Repositioning accuracy with the Laitinen frame for fractionated stereotactic radiation therapy in adult and pediatric brain tumors: preliminary report

PURPOSE

To determine the repositioning accuracy, patient tolerance, and clinical efficacy of stereotactic radiation therapy for brain tumors in children and adults performed with the Laitinen stereotactic localizer and head holder.

MATERIALS AND METHODS

In this retrospective analysis, stereotactic frame tolerance was assessed by recording patient discomfort or pain in the ear and nose during each treatment in 34 patients, including 21 children and 13 adults with 37 lesions treated with fractionated stereotactic radiation therapy. Radiation doses ranged from 10-60 Gy at 1.0-4.0 Gy per fraction. Repositioning accuracy was assessed by comparing portal radiographs with setup fields on computed tomographic (CT) scout images. Clinical efficacy was assessed by analyzing posttreatment CT and magnetic resonance images.

RESULTS

The stereotactic localizer was well tolerated. The mean isocenter shifts observed after studying 305 portal radiographs were x-coordinate shift of 1.0 mm +/- 0.7 (SD), y-coordinate shift of 0.8 mm +/- 0.8, and z-coordinate shift of 1.7 mm +/- 1.0. At a median follow-up of 16 months, local control was achieved in 18 of 22 primary and in one of eight of recurrent tumors.

CONCLUSION

The Laitinen stereotactic localizer is well tolerated with accurate reproducibility during stereotactic radiation therapy. Preliminary local control rates are consistent with those in other reports.

Adverse impact of multileaf collimator field shaping on lens dose in children with acute leukemia receiving cranial irradiation

PURPOSE

This study was designed to investigate the impact of multileaf collimator (MLC) on lens dose in children with leukemia undergoing cranial irradiation.

METHODS AND MATERIALS

This is a prospective study utilizing three common cranial irradiation techniques. Technique A uses a half-beam, nondivergent radiation field. Technique B has the anterior divergent field edge at the lateral bony canthus. Technique C is similar to B, but with a field collimator angle. Thermoluminescent dosimeter (TLD) lens dose measurements were obtained in children and phantom with all three techniques.

RESULTS

Seventeen children were studied. Lens dose measurements were obtained in 14 children with technique A using MLC and blocks. In 7 of 14 children, dose measurements were obtained with MLC only. One child was treated with technique B and 2 children were treated with C, with MLC +/- blocks. In all 3 techniques, with MLC alone, the lens dose increased by 64%, 119%, and 72%, respectively. Similar results were obtained in phantom.

CONCLUSION

This study demonstrates that independent of irradiation technique, additional custom blocking is required to maximally protect the lens with MLC shaped fields. This is due to the lack of conformity between MLC and the desired field edge at the lateral bony canthus.

Fractionated stereotactic radiotherapy for pediatric brain tumors: the Chicago children's experience

Thirty-three children with a total of 35 benign/malignant brain and eye neoplasms were treated with fractionated stereotactic radiotherapy. In the first 11 children immobilization for treatment was achieved with plaster of Paris casts or aquaplast masks. In the remaining 22 children the Laitinen stereoadapter was used. Radiation was delivered with noncoplanar static or rotational beams. The dose fractionation used was 50.4-60 Gy in 28-30 fractions in patients receiving treatment with curative intent, and 10-32 Gy at 2-4 Gy/fraction for reirradiation. The accuracy of daily treatment was < 2 mm. After a median follow-up of 27 months, 22 of the 25 children treated with curative intent achieved local control. One child had progressive brain necrosis following 54 Gy in 30 fractions for a pontine astrocytoma. The exact etiology of this complication is unknown. This series demonstrates that in children fractionated stereotactic radiotherapy using the Laitinen stereoadapter is well tolerated and accurate and results in good local control.