Focal stereotactic external beam radiotherapy as a vision-sparing method for the treatment of peripapillary and perimacular retinoblastoma: preliminary results.

AIMS: Chemotherapy with aggressive focal ablative therapy is now the mainstay of retinoblastoma therapy. Our experience presents an evolution from conventional radiotherapy by treating posterior pole tumours with focal stereotactic fractionated radiotherapy (SRT). MATERIALS AND METHODS: A retrospective chart review was conducted of five patients (six eyes) treated with SRT at the Hospital for Sick Children and Princess Margaret Hospital, Toronto, Canada, between 1999 and 2004. The prescribed dose was 40 Gy delivered in 20 fractions once daily using 6 MV photons. RESULTS: Five patients (six eyes) were treated. The median age at the time of SRT was 18 months. The median follow-up was 46.5 months as of September 2004. Four patients were treated for a posterior pole focal tumour by focal SRT, and one patient was treated for vitreous seeding with whole-eye SRT. In patients treated with focal SRT, the median doses to the tumour, optic chiasm and brainstem were 41.92, 0.25 and 0.07 Gy, respectively, and to the ipsilateral optic nerve, globe and lens were 9.98, 19.11 and 3.74 Gy, respectively. The median doses to the ipsilateral and contralateral orbital bone were 6.73 Gy (range 5.99-8.29 Gy) and 2.31 Gy (range 0.88-7.08 Gy), respectively. A complete response (residual inactive scar tissue) was seen in four of the five focal tumours treated, with one tumour responding with a partial response (suspicious residual scar tissue). No acute or late side-effects occurred in patients treated with focal SRT. Only the patient treated with whole-eye SRT developed late effects of cataract and corneal ulceration. One patient suffered recurrence within the radiation field 5 months after focal SRT. Control of this recurrence was successful using chemotherapy and focal therapy. No eye has been enucleated. CONCLUSION: Vision-sparing focal SRT for localised tumour masses in critical locations can control tumours with minimal side-effects and a minimal dose to the surrounding critical normal tissue.

Stereotactic radiotherapy in the treatment of ocular melanoma: a noninvasive eye fixation aid and tracking system.

Ocular melanoma is frequently treated using brachytherapy implants (such as 125I and 60Co plaques or 184Ta wire), surgery, or external beam radiotherapy using small 60Co beams, high energy x-rays, or proton therapy. The last technique, though very expensive, provides improved dose distributions and dose localizations in the treatment of tumours adjacent to critical normal tissues. The technique of fractionated stereotactic radiotherapy is now being used at an increasingly large number of centers in the treatment of lesions in the brain, and the head and neck. This article describes the successful extension of the stereotactic technique to the treatment of ocular melanoma: an eye fixation aid is attached to a noninvasive, relocatable Gill-Thomas-Cosman head frame together with a simple eye-movement tracking system.

Immobilization in stereotactic radiotherapy: the head and neck localizer frame.

Stereotactic radiotherapy refers to multiple daily fractions of radiation, over days or weeks of treatment, with the patient in a relocatable stereotactic frame. The linear accelerator-based, couch-mounted system from Radionics utilizes the Gill-Thomas-Cosman (GTC) frame and the new Tarbell-Loeffler-Cosman (TLC) pediatric frame for accurate positioning reproducibility. Radionics has now made available the Head and Neck Localizer (HNL) frame to be used with its XPlan treatment planning system and the mini multileaf collimator (MMLC). This will extend the overall capability of stereotactic radiotherapy to the treatment of head and neck cancers. However, with no data available on the HNL frame, a study is being undertaken to assess the accuracy in patient position reproducibility using the frame. This report provides the preliminary findings of comparing depth-helmet readings with radiographic data, together with recommended modifications to the frame.

Phantom dosimetry for conformal stereotactic radiotherapy with a head and neck localizer frame.

Linear accelerator based stereotactic radiotherapy (SRT) with the Gill-Thomas-Cosman (GTC) re-locatable frame has been in use for several years. The use of the frame is limited to treating lesions above the hard palate. For treating tumours in the head and neck region, the Head and Neck Localizer (HNL) frame has been designed by Radionics Inc. for use with their XPlan treatment planning software. In this study we have used a spherical acrylic phantom commercially known as the 'Lucy' phantom (Sandstrom Sandstrom Trade and Technology Inc.) to perform thermoluminiscent as well as film dosimetry for the HNL frame. A radio-opaque marker was placed in the phantom and a film test carried out to verify the accuracy in isocentre positioning. The results of the dosimetry with TLD were within 2% for points near the isocentre and 5% (or 2 mm in steep gradients) in the planning target volume (PTV). In regions of low dose, larger percentage differences in local dose were observed, but all differences were within 5% of isocentre dose. The film dosimetry provided dose distributions that matched well with those generated by the XPlan stereotactic treatment planning software.

Implementation of total skin electron therapy using an optional high dose rate mode on a conventional linear accelerator.

A technique for total skin electron therapy (TSET) has been implemented using a standard accelerator that has been equipped with an optional special procedures mode to permit high dose-rate therapy with a 6-MeV electron beam. Patients are treated in a standing position using dual angled fields at a source to skin distance of 3.6 m. Dosimetric characteristics of the dual field technique were investigated for the 6-MeV beam as well as for a lower energy beam produced by the introduction of an acrylic beam degrader. A treatment stand, which incorporates the degrader in addition to devices used for patient support and shielding, is described. Acceptable beam uniformity and depth dose have been achieved while maintaining a low level of x-ray contamination. Treatment times are reasonably short since the output of the machine in the high-dose-rate mode is 25 Gy/min at the isocenter. Beam uniformity, dose rate, and x-ray contamination are relatively unaffected by the presence of the beam degrader if it is positioned near the treatment plane. The high dose-rate electron option is a useful treatment mode that provides the advantage of reduced treatment times while retaining proper functioning of all accelerator dosimetry systems and interlocks. Use of a dual field technique permits TSET in a treatment room of standard dimensions. The machine is easily set up for treatment, and patient setup is simplified through use of a customized support system.