I. J. Radiation Oncology d Biology d Physics
Volume 78, Number 3, Supplement, 2010
and V5 was 20.85 ± 4.53 Gy, 15.80 ± 3.07 Gy, 20.08 ± 4.32 Gy. Total maximum dose to organs at risk for FBCRT, HT, and AT respectively, were heart: 18.01 ± 17.43 Gy, 15.76 ± 17.57 Gy, 21.80 ± 18.92 Gy; esophagus: 8.25 ± 2.89 Gy, 8.46 ± 2.81 Gy, 8.13 ± 3.31 Gy; spinal cord: 8.33 ± 4.87 Gy, 10.16 ± 2.64 Gy, 11.33 ± 4.29 Gy; proximal trachea and bronchial tree: 11.79 ± 5.0 Gy, 8.50 ± 5.82 Gy, 9.71 ± 7.68 Gy. Treatment times in minutes for FBCRT, HT, AT respectively were 15.2 ± 1.15 min, 37.94 ± 5.58 min, 8.05 ± 1.26min. Conclusions: HT appears to provide excellent high and low dose conformality, as well as improved lung (mean dose, V5) and heart dosimetry, at the cost of increased treatment time. Standard FBCRT had superior cord sparing, and meets all dosimetric constraints while simultaneously providing an acceptable overall treatment time. In properly selected patients, AT is an interesting new delivery technique which appears comparable to FBCRT, while potentially decreasing treatment time by up to 50%. Future comparisons of these disparate SBRT techniques are warranted. Author Disclosure: M. Michaletz-Lorenz, Tomotherapy, B. Research Grant; C.G. Robinson, None; D.A. Low, Tomotherapy, B. Research Grant; C. Bloch, None; R.J. Bertrand, None; A.P. Apte, None; D.F. Mullen, None; F.A. Sandra, None; S.M. Goddu, Tomotherapy, B. Research Grant.
Dosimetric Characteristics of a New Helical Applicator for APBI Delivery
R. Rice D. Scanderbeg Moores UCSD Cancer Center, La Jolla, CA Purpose/Objective(s): There are currently several different single-entry, intracavitary, breast brachytherapy applicators including the MammoSite, MammoSite Multi-Lumen, Contura MLB, and SAVI. The multi-lumen devices provide a multitude of dwell positions which have improved normal tissue sparring by allowing the user to modulate dose away from the skin, chestwall, or lung. A new prototype of a single-entry intracavitary applicator has emerged from Cianna Medical, the manufacturer of SAVI. This new device is a revolution in the design of an intracavitary applicator taking the shape of a double helix. This helical design allows multiple, peripheral dwell positions without adding several additional lumens. In this study, we assess the dose distribution of this new device compared with the MammoSite, MammoSite ML, Contura, MLB and the SAVI 6-1 applicators. Materials/Methods: A breast phantom was CT scanned with each of the devices in the cavity. Each CT data set was fused to the other and contours were drawn on one data set and copied to each of the other devices, ensuring an exact comparison between structures. The cavity, PTV, and PTV-EVAL were all contoured and then each of the devices was digitized and planned. A prescription dose of 3.4 Gy/fx was assigned and the dose was optimized. Dose volume histograms (DVHs) were used for evaluation of the plans. Results: The single channel MammoSite had the lowest coverage, followed by the Contura and MammoSite ML. The helical SAVI and the SAVI 6-1 provided identical target coverage. The volume covered by 90% of the dose (V90) for each was 80.3%, 95.0%, 95.5%, 100%, and 100%, respectively. The V150 and V200 for each of the devices, respectively, were: 29.8 cc and 11.9 cc, 30.1 cc and 8.0 cc, 29.8 cc and 7.9 cc, 32.3 cc and 11.2 cc, and finally, 32.4 cc and 10.2 cc. Conclusions: The new helical SAVI has three lumens, making it less time consuming to digitize each of the catheters, and no more difficult to plan than any of the other treatment devices. Additionally, this design provides compatibility to 3-channel afterloaders with no loss in coverage and no need to split a treatment plan. Dosimetric results demonstrate the feasibility of this new device as a potential delivery system for accelerated partial breast irradiation. The hotspots (V150 and V200) for each of the devices were similar; however, their PTV-EVAL coverage differed substantially. The single channel MammoSite would not have been a viable option for treatment due to its coverage of \90% of the PTV_EVAL by 90% of the dose. The Contura and MammoSite ML would have been appropriate for treatment; however, the new helical SAVI and SAVI 6-1 both had better coverage of the target with similar hotspots. Further study is warranted to evaluate the feasibility and ease of use of the new helical design, but preliminary results are positive. Author Disclosure: R. Rice, None; D. Scanderbeg, Cianna Medical, F. Consultant/Advisory Board.
Analyses of the Mechanical Accuracy of RapidArc Treatment using Log File Data
K. Sasaki , S. Sato2, Y. Miyabe2, T. Takakura3, E. Tsubota3, M. Nakata3, A. Sawada2, T. Mizowaki2, A. Itoh1, M. Hiraoka2 Graduate School of Engineering Department of Nuclear Engineering, Kyoto University, Kyoto, Japan, 2Department of Radiation Oncology and Image-applied Therapy Kyoto University Graduate School of Medicine, Kyoto, Japan, 3Division of Clinical Radiology Service, Kyoto University Hospital, Kyoto, Japan 1
Purpose/Objective(s): RapidArc technology is a novel delivery method that enables high-dose conformality by optimizing the dose rate, gantry speed, and multi-leaf collimator (MLC) shapes. In evaluating RapidArc using radiographic film, it has been reported that the MLC movement, variable dose rate, and gantry speed can be controlled precisely during RapidArc. However, the gravity effect due to the gantry angle could not be taken into account because the radiographic film rotated with the gantry. Therefore, this study evaluated the accuracy of the MLC leaf position, gantry angle, and monitor units (MUs) using log files. Furthermore, the effects of variable gantry speed and dose rate on the accuracy of these parameters were evaluated. Materials/Methods: The accuracy of the MLC leaf position, the control of the variable dose rate and gantry speed, and the combined use of different leaf speeds and dose rates to obtain a designed dose pattern were examined when performing RapidArc. The MLC leaf positions and gantry angles were stored in a Dynalog file every 50 ms. In addition, the gantry angles and cumulative MUs were recorded in a Dynamic beam delivery log file at every control point for operating of these parameters. An error was defined as a difference between the actual and planned values for the MLC leaf positions, gantry angles, and cumulative MUs. The accuracy of the MLC leaf position and gantry rotation could be estimated every 50 ms using a combination of the Dynalog file and Dynamic beam delivery log file. Results: The maximum MLC leaf positional error at the isocenter plane was 0.21 mm. The MLC carriage tended to be delayed in the leaf traveling direction. When the MLC was retracted in the direction opposite to gantry rotation, leaf positional errors were