Electron
-conformal
-eMLC
-arc beam
-custom bolus
Electron + photon
TOMO – do we need electrons
Mixed beam
1) For what sites can tomo replace 100% e- select sites
- accrue patients
- methodology
development of electron plan
development of tomo plan
comparing plans
tumore control
normal tissue complication
late effects
practicality
Project A – tomo vs conventional
Project B – conformal vs tomo
For what sites is a e+tomo an improvement over tomo?
Tomotherapy vs conventional electron and electron/photon treatment
I. Introduction
During the last decade, the radiotherapy clinic has been inundated with advanced
technology designed to deliver practical and highly conformal dose distributions that
better spares critical organs while dosing target volumes to tumorcidal levels. Intensitymodulated radiotherapy (IMRT), using multi-leaf collimators and advanced 3D treatment
planning systems capable of inverse planning, is the most well known recent advance in
radiotherapy technology [Galvin, et al. 2002].
Tomotherapy is the on the forefront of IMRT and image-guided radiotherapy (IGRT)
technology push. Tomotherapy delivers photon intensity-modulated radiotherapy (IMRT)
dose distributions with a continuously rotating, helical fan beam using a binary multi-leaf
collimator. Tomotherapy is an offshoot of the MIMiC system where a binary multi-leaf
was attached to a linear accelerator as a tertiary collimator and intensity-modulated dose
distributions were delivered in a serial fan beam, slice-by-slice method. Tomotherapy
includes an onboard mega-voltage computerized tomography (MVCT) imaging system
that allows for IGRT.
Tomotherapy differs from fixed-beam linear accelerator IMRT in several ways. First,
beam direction is selected by the planner before the beam’s intensity is modulated with
the optimizer. Tomotherapy uses all beamlet orientations that intersect the target volumes
and optimally weights them to achieve prescribed volumetric dose goals and limitations.
This greater degree of freedom on part of the optimizer in selecting beam incidence
allows more complex treatments to be planned and delivered.
With technological improvements that Tomotherapy provides in the ability to plan and
deliver intensity-modulated, image guided photon therapy, the question now begs as to
whether conventional treatment techniques using multi-modality, multi-energy fixed
beams from a linear accelerator will become obsolescent. In short, can a radiotherapy
clinic treat common sites with only Tomotherapy?
One obvious difference between a multi-modality linear accelerator and Tomotherapy is
the latter does not employ electron beams although it is technically feasible to do so.
Electron beams are advantageous in that dose falls rapidly off distal to the treatment
volume, and there are multitude of treatment sites that use electrons exclusively or in
combination with photon beams, namely breast and head/neck. Locke et al. [2002]
showed that a conventional photon/electron treatment technique was superior to a
tomotherapy treatment delivered with the MIMiC system in sparing critical structures
such as lens of the eye, optic nerves, brain, and brain stem, although the tomotherapy
treatment delivered much greater dose homogeneity in the target volume and provided
better sparing of the parotid glands.
II. Purpose of Study
To determine if Tomotherapy can replace conventional fixed-beam treatments requiring
electron beams. It is assume that conventional electron beam therapy or mixed-beam
therapy is adequate for each particular site studied, i.e., intensity- and energy-modulated
electron beams and or intensity-modulated photon beams are not needed.
III. Hypothesis and Specific Aims
Hypothesis:
Tomotherapy can deliver an adequate treatment for sites normally treated with electron
beams, alone or in combination with photon beams, based upon a scoring system that
accounts for target dose homogeneity, dose to critical organs, and dose peripheral to
target volume.
Specific Aims:
1) Develop a treatment scoring system based on physical dose parameters.
2) Develop methodology for planning a Tomotherapy treatment that achieves a treatment
score similar to that achieved by conventional therapy with electron beams.
IV. Methods and Materials
A) Study flow
i) Patient selection
a) Select patients that have been treated or are being considered for
treatment with conventional methods that includes at least one nonsupplemental electron beam, and whose anatomy has been imaged with a
CT scanner. Patients receiving treatments with electron beams only will be
given higher priority over mixed-beam treatments in the study.
b) A radiation oncologist will delineate the PTV, organs at risk, and any
other pertinent anatomy if such volumes have not been contoured on the
CT data set.
c) Proposed number of patients for study: 20.
ii) Generate a conventional plan on Pinnacle.
a) If patient has been treated with conventional methods already, then the
patient treatment plan, if it exists, will be used without further
modification.
b) If a treatment plan has not been completed, then one will be generated
under the guidance of a radiation oncologist.
iii) Score the conventional plan based on physical dose distribution parameters.
a) Target dose homogeneity.
b) OAR volumetric dose limits.
c) Dose peripheral to target volume.
iv) Generate a Tomotherapy treatment plan.
a) Generate a Tomotherapy plan that achieves a similar score or better
based on physical dose distribution parameters used to score the
conventional plan.
v) Import Tomotherapy dose distribution to Pinnacle for a side-by-side
comparison of isodose lines and DVHs.
a) Radiation oncologist will select which plan is better and provide
comments should the prefered plan scored lower.
b) Should the Tomotherapy plan be considered inferior, determine if there
are ways to improve the planning process or the scoring system to achieve
better results in the Tomotherapy plan.
B) Additional considerations.
i) Intra-fractional patient movement is not considered for the study. It is assumed
that the patient is perfectly immobile during treatment and setup is perfectly
reproducible between fractions.
ii) Pencil Beam Redefinition Algorithm should be used for better assessment of
electron dose distribution.
V. References
J. M. Galvin, G. Ezzell, A. Eisbrauch, C. Yu, B. Butler, Y. Xiao, I. Rosen, J. Rosenman,
M. Sharpe, L. Xing, P. Xia, T. Lomax, D. A. Low, and J. Palta
, “Intensity-modulated radiotherapy: current status and issues of interest,” Int. J. Radiat.
Oncol. Biol. Phys. 51, 880-914 (2001).
J. Locke, D. A. Low, T. Grigireit, and K. S. C. Chao, “Potential of tomotherapy for total
scalp treatment,” Int. J. Radiat. Oncol. Biol. Phys. 52, 553-559 (2002).