Proceedings of the 52nd Annual ASTRO Meeting S841

3424 Presentation and Evaluation of a Novel, Combined-mode Intensity-modulated-arc/Static-gantry-IMRT

Planning and Delivery Method

B. J. Salter, V. Sarkar, B. Wang, M. W. Szegedi, P. Rassiah-Szegedi, H. Zhao, Y. J. Huang

Huntsman Cancer Institute, University of Utah, Salt Lake City, UT

Purpose/Objective(s): A fully digital linac design can have specific advantages in the timing of high dose-rate, discontinuous beamsused for creation of a novel Combined-Mode (CM) delivery approach; e.g., an intensity-modulated-arc (IMA) combined with a static-gantry-IMRT (SG-IMRT) approach. Such a combined approach can potentially overcome limited IMA modulation from any givendelivery angle by augmenting with fully modulated static gantry field(s) from a few ‘key’ angles of approach. Such an approach re-quires the availability of a planning solution capable of simultaneously optimizing both modalities and, for maximum efficiency, a de-livery approach which can deliver both treatment components in an integrated (i.e. ‘simultaneous’) single arc gantry rotation fashion.Here we present such an approach on a prototype configuration of a Siemens Artiste, and demonstrate both feasibility and dosimetricaccuracy from a delivery perspective, along with viability and dosimetric ‘value’ from a treatment planning perspective.

Materials/Methods: Thirteen CM IMA/SG-IMRT treatment plans were optimized by a ProArc prototype version of the Prowesstreatment planning system-TPS (3 rectal ca plans at 1.8 Gy/fx; 3 lung SBRT plans at 20 Gy/fx; 3 lung ca plans at 2 Gy/fx; and 4prostate plans at 1.8 Gy/fx). The TPS allowed for an integrated optimization of both options (i.e. IMA combined with 1 or 2 SG-IMRT fields) and exported a CM delivery file to the prototype Artiste system for delivery. All 13 plans were delivered on the Ar-tiste, and ion chamber and coronal-plane film dosimetry was collected in phantom to validate dosimetric accuracy. Delivery timeswere recorded for each plan to quantify efficiency of delivery. Lastly, to demonstrate potential value of the CM approach, an IMA-only plan was developed for the prostate ca case and relevant dosimetric metrics were collected.

Results: Dosimetric accuracy was seen to be excellent with mean high-dose-region ion chamber agreement of 0.6% ±1.96%, andfilm gamma analysis (3%/3 mm) showing mean percent agreement of 98.6% ± 0.88%. Delivery efficiency of the CM plans wasexcellent, as well, with mean delivery times of 2.7 min, 3.0 min, 8.9 min, and 2.7 min for prostate, lung, lung SBRT and rectal plans,respectively. Lastly, the CM plan was seen to provide for significant reductions in mean penile bulb and rectal doses for the prostatecase (16.2% and 10.3%, respectively).

Conclusions: A novel treatment planning and high dose rate delivery approach has been presented which combines an IntensityModulated Arc with 1 or 2 fully modulated Static Gantry IMRT fields. The approach was seen to be viable, accurate, efficient anddosimetrically valuable.

Author Disclosure: B.J. Salter, Siemens Research Grant, B. Research Grant; V. Sarkar, Postdoctoral Fellowship funded by Sie-mens, C. Other Research Support; B. Wang, None; M.W. Szegedi, None; P. Rassiah-Szegedi, None; H. Zhao, None; Y.J. Huang,None.

3425 Comparison of VMAT and Fixed Field IMRT Delivery Times: Clinical Results from an

Implementation Study

W. Logan, V. Mehta, F. Chen, K. McCune, J. Saini

Swedish Medical Center, Seattle, WA

Purpose/Objective(s): VMAT has been suggested to improve the efficiency of radiation delivery. We initiated a clinical study ina community cancer center to evaluate the gains in delivery efficiency for a fairly standard population of patients receiving radio-therapy.

Materials/Methods: Patients were enrolled in an IRB approved clinical study and consented to having both fixed field IMRT andVMAT plans prepared. IMRT plans were first generated in CMS XiO. VMAT plans were then created in Pinnacle3 SmartArc tomatch the quality of the IMRT plans. All plans were reviewed by the treating physician. QA was performed on an Elekta Synergylinac for both sets of plans. If the VMAT plan matched all the parameters of the IMRT plan, than 20% of the prescribed fractionswere treated with VMAT (in most instances one fraction per week was VMAT while the remaining 4 treatments were IMRT).

Results: Since each patient was treated on the same machine using both an IMRT and VMAT plan, the delivery efficiency could bereported against an internal control. The 17 patients enrolled in this study included 3 brain, 2 head and neck, 10 abdomen, and 3pelvic cases. The number of IMRT fields varied from 6 to 9 depending on the complexity of the treatment site. The delivery time forthe IMRT plans were primary determined by the number of control points. VMAT plans had different numbers of arcs, for instance,1 arc for the brain, abdomen, and pelvic cases, and 2 to 3 arcs for the head and neck cases. For brain, head and neck, abdominal, andpelvic cases respectively, the average IMRT treatment times were 14, 18, 17, and 18 minutes, while the average VMAT treatmenttimes were 2.1, 5.4, 2.3, and 2.8 minutes.

Conclusions: VMAT plans were delivered on average 13.6 minutes faster than fixed field IMRT.

Author Disclosure: W. Logan, Elekta, B. Research Grant; V. Mehta, Elekta, B. Research Grant; F. Chen, Elekta, B. Research Grant;K. McCune, Elekta, B. Research Grant; J. Saini, None.

3426 Intensity Modulated Radiation Therapy Compared with 3D Conformal Radiotherapy for Craniospinal

Irradiation in Adults: Do We Gain Anything?

X. Shen, M. Studenski, A. Harrison, Y. Xiao, T. Biswas

Department of Radiation Oncology, Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA

Purpose/Objective(s): Craniospinal irradiation (CSI) remains one of the most technically challenging planning processes in ra-diation oncology due to its long shape especially in adults and complex target volume. In addition, CSI is associated with significantacute and late morbidities. We undertook a dosimetric analysis to determine if intensity modulated radiation therapy (IMRT) couldimprove target coverage while sparing normal tissue structures compared to classic 3D conformal radiation (3D-CRT) planning.