M.W. Ho

SU-E-J-70: Feasibility Study of Dynamic Arc and IMRT Treatment Plans Utilizing Vero Treatment Unit and IPlan Planning Computer for SRS/FSRT Brain Cancer Patients

PURPOSE To investigate the feasibility of utilizing Dynamic Arc (DA) and IMRT with 5mm MLC leaf of VERO treatment unit for SRS/FSRT brain cancer patients with non-invasive stereotactic treatments. The DA and IMRT plans using the VERO unit (BrainLab Inc, USA) are compared with cone-based planning and proton plans to evaluate their dosimetric advantages. METHODS The Vero treatment has unique features like no rotational or translational movements of the table during treatments, Dynamic Arc/IMRT, tracking of IR markers, limitation of Ring rotation. Accuracies of the image fusions using CBCT, orthogonal x-rays, and CT are evaluated less than ∼ 0.7mm with a custom-made target phantom with 18 hidden targets. 1mm margin is given to GTV to determine PTV for planning constraints considering all the uncertainties of planning computer and mechanical uncertainties of the treatment unit. Also, double-scattering proton plans with 6F to 9F beams and typical clinical parameters, multiple isocenter plans with 6 to 21 isocenters, and DA/IMRT plans are evaluated to investigate the dosimetric advantages of the DA/IMRT for complex shape of targets. RESULTS 3 Groups of the patients are divided: (1) Group A (complex target shape), CIs are same for IMRT, and DGI of the proton plan are better by 9.5% than that of the IMRT, (2) Group B, CI of the DA plans (1.91+/-0.4) are better than cone-based plan, while DGI of the DA plan is 4.60+/-1.1 is better than cone-based plan (5.32+/-1.4), (3) Group C (small spherical targets), CI of the DA and cone-based plans are almost the same. CONCLUSION For small spherical targets, cone-based plans are superior to other 2 plans: DS proton and DA plans. For complex or irregular plans, dynamic and IMRT plans are comparable to cone-based and proton plans for complex targets.

SU‐GG‐I‐18: Feasibility Study and Clinical Application of Partial Conebeam Computed Tomography (pCBCT) for Boost Breast Treatment in RT

Purpose: To investigate the feasibility of using partial CBCT (pCBCT) as a setup aid for boost field verification of conventional breast treatments in RT Method and Materials: Elekta XVILinacs (Synergy) and XVI (v. 3.5) are used to take pCBCT images of the boost breast with S20 collimator, H&N Reconstruction options, and 240° scan angles. 2 breast phantoms are used: water‐filled mannequins phantom, and acrylic cone attached onto humanoid phantom. They are used to estimate the patient dose, and to investigate geometrical distortions caused by partial volume scans: mainly determined by clearances between patient body and treatment head. The commercial XVIsoftware is used without any modifications. CTimages with extra contours including surgical clips, lung, skin, and nipples with their 3–5mm margins are exported and correlated with those in pCBCT images. The patient dose was also measured with standard commercial phantom with pencil chambers using a commercial phantom using TLD.This pCBCT procedure has been used to determine its clinical advantage with 8 patients compared with MV/KV images. All the surgical clips are well defined in 3 planes of the pCBCT images. The image fusion is based upon bone, clip, skins, and/or breast implant. They are mainly chosen by a physician. Results:The setup uncertainties can be as much as 8mm, which seems to be related to deformation of the breast, and seroma changes. The clips can be defined in the 3 planes or all the patients. The MV/KV portal images are used to confirm the image matching procedure of partial CBCT.Conclusion: The pCBCT is a reliable and convenient tool to verify the treatment setup as well as treatment fields. The pCBCT with smaller collimators (16cm*20cm, and 12cm*20cm) are under investigation to improve image quality so that the seroma could be defined for the ABC breast patients.

SU‐GG‐I‐30: Feasibility Study and Clinical Application of the 100 Degree Limited‐Angle CBCT for Sarcoma Treatments in RT

Purpose: 100° Limited‐Angle (LA) CBCT is developed and applied clinically to treatsarcoma patients without moving the table during treatment in radiation therapy, and investigate its efficacy in routine clinics. Method and Materials: Elekta Synergy Linear accelerator and XVI (v. 3.5) are used to develop 100° LA CBCT to take the CBCTimages without any special software. The CBCTimages of the scanning angles ranging from 200° to 60° are investigated with S20 option, H&N construction, 10mA/frame, and 10ms. The field‐of‐view (FOV) with S20 option is about 26cm in each plane, large enough to cover most treatment volume of the sarcoma patients. The image quality such as the soft‐tissue contrast is not sensitive to mA (10 – 40mA). 120KVp is used (In XVI, we have only two options:100 or 120KVp). Several phantoms are fabricated to investigate the geometical distortions: humanoid phantom, geometry phantom, “deer leg” phantom. The distortion is dependent upon the scanning angles as well as the geometry of the scanned object The deers leg phantom was used to see hoe the bone artifacts affect the image quality, specially, the distortion of the skin.Results: The CBCTimages with the use of CT wires on the skin are used for sarcomatreatment. The setup uncertainties of the extremities (arm and thigh) are less than “5mm” over the treatment volume. This accuracy is estimated using the CT wires, the bone structures, and surgical clips if used. Conclusion: The limited angle CBCT is implemented for the treatment of extremities like proximal upper and lower extremities. The advantage of the LA CBCT is faster scan, and image quality when motion is an issue, while the disadvantage is the geometrical distortion of the skin regions. This procedure is modified and be used for prostate, lung, and H&N with titanium supporters.