Minesh P. Mehta

Meningeal hemangiopericytoma: defining the role for radiation therapy

SummaryMeningeal hemangiopericytoma is a rare neoplasm arising from perivascular pericytes. Accounting for < 1% of all brain tumors, these neoplasms are characterized by a high local recurrence rate and metastatic potential. Meningeal hemangiopericytoma occur most frequently during the fifth decade of life, with an almost equal sex incidence. To evaluate and define the role for primary, postoperative, or palliative radiotherapy in meningeal hemangiopericytoma, data were gathered from our own tumor registry and compiled with an extensive analysis of published series and case reports. This analysis reveals a 90%, 9 year actuarial risk for local recurrence following surgical resection only. Interestingly, less than 33% of these recurrences were noted within the first five years, which may account for the false assumption that these tumors are highly curable with surgical resection only. Radiation therapy appears to reduce this local recurrence rate, prolonging disease-free and overall survival. Radiation responses are dose dependent, with > 50 Gray providing superior long-term disease-free survival. Meningeal hemangiopericytoma are characterized by a slow, but progressive radiographic response to ionizing radiation, not unlike other radiated, highly vascular brain lesions, such as arteriovenous malformations. A retrospective review of clinical demographics, sites of meningeal origin, radiographic and pathologic findings and the role of chemotherapy is also presented.

Treatment of arteriovenous malformations with stereotactic radiosurgery employing both magnetic resonance angiography and standard angiography as a database

Twenty-one arteriovenous malformations were prospectively evaluated using magnetic resonance angiography and compared with stereotactic angiography. The goals were to establish the feasibility of magnetic resonance angiography, compare it to stereotactic angiography, employ magnetic resonance angiography in follow-up, and semiquantify flow. A correlative evaluation between flow and response to stereotactic radiosurgery was carried out. Phase contrast angiograms were obtained at flow velocities of 400, 200, 100, 60, and 20 cm/sec. The fractionated velocities provided images that selectively demonstrated the arterial and venous components of the arteriovenous malformations. Qualitative assessment of the velocity within the arteriovenous malformations and the presence of fistulae were also determined by multiple velocity images. In addition, 3-dimensional time-of-flight magnetic resonance angiograms were obtained to define the exact size and shape of the nidus. This technique also permitted evaluation of the nidus and feeding arteries for the presence of low flow aneurysms. Correlation between the two imaging modalities was carried out by subjective and semiquantitative estimation of flow velocity and estimation of nidus size. The following velocity parameters were employed: fast, intermediate, slow, and none (arteriovenous malformation obliterated). In 19 of 21 (90.5%) arteriovenous malformations, magnetic resonance angiography was equal or superior to stereotactic angiography for flow quantification and visualization of the nidus. Only 2 of 21 arteriovenous malformations were better demonstrated by stereotactic angiography than by magnetic resonance angiography (failure rate of 9.5%). The nidus size in one case was clearly underestimated by stereotactic angiography and would have resulted in a geographic miss without magnetic resonance angiography. Seven post-radiosurgery arteriovenous malformations were evaluated for follow-up with both magnetic resonance angiography and stereotactic angiography. In 6 of 7 arteriovenous malformations, magnetic resonance angiography response matched stereotactic angiography response. Correlation of flow with outcome was carried out for 14 arteriovenous malformations using magnetic resonance angiography only. Interestingly, all nine arteriovenous malformations with intermediate or slow flow demonstrated partial or complete obliteration; whereas only 3 of 5 fast flow arteriovenous malformations achieved a response with a median follow-up of 10 months. This early analysis suggests that slower flowing arteriovenous malformations may obliterate faster after stereotactic radiosurgery and flow parameters could be employed to predict response. In conclusion, magnetic resonance angiography permits semiquantitative flow velocity assessment and may therefore be superior to stereotactic angiography. An additional advantage of magnetic resonance angiography is the generation of serial transverse images which can replace the conventional CT scan employed for stereotactic radiosurgery treatment planning.(ABSTRACT TRUNCATED AT 400 WORDS)

The physical, biologic, and clinical basis of radiosurgery

Since Leksells description of the concept of radiosurgery in 1951, probably more than 20,000 patients worldwide have been treated with this technique. Initially designed as a tool for functional neurostereotaxis, it has found widespread applicability for conditions as diverse as vascular malformations, benign tumors such as acoustic neuroma, meningioma, pituitary adenoma, and also malignant tumors such as brain metastases and malignant glioma. From rudimentary knowledge of the ability to produce focal necrotic lesions, the biologic understanding of the process of single-fraction, small-volume, high-dose brain radiation has evolved into a multicompartmental model, with reasonable appreciation of the dose, volume, and time factors involved. With the explosion of technology on several fronts in the 1980s and 1990s, a multitude of devices for radiosurgery, ranging from cyclotron-generated particle beams to multisource cobalt-60 units to an immense variety of modified linear accelerators has become available. A parallel explosion of technology in the fields of imaging and computing will ensure that this is just the beginning; already, technologies for automated image segmentation and target identification, long the physicians monopoly, are around the corner; image fusion now allows simultaneous visualization of target and normal tissue anatomy, physiology, and other exciting possibilities such as chemical composition and vascular characteristics. Advances in physics and robotics have led to development of prototypical machines that will blur the distinction between radiosurgery and conformal radiotherapy. Already, several first generation devices to free stereotaxis from its fixation to frames are available. Substantial enthusiasm among clinicians has ensured that, unlike many fleetingly and momentarily exciting technologies of the last 2 decades, radiosurgery has made and will continue to make a strong commitment for clinical efficacy, safety, and cost-effectiveness through the process of thorough multiinstitutional clinical trials, as opposed to seeking validation from anecdotal experiences. In this regard, the Radiation Therapy Oncology Group (RTOG) and the Gamma Knife Users Group (GKUG) are to be commended; if the plethora of radiosurgery-related publications is evidence of scientific interest, the field will likely continue to expand. In the future, issues pertaining to appropriate regulatory review, patient selection, quality assurance, and training will need to be addressed. Major clinical and biological studies still need to be undertaken.

Thoracic volume radiation sparing following endobronchial brachytherapy: A quantitative analysis☆

A retrospective analysis of patients with inoperable, Stage III non-small cell lung carcinoma presenting with malignant airway occlusion and treated with endobronchial brachytherapy boost prior to radical radiotherapy is reported. Of the 102 patients treated with endobronchial brachytherapy between October 1986 and January 1991, 22 were newly diagnosed, biopsy-proven Stage IIIA (14/22) or IIIB (8/22) non-small cell carcinoma with > 80% endoscopically demonstrated airway occlusion of the carina (1/22), mainstem bronchus (10/22) or lobar bronchus (11/22). Fifteen patients had complete lung or lobar atelectasis. Poor performance status (KPS < 70% in 13/22) and/or weight loss (> 10% in 9/22) rendered these patients ineligible for multi-institutional trials. Endobronchial boost was delivered using low dose rate (20 Gy at 2 cm) or high dose rate brachytherapy (16 Gy in 4 fractions over 2 days at 2 cm). Following a 10-14 day post-endobronchial period to allow for reaeration, patients underwent additional external beam radiotherapy (60 Gy in 30 fractions). Of the 15 patients with atelectasis, 6/15 (40%) reaerated completely, 4/15 (27%) partially, and 5/15 (33%) failed to reaerate. A new method, called sequential volume integration was used on the pre- and post-endobronchial films to analyze sparing of thoracic volume from external beam radiation as a consequence of reaeration. Patients with complete reaeration required 47% less and those patients with partial reaeration required 25% less ipsilateral thoracic volume radiation. There was a tend toward improved survival in reaerators (36 weeks) as compared to non-reaerators (24 weeks).

Treatment of Wilms’ Tumour

SummaryWilms’ tumour (nephroblastoma, renal embryoma) is the fifth most common paediatric malignancy, arising from the embryonal tissue of kidneys and first formally described by Max Wilms in his classic 1899 monograph. Until the early part of this century, Wilms’ tumour was associated with a less than 20% survival rate. The current survival rate exceeds 80%, primarily due to large multi-institutional trials such as the National Wilms’ Tumor Study (NWTS). These studies have refined and defined the roles of surgery, chemotherapy, and radiation in treating Wilms’ tumour, based on staging and histology. The dramatic improvement in the prognosis for children with Wilms’ tumour, especially over the past 20 years, represents a landmark achievement in the history of paediatric oncology.Specific treatment recommendations are based on the current National Wilms’ Tumor Study IV schema. Stages I and II favourable histology patients do not receive radiotherapy, but are treated postoperatively with ‘pulsed’ or ‘conventional’ dactinomycin and vincristine; stage III favourable histology requires postoperative abdominal radiotherapy followed by triple agent, ‘conventional’ or ‘pulsed’ chemotherapy (dactinomycin, doxorubicin and vincristine). Patients with stage IV favourable histology, stages II to IV anaplastic, clear cell or rhabdoid histology, are treated similarly with aggressive triple-agent chemotherapy, with the addition of radiotherapy to selected sites. Recurrent and adult Wilms’ tumours have poor prognoses and are treated with aggressive surgery, radiotherapy and chemotherapy.

Linear accelerator configurations for radiosurgery

The dramatic proliferation of radiosurgery in the 1980s and 1990s has resulted in the development of a plethora of hardware systems and an exponential increase in clinical use. This article summarizes the initial, now mostly historical, developments and emphasizes that most linear accelerator radiosurgery systems are based on three early prototypical systems from Buenos Aires, Heidelberg, and Montréal. These systems have more recently been tailored to permit fractionated radiosurgery, blurring the distinction between radiosurgery and radiotherapy. The commonly used fractionated systems are described. Clinical outcome data for arteriovenous are described. Clinical outcome data for arteriovenous malformations, acoustic neuroma, and meningioma, are mostly preliminary but substantial data are available for the radiosurgical management of metastases. With the recent emphasis on cost containment, cost-effectiveness issues have become significant and at least for metastases some preliminary data suggest a potential cost benefit with radiosurgery. The recent publication of data from a prospective randomized trial has established the superiority of boost therapy for malignant glioma and in this article, we present preliminary evidence supporting the use of radiosurgery. Finally, some of the new and exciting developments such as the robot-mounted linear accelerator, the use of shaped fields, and tomotherapy are described.

Technical Aspects in the Use of “Belly Boards” for Small Bowel Minimization

The position in which a patient is treated for pelvic irradiation has been shown to have dramatic significance in regard to the volume of small bowel within the treatment field. Previous studies in the literature have repeatedly supported the fact that volume may be the leading factor in both acute and chronic morbidity. We have prospectively evaluated and treated 30 patients utilizing a custom-made polyurethane foam and styrofoam belly board with a dropout cut from the level of the xyphoid process to the superior border of the treatment field, specifically designed to allow maximal superior and anterior displacement of small bowel by bladder distention and gravity, while allowing reliable daily reproducibility, accurate immobilization and equally important, increased patient comfort and compliance. By evaluating all patients (in both the supine position alone, and prone in the Belly Board) with a dedicated treatment planning CT scanner, we have been able to achieve 80-100% reduction in the volume of small bowel within the radiation portals. We will discuss data on the technical set-up, cost, and variations which allow the Belly Board to be specifically tailored for use when treating other intraabdominal sites. This technique is simple, inexpensive, highly reproducible, and permits maximal bowel displacement outside the treatment fields.

Weight Consideration in the Use of Cerrobend Beam Blocks

The technique of using customized field blocking to protect sensitive normal tissue during megavoltage radiation treatment is common practice in modern radiation therapy. The introduction of CT-based treatment planning has revolutionized customized field shaping. We carried out a prospective evaluation of 54 cerrobend blocks during a one-month time period. The goals of this study were to analyze the specific block patterns and correlate these with field size, block weight, and field setup. Factors contributing to excessively large and heavy cerrobend blocks defined as > or = 20 lbs. were identified. Twenty-two percent of blocks were found to be excessively large and one-third of these were a consequence of planning decisions. A review of these situations suggests that alternative methods would have avoided the excessive weight. Concerns have been raised regarding the safety of large and heavy cerrobend blocks. These blocks were therefore analyzed in terms of tray sag and tray break-point. Our data suggest that within this clinical range of block weight, neither tray sag nor tray break-point are of significant concern.

Implementing Hybrid CT/PET: The University of Wisconsin Experience

Oncology Issues November/December 2006 In Brief In late 2001, the University of Wisconsin’s Radiation Oncology Department installed one of the first radiotherapy-dedicated hybrid CT/PET scanners in the country. This scanner is shared between Radiation Oncology and Nuclear Medicine. In the last five years, the technology has proven valuable for diagnostic purposes and radiotherapy treatment planning. While the CT/PET acquisition benefited our hospital and patients, implementation of the new technology was not a seamless process. The adoption of the hybrid CT/PET posed challenges to our institution and, in particular, to the Radiation Oncology and Nuclear Medicine Departments that jointly share the equipment (see box, page 27). Now, a few years after its acquisition, the CT/PET scanner plays a vital role in the functioning of both departments. This new technology has significantly altered the way we design radiation treatment plans for our cancer patients.