Volumetric Modulated Arc Therapy Treatment Protocol for Hypo-fractionated Stereotactic Body
Radiotherapy for Localized Prostate Cancer
N. Agazaryan, S. Tenn, P. Chow, C. Lee, P. Lee, M. Steinberg, C. King
University of California Los Angeles, Los Angeles, CA
Purpose/Objective(s): To establish treatment planning, image guidance and treatment delivery protocol for a prospective single
arm Phase IIa clinical trial designed to obtain systematic quality of life data after a hypo-fractionated course of Stereotactic Body
Radiotherapy (SBRT) for the treatment of localized prostate cancer.
Materials/Methods: Treatment planning, image guidance and treatment delivery protocol for hypo-fractionated prostate SBRT
was developed with RapidArc VMAT using Novalis Tx, Novalis Body stereoscopic imaging and Cone Beam Computed Tomog-
raphy (CBCT). Three patients were included in our initial investigation prior to the start of the protocol and seven additional pa-
tients have since been added to the investigation and treated. The dosimetric and other clinical consequences of number of arcs,
table rotations, collimator angle and photon beam energy have been investigated.
Results: VMAT plans with ±45 degree collimator rotations required on average 38% less monitor units compared to plans with no
collimator rotations and 20% less monitor units than plans with ±22.5 degree rotations. Plans with ±45 degree collimator rotations
provided more homogeneous dose distribution with an average of 6% less maximal dose. VMAT plans with two arcs provided
improved conformality and homogeneity with an average of 3% lower maximal dose compared to single arc plans. However, in-
creasing the number of arcs to three did not provide any signiﬁcant improvement. Introduction of ±5 and ±10 degree table rotations
between arcs did not result in any signiﬁcant dosimetric improvements. The selection of photon beam energy between 6MV and
10MV did not provide any notable dosimetric differences either.
Conclusions: The ﬁnal selection of the protocol includes two coplanar 10 MV Rapid Arcs with ±45 degree collimator rotations. This
prospective clinical trial is designed to deliver 5 fractions of 8 Gy with the prescription dose covering the 95% of the planning target
volume. The beam-on time for each of the coplanar arcs is approximately 2 minutes. For the purpose of intrafraction motion manage-
ment, two Rapid Arcs are further split to 4 half arcs with approximately one minute treatment time for each segment. The patient is
stereoscopically imaged and repositioned if necessary using ExacTrac prior to the delivery of each arc. Additionally, CBCT is obtained
prior to each fraction for the purposes of conﬁrmation of ExacTrac positioning and volumetric evaluation of bladder and rectal ﬁlling.
Author Disclosure: N. Agazaryan, University of California Los Angeles, A. Employment; Varian Medical Systems, B. Research
Grant; Scientiﬁc Advisory Board, ViewRay, F. Consultant/Advisory Board; S. Tenn, University of California Los Angeles, A.
Employment; P. Chow, University of California Los Angeles, A. Employment; C. Lee, University of California Los Angeles,
A. Employment; P. Lee, University of California Los Angeles, A. Employment; M. Steinberg, University of California Los
Angeles, A. Employment; C. King, University of California Los Angeles, A. Employment.
Evaluation of a Monte Carlo Based Commercial Electron Beam Treatment Planning System
M. Al Kaﬁ
King Faisal Specialist Hospital and Research Centre, Riyadh 11211, Saudi Arabia
Purpose/Objective(s): Evaluation of a commercial electron dose calculation method using electron Monte Carlo (eMC) algorithm.
Materials/Methods: A commercial electron dose calculation method using electron Monte Carlo (eMC) algorithm has been eval-
uated. Calculations were performed over the range of different user selectable algorithm parameters: calculation grid size, accuracy,
smoothing method and smoothing level. Although the best results were obtained for the smallest grid size, for the highest statistical
accuracy and for the smoothed dose distribution but it requires very long calculation time. We found that a grid size of 0.25 cm and
a medium level smoothing would produce very good results with reasonably acceptable calculation time. The dose distributions
using the optimized calculation parameters for electron energies 6, 9, 12, 15, 18, and 22 MeV with different applicators (4, 6, 8, 10,
15, 20 and 25 cm) were compared with that measured from a Varian 23 EX linac. The above mentioned algorithm parameters were
used to calculate dose for about 10 patients and veriﬁed with a chamber in solid water phantom.
Results: The calculated central axis depth doses agree well with the measurements within 3 mm for all energies and applicators
used. The calculated bremsstrahlung dose is always found slightly higher than the measurements with a maximum discrepancy of
less than 0.5% for higher energies (18 and 22 MeV). For proﬁles, ﬁeld width and penumbra agree within 3 mm. The depth dose for
gantry angles and for extended source-to-surface distance (SSD) also agree within 3 mm with a maximum bremsstrahlung dose
discrepancy is 1% for 22 MeV. The proﬁles also agree within 3 mm. The calculated doses agree within 3-6% for all the patients.
Conclusions: Our results suggest that clinically acceptable results can be achieved with reasonable calculation time by selecting
some speciﬁc eMC algorithm parameters.
Author Disclosure: M. Al Kaﬁ, None; B. Moftah, None.
Prospective Study of Accelerated Radiation Therapy using Tomotherapy Simultaneous Integrated Boost
with Concurrent and Adjuvant Temozolomide Chemotherapy in the Treatment of Glioblastoma
Multiforme: Dosimetric Data
H. A. Alhussain, J. Caudrelier, S. Malone, O. Agboola, T. Nguyen, J. Belec, K. Carty, J. Bahm, L. Montgomery
The Ottawa Hospital Cancer Center, Ottawa, On, Canada
Purpose/Objective(s): To report the dosimetric data of Glioblastome Multiforme patients treated in a prospective study evaluating
Accelerated Radiation Therapy with Tomotherapy Simultaneous Integrated Boost using Intensity Modulated Radiation Therapy
(IMRT) with Concurrent and Adjuvant Temozolomide.
Materials/Methods: Between May 2008 and March 2010, 30 patients have been accrued on this Prospective Trial . Treatment plan-
ning was done by using 3 mm CT images that were fused with post operative MRI. Three separate target volumes were deﬁned as
follows : CTV1 (Clinical Target Volume) was the surgical cavity or contrast enhancing tumor plus a maximum of 5 mm margins.
S844 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010