Intensity modulated radiosurgery for the spine: dosimetric impact of beamlet size variation in the leaf travel direction.
OBJECTIVE
To investigate the dosimetric impact of beamlet size in the leaf travel direction for the spinal treatment using intensity-modulated radiosurgery (IMRS).


METHODS
The IMRS plans of ten patients (11 lesions - 6 thoracic, 2 cervical, 3 lumbar) were re-planned using four different beamlet sizes (1, 2, 5, and 10 mm) - in the leaf travel direction, while keeping the Y-dimension by multi-leaf collimator (MLC) width fixed, and compared to the reference plan with beamlet size of 3 mm. To evaluate the beamlet size effect, target volumes (coverage, conformity, and size effect), organ at risks (OARS) (doses to the spinal cord, lung and kidneys), and integral dose, and monitor units (MUs) were calculated.


RESULTS
Target coverage and dose conformity for planning target volume (PTV) were not correlated with beamlet size. Maximum (p=0.000) and mean (p=0.000) spinal cord doses decreased by 4.0% and 3.4% from 23.4% and 28.6% as beamlet size decreased from 10 to 1 mm. The integral doses, MUs and doses to other organs increased at smaller beamlet sizes. MUs for a beamlet size of 10 mm decreased by 31.4%, as compared with that at the reference beamlet size.


CONCLUSIONS
Despite no dosimetric benefits with respect to target volume and an MU increase, a definite dose reduction was observed at the spinal cord for smaller beamlet sizes. Treatment with IMRS planning for the spine will benefit from the use of a beamlet size between 2 and 4 mm.
Department of Radiation Oncology, CHA University, Seongnam-si, Gyeonggi-do, South Korea.
Joo Young
JY
Kim
Hyun Soo
HS
Shin
Ja Young
JY
Kim
Hyeli
H
Park
Sung Joon
SJ
Kim
D006801:Humans; D007668:Kidney / Q000528:radiation effects; D008168:Lung / Q000528:radiation effects; D011829:Radiation Dosage; D016634:Radiosurgery / Q000379:methods*; D013116:Spinal Cord / Q000528:radiation effects; D013125:Spinal Neoplasms / Q000601:surgery*; D014057:Tomography, X-Ray Computed