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


METHODS
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.


CONCLUSIONS
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.
Kalapurakal
J A
JA
Division of Radiation Oncology, Robert H. Lurie Comprehensive Cancer Center, Northwestern Memorial Hospital, Chicago, IL 60611, USA. j-kalapurakal@nwu.edu
Sathiaseelan
V
V
Bista
T
T
Marymont
M H
MH
D000293:Adolescent; D000328:Adult; D001932:Brain Neoplasms / Q000517:prevention & control*; D002648:Child; D002675:Child, Preschool; D016371:Cranial Irradiation / Q000009:adverse effects* / Q000379:methods; D006801:Humans; D007908:Lens, Crystalline / Q000528:radiation effects*; D016399:Lymphoma, T-Cell / Q000517:prevention & control / Q000532:radiotherapy; D010315:Particle Accelerators; D055585:Physical Phenomena; D010825:Physics; D054198:Precursor Cell Lymphoblastic Leukemia-Lymphoma / Q000517:prevention & control / Q000532:radiotherapy; D011446:Prospective Studies; D011829:Radiation Dosage