Cerebellar medulloblastoma: results of a new method of radiation treatment

Metachronous secondary atypical meningioma and anaplastic astrocytoma after postoperative craniospinal irradiation for medulloblastoma

INTRODUCTION

Malignant brain tumors have been reported to occur after childhood irradiation more frequently than in the nonirradiated population.

DISCUSSION

In this study, we report the case of a 15-year-old boy treated for medulloblastoma with surgery and craniospinal radiotherapy, who developed a meningioma 18 years after initial treatment and subsequently an anaplastic astrocytoma 23 years after primary treatment. The meningioma was resected without complications. The patient is currently alive but with recurrent astrocytoma after a complete remission on temozolomide monotherapy. Second malignancies are a rare, potentially devastating risk in cancer survivors, with risk continuing lifelong.

The use of tertiary collimation for spinal irradiation with extended SSD electron fields

PURPOSE

The spine can be treated with an electron beam when its maximum posterior depth is within the therapeutic range of electrons. Electron fields treated at extended source-to-surface distances (SSDs), however, have larger penumbras and narrower therapeutic isodose widths relative to those at the standard SSD of 100 cm. We investigated the use of tertiary collimation close to the patient surface for these fields to sharpen the penumbra, minimizing dose to normal tissue and maximizing target coverage.

METHODS AND MATERIALS

Using film dosimetry in a polystyrene phantom, we measured the dose distribution for electron fields at extended SSD under varying collimation conditions. Beam penumbra and therapeutic width as a function of depth, SSD, applicator insert size, and tertiary collimator opening were determined. We also measured the dose distributions in the junction region for various gaps between x-ray fields and an electron field as used for craniospinal irradiation.

RESULTS

Measurements show that tertiary collimation close to the skin surface reduces penumbra width (lateral distance between the 90 and 20% isodose lines) by 56% and increases therapeutic isodose width (lateral width of the 90% isodose curve) by 25% at a depth of dmax relative to standard collimation. These numbers change to 23 and 13%, respectively, at an average depth of the spine. When lateral brain and posterior spine fields are used to irradiate the entire craniospinal axis, tertiary collimation aids in reducing the volume of the hot spot in the junction region by as much as 10% without compromising target coverage.

CONCLUSIONS

Tertiary collimation for extended SSD electron fields is preferable to standard collimation in order to minimize dose to normal tissue and increase target coverage. This technique can be applied to both spinal and craniospinal irradiation. Support structures for the tertiary blocking are needed because the weight of the lead is usually too great for placement on the skin.

Craniospinal axis irradiation: an improved electron technique for irradiation of the spinal axis

In this work we review the dosimetric features of craniospinal axis irradiation in the areas of matching cranial and spinal fields, with reference to the normal structures within the spinal field. The implications of the use of photon or electron modalities for the spinal port were evaluated. A novel method of matching the cranial photon and the spinal electron fields involving a computer-aided junction design is presented. The technique involves moving the photon beam in three steps to degrade its penumbra to match that of the electron field. Thermoluminescent dosimetry in a Rando phantom and computed tomography-based dose-volume histogram study for an illustrative paediatric case were used to compare the dose to normal structures within the spinal field. Our results show that the use of electrons for the spinal field leads to better sparing of deep seated normal structures. In the case of bone marrow, the use of a customized bolus for the spinal field results in an improved dose distribution, making electrons potentially superior to photons for radiobiological reasons.

A newly designed radiation port for medulloblastoma to prevent metastasis to the cribriform plate region

Nine children with medulloblastoma were treated at Chiba University Hospital from 1977 to 1983. Of these cases, metastases to the cribriform plate region were found in two cases. Portal film showed that cribriform-plate region was not included in a conventional whole-brain radiation port to shield the eyes. Since 1983, we have applied a newly designed radiation port to treat childhood medulloblastoma. The new method consists of two parallel, opposed, lateral ports including the cribriform plate and the first two cervical vertebrae, similar to Pinkel's method. It has been confirmed that this method covers completely the whole brain and is safe for the lens. A characteristic of our method is that the landmark of the lower margin of the radiation port can be easily delineated on the patient's face. We believe that this method contributes to the treatment of medulloblastoma.

Prognostic implications of the bromodeoxyuridine labeling index of human gliomas

This study includes 182 patients with intracranial gliomas who received bromodeoxyuridine (BUdR), 200 mg/sq m intravenously, at the time of craniotomy but before tumor biopsy. The tumor specimens were stained for BUdR using the immunoperoxidase method; the BUdR labeling index (LI), or S-phase fraction, was calculated as the percentage of BUdR-positive cells. The median BUdR LI's for 127 primary moderately anaplastic astrocytomas, highly anaplastic astrocytomas, and glioblastomas (less than 1%, 2.7%, and 7.3%, respectively; range 0% to 38.1%) were not significantly different from those of 55 similar recurrent tumors (less than 1%, 4.3%, and 7.4%, respectively; range 0% to 30.5%). The mean LI was significantly higher in tumors from patients over 50 years of age than in tumors from younger patients (p less than 0.001). The age-related difference in LI's was found in both groups of patients with astrocytomas but not in those with glioblastomas. Kaplan-Meier survival curves showed a significantly greater probability of survival among patients whose tumors had LI's of less than 1% than among those with LI's greater than 5%; survival probability of patients with tumor LI's of 1% to 5% was intermediate between the two extremes. Thus, the BUdR LI appears to reflect the proliferative potential more accurately than the histopathological diagnosis and should therefore be considered an important factor in determining the prognosis of individual patients with intracranial gliomas and in selecting their treatment.

Correlation of histopathological features and proliferative potential of gliomas

One hundred fifty-two intracranial gliomas of various types were reviewed in order to correlate the histopathological features with the proliferative potential of each tumor as reflected by the bromodeoxyuridine (BUdR) labeling index (LI). Patients undergoing surgical removal of gliomas were given a 30-minute intravenous infusion of BUdR (150 to 200 mg/sq m) to label S-phase tumor cells. The tumor specimens were stained immunohistochemically for BUdR and processed for routine histopathological diagnosis. The BUdR LI was calculated as the percentage of labeled cells among cells analyzed. Twenty-seven histological features in three categories (degenerative, vascular, and cellular changes) were considered. A significantly higher BUdR LI (p less than 0.05) was found in tumors with necrosis than in those without this feature; tumors with both coagulative and liquefactive necrosis had the highest BUdR LI (p less than 0.05). Increased vascularity was also associated with a higher BUdR LI (p less than 0.05). Although tumors with abnormal mitotic figures had a significantly higher BUdR LI than those without, the number of mitoses did not correlate with a higher BUdR LI. These results suggest that the number of mitoses is not a good indicator of tumor growth rate. Necrosis and increased vascularity should be heavily weighted in predicting the proliferative potential of individual gliomas.

Intermittent central nervous system irradiation and intrathecal chemotherapy for central nervous system leukemia in children

Between 1979 and 1985, nine children with recurrent CNS leukemia who had previous radiation of more than 1800 cGy to the brain were treated with intermittent central nervous system irradiation and intrathecal chemotherapy (IIIC). There was no isolated CNS recurrence. Three patients died; one from generalized recurrent disease, two from complications associated with bone marrow transplantation. Six patients are alive without evidence of disease between 9 years and 2 4/12 years from the diagnosis of recurrent CNS leukemia. This experience suggests that IIIC may be an effective treatment for preventing the recurrence of CNS leukemia with minimal side effects.

Recent developments in pediatric neuro-oncology

Although brain tumors represent the second most common malignancy in childhood, there are only 1200 to 1500 children diagnosed with brain tumors each year in the US. Approximately 50% of these children are treated at university or cancer treatment centers. Thus, therapeutic trials by default rather than design have been restricted to small numbers of patients. Information on histopathologic groupings, incidence of various tumor types according to age, general treatment trends and survival statistics are available from the Surveillance, Epidemiology, and End Results (SEER) registries of the National Cancer Institute. Although survivals in brain tumor cancers are worse than in other forms of childhood cancer, treatment advances in surgery, radiation and chemotherapy have significantly improved survivals in at least one brain tumor of childhood, medulloblastoma. Ironically, this treatment may have significant long-term adverse effects on intellect, endocrine function, and on the development of second malignancies. Prompt recognition of these delayed effects is of clinical importance, as some effects are amenable to treatment and others may be prevented by careful monitoring of drug and radiation administration.

Results of radiation treatment of medulloblastoma in adults

From 1961 to 1982, 20 adults (greater than 16 years of age) were treated with radiation therapy following surgery for medulloblastoma. All patients received neuro-axis irradiation. Five patients received adjuvant chemotherapy. A 5- and 10-year survival rate of 78 and 55%, respectively, were achieved. Treatment failures were mainly a result of local recurrences, but also of metastases. One patient died of acute myeloid leukemia. One patient developed paraplegia. The survival rate was better in males (2 deaths out of 14) than in females (5 deaths out of 6). All the survivors are free of deficit or sequelae, except the patient with paraplegia.

The argument for a combined cancer consortium research data base

Epidemiologic data that were obtained through the SEER registry (Surveillance Epidemiology End Results Program) are presented. Survival statistics for five major brain tumor types in childhood are presented for the years 1968 through 1979. Further survival statistics are compared in patients treated in community hospitals versus university hospitals. The lack of uniform reporting, absence of pathologic conformation, and limited number of patients seen throughout the country are emphasized. There is a need for the establishment of a data base composed of the member institutions of the childhood cancer consortiums. This data base would address questions of patterns of failure, benefits of surgical and clinical staging, and the value of a new putative pathologic grading system. Additionally, the opportunity to collect these patients should permit identification of long-term treatment effects. Identification of early morbidity may lead to modification of treatment programs. A data base containing treatment and diagnostic parameters would allow significant cross-correlations and would lead to the design of future studies that are based upon accurate data.

A cell kinetic study on medulloblastomas

The cell kinetics of medulloblastoma were studied to define characteristic proliferation for comparison with other neuroectodermal tumors. Four patients with cerebellar medulloblastoma received 3H-thymidine intravenously 1 to 2 days before surgery. Biopsy specimens from each tumor were processed for autoradiography. The respective average labeling indices were 14.4%, 14.1%, and 11.2% in the three mid-cerebellar medulloblastomas and 8.0% in the cerebellar hemispheric medulloblastoma. The mean survival time with various treatments including radiation therapy before or after the study in these four patients was 6 years (range, 3-9 years). In contrast, patients with malignant gliomas that had a labeling index greater than 5% died within 1 year. This difference in survival was attributed to the greater sensitivity of medulloblastoma to radiation therapy.

Radiation for medulloblastoma adjusted to prevent recurrence to the cribriform plate region

In a recent survey of the recurrence pattern in 40 medulloblastoma patients treated at Memorial Hospital between 1970 and 1979, 15% of all recurrences were in the region of the cribriform plate, which is an area that is undertreated with commonly employed radiation therapy techniques. The authors, therefore, modified their technique to increase the dose in this area. They report on the initial results in 15 subsequent patients treated with this modification. Ten of the 15 patients had localized tumors (Groups I and II) and 8 of these patients are alive disease-free compared with 7 of 17 Group I and II patients treated between 1970 and 1979. Three of five patients with disseminated tumors (Groups III and IV) are alive disease-free compared with none in the previous series. Although the period of follow-up is relatively short (median, 32 months), the overall survival of patients with medulloblastoma seems to be improved with additional radiation to the region of the cribriform plate. No side effects attributable to this modification were observed. In the opinion of the authors, this modification should be used routinely in patients with medulloblastoma.

Age at treatment and long-term performance results in medulloblastoma

Medulloblastoma is highly radioresponsive, and recent treatment results have improved greatly since the introduction of megavoltage machine in 1960s. There is increasing evidence for the potential cure of medulloblastoma if properly treated in its early stages. The curable group represents approximately 75% of diagnosed patients. Long-term treatment effects were examined in this study. The study reveals age-dependent late effects in learning ability; the patients less than 4-years-old at treatment had major learning problems; patients of 5 to 7 years old performed at satisfactory-to-low passing levels in school work; patients older than 8 years old had no major intellectual impairment. Short stature was common when growth potential was present at the time of therapy, but endocrine tests were generally negative. These observations indicate special educational requirement needs, especially for children treated at a young age.

Calcified basal ganglionic mass 12 years after radiation therapy for medulloblastoma

A patient treated 12 years previously with an operation and radiation therapy for a medulloblastoma developed weakness of the left hand and perivascular calcification involving the right internal capsule and caudate nucleus. These findings are considered possible long-term complications of the radiation therapy.

A modified radiotherapy technique in the treatment of medulloblastoma

Craniospinal irradiation is a standard treatment technique in patients who receive surgery for medulloblastoma. In most centers megavoltage photon irradiation is used, resulting in significant irradiation exposure to critical organs. In order to overcome this difficulty, we recently modified the technique applied in our center, by using high energy electrons (20 MeV) for irradiation of the spinal cord. The reliability of this technique was checked by performing dosimetry in a specially constructed wax phantom. Attention was focused upon dose variations at the junction of fields. Furthermore, the influence of vertebrae on the absorbed dose distribution of high energy electrons is presented. This technique seems to be safe and reliable in selected patients (children and teenagers).

Cerebellar medulloblastoma: the importance of posterior fossa dose to survival and patterns of failure

Fifty patients with biopsy-proven cerebellar medulloblastoma were retrospectively analyzed for prognostic factors, survival and patterns of failure. Five- and ten-year actuarial survivals for the entire group were 51% and 42%. Survival and local control were significantly better for the 21 patients who received doses greater than 5000 rad to the posterior fossa (85% and 80% respectively) than for the remaining patients (38% and 38%, respectively). Significant prognostic factors included achievement of local control in the posterior fossa (p = .0001) and dose to the posterior fossa (p = .0005). Sex, age, duration of symptoms, extent of surgery and initial T-stage of disease were not significant. Posterior fossa was the predominant site of failure (71% of failures), but 10% of patients failed in the cerebrum and 12% outside the CNS. This experience confirms that survival rates of 70-80% are achievable with current treatment policies but accurate and consistent dose delivery to the posterior fossa is essential.

Multiple meningiomas following radiation therapy for medulloblastoma. Case report

✓ A patient is reported who was found to harbor multiple benign meningiomas 27 years after radiation therapy for medulloblastoma. Thirty-eight cases of meningiomas occurring after radiation are reviewed and analyzed. Statistical data from these cases support the concept of radiation-induced benign tumors.

Radiation treatment for medulloblastoma. A 21-year review

One hundred and twenty-two patients with medulloblastoma received postoperative irradiation at the Princess Margaret Hospital, Toronto, from 1958 to 1978, inclusive. The surgical procedure in these patients was total resection (44 patients), subtotal resection (66 patients), or biopsy alone (12 patients). Twenty-five patients received adjuvant chemotherapy. Overall 5- and 10-year survival rates were 56% and 43%, respectively. Improved survival rates were associated with an increased degree of resection and with posterior fossa radiation doses of 5200 rads or more. The posterior fossa was the common site of first relapse (in 56 patients, 46%). Systemic metastases at first relapse occurred in 18 of 52 patients (35%), and were associated with the use of ventriculosystemic shunts. Millipore filters did not prevent systemic relapse in shunted patients. A subset of 15 patients who received a posterior fossa dose of 5200 rads or more after a total resection had a 5-year survival rate of 77%, which remained constant to 10 years. This result is considered to be the upper limit that can be achieved by current treatment methods.

Supratentorial recurrences in medulloblastoma

Four children with medulloblastoma had massive supratentorial recurrences in the region of the cribriform plate after adequate craniospinal irradiation. The pathogenesis of these recurrences is probably related to underdosage to this region by shielding of the eyes. This hypothesis was corroborated by autopsy findings in two other patients in whom subfrontal implants were histologically different from recurrences elsewhere. Two possible solutions to avoid this problem in the future are suggested.