TITLE:
Investigation of Hot-Spots in TomoDirect 3DCRT Breast Treatment
AUTHORS:
Quan Chen, Matthew Mallory, Edwin Crandley, Shiv Khandelwal
KEYWORDS:
TomoTherapy, TomoDirect, Accelerated Whole Breast Irradiation, 3DCRT, RTOG-1005
JOURNAL NAME:
International Journal of Medical Physics, Clinical Engineering and Radiation Oncology,
Vol.7 No.3,
August
20,
2018
ABSTRACT: Background: Conventional tomotherapy
platforms only allow for the delivery of helical IMRT. However the use of IMRT
and helical delivery in breast cancer treatment is non-standard. Newer
tomotherapy units are equipped with a static-beam mode with 3DCRT capabilities.
During the clinical use, we frequently observe hot-spots in the plan that
renders the plan clinically unacceptable. The purpose of this study is to
investigate the underlying cause of the hot-spots in tomotherapy static-beam
breast treatment and possible solutions. Materials/Methods: Theories
about the formation of the hot-spot were developed. Eight lumpectomy patients
contoured according to RTOG-1005 specifications were also used to illustrate
the magnitude of hot-spots under various planning strategies. Two tangential
beams were used for the whole breast irradiation plan with prescription dose of
40 Gy in 15 fractions. Results: The hot-spot was identified as the
behavior of the optimization engine when part of the target region was blocked.
With the current design of tomotherapy’s 3DCRT planning where user adjustment
was greatly limited, none of the planning strategies were able to reduce the
hot-spots to acceptable levels in the eight patients studied. The best strategy
still produced an average of 48.5 Gy (121% of prescription dose) hot-spot dose
and 30.4 cc hot-spot volume (volume receiving > 110% prescription dose). It is also shown that the
hot-spot was not a result of energy or other physical limitation of the
radiation device. By manually adjusting the plan sinogram, the maximum hot-spot
dose drops from 121% to 111% and the hot-spot volume drops from 30 cc to 6 cc on average. Conclusions: While
TomoDirect 3DCRT showed great promise in breast treatment, treatment
planning software improvements may be needed in order to improve the clinical
acceptability by reducing hot-spots in normal tissue.