On a method of dosimetry planning and implantation of 125I for interstitial irradiation of malignant gliomas

Permanent 125iodine implants for recurrent malignant gliomas

PURPOSE

To determine the efficacy and toxicity of permanent 125iodine implants for recurrent malignant gliomas.

METHODS AND MATERIALS

Between January 1989 and January:, 59 patients with histologically confirmed recurrent malignant gliomas (22 nonglioblastoma malignant gliomas, 37 glioblastoma multiforme at the time of implant) received a permanent 125iodine implant. Patients ranged in age from 13-74 years. The median ages for the overall group, nonglioblastoma (nonGBM), and glioblastoma (GBM) groups was 47 years, 39 years, and 53 years, respectively.

RESULTS

With a median follow-up of 40 months, the median survival for the 59 total patients is 1.34 years; nonGBM 2.04 years, GBM 0.9 years. Factors predictive for poor prognosis were GBM histology, age 60 years or more, target volume 17 cc or more, and/or tumor location within the corpus callosum or thalamus. Reoperations have been performed in 24 (40%) patients; 15 (25%) for tumor progression; 3 (5%) for radiation necrosis; 2 (3%) for skull necrosis/infection, and 4 (7%) for other reasons (Ommaya reservoir insertion, catheter removal, hematoma evacuation).

CONCLUSION

Permanent 125iodine implants in selected patients with recurrent malignant gliomas are associated with reasonable long-term survival and a low risk of complications. Given the low incidence of radiation necrosis, future plans are to increase dose rate and/or total dose delivered with the permanent implant.

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.

On the development of an interstitial radiation protocol for a multicenter consortium. Experience with permanent low-dose rate and temporary high-dose rate 125I implants in 'failed' and 'newly diagnosed' glioblastoma patients: quality assurance methodology and a possible future adjuvant for therapeutic enhancement

Three interstitial implant trial groups (one permanent low-dose rate 125I and two temporary high-dose rate 125I implants) in glioblastoma patients ('newly diagnosed' and 'failed') were compared to non-randomized similar control groups for efficacy. The results formed the basis for the BTCG 87-01 national implant trial. The 'pilot' trial demonstrated: 1) the effectiveness of a temporary high-dose rate 125I implant in 'failed' and 'newly diagnosed' patients; 2) the ability of a multicenter consortium to adhere to a standard protocol; 3) a methodology to insure quality assurance; and 4) the possibility of the future adjuvant application of hyperthermia using a single catheter system.

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)

Stereotactic treatment of brain tumors with radioactive implants or external photon beams: radiobiophysical aspects

We perform calculations, based on the linear-quadratic model, to assess the biologically effective doses (BED) of tumor and normal tissue in the stereotactic irradiation of brain tumors with either radioactive implants or radiosurgery techniques. Treatment protocols for radiosurgery and radioactive implants, as obtained from the literature, are reviewed and compared. A figure of merit is defined to be the ratio of tumor to normal tissue BED, expressed in units of Gy10/Gy3. These comparisons indicate a clear radiobiological advantage for brachytherapy, unless the radiosurgery is to be delivered in a large number of fractions. The differences in dose uniformity, and in the volume of normal tissue encompassed by the high dose regions, are factors that may also influence clinical results.

A CT-based computerized treatment planning system for I-125 stereotactic brain implants

A computer program has been developed at the University of California, San Francisco, as an aid in planning and evaluating stereotactic brain implants made with 125I seeds. The program allows images of seeds and catheters to be positioned in the target volume revealed by CT. It then generates and displays the resulting isodose distributions. Catheters may be changed interactively until an optimum implant is achieved. From the geometry of a stereotactic implant frame as measured by CT, the program calculates the approach angles of the catheters in the frame coordinate system. After the seeds are implanted, films made with a fiducial marker box can be used to generate true seed positions and hence true isodoses. This paper describes mathematically the geometrical transformations used by the program, and also outlines its many features and options. In its first 2 years of use the program has proved to be a valuable contributor to improved patient care.

Survival and quality of life after interstitial implantation of removable high-activity iodine-125 sources for the treatment of patients with recurrent malignant gliomas

Between January 1980 and January 1988, 95 evaluable patients with recurrent, unifocal, supratentorial malignant gliomas were reirradiated with high-activity iodine-125 sources implanted directly into tumor in afterloaded, removable catheters using computerized tomography-directed stereotaxy. A tumor dose of 5270-15,000 cGy was delivered at a maximum distance of 0.5 cm from the rim of the contrast-enhancing mass seen on CT scans. The median survival for the 50 patients with anaplastic astrocytoma was 81 weeks and for 45 patients with glioblastoma multiforme it was 54 weeks. The 18- and 36-month survival rates for patients with anaplastic astrocytoma were 46% and 28%, respectively; the 18- and 36-month survival rates for patients with glioblastoma multiforme were 22% and 8%, respectively. Because of clinical deterioration, increasing steroid dependency, and increasing mass effect at the implantation site seen on CT scans, necrotic tissue was excised from 47 patients (49%) at craniotomy; in some patients, tumor was mixed with necrotic tissue. The survival of reoperated patients was significantly longer compared with patients who did not undergo this procedure. Serial determination of the Karnofsky Performance Score (KPS) showed that there was no significant deterioration for the group as a whole during the 6 months immediately after implantation. At 18 months, 33 of the patients were alive; KPS ranged between 50 to 90 (mean 79) and 67% were steroid dependent. At 36 months, 18 patients were alive; 17 patients were evaluable with KPS that ranged between 40 to 90 (mean 76) and 53% were steroid dependent. Eleven of the 17 evaluable long-term survivors had a KPS of 80 or higher with a mean of 87. Interstitial brachytherapy may provide long-term survival in selected patients with recurrent malignant gliomas who have been irradiated previously with conventional teletherapy. The quality of life in the majority of long-term survivors appears to be quite satisfactory. Further attempts to control tumor growth using this modality appear to be warranted.

Interstitial iridium-192 implantation for malignant brain tumours. Part II: Clinical experience

The treatment results of 37 patients with malignant brain neoplasms treated with a computed-tomography-guided stereotactic iridium-192 implant are reviewed. Of these, 29 patients with high-grade gliomas (20 with glioblastoma multiforme (GBM), nine with anaplastic astrocytoma (AA] received an implant as part of their initial management. The median survival was 14.5 and 15.5 months in the patients with previously untreated GBM and AA, respectively. In those patients with recurrent tumour after external-beam irradiation, durable local control over a year was achieved with implantation. Increasing the total tumour dose from 120 to 160 Gy did not improve survival or local control. Karnofsky Performance Status (KPS) was used as an indicator of quality of life and was seen to decrease with a median interval of 8.5 months following treatment. No severe complications were noted in the entire group of patients treated with this implant procedure.

Interstitial iridium-192 implantation for malignant brain tumours. Part I: Techniques of dosimetry planning

Interstitial implants for brain tumours with removable iridium-192 radioactive seeds have been performed using a Brown-Roberts-Wells stereotactic frame. A simple and accurate computed-tomography-guided dosimetry pre-planning technique and procedure prior to implant have been developed and are discussed.

Topographic anatomy and CT correlations in the untreated glioblastoma multiforme

To provide baseline information for the "local" therapy of the glioblastoma multiforme (GBM), whole-brain histological sections of 15 untreated GBM's were studied to determine the distribution of neoplastic cells. These findings were then compared with the computerized tomography (CT) scans in 11 cases in order to determine the extent to which the peripheral portion of the neoplasm can be estimated by the presence of a low-density area without contrast enhancement. The results of the histological study confirmed the marked heterogeneity of GBM's and disclosed a great variability in the geometry, extent, and character of the peripheral "infiltrating" margin. In spite of the widely held concept that glioblastomas are localized within 2 cm of the contrast-enhanced rim, there were three cases in this two-dimensional study in which this distance was exceeded, and it seems likely that three-dimensional reconstructions would have detected additional cases in which neoplastic cells extended beyond this arbitrary limit. Only three of the 15 GBM's were restricted to the distribution of one internal carotid or one vertebral artery. To the extent that the neoplasms in the present series are representative, this suggests that glioblastomas will be difficult to treat successfully by intra-arterial therapy using existing therapeutic agents. Correlations of histological sections with the CT scans revealed that the vast majority of the neoplastic tissue was contained within the contrast-enhancing and "peritumoral" areas of low density, but that in five cases fingers of neoplasm extended for short distances beyond the outer margin of the latter region. This indicates that the distribution of cells of a GBM cannot be inferred from CT images since the "peritumoral" area of low density can over- or underestimate the extent of the lesion.

Recurrent malignant gliomas: survival following interstitial brachytherapy with high-activity iodine-125 sources

The authors report survival data for the first 41 patients treated for recurrent malignant gliomas with interstitial brachytherapy at the University of California, San Francisco (1980-1984). Iodine-125 (125I) sources were temporarily implanted using stereotaxic techniques. The median survival period for 18 patients with recurrent glioblastomas was 52 weeks after brachytherapy; two patients are alive more than 5 years after brachytherapy. The median survival period for 23 patients with recurrent anaplastic astrocytomas is 153 weeks after brachytherapy, with 10 patients alive more than 3 years and four patients alive more than 4 years after brachytherapy. Both groups did significantly better (p less than 0.01) than groups of patients with the same diagnoses and similar general characteristics who were treated at recurrence with chemotherapy alone. Because of deterioration of their clinical condition and evidence of recurrence from computerized tomographic scans, 17 (41%) of 41 patients required reoperation 20 to 72 weeks after brachytherapy. Despite the invariable presence of apparently viable tumor cells mixed with necrotic tissue in the resected specimen, nine patients have survived more than 2 years after reoperation and two of the nine are still alive 4 years after reoperation. The authors conclude that brachytherapy with temporarily implanted 125I sources for well-circumscribed, hemispheric, recurrent malignant gliomas is effective and offers a chance for long-term survival even though focal radiation necrosis can seriously degrade the quality of survival in a minority of patients.