Fractionated brain stereotactic irradiation using a non-invasive frame:Technique and preliminary results

2D/3D Image fusion for accurate target localization and evaluation of a mask based stereotactic system in fractionated stereotactic radiotherapy of cranial lesions

The purpose of this study was to evaluate the accuracy of a two-dimensional (2D) to three-dimensional (3D) image-fusion-guided target localization system and a mask based stereotactic system for fractionated stereotactic radiotherapy (FSRT) of cranial lesions. A commercial x-ray image guidance system originally developed for extracranial radiosurgery was used for FSRT of cranial lesions. The localization accuracy was quantitatively evaluated with an anthropomorphic head phantom implanted with eight small radiopaque markers (BBs) in different locations. The accuracy and its clinical reliability were also qualitatively evaluated for a total of 127 fractions in 12 patients with both kV x-ray images and MV portal films. The image-guided system was then used as a standard to evaluate the overall uncertainty and reproducibility of the head mask based stereotactic system in these patients. The phantom study demonstrated that the maximal random error of the image-guided target localization was +/-0.6 mm in each direction in terms of the 95% confidence interval (CI). The systematic error varied with measurement methods. It was approximately 0.4 mm, mainly in the longitudinal direction, for the kV x-ray method. There was a 0.5 mm systematic difference, primarily in the lateral direction, between the kV x-ray and the MV portal methods. The patient study suggested that the accuracy of the image-guided system in patients was comparable to that in the phantom. The overall uncertainty of the mask system was +/-4 mm, and the reproducibility was +/-2.9 mm in terms of 95% CI. The study demonstrated that the image guidance system provides accurate and precise target positioning.

Intracranial stereotactic positioning systems: Report of the American Association of Physicists in Medicine Radiation Therapy Committee Task Group No. 68

Intracranial stereotactic positioning systems (ISPSs) are used to position patients prior to precise radiation treatment of localized lesions of the brain. Often, the lesion is located in close proximity to critical anatomic features whose functions should be maintained. Many types of ISPSs have been described in the literature and are commercially available. These are briefly reviewed. ISPS systems provide two critical functions. The first is to establish a coordinate system upon which a guided therapy can be applied. The second is to provide a method to reapply the coordinate system to the patient such that the coordinates assigned to the patient's anatomy are identical from application to application. Without limiting this study to any particular approach to ISPSs, this report introduces nomenclature and suggests performance tests to quantify both the stability of the ISPS to map diagnostic data to a coordinate system, as well as the ISPS's ability to be realigned to the patient's anatomy. For users who desire to develop a new ISPS system, it may be necessary for the clinical team to establish the accuracy and precision of each of these functions. For commercially available systems that have demonstrated an acceptable level of accuracy and precision, the clinical team may need to demonstrate local ability to apply the system in a manner consistent with that employed during the published testing. The level of accuracy and precision required of an individual ISPS system is dependent upon the clinical protocol (e.g., fractionation, margin, pathology, etc.). Each clinical team should provide routine quality assurance procedures that are sufficient to support the assumptions of accuracy and precision used during the planning process. The testing of ISPS systems can be grouped into two broad categories, type testing, which occurs prior to general commercialization, and site testing, performed when a commercial system is installed at a clinic. Guidelines to help select the appropriate tests as well as recommendations to help establish the required frequency of testing are provided. Because of the broad scope of different systems, it is important that both the manufacturer and user rigorously critique the system and set QA tests appropriate to the particular device and its possible weaknesses. Major recommendations of the Task Group include: introduction of a new nomenclature for reporting repositioning accuracy; comprehensive analysis of patient characteristics that might adversely affect positioning accuracy; performance of testing immediately before each treatment to establish that there are no gross positioning errors; a general request to the Medical Physics community for improved QA tools; implementation of weekly portal imaging (perhaps cone beam CT in the future) as a method of tracking fractionated patients (as per TG 40); and periodic routine reviews of positioning accuracy.

Treatment of pituitary adenomas by fractionated stereotactic radiotherapy: A prospective study of 110 patients

PURPOSE

To optimize and reduce the toxicity of pituitary adenoma irradiation by assessing the feasibility and effectiveness of fractionated stereotactic radiotherapy (FSR).

METHODS AND MATERIALS

Between 1990 and 1999, 110 consecutive patients, 47 with a functioning adenoma, were treated according to a strategy of either early surgery and FSR (n = 89) or FSR only (n = 21). Of the 110 patients, 75 had persistent macroscopic tumor and 47 persistent hormonal secretions; 15 were treated in the prophylactic setting. The linear accelerator-delivered dose was 50.4 Gy (5 x 1.8 Gy weekly), with a 2-mm safety margin.

RESULTS

After a minimal follow-up of 48 months, only 1 patient had developed progression. Of the 110 patients, 27 (36%) had a complete tumor response, 67 (89.3%) had an objective tumor response, 20 (42%) had a hormonal complete response, and 47 (100%) had a hormonal objective tumor response. The proportion of patients without a complete tumor response, objective tumor response, complete hormonal response, and objective hormonal response was 85.1%, 62%, 83%, and 59.3% at 4 years and 49.3%, 9%, 59.3%, and 10.6% at 8 years, respectively. The sole unfavorable predictive factor was preoperative SSE >20 mm for tumor response (p = 0.01) and growth hormone adenoma for the hormonal response (p <0.001). No late complications, except for pituitary deficiency, were reported, with a probability of requiring hormonal replacement of 28.5% and 35% at 4 and 8 years, respectively. Nonfunctioning status was the sole unfavorable factor (p = 0.0016).

CONCLUSIONS

Surgery plus FSR is safe and effective. FSR focused to the target volume seems more suitable than standard radiotherapy, and standard fractionation reduces the risk of optic neuropathy sometimes observed after single-dose radiosurgery. Therefore, FSR allows us to consider combined transrhinoseptal surgery and early radiotherapy, with a curative goal without patient selection.

Fractionated stereotactic radiotherapy: rationale and methods

Stereotactic radiosurgery (SRS) has become a widely accepted technique for the treatment intracranial neoplasms. Combined with modern imaging modalities, SRS has established its efficacy in a variety of indications. From the outset, however, it was recognized that the delivery of a single large dose of radiation was essentially "bad biology made better by good physics." To achieve the accuracy required to compensate for this biological shortcoming, the application of SRS has required that a neurosurgical head frame of some sort be rigidly attached to the patients head. Historically, this prerequisite has, primarily for practical reasons, precluded the delivery of multiple fractions over multiple days. With recent improvements in immobilization and repeat fixation, the good biology of fractionated delivery has been realized. This technique, which has come to be known as stereotactic radiotherapy (SRT), has significantly expanded the efficacy of the technique through the use of accurate physical targeting coupled with the basic radiobiological principles gleaned from decades of clinical experience.

[Technical evolution of irradiation in stereotactic conditions: dose fractionation]

The development of non-invasive head fixation systems, allowing 3D determination of the target coordinates, has lead to the increased use of fractionated stereotactic irradiation. These systems have been checked for accuracy and the mean precision of repositioning has been evaluated to +/- 1 mm. With the mean geometrical accuracy set at +/- 1 mm, a 2 mm safety margin is usually added to the clinical target volume in order to define the planning target volume. Quality assurance procedures must conform to the required precision of the technique while remaining realistic in day-to-day use relative to planned conventional treatments. Biologically different from single dose irradiation, the fractionated stereotactic irradiation completes the range of techniques used in the treatment of intra-cerebral lesions.

[Fractionated stereotactic radiotherapy: results in hypophyseal adenomas, acoustic neurinomas, and meningiomas of the cavernous sinus]

PURPOSE

In order to optimize cerebral benign tumor irradiation, fractionated stereotactic radiotherapy allows a focused-volume irradiation (2.1 cm3, 16 mm diameter) under standard fractionation conditions. Results of a retrospective and multicentric analysis are presented.

PATIENTS AND METHODS

Fractionated stereotactic radiotherapy uses the ballistic principles of the radiosurgery: stereotactic localization, multi-beam irradiation, secondary collimation, three-dimensional dosimetry. Standard fractionation is possible with a re-locatable non-invasive stereotactic device. The technique has been used for treating pituitary adenomas (86 patients), acoustic neuromas (32 patients) and cavernous meningiomas (26 patients).

RESULTS

1) pituitary adenomas: cumulative tumoral objective-response rates (42 patients) were respectively 42%, 69% and 88% at 24, 48 and 60 months. The cumulative endocrinologic objective-response rates (32 patients) were respectively 53%, 75% and 85% at 24, 48 and 60 months. The cumulative risk of radio-induced hormonal deficiency varied from 18% (growth hormone [GH]) to 42% for TSH (thyroid stimulating hormone) at 48 months. No other complication was observed; 2) acoustic neuromas: 33 tumors, < 25 mm in diameter, were treated in 32 patients. Tumor control was observed in 29/33 tumors: 14 were stable, 15 decreased and three progressed. Useful hearing was maintained in 9/10 patients. Only three patients (9%) presented persistent complications; 3) cavernous meningioma: 17/19 clinical responses were noted, 20 tumoral stabilisations, one partial response and one progression (22 magnetic resonance imaging [MRI] evaluable patients). One unilateral radio-induced blindness was observed.

CONCLUSION

For these benign tumors, the focused target volume obtained by the fractionated stereotactic radiotherapy seems to be better adapted to the treatment of limited benign tumors than standard radiotherapy. The use of standard fractionation reduces the risk of severe normal tissue damage, sometimes observed for radiosurgery and inherent in the use of single fraction.

[The point of view of the radiotherapist]

During the last decade, stereotactic radiotherapy has widely improved in France. Thus one should study the present situation and its future trend. QUANTITATIVE NEED: Considering single dose radiotherapy, there are about 900 to 1,000 cases treated per year. However, the trend towards more fractionated treatment will disturb this temporary equilibrium; thus more machine time will be necessary. QUALITATIVE NEED: Stereotactic radiotherapy is practiced by multi-disciplinary teams including physicians, physicists and scientific specialists. Radiotherapists and physicist are responsible for treatment planning and evaluation as well as for clinical and methodological research. Accordingly, they should possess computers, treatment planning systems, etc. Such teams are necessary to carry out complex irradiations. GENERAL EVOLUTION: Fractionation of irradiation nowadays seems mandatory for most intracranial tumors except metastases and small regular arteriovenous malformations. Heterogeneity of lesion dose is related to the geometry and the physics of convergent fixed or mobile beams. It can be improved and the healthy tissue irradiation can be diminished using the multi-isocentric planning for complex lesion or with micro multi leaf collimators. MODALITIES OF STEREOTACTIC RADIOTHERAPY ACCORDING TO LESION TYPE: For neurinomas of the acoustic nerve, fractionated stereotactic radiotherapy yields few of the complications published after single dose stereotactic radiotherapy. The same can be said for meningiomas although some series reported very few complications after single dose stereotactic radiotherapy. Solitary metastases without systemic evolution, not situated on the mid-line, are favorable candidates for palliative single dose stereotactic radiotherapy. The conjunction with total brain irradiation seems to be useful. Small arteriovenous malformations will be treated with single dose stereotactic radiotherapy, whereas voluminous and/or geometrically complex nidus could benefit from protons or photon beams modulated by micro multi leaf collimators and a few fractions. EXTRA-CRANIAL STEREOTACTIC RADIOTHERAPY: Single dose stereotactic radiotherapy and fractionated stereotactic radiotherapy will be used as boost in various situations such as massif facial and in all sorts of tumors in the body specially when lesions are close to critical organs.