Impact of Cochlear Dose on Hearing Preservation Following Stereotactic Radiosurgery in Treatment of Vestibular Schwannomas: A Multi-Center Study

OBJECTIVE

Stereotactic radiosurgery (SRS) is a well-established treatment for vestibular schwannomas (VS). Hearing loss remains a main morbidity of VS and its treatments, including SRS. The effects of radiation parameters of SRS on hearing remain unknown. The goal of this study is to determine the effect of tumor volume, patient demographics, pretreatment hearing status, cochlear radiation dose, total tumor radiation dose, fractionation, and other radiotherapy parameters on hearing deterioration.

METHODS

Multicenter retrospective analysis of 611 patients who underwent SRS for VS from 1990-2020 and had pre- and post-treatment audiograms.

RESULTS

Pure tone averages (PTAs) increased and word recognition scores (WRSs) decreased in treated ears at 12-60 months while remaining stable in untreated ears. Higher baseline PTA, higher tumor radiation dose, higher maximum cochlear dose, and usage of single fraction resulted in higher post radiation PTA; WRS was only predicted by baseline WRS and age. Higher baseline PTA, single fraction treatment, higher tumor radiation dose, and higher maximum cochlear dose resulted in a faster deterioration in PTA. Below a maximum cochlear dose of 3 Gy, there were no statistically significant changes in PTA or WRS.

CONCLUSIONS

Decline of hearing at one year in VS patients after SRS is directly related to maximum cochlear dose, single versus 3-fraction treatment, total tumor radiation dose, and baseline hearing level. The maximum safe cochlear dose for hearingtbrowd preservation at one year is 3 Gy, and the use of 3 fractions instead of one fraction was better at preserving hearing.

NCCN Guidelines® Insights: Central Nervous System Cancers, Version 2.2022

The NCCN Guidelines for Central Nervous System (CNS) Cancers focus on management of the following adult CNS cancers: glioma (WHO grade 1, WHO grade 2-3 oligodendroglioma [1p19q codeleted, IDH-mutant], WHO grade 2-4 IDH-mutant astrocytoma, WHO grade 4 glioblastoma), intracranial and spinal ependymomas, medulloblastoma, limited and extensive brain metastases, leptomeningeal metastases, non-AIDS-related primary CNS lymphomas, metastatic spine tumors, meningiomas, and primary spinal cord tumors. The information contained in the algorithms and principles of management sections in the NCCN Guidelines for CNS Cancers are designed to help clinicians navigate through the complex management of patients with CNS tumors. Several important principles guide surgical management and treatment with radiotherapy and systemic therapy for adults with brain tumors. The NCCN CNS Cancers Panel meets at least annually to review comments from reviewers within their institutions, examine relevant new data from publications and abstracts, and reevaluate and update their recommendations. These NCCN Guidelines Insights summarize the panel's most recent recommendations regarding molecular profiling of gliomas.

Fundamentals of Radiation Oncology for Neurologic Imaging

Although the physical and biologic principles of radiation therapy have remained relatively unchanged, a technologic renaissance has led to continuous and ever-changing growth in the field of radiation oncology. As a result, medical devices, techniques, and indications have changed considerably during the past 20-30 years. For example, advances in CT and MRI have revolutionized the treatment planning process for a variety of central nervous system diseases, including primary and metastatic tumors, vascular malformations, and inflammatory diseases. The resultant improved ability to delineate normal from abnormal tissue has enabled radiation oncologists to achieve more precise targeting and helped to mitigate treatment-related complications. Nevertheless, posttreatment complications still occur and can pose a diagnostic challenge for radiologists. These complications can be divided into acute, early-delayed, and late-delayed complications on the basis of the time that they manifest after radiation therapy and include leukoencephalopathy, vascular complications, and secondary neoplasms. The different irradiation technologies and applications of these technologies in the brain, current concepts used in treatment planning, and essential roles of the radiation oncologist in the setting of brain disease are reviewed. In addition, relevant imaging findings that can be used to delineate the extent of disease before treatment, and the expected posttreatment imaging changes are described. Common and uncommon complications related to radiation therapy and the associated imaging manifestations also are discussed. Familiarity with these entities may aid the radiologist in making the diagnosis and help guide appropriate management. ^©RSNA, 2020.

Stereotactic Body Radiation Therapy for Operable Early-Stage Lung Cancer: Findings From the NRG Oncology RTOG 0618 Trial

Importance

Stereotactic body radiation therapy (SBRT) has become a standard treatment for patients with medically inoperable early-stage lung cancer. However, its effectiveness in patients medically suitable for surgery is unclear.

Objective

To evaluate whether noninvasive SBRT delivered on an outpatient basis can safely eradicate lung cancer and cure selected patients with operable lung cancer, obviating the need for surgical resection.

Design, Setting, and Participants

Single-arm phase 2 NRG Oncology Radiation Therapy Oncology Group 0618 study enrolled patients from December 2007 to May 2010 with median follow-up of 48.1 months (range, 15.4-73.7 months). The setting was a multicenter North American academic and community practice cancer center consortium. Patients had operable biopsy-proven peripheral T1 to T2, N0, M0 non-small cell tumors no more than 5 cm in diameter, forced expiratory volume in 1 second (FEV1) and diffusing capacity greater than 35% predicted, arterial oxygen tension greater than 60 mm Hg, arterial carbon dioxide tension less than 50 mm Hg, and no severe medical problems. The data analysis was performed in October 2014.

Interventions

The SBRT prescription dose was 54 Gy delivered in 3 18-Gy fractions over 1.5 to 2.0 weeks.

Main Outcomes and Measures

Primary end point was primary tumor control, with survival, adverse events, and the incidence and outcome of surgical salvage as secondary end points.

Results

Of 33 patients accrued, 26 were evaluable (23 T1 and 3 T2 tumors; 15 [58%] male; median age, 72.5 [range, 54-88] years). Median FEV1 and diffusing capacity of the lung for carbon monoxide at enrollment were 72.5% (range, 38%-136%) and 68% (range, 22%-96%) of predicted, respectively. Only 1 patient had a primary tumor recurrence. Involved lobe failure, the other component defining local failure, did not occur in any patient, so the estimated 4-year primary tumor control and local control rate were both 96% (95% CI, 83%-100%). As per protocol guidelines, the single patient with local recurrence underwent salvage lobectomy 1.2 years after SBRT, complicated by a grade 4 cardiac arrhythmia. The 4-year estimates of disease-free and overall survival were 57% (95% CI, 36%-74%) and 56% (95% CI, 35%-73%), respectively. Median overall survival was 55.2 months (95% CI, 37.7 months to not reached). Protocol-specified treatment-related grade 3, 4, and 5 adverse events were reported in 2 (8%; 95% CI, 0.1%-25%), 0, and 0 patients, respectively.

Conclusions and Relevance

As given, SBRT appears to be associated with a high rate of primary tumor control, low treatment-related morbidity, and infrequent need for surgical salvage in patients with operable early-stage lung cancer.

Trial Registration

ClinicalTrials.gov Identifier: NCT00551369.

Phantom-to-clinic development of hypofractionated stereotactic body radiotherapy for early-stage glottic laryngeal cancer

The purpose of this study was to commission and clinically test a robotic stereotactic delivery system (CyberKnife, Sunnyvale, CA) to treat early-stage glottic laryngeal cancer. We enrolled 15 patients with cTis-T2N0M0 carcinoma of the glottic larynx onto an institutional review board (IRB)-approved clinical trial. Stereotactic body radiotherapy (SBRT) plans prescribed 45 Gy/10 fractions to the involved hemilarynx. SBRT dosimetry was compared with (1) standard carotid-sparing laryngeal intensity-modulated radiation therapy (IMRT) and (2) selective hemilaryngeal IMRT. Our results demonstrate that SBRT plans improved sparing of the contralateral arytenoid (mean 20.0 Gy reduction, p <0.001), ipsilateral carotid D_max (mean 20.6 Gy reduction, p <0.001), contralateral carotid D_max (mean 28.1 Gy reduction, p <0.001), and thyroid D_mean (mean 15.0 Gy reduction, p <0.001) relative to carotid-sparing IMRT. SBRT also modestly improved dose sparing to the contralateral arytenoid (mean 4.8 Gy reduction, p = 0.13) and spinal cord D_max (mean 4.9 Gy reduction, p = 0.015) relative to selective hemilaryngeal IMRT plans. This "phantom-to-clinic" feasibility study confirmed that hypofractionated SBRT treatment for early-stage laryngeal cancer can potentially spare dose to adjacent normal tissues relative to current IMRT standards. Clinical efficacy and toxicity correlates continue to be collected through an ongoing prospective trial.

SBRT for early-stage glottic larynx cancer-Initial clinical outcomes from a phase I clinical trial

Purpose

To confirm safety and feasibility of hypofractionated SBRT for early-stage glottic laryngeal cancer.

Methods

Twenty consecutive patients with cTis-T2N0M0 carcinoma of glottic larynx were enrolled. Patients entered dose-fractionation cohorts of incrementally shorter bio-equivalent schedules starting with 50 Gy in 15 fractions (fx), followed by 45 Gy/10 fx and, finally, 42.5 Gy/5 fx. Maximum combined CTV-PTV expansion was limited to 5 mm. Patients were treated on a Model G5 Cyberknife (Accuray, Sunnyvale, CA).

Results

Median follow-up is 13.4 months (range: 5.6–24.6 months), with 12 patients followed for at least one year. Maximum acute toxicity consisted of grade 2 hoarseness and dysphagia. Maximum chronic toxicity was seen in one patient treated with 45 Gy/10 fx who continued to smoke >1 pack/day and ultimately required protective tracheostomy. At 1-year follow-up, estimated local disease free survival for the full cohort was 82%. Overall survival is 100% at last follow-up.

Conclusions

We were able to reduce equipotent total fractions of SBRT from 15 to 5 without exceeding protocol-defined acute/subacute toxicity limits. With limited follow-up, disease control appears comparable to standard treatment. We continue to enroll to the 42.5 Gy/5 fx cohort and follow patients for late toxicity.

Trial registration

ClinicalTrials.gov NCT01984502

A Phase I/II Study of Nab-Paclitaxel, Cisplatin, and Cetuximab With Concurrent Radiation Therapy for Locally Advanced Squamous Cell Cancer of the Head and Neck

Nab-paclitaxel might impact efficacy of radiation for head and neck (H&N) cancer. Nab-paclitaxel, cisplatin, cetuximab, and radiation were evaluated in patients with locally advanced head and neck cancer in this phase I/II trial. Median follow-up was 24 months for 34 patients. The maximum tolerated dose of nab-paclitaxel was 20 mg/m² with 20 mg/m² cisplatin and 250 mg/m² cetuximab. The 2-year progression-free survival (PFS) was 60% (95% confidence interval (CI) 0.42, 0.78), local control 71% (95% CI 0.55, 0.87), and overall survival 68% (95% CI 0.50, 0.86). This is the first study evaluating these agents with radiation in humans, with similar 2-year PFS as historic control.

A phase 3 trial of whole brain radiation therapy and stereotactic radiosurgery alone versus WBRT and SRS with temozolomide or erlotinib for non-small cell lung cancer and 1 to 3 brain metastases: Radiation Therapy Oncology Group 0320

BACKGROUND

A phase 3 Radiation Therapy Oncology Group (RTOG) study subset analysis demonstrated improved overall survival (OS) with the addition of stereotactic radiosurgery (SRS) to whole brain radiation therapy (WBRT) in non-small cell lung cancer (NSCLC) patients with 1 to 3 brain metastases. Because temozolomide (TMZ) and erlotinib (ETN) cross the blood-brain barrier and have documented activity in NSCLC, a phase 3 study was designed to test whether these drugs would improve the OS associated with WBRT + SRS.

METHODS AND MATERIALS

NSCLC patients with 1 to 3 brain metastases were randomized to receive WBRT (2.5 Gy × 15 to 37.5 Gy) and SRS alone, versus WBRT + SRS + TMZ (75 mg/m(2)/day × 21 days) or ETN (150 mg/day). ETN (150 mg/day) or TMZ (150-200 mg/m(2)/day × 5 days/month) could be continued for as long as 6 months after WBRT + SRS. The primary endpoint was OS.

RESULTS

After 126 patients were enrolled, the study closed because of accrual limitations. The median survival times (MST) for WBRT + SRS, WBRT + SRS + TMZ, and WBRT + SRS + ETN were qualitatively different (13.4, 6.3, and 6.1 months, respectively), although the differences were not statistically significant. Time to central nervous system progression and performance status at 6 months were better in the WBRT + SRS arm. Grade 3 to 5 toxicity was 11%, 41%, and 49% in arms 1, 2, and 3, respectively (P<.001).

CONCLUSION

The addition of TMZ or ETN to WBRT + SRS in NSCLC patients with 1 to 3 brain metastases did not improve survival and possibly had a deleterious effect. Because the analysis is underpowered, these data suggest but do not prove that increased toxicity was the cause of inferior survival in the drug arms.

Abstract 736: RTOG 0320:A phase III trial comparing whole brain radiation therapy (WBRT) and stereotactic radiosurgery (SRS) alone versus WBRT with temozolomide (TMZ) or erlotinib for non-small cell lung cancer (NSCLC) and 1-3 brain metastases

Background: A previous phase III RTOG study subset analysis demonstrated improvement in overall survival (OS) with the addition of SRS to WBRT in NSCLC patients with 1 to 3 brain metastases. As both TMZ and erlotinib are known to cross the blood brain barrier (potentially providing radiosensitization), and have documented activity in NSCLC, a phase III study was designed to test whether either of these drugs would improve outcome of WBRT/SRS. Methods: NSCLC patients (n=126) with 1-3 brain metastases were randomized (10/2005 to 8/2009; study closed prematurely due to slow accrual) to receive WBRT (2.5 Gy x 15 to 37.5Gy) + SRS alone, vs. WBRT/SRS with TMZ (75mg/m2/D x 21) or erlotinib (150mg/D). Erlotinib or TMZ (150-200 mg/m2/D x 5/mo) could be given in the drug arms post-WBRT/SRS at the discretion of the investigator. The primary endpoint was overall survival (OS). Results: Arms were stratified by RTOG recursive partitioning analysis (RPA) class and balanced for prognostic variables including the Graded Prognostic Assessment (GPA) score. Neither the addition of erlotinib nor TMZ to WBRT/SRS resulted in an improvement in OS, or time to CNS progression compared to WBRT/SRS alone. Patients in the WBRT/SRS arm had longer MST (Median Survival Time) (13.4 mo, 95% CI = 6.5-20.8 mo.) compared to the WBRT+SRS+ erlotinib (6.1 mo, 95% CI = 3.6-12.1 mo)[Hazard ratio (≥2 / α1) and 95% CI; 1.47 (0.92 to 2.36)], or TMZ (6.3 mo, 95% CI= 3.4-10.1 mo.) [Hazard ratio (β3 / α1) and 95% CI; 1.43 (0.89 to 2.31)]. This surprising result was not related to excess toxicity. In fact, patients experiencing grade 3+ Adverse Events (AE) appear to have longer OS than those patients without grade 3+ AE for both drug arms. The WBRT/SRS arm had significantly less deterioration in performance status at 6 mo. There were no significant differences between arms for steroid dependence at 6 mo, or causes of death. Conclusion: The addition of either TMZ or erlotinib to WBRT/SRS in this unselected population of NSCLC patients with 1-3 brain metastases provided no clinical advantage. Treatment with WBRT/SRS alone appeared to result in superior outcome data (compared to the addition of TMZ or erlotinib) relative to OS in this limited data set. Detailed analysis to date provides no obvious explanation for these unexpected results. Support: RTOG grant U10 CA21661, and CCOP grant U10 CA37422 from the National Cancer Institute (NCI)

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 736. doi:1538-7445.AM2012-736

The implementation of ablative hypofractionated radiotherapy for stereotactic treatments in the brain and body: observations on efficacy and toxicity in clinical practice

Radiosurgery has a long history dating back to the 1950s. Only in the last decade or so have advances in radiation delivery and visualization allowed export of this paradigm to extracranial sites. This review evaluates the efficacy and safety of such ablative radiation courses using dose per fraction schedules of 10 Gy or above. Retrospective published experience in functional and benign tumor radiosurgery is reviewed. Prospective controlled clinical trials in ablative cancer therapy of early-stage lung cancer and metastatic disease in the brain, liver, and spine are reviewed.

Interim analysis of a prospective phase I/II trial of SBRT for liver metastases

Stereotactic Body Radiation Therapy (SBRT) is a potent means of systemic cytoreductive therapy for selected patients with metastatic cancer. We here report an interim analysis of a prospective Phase I/II study of SBRT for liver metastases. Eligible patients with liver metastases met these criteria: (1) maximum tumor diameter < 6 cm; (2) < or =3 discrete lesions; (3) treatment planning confirmed > or = 700 cm3 of normal liver receives < or =15 Gy. The gross tumor volume (GTV) was expanded 5-10 mm to yield the planning target volume, which received 60 Gy in 3 fractions of SBRT over 3-14 days in the Phase II component of the trial. As of July, 2006, 36 patients have been enrolled: 18 in Phase I, 18 in Phase II. The median age was 58 years (range 27-91); the M:F ratio was 20:16. The most common primary sites were lung (n = 10), colorectal (n = 9), and breast (n = 4). Among 21 pts with > or = 6 months post-SBRT follow-up (median 19 months, range 6-29), one instance of SBRT-related grade 3 toxicity occurred in subcutaneous tissue superficial to the liver. No grade IV toxicity occurred. For 28 discrete lesions treated (median GTV 14 cm3, range 1-98) the 18 month actuarial local control estimate is 93%. This interim analysis indicates that a very high rate of durable in-field tumor control can be safely achieved with SBRT to 1-3 liver lesions as administered in this protocol, to a prescription dose of 60 Gy in 3 fractions.

Prostate adenocarcinoma and human immunodeficiency virus: report of three cases and review of the literature

The objective of this study was to evaluate the acute tolerance to definitive external-beam radiation therapy (RT; EBRT) in patients with prostate adenocarcinoma and HIV and to review the published literature for this population. Three patients with prostate adenocarcinoma and HIV were treated with definitive RT. Medical records were reviewed for prostate cancer and HIV characteristics, RT details, and acute toxicity. A review of the published literature was performed for epidemiology, management, and outcome of these patients. All 3 patients had excellent acute tolerance to definitive EBRT and, with short follow-up, all had decreasing prostate-specific antigen levels. The published literature regarding patients with prostate adenocarcinoma and HIV is scarce but suggests that men with HIV might be at higher risk of developing prostate cancer. External-beam radiation therapy, brachytherapy, and surgery have all been used in the management of these patients. All 3 patients with prostate adenocarcinoma and HIV had an excellent acute tolerance to EBRT. Prostate cancer is expected to become an increasingly important health problem for men infected with HIV as their life expectancy lengthens.

Predisposition to atypical teratoid/rhabdoid tumor due to an inherited INI1 mutation

BACKGROUND

Germline mutations of the INI1 gene predispose children to the development of rhabdoid tumors. Reports of familial cases, however, are extremely rare.

PROCEDURE

We have identified a three-generation family in which two half-brothers were diagnosed with central nervous system atypical teratoid/rhabdoid tumors (AT/RT). The two boys, diagnosed at 2 months and 17 months of age, had a germline insertion mutation in exon 4 of the INI1 gene that was inherited from their healthy mother. A maternal uncle died in childhood from a brain tumor and a malignant rhabdoid tumor of the kidney, and presumably carried the same germline mutation. As the mother and uncle had different fathers, the grandmother is also an obligate carrier of the mutation.

CONCLUSION

The identification of two unaffected carriers in a family segregating a germline mutation and rhabdoid tumor supports the hypothesis that there may be variable risks of development of rhabdoid tumor in the context of a germline mutation. There may be a developmental window in which most rhabdoid tumors occur. This family highlights the importance of mutation analysis in all patients with a suspected rhabdoid tumor.

Dose-volume histogram computations for small intracranial volumes

A sampling formalism is presented to accurately compute the absolute volumes and integral dose-volume histograms of small volumes treated in stereotactic radiosurgery. The presence of small volumes and sharp dose gradients places special constraints on the computational formalism and the accuracy required to compute the dose-volume relationships. We use a spatially nonuniform random sampling method to allow an efficient and accurate computation of the dose-volume histograms for an arbitrary number of volumes. The computation of absolute volume vs dose allows intercomparison of dose delivered to target and dose-critical volumes and allows a quantitative trade-off analysis often critical to an optimal treatment of the lesion.

Dynamic field shaping for stereotactic radiosurgery: a modeling study

PURPOSE

This work assesses the relative field shaping advantages of dynamic field shaping devices for stereotactic radiosurgery using a linear accelerator.

METHODS AND MATERIALS

We selected 43 intracranial tumors (2.0-4.2 cm maximum dimension, 1.5-25.5 cc tumor volume) out of the first 64 intracranial tumors treated with radiosurgery at the Joint Center for Radiation Therapy. We modeled five field shaping devices, each including a fixed auxiliary circular collimator: (a) fixed circular collimator alone; (b) two independent parallel jaws; (c) four independent rectangular jaws; (d) four independent rotatable jaws; and (e) "ideal" multileaf collimator. We adjusted the model parameters until the minimum target isodose was 80% of the dose delivered to isocenter. We defined the treatment volume ratio as the target volume divided by the treatment volume (volume receiving at least the minimum target dose). We used the treatment volume ratio to compare the five models and the actual patient treatments.

RESULTS

For 34 tumors originally treated with one isocenter, the median Treatment Volume Ratio was higher for all of the device models except the fixed circular collimator compared to the actual patient treatments. For the nine tumors originally treated with multiple isocenters, the median Treatment Volume Ratio for the actual multiple isocenter treatments was similar to that for two parallel jaws, four rectangular jaws and four rotatable jaws. Only the median "ideal" collimator treatment volume ratio was higher for these nine tumors.

CONCLUSION

Simple field shaping devices have approximately 50% of the conformal advantage of an "ideal" multileaf collimator. Approximately 50% of typical radiosurgical tumors between 2 and 4 cm have field shaping advantages which exceed the geometrical uncertainties inherent in linear accelerator radiosurgery treatments. The three models, two parallel, four rectangular, or four rotatable independent jaws would improve current linear accelerator technology by providing homogeneous doses with equivalent field shaping for most tumors originally treated with inhomogeneous multiple isocenter plans (6/9 tumors in the current series).

Stereotactic radiosurgery: principles and comparison of treatment methods

Methods of stereotactic radiosurgery are reviewed and compared with respect to technical factors and published clinical results. Heavy-ion beams, the Leksell cobalt-60 gamma knife, and the conventional linear accelerator (linac) are compared with respect to dosimetry, radiobiology, treatment planning, cost, staffing requirements, and ease of use. Clinical results on the efficacy of treatment of arteriovenous malformations are tabulated, and other applications of radiosurgery are described. It is concluded that although there are dosimetric and radiobiological advantages to charged-particle beams that may ultimately prove critical in the application of radiosurgery to large (> 30 mm) lesions, these advantages have not yet demonstrated clinical effect. On the other hand, equally excellent clinical results are obtained for small lesions with photon beams--the gamma knife and the linac. There are only minor differences between gamma and x-ray beam dose distributions for small, spherical-shaped targets. Mechanical precision is superior for the gamma knife as compared with the linac. The superior mechanical precision is of limited importance for most clinical targets, because inaccuracy of cranial target localization based on radiological imaging is greater than the typical linac imprecision of +/- 1 mm. Treatment planning for the linac is not standardized, but existing systems are based on well-known algorithms. The linac allows flexible, ready access to individualized beam control, without intrinsic field size limitations. Thus, it is more readily possible to achieve homogeneous dose distributions for nonspherical targets with one or more dimensions greater than 25 mm, as compared with that achieved with the gamma unit.(ABSTRACT TRUNCATED AT 250 WORDS)

Variables associated with the development of complications from radiosurgery of intracranial tumors

Between 5/21/86 and 11/1/89, we treated 64 recurrent or inoperable intracranial tumors in 60 patients (40 primary, 24 metastatic) with stereotactic radiosurgery using a modified 6 MeV linear accelerator at the Joint Center for Radiation Therapy. Patients were followed until death or 1/1/90. The median follow-up was 8 months (2-43 months). Fourteen patients experienced complications from 12 hours to 7 months (median 3 months, but only two patients more than 4 months) following radiosurgery. To determine variables related to complication, we calculated integral dose-volume histograms for 61/64 lesions and the surrounding CT-defined normal tissue. We excluded 16 lesions in 15 patients for follow-up less than 4 months (12 patients) or insufficient treatment information (3 patients). The variables for which higher values were associated with significantly more toxicity in a univariate score test were: a) tumor dose inhomogeneity (p less than 0.00001), b) maximum tumor dose (p = 0.00002), c) number of isocenters (p = 0.00002), d) maximum normal tissue dose (p = 0.00005) and e) tumor volume (p = 0.0001). These variables were all highly correlated with tumor dose inhomogeneity (coefficients of rank correlation 0.75-0.81). Tumor dose inhomogeneity had a much higher loglikelihood in a logistic model than any other single variable and a higher loglikelihood than any other two variables combined. None of the 21 patients with metastatic lesions experienced a complication. When we excluded the metastatic lesions, the above five variables remained significant in univariate tests. The mean tumor dose, number of treatment arcs, total degrees of arc, tumor location, previous radiotherapy, tumor geometry, pretreatment performance status, collimator size, and age were not significantly associated with toxicity. We conclude that radiosurgery of intracranial tumors is associated with a low risk of complications for lesions less than 10cc treated with a single isocenter to maximum tumor doses less than 25 Gy with tumor dose inhomogeneity less than 10 Gy, but that treatment of larger lesions will require new treatment strategies which reduce the tumor dose inhomogeneity associated with multiple isocenter treatments.

Treatment planning for stereotactic radiosurgery of intra-cranial lesions

Stereotactic radiosurgery of intra-cranial lesions is a treatment modality where a well defined target volume receives a high radiation dose in a single treatment. Our technique delivers this dose using a set of non-coplanar arcs and small circular collimators. We use a standard linear accelerator in our treatments, and the adjustable treatment parameters are: isocenter location, gantry arc rotation interval, couch angle, collimator field size, and dose. The treatment planning phase of the treatment determines these parameters such that the target volume is sufficiently irradiated, and dose to surrounding healthy tissue and critical, dose-limiting structures is minimized. The attachment of a BRW localizing frame to the patient's cranium combined with CT imaging (and optionally MRI or angiography) provides the required accuracy for localizing individual structures in the treatment volume. The treatment is fundamentally 3-dimensional and requires a volumetric assessment of the treatment plan. The selection of treatment arcs relies primarily on geometric constraints and the beam's eye view concept to avoid irradiating critical structures. The assessment of a treatment plan involves isodose distributions throughout the volume and integral dose-volume histograms. We present the essential concepts of our treatment planning approach, and illustrate these in three clinical cases.

Results of stereotactic brachytherapy used in the initial management of patients with glioblastoma

Recent studies have shown a survival benefit for patients with recurrent glioblastomas treated with stereotactic brachytherapy. On the basis of these encouraging results, we began a prospective study in 1987 to evaluate the use of brachytherapy in patients with newly diagnosed glioblastoma. Patients were considered eligible for this study if they met the following criteria: Karnofsky performance status 70% or greater; tumor size not greater than 5 cm in any dimension; a radiographically well delineated, supratentorial lesion not involving the ependymal surfaces; and pathologically confirmed glioblastoma. We treated 35 such patients between 1987 and 1990 with stereotactic brachytherapy as part of their initial therapy. The treatment protocol involved surgery, partial brain external-beam radiotherapy (59.4 Gy in 33 fractions), and stereotactic brachytherapy with temporary high-activity iodine 125 sources giving an additional 50 Gy to the tumor bed. Chemotherapy was not used in the initial management of these 35 patients. To compare our results with those obtained in a matched control group, we identified 40 patients with glioblastoma treated with surgery and external radiotherapy, with or without chemotherapy, between 1977 and 1986 at our institution. These patients had clinical and radiographic characteristics that would have made them eligible for the brachytherapy protocol. Survival rates at 1 and 2 years after diagnosis were 87% and 57%, respectively, for patients receiving brachytherapy versus 40% and 12.5%, respectively, for the controls (P less than .001). We conclude that stereotactic brachytherapy improves the survival of patients with glioblastoma when it can be incorporated into the initial treatment approach. Unfortunately, only about one in four patients with glioblastoma are suitable candidates for brachytherapy at the time of initial presentation.

Stereotactic radiosurgery of the brain using a standard linear accelerator: a study of early and late effects

Between February 1986 and December 1988, 44 patients were treated with stereotactic radiosurgery using a standard linear accelerator. Twenty one patients were treated for cerebrovascular abnormalities and 23 patients were treated for intracranial tumors. Fifteen of the 23 patients treated for intracranial tumors had received previous radiotherapy. The range of doses given by radiosurgery was 1000-2500 cGy. Nausea and vomiting occurred in seven patients within six hours of treatment. The incidence and symptoms were correlated with the dose of radiation to the vomiting center (area postrema) with the median dose to the postrema in symptomatic patients being 618 cGy compared to a range of less than 5 to 184 cGy in the remaining 36 asymptomatic patients. Temporary alopecia occurred in a single patient who received 400 cGy to the scalp. Alopecia did not occur in the remaining 43 patients who received from less than 5 to 175 cGy. Two patients treated for arteriovenous malformations developed an enhancing lesion on CT scanning (one with cerebral edema) on follow-up CT scanning six and twenty-eight months following radiosurgery. The location of these enhancing lesions corresponded to the volumes treated. In one patient, the enhancing pattern and edema disappeared within 18 months of treatment and no neurological deficits developed. Aphasia occurred in one patient treated for a recurrent glioma two hours following treatment to the left temporal lobe and cleared within 12 h of radiosurgery. One patient with an arteriovenous malformation of the pons developed weakness of the contralateral arm and leg six weeks following treatment and this has slowly resolved over the last 12 months. In conclusion, the complications to date have been self-limited and appear to be directly related to the dose and area of brain treated. Prior radiation therapy has not been associated with increased risk of complication in patients treated with radiosurgery for recurrent tumors to date.