Field-in-field technique with intrafractionally modulated junction shifts for craniospinal irradiation.
OBJECTIVE
To plan craniospinal irradiation with "field-in-field" (FIF) homogenization in combination with daily, intrafractional modulation of the field junctions, to minimize the possibility of spinal cord overdose.


METHODS
Lateral cranial fields and posterior spinal fields were planned using a forward-planned, step-and-shoot FIF technique. Field junctions were automatically modulated and custom-weighted for maximal homogeneity within each treatment fraction. Dose-volume histogram analyses and film dosimetry were used to assess results.


RESULTS
Plan inhomogeneity improved with FIF. Planning with daily modulated junction shifts provided consistent dose delivery during each fraction of treatment across the junctions. Modulation minimized the impact of a 5-mm setup error at the junction. Film dosimetry confirmed that no point in the junction exceeded the anticipated dose.


CONCLUSIONS
Field-in-field planning and modulated junction shifts improve the homogeneity and consistency of daily dose delivery, simplify treatment, and reduce the impact of setup errors.
Yom
Sue S
SS
Division of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
Frija
Erik K
EK
Mahajan
Anita
A
Chang
Eric
E
Klein
Kelli
K
Shiu
Almon
A
Ohrt
Jared
J
Woo
Shiao
S
D000293:Adolescent; D000328:Adult; D016371:Cranial Irradiation / Q000379:methods*; D019583:Dose Fractionation, Radiation; D005373:Film Dosimetry / Q000379:methods; D006801:Humans; D019047:Phantoms, Imaging; D011832:Radiation Injuries / Q000517:prevention & control*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013116:Spinal Cord / Q000528:radiation effects*