 30. The maximum seed displacement for each patient ranged from 2.3 mm to 7.3 mm. The mean V100 difference between day one and day 30 was 2.5 cc (range = 0.5-6.5 cc). The mean D90_PTVs were 95.5% (range = 69.0%-131.0%) and 98.1% (range = 19.9%-149.0%) on day one and day 30, respectively. The mean V100_PTVs were 88.4% (range = 81.3%-99.1%) and 87.9% (range = 47.0%-99.7%) on day one and day 30, respectively. On day one, the brainstem dose was 63.5 Gy for one case and 28.1 Gy for another case; while on day 30, the brainstem dose was 55.8 Gy and 20.6 Gy for the same patients, contributing to 7.7 Gy (12.8%) and 7.5 Gy (12.5%) dose reductions to brainstem for these patients, respectively. Only two patients received a dose to the optic nerves (34.1 Gy and 5.2 Gy). There were small changes (1.8 Gy and 0.5 Gy, respectively) in the dose to optic nerves when comparing the dose calculated on day one and the dose calculated on day 30 CT images. The same two patients received 30.4 Gy and 6.8 Gy to the chiasm, respectively. Small changes in the dose to the chiasm (≤1.1 Gy) were noted between day one and day 30. Conclusions A maximum seed displacement of up to 7.3 mm and a mean seed displacement of 1.8 mm caused by cavity shrinkage were observed during the first month after GammaTile STaRT for gliomas. There were noticeable changes in dosimetry parameters. Changes in the doses to OARs, particularly the brainstem, were large (up to 12.8% of the prescription dose). These changes in dosimetry should be considered when evaluating treatment outcomes and planning future GammaTile treatments.

The American Brachytherapy Society consensus statement on intraoperative radiation therapy

PURPOSE

Although radiation therapy has traditionally been delivered with external beam or brachytherapy, intraoperative radiation therapy (IORT) represents an alternative that may shorten the course of therapy, reduce toxicities, and improve patient satisfaction while potentially lowering the cost of care. At this time, there are limited evidence-based guidelines to assist clinicians with patient selection for IORT. As such, the American Brachytherapy Society presents a consensus statement on the use of IORT.

METHODS

Physicians and physicists with expertise in intraoperative radiation created a site-directed guideline for appropriate patient selection and utilization of IORT.

RESULTS

Several IORT techniques exist including radionuclide-based high-dose-rate, low-dose-rate, electron, and low-energy electronic. In breast cancer, IORT as monotherapy should only be used on prospective studies. IORT can be considered in the treatment of sarcomas with close/positive margins or recurrent sarcomas. IORT can be considered in conjunction with external beam radiotherapy for retroperitoneal sarcomas. IORT can be considered for colorectal malignancies with concern for positive margins and in the setting of recurrent gynecologic cancers. For thoracic, head and neck, and central nervous system malignancies, utilization of IORT should be evaluated on a case-by-case basis.

CONCLUSIONS

The present guidelines provide clinicians with a summary of current data regarding IORT by treatment site and guidelines for the appropriate patient selection and safe utilization of the technique. High-dose-rate, low-dose-rate brachytherapy methods are appropriate when IORT is to be delivered as are electron and low-energy based on the clinical scenario.

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.

Surgical Technique and Clinically Relevant Resection Cavity Dynamics Following Implantation of Cesium-131 (Cs-131) Brachytherapy in Patients With Brain Metastases

BACKGROUND

Cesium-131 (Cs-131) brachytherapy is used to reduce local recurrence of resected brain metastases. In order to ensure dose homogeneity and reduce risk of radiation necrosis, inter-seed distance and cavity volume must remain stable during delivery.

OBJECTIVE

To investigate the efficacy of the "seeds-on-a-string" technique with intracavitary fibrin glue in achieving cavity volume stability.

METHODS

We placed intra-operative Cs-131 brachytherapy in 30 cavities post-resection of brain metastases. Seeds-on-a-string were placed like barrel staves within the cavity with fibrin glue. Serial MRI imaging occurred post-operatively. Pre-operative tumor volumes were compared with post-operative cavity volumes to evaluate volume stability. Thirty patients who underwent post-resective stereotactic radiosurgery (SRS) were used as a control group for volumetric comparison.

RESULTS

Cs-131 and SRS patients exhibited consistent cavity shrinkage over the median 110-day follow-up (p<.001), with total median shrinkage of 56.5% (Cs-131) and 84.8% (SRS). During the first month when ~88% of Cs-131 dosage is delivered, however, there was non-significant volume decrease in the Cs-131 group (median 22.0%; p=.063), while SRS patients showed significantly more shrinkage (46.7%; p=.042). No events of radiation necrosis occurred in either group.

CONCLUSION

Cs-131 patients exhibited significantly less cavity shrinkage than SRS patients during the first critical month with 88% Cs-131 dose delivery. This significant difference in shrinkage suggests that the intracavitary seeds-on-a-string technique facilitates increased cavity stability, promoting more homogenous dose delivery.

Cerebral radiation necrosis: a review of the pathobiology, diagnosis and management considerations

Radiation therapy forms one of the building blocks of the multi-disciplinary management of patients with brain tumors. Improved survival following radiation therapy may come with a cost, including the potential complication of radiation necrosis. Radiation necrosis impacts the quality of life in cancer survivors, and it is essential to detect and effectively treat this entity as early as possible. Significant progress in neuro-radiology and molecular pathology facilitate more straightforward diagnosis and characterization of cerebral radiation necrosis. Several therapeutic interventions, both medical and surgical, may halt the progression of radiation necrosis and diminish or abrogate its clinical manifestations, but there are still no definitive guidelines to follow explicitly that guide treatment of radiation necrosis. We discuss the pathobiology, clinical features, diagnosis, available treatment modalities, and outcomes in the management of patients with intracranial radiation necrosis that follows radiation used to treat brain tumors.

Iodine-125 brachytherapy for brain tumours--a review

Iodine-125 brachytherapy has been applied to brain tumours since 1979. Even though the physical and biological characteristics make these implants particularly attractive for minimal invasive treatment, the place for stereotactic brachytherapy is still poorly defined.An extensive review of the literature has been performed, especially concerning indications, results and complications. Iodine-125 seeds have been implanted in astrocytomas I-III, glioblastomas, metastases and several other tumour entities. Outcome data given in the literature are summarized. Complications are rare in carefully selected patients.All in all, for highly selected patients with newly diagnosed or recurrent primary or metastatic tumours, this method provides encouraging survival rates with relatively low complication rates and a good quality of life.

The impact of recent data on the optimization of standards of care in newly diagnosed glioblastoma

Glioblastoma is an aggressive form of brain cancer with a poor long-term prognosis. Treatment regimens for newly diagnosed disease range from surgical resection alone to surgery followed by radiotherapy with concurrent and adjuvant chemotherapy. Ongoing investigations are focused on optimization of chemotherapy by improving dosing and duration schedules and utilization of biomarkers for patient selection. Our understanding of glioblastoma tumor biology, the role of molecular signaling pathways, cellular repair mechanisms, and angiogenesis has increased greatly over the past few years, leading to the investigation of a variety of targeted therapies. In addition, advances in radiographic assessment have significantly impacted not only improvement in diagnosis, but interpretation of response to therapy. In order to effectively evaluate the clinical utility of new agents, as well as incorporate advances in radiographic assessment, changes to current clinical trial design need to be considered. This article reviews the care for newly diagnosed glioblastoma, as well as how recent findings might be incorporated into patient care.

The place of interstitial brachytherapy and radiosurgery for low-grade gliomas

Even though stereotactic brachytherapy has been used for treatment of complex located low-grade glioma for many years, its place within modern treatment concepts is still debated and only a few centers have gained experience with this complex treatment modality. The current article reviews selection criteria, treatment protocols, radiobiology, treatment effects, risk models and side effects of stereotactic brachytherapy. Potentially alternative techniques such as radiosurgery were also reviewed under consideration of radiobiological similarities and differences.

Local targeting of malignant gliomas by the diffusible peptidic vector 1,4,7,10-tetraazacyclododecane-1-glutaric acid-4,7,10-triacetic acid-substance p

PURPOSE

Malignant glial brain tumors consistently overexpress neurokinin type 1 receptors. In classic seed-based brachytherapy, one to several rigid (125)I seeds are inserted, mainly for the treatment of small low-grade gliomas. The complex geometry of rapidly proliferating high-grade gliomas requires a diffusible system targeting tumor-associated surface structures to saturate the tumor, including its margins.

EXPERIMENTAL DESIGN

We developed a new targeting vector by conjugating the chelator 1,4,7,10-tetraazacyclododecane-1-glutaric acid-4,7,10-triacetic acid to Arg(1) of substance P, generating a radiopharmaceutical with a molecular weight of 1,806 Da and an IC(50) of 0.88 +/- 0.34 nmol/L. Cell biological studies were done with glioblastoma cell lines. neurokinin type-1 receptor (NK1R) autoradiography was done with 58 tumor biopsies. For labeling, (90)Y was mostly used. To reduce the "cross-fire effect" in critically located tumors, (177)Lut and (213)Bi were used instead. In a pilot study, we assessed feasibility, biodistribution, and early and long-term toxicity following i.t. injection of radiolabeled 1,4,7,10-tetraazacyclododecane-1-glutaric acid-4,7,10-triacetic acid substance P in 14 glioblastoma and six glioma patients of WHO grades 2 to 3.

RESULTS

Autoradiography disclosed overexpression of NK1R in 55 of 58 gliomas of WHO grades 2 to 4. Internalization of the peptidic vector was found to be specific. Clinically, the radiopharmeutical was distributed according to tumor geometry. Only transient toxicity was seen as symptomatic radiogenic edema in one patient (observation period, 7-66 months). Disease stabilization and/or improved neurologic status was observed in 13 of 20 patients. Secondary resection disclosed widespread radiation necrosis with improved demarcation.

CONCLUSIONS

Targeted radiotherapy using diffusible peptidic vectors represents an innovative strategy for local control of malignant gliomas, which will be further assessed as a neoadjuvant approach.

Cerebral radiation necrosis: incidence, outcomes, and risk factors with emphasis on radiation parameters and chemotherapy

PURPOSE

To investigate radiation necrosis in patients treated for glioma in terms of incidence, outcomes, predictive and prognostic factors.

METHODS AND MATERIALS

Records were reviewed for 426 patients followed up until death or for at least 3 years. Logistic regression analysis was performed to identify predictive and prognostic factors. Multivariate survival analysis was conducted using Cox proportional hazards regression. Separate analyses were performed for the subset of 352 patients who received a biologically effective dose (BED) > or =85.5 Gy2 (> or =45 Gy/25 fractions) who were at highest risk for radionecrosis.

RESULTS

Twenty-one patients developed radionecrosis (4.9%). Actuarial incidence plateaued at 13.3% after 3 years. In the high-risk subset, radiation parameters confirmed as risk factors included total dose (p < 0.001), BED (p < 0.005), neuret (p < 0.001), fraction size (p = 0.028), and the product of total dose and fraction size (p = 0.001). No patient receiving a BED <96 Gy2 developed radionecrosis. Subsequent chemotherapy significantly increased the risk of cerebral necrosis (p = 0.001) even when adjusted for BED (odds ratio [OR], 5.8; 95% confidence interval [CI], 1.6-20.3) or length of follow-up (OR, 5.4; 95% CI, 1.5-19.3). Concurrent use of valproate appeared to delay the onset of necrosis (p = 0.013). The development of radionecrosis did not affect survival (p = 0.09).

CONCLUSIONS

Cerebral necrosis is unlikely at doses below 50 Gy in 25 fractions. The risk increases significantly with increasing radiation dose, fraction size, and the subsequent administration of chemotherapy.

The protective effect of dexamethasone against radiation damage induced by interstitial irradiation in normal monkey brain

OBJECTIVE

The protective effect of dexamethasone against radiation damage is unclear. We examined the effect of early treatment of high-dose dexamethasone on iridium-192-induced damage to normal brain tissue.

METHODS

Brain damage induced by interstitial irradiation with iridium-192 was evaluated with sequential magnetic resonance imaging and proton magnetic resonance spectroscopy in 11 adult monkeys, with or without short-term high-dose dexamethasone treatment. Dexamethasone (1 mg/kg of body weight/d) was administered intramuscularly to five irradiated animals every 24 hours, beginning 2 days before and ending 7 days after irradiation. Magnetic resonance imaging and proton magnetic resonance spectroscopy were performed 1 week, 1 month, and 3 months after irradiation.

RESULTS

Magnetic resonance imaging performed 1 week after irradiation revealed marked edema in five nontreated animals. In dexamethasone-treated animals, the volume of edema was reduced significantly, compared to that of nontreated animals, 1 week and 1 month after irradiation. The volume of ring enhancement in dexamethasone-treated animals was also reduced significantly, compared to that of nontreated animals, 3 months after the irradiation. Proton magnetic resonance spectroscopy spectra revealed that N-acetylaspartate and choline peaks were reduced 1 week after irradiation in both groups. However, there were no statistically significant differences between the two groups at any time points.

CONCLUSION

These results suggest that dexamethasone treatment may have an antiedema effect at an early stage and may modify subsequent development of vascular and inflammatory changes but may have no effect of preventing radiation-induced necrosis and the reduction of N-acetylaspartate after brachytherapy.

The risk of interstitial radiotherapy of low-grade gliomas

BACKGROUND AND PURPOSE

The risk of side effects of low activity (i.e. <20 mCi) Iodine-125I (125I) interstitial radiotherapy was analyzed in patients with low-grade gliomas.

MATERIALS AND METHODS

Permanent (247 patients) or temporary 125I-implants (268 patients) were used with a median reference dose of 60 Gy and 100 Gy, respectively, which was calculated to the outer rim of the tumour. The mean dose rate for temporary implants was low (median, 10 cGy/h). Risk factors were obtained from the multivariate proportional-hazards model.

RESULTS

Radiogenic complications occurred in 39/515 patients (28 patients with transient symptoms and 11 patients with progressive symptoms). The most important risk factor was the volume of the intratumoural 200 Gy isodose. Available experimental data have associated a high dose zone in this range with the size of the treatment induced radionecrosis. Rapid tumour shrinkage (decrease of the tumour volume > or =50%) within the first 6 months with subsequent centripetal movement of non-pathologic tissue into the high dose zone and a reimplantation were additional risk factors. Radiation injury after rapid tumour shrinkage could be better avoided with temporary implants. A 200 Gy isodose volume <4.5 ml corresponded to an estimated risk of radiogenic complications <3%. There was a steep increase of the risk beyond this limit. Translation of the 200 Gy isodose volume in terms of the treatment volume and the reference dose allows rational treatment planning. The estimated risk of a temporary implant with an applied reference dose of 60 Gy and a treatment volume <23 ml was <3%.

CONCLUSIONS

The intratumoural necrotizing effect of a low activity 125I implant limits its application to small treatment volumes. Radiation injury outside the treatment volume can be better avoided with temporary implants in the case of rapid tumour shrinkage.

Short-term CT and MR changes in brain tumors following 125I interstitial irradiation

PURPOSE

The study was undertaken to assess characteristic short-term CT and MR changes in brain tumors following 125I interstitial irradiation.

METHOD

Sixteen patients were included who had both CT and MR control examinations at regular intervals over a period of 18 months following treatment. Two groups were distinguished: low grade tumors (11 cases) and high grade malignancies (5 patients). 125I seeds were used as temporary implants. The cumulative dose was 50-60 Gy.

RESULTS

In some patients of both groups, a low attenuation spheric structure with a contrast-medium-enhanced ring and a diameter of 6-8 mm was observed. There was no edema around the structure, which represents a zone of tissue necrosis at the site of the temporary 125I implant. Tumors in both groups were completely destroyed, some decreased in size, and others were unchanged. Pseudotumor necrosis with accompanying edema occurred in two patients with low grade astrocytoma, the diameter of which was > 4 cm.

CONCLUSION

The behavior of cerebral tumors and their appearance on CT and MR images after interstitial irradiation seem to be variable. Decrease in tumor size may take place at different intervals after therapy. Brachytherapy of tumors with a diameter of > 4 cm may produce space-occupying radionecrosis.

Radiation response of the central nervous system

This report reviews the anatomical, pathophysiological, and clinical aspects of radiation injury to the central nervous system (CNS). Despite the lack of pathognomonic characteristics for CNS radiation lesions, demyelination and malacia are consistently the dominant morphological features of radiation myelopathy. In addition, cerebral atrophy is commonly observed in patients with neurological deficits related to chemotherapy and radiation, and neurocognitive deficits are associated with diffuse white matter changes. Clinical and experimental dose-response information have been evaluated and summarized into specific recommendations for the spinal cord and brain. The common spinal cord dose limit of 45 Gy in 22 to 25 fractions is conservative and can be relaxed if respecting this limit materially reduces the probability of tumor control. It is suggested that the 5% incidence of radiation myelopathy probably lies between 57 and 61 Gy to the spinal cord in the absence of dose modifying chemotherapy. A clinically detectable length effect for the spinal cord has not been observed. The effects of chemotherapy and altered fractionation are also discussed. Brain necrosis in adults is rarely noted below 60 Gy in conventional fractionation, with imaging and clinical changes being observed generally only above 50 Gy. However, neurocognitive effects are observed at lower doses, especially in children. A more pronounced volume effect is believed to exist in the brain than in the spinal cord. Tumor progression may be hard to distinguish from radiation and chemotherapy effects. Diffuse white matter injury can be attributed to radiation and associated with neurological deficits, but leukoencephalopathy is rarely observed in the absence of chemotherapy. Subjective, objective, management, and analytic (SOMA) parameters related to radiation spinal cord and brain injury have been developed and presented on ordinal scales.

Pineal region tumours treated with interstitial brachytherapy with low activity sources (192-iridium)

Three patients with tumours of the pineal region underwent interstitial Ir-192 brachytherapy. Histological diagnoses were obtained in all patients, by stereotactic biopsy and included one germinoma, one mixed pineoblastoma/pineocytoma, and one astrocytoma grade III. Our approach to pineal region neoplasms is first to decide whether stereotactic biopsy or surgery should be performed. When a pineal lesion is thought to be benign on the basis of imaging, such as benign teratoma, surgery is performed to resect the entire lesion. When a definitive diagnosis is not possible, stereotactic biopsy is performed to obtain a histological diagnosis for treatment planning, using a Brown-Roberts-Wells (BRW) stereotactic apparatus with computed tomography (CT) or magnetic resonance imaging (MRI). When a lesion is malignant and localized, stereotactic implantation of catheters for interstitial brachytherapy is performed simultaneously. Radioactive Ir-192 seeds are inserted into the catheters and maintained for 5-10 days to give 36 Gy of irradiation at the tumour periphery. Sequential CT scans and MRI after treatment revealed tumour disappearance in two patients with germinoma and high grade astrocytoma and tumour reduction in the patient with mixed pineoblastoma/pineocytoma. No significant morbidity or mortality occurred in any of these patients after stereotactic biopsy and brachytherapy. The technique and the advantages of this therapeutic approach to selected pineal region tumours are described and discussed.

Malignant transformation of benign gliomas during interstitial irradiation

Interstitial curietherapy with 125-Iodine is an effective therapeutic option in the treatment of low grade gliomas. Four cases with astrocytoma grade II are presented, where tumour growth characteristics have changed to anaplasia during interstitial irradiation after a primary period of tumour regression. Anaplastic transformation could be due to a radiation effect or an insufficient therapeutic influence of interstitial irradiation on natural tumour progression of glioma growth due to genetic events.

Intra-operative radiation therapy for malignant brain tumors: rationale, method, and treatment results of cerebral glioblastomas

In radiation therapy for malignant brain tumours, the dose of radiation that can be safely delivered to a tumour is limited by the radiation tolerance of the adjacent normal brain tissue. Among various radiation modalities to produce local tumour eradication without unacceptable complications, we chose a large, single irradiation dose during the operation (intra-operative radiation therapy, IORT). In contrast to X-ray or Cobalt-60 gamma ray irradiation, IORT with a high-energy electron beam delivered by the Shimadzu 20 MeV betatron provides acceptable dose homogeneity with rapid fall-off of the radiation dose beyond the treatment volume. Thus, IORT has the advantage of precise demarcation of the target volume, minimum damage to surrounding normal tissues, and a high absorbed target dose (15-25 Gy in 5-10 min). On the basis of our experience with 170 patients treated by IORT, we established the treatment indications and method in patients with malignant brain tumours. IORT with a dose of 15-25 Gy was delivered to widely resected tumours followed by external radiation therapy. No acute or subacute complications were observed. Treatment results of 30 patients with glioblastoma treated by IORT (mean 18.3 Gy) combined with external radiation therapy (mean 58.5 Gy) resulted in a median survival of 119 weeks and a 2-year survival rate of 61%.

Interstitial brachytherapy for low-grade cerebral gliomas: analysis of results in a series of 36 cases

The results obtained with interstitial brachytherapy in thirty-six low-grade cerebral gliomas (2 pilocytic astrocytomas, 23 astrocytomas and 11 oligodendrogliomas) are reported (mean follow-up: 75 months, range 37-159). All tumours were situated in locations which did not call for surgical removal as the treatment of choice. Their volume ranged from 4 to 82 cc (m = 32); the Karnofsky performance status (KPS) of the treated patients lay between 0.60 and 0.90. The sources utilized (Iridium-192 in 32 cases and Iodine-125 in 4) were implanted permanently in 22 patients and temporarily in 14, using the Talairach stereotactic apparatus. The mean peripheral dose was 89.7 Gy for the permanent implants and and 42.8 Gy with a rate of 32.05 cGy/h for the temporary implants. External beam irradiation was added for tumour volumes greater than 35 cc (19 cases) on a second target volume extending 2 cm beyond the tumoural borders treated with interstitial irradiation. The survival estimates for the entire group showed a probability of 82.9% at 60 months, of 56.8% at 96, 39.4% at 120 (m.s.t.: 112 months). The quality of life in the treated patients was satisfactory, KPS never falling below a mean score of 0.70. The extent of the target volume turned out to be the most significant factor influencing survival at the multivariate analysis. Severe neurological impairment due to radionecrosis occurred in 4 patients (11%), three of them requiring surgical decompression.(ABSTRACT TRUNCATED AT 250 WORDS)

The radiobiology of radiosurgery: rationale for different treatment regimes for AVMs and malignancies

Based on basic radiobiological principles, we suggest that the radiosurgery technique of delivering a radiation dose in a single fraction, whilst appropriate for benign brain lesions such as arteriovenous malformations (AVM), is not optimal for treating malignant tumors. Radiosurgery was originally developed to treat benign lesions in the brain, such as AVMs, and has been successfully used for this purpose for over four decades. Recently, the technique has been adopted for treating small primary malignant brain tumors or single metastases. We argue, and derive radio-biological data to support the view that, treating malignant tumors with a single fraction will result in a suboptimal therapeutic ratio between tumor control and late effects, even for small tumors; and that improved therapeutic ratios would be expected if the treatment were fractionated into a small number of fractions. On the other hand, no therapeutic gain is to be expected from fractionating treatment of AVMs. A new generation of noninvasive relocatable stereotactic head frames makes feasible the use of fractionated stereotactic external-beam radiotherapy, and may allow significant benefits over single, radiosurgical, treatments for malignant brain tumors. As stereotactic fractionation/protraction regimes become more widespread, a uniform approach for determining equivalent fractionation schemes becomes important for intercomparing clinical results, and such calculations can be reliably carried out using the linear-quadratic formalism.

Gene therapy of malignant brain tumors: a rat glioma line bearing the herpes simplex virus type 1-thymidine kinase gene and wild type retrovirus kills other tumor cells

Tumor cells infected with a retrovirus vector (VIK) containing the herpes simplex virus thymidine kinase (HSV-TK) gene can be selectively killed by treatment with nucleoside analogues, such as ganciclovir. To mediate delivery of the HSV-TK gene to "recipient" tumor cells, "donor" C6 rat glioma cells infected with the VIK vector (C6VIK) were superinfected with wild type Moloney murine leukemia virus (WT Mo-MLV). These modified donor cells (C6VIKWT) produced both wild type retrovirus and the VIK vector. In culture, C6VIKWT cells were 300-fold more sensitive to the toxicity of ganciclovir than were C6VIK cells, suggesting that the presence of wild type retrovirus contributed to the toxicity. Co-culture of C6VIKWT cells with the C6 subline, C6BAG, sensitized the latter to ganciclovir treatment. Nude mice inoculated subcutaneously with a mixture of C6VIKWT and C6BAG cells showed regression of subsequent tumors when treated with ganciclovir. The observations show that tumor cells modified in culture by infection with a retrovirus bearing the HSV-TK gene and wild type retrovirus are not only sensitive to ganciclovir, but can transfer this sensitivity to neighboring "naive" tumor cells in culture and in vivo.

Fractionated regimens for stereotactic radiotherapy of recurrent tumors in the brain

Radiosurgery (single-fraction stereotactic radiotherapy) was initially developed to treat non-malignant arteriovenous malformations, but there is growing interest in its use for the treatment of recurrent brain tumors. We suggest that there are sound reasons to expect improved results for tumor radiotherapy, in terms of late effects, if a fractionated regimen is used. At present, no published guidelines are available for choosing appropriate doses for fractionated regimens. We present two sets of guidelines, based on experimentally derived radiobiological parameters: first, we estimate gamma-ray doses which, if delivered in various numbers of fractions, should produce equivalent early effects to 70 Gy of 125I X rays delivered at low dose rate; this latter regimen is currently used in RTOG interstitial brachytherapy trials. Second, we estimate doses for multi-fractioned stereotactic radiotherapy which may be advantageous alternatives to particular doses of single-fractioned radiosurgical therapy. As the appropriate hardware is available, the use of fractionated stereotactic radiotherapy deserves serious consideration for the treatment of recurrent tumors in the brain.