SU-E-T-372: Dosimetric Comparison of Craniospinal Irradiation Using Different Tomotherapy Techniques

Authors


Abstract

Purpose:

TomoHDA can treat with fixed jaws, dynamic jaws, and fixed gantry using either 3DCRT or IMRT. This study compares PTV coverage, OAR sparing, and beam-on-time (BOT) among these techniques for craniospinal irradiation (CSI).

Methods:

This study includes ten CSI patients treated to 23.4 Gy/13 fractions with Hi-Art 3.0 unit (HT-IMRT fixed 5 cm jaw). New plans were regenerated with 5 cm jaw for TomoHDA Hi-Art 5.0 using dynamic jaw (HD-IMRT), TomoDirect_IMRT (TD-IMRT), and Helical Tomotherapy 3DCRT (HT-3DCRT using 5 cm and 2.5 cm jaws with various pitches). Studied parameters include PTV mean dose, D95 (dose covering 95% of PTV), Paddick's conformity index (CI) and homogeneity index (HI – standard deviation of PTV dose/average PTV dose), BOT, and average OAR doses.

Results:

PTV coverage from these techniques were comparable (p>0.05). The main differences were in OAR sparing; HDIMRT reduced more OAR doses for lenses, bladder and rectum compared to HT-IMRT. For the sparing of visceral organs: liver, lung, heart, and kidneys, the three IMRT techniques gave comparable results. HD-IMRT gave best heart sparing; HT-IMRT best kidney sparing. Liver and lung doses were best reduced by TD-IMRT. All three IMRT techniques gave comparable BOT. OARs sparing was achieved for jaw size of 2.5 cm. HI was also improved but with doubling of BOT. Increasing the pitch number from 0.2 to 0.43 produced no significant improvement in OAR sparing but CI and HI did improve.

Conclusion:

HT-3DCRT, HT-IMRT, HD-IMRT or TD-IMRT techniques give comparable PTV coverage but the three IMRT plans better spared OARs compared with 3DCRT plans. Dynamic jaw plan is superior to fixed jaw plan to spare more OAR doses at field edge. TD_IMRT cannot reduce BOT for CSI patient but for sparing certain OAR, TD-IMRT may be used to avoid the beam going through the structures of interest.

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