Materials/Methods: We hypothesized that the synergistic use of a focused beam with polycapillary x-ray optics and NP dose enhancement can achieve high-quality dose distribution for treatment of shallow tumors, such as intraocular melanoma and other eye diseases as our first intended targets. Radiosensitization using high-Z NPs is based on the fact that in kV range, photoelectric absorption is several orders of magnitude higher for high-Z material compared to soft tissue, and conjugated NPs tend to concentrate in the tumor and tumor vasculatures. Polycapillary x-ray optics can accurately focus x-rays to a small volume that cannot be achieved using conventional divergent beams. We measured key optic parameters of a prototype system. The measured beam profiles were used to configure our Monte Carlo (MC) simulation for relative dose calculation. Simulation of the optics was achieved via MC-based 3D geometric ray tracing. Because the focused x-ray needs to pass through some thickness of tissue to reach the tumor, we placed varying thickness of tissue-equivalent solid water blocks between the optic and focal point to determine whether the focusing was maintained through the tissue. Results: Measurement result shows that the focal point was well main- tained up to at least 4 cm into the phantom. Percent depth dose calculated inside a phantom from a single beam showed that the focused beam was able to concentrate high dose within a target volume with sharp fall off before and after the target. The surface dose was below 10% of target dose. The depth dose, with a peak deep in the tissue, is very different from conventional MV/KV beam depth dose. The output focus was very small (<0.5 mm) in the direction perpendicular to the beam; therefore, tumor radiation will be delivered by rotational beam scanning. Our initial MC study for treating a tumor of 1 cm size by scanning, while rotating the focused beam showed a very large mean tumor to skin dose ratio of 35. Conclusion: Our proposed NP-enhanced focused kV x-ray RT can provide pinpoint radiation delivery accuracy, most efficient NP radiosensitization, and dramatically lower cost. The innovative combination of focused x-ray with NP radiosensitizer has never been exploited before. The proposed low-cost, while high-performance, system suits the healthcare trend toward value-based medicine. Author Disclosure: W. Liu: None. C. MacDonald: None. H. Abbas: None. R. Nath: None. Z. Chen: None. 335 A Novel Design for Rectal Dose Reduction and Applicator Immobilizations for HDR Treatment of Cervical Carcinoma Q. Fan, A.R. Yeung, R. Helmig, J.C. Park, J.G. Li, C. Liu, and B. Lu; University of Florida, Gainesville, FL Purpose/Objective(s): Image guided high-dose-rate (HDR) brachyther- apy has been extensively used as a boost treatment for cervical cancer. Its efficacy, however, is severely limited by the clumsy rectal sparing devices available commercially and the potential applicator movement. To tackle these two critical issues for Tandem & Ring (T&R) HDR treatment, we developed a novel device using a balloon and a bracket system, serving for both rectal dose reduction and applicator immobilization purposes. Materials/Methods: The balloon catheter was constructed by gluing a short inflatable tube to a long regular open-end catheter. While the open end of the catheter connects to a syringe for contrast agent injection, the other end (inflatable tube) is affixed to the inferior-posterior side of the ring applicator. Once the T&R applicator sets were inserted in place, 10 cm 3 of IV contrast was injected to the inflatable tube of the balloon catheter in order to push the posterior vaginal wall away from the ring applicator. The bracket system consists of a special designed bracket, which can hold and fix itself to the T&R applicator set, a diaper-like Velcro fastener package used for connecting the patient pelvis structure to the bracket, and a buckle that holds the fasteners to stabilize the whole system. The treatment data for 21 cervical cancer patients treated with 27.5 Gy in 5 fractions were retrospectively analyzed. For each patient, CT and MRI images, acquired about 30 min apart, were registered to evaluate the effectiveness of the immobilization system. The translational and rota- tional displacements of the applicator sets between the two images were calculated. Patients were also surveyed for the comfort level during the treatments. Results: Compared to the commercial solution of rectal blade, the rectal point dose when using the balloon was decreased by 344.2%, corre- sponding to an extra sparing distance of 7.91.1 mm. The maximum sparing distance variation per patient is 1.40.6 mm, indicating the high interfractional reproducibility. Half of the patients had a translational and rotational displacements of <2 mm and <1 degree, respectively, in all directions. The mean translational and rotational displacements were <3 mm and <1.5 degree, respectively, in all directions. All patients indicated minor or no difference in comfort level with or without the balloon. Conclusion: The rectum balloon provides significant dose reduction compared to commercial solution while minimizing patient discomfort. The immobilization system permits almost no movement of applicator during the treatment. This work can be promoted as a standardized solution for HDR treatment of cervix cancer. Author Disclosure: Q. Fan: None. A.R. Yeung: None. R. Helmig: Part- nership; Medical Tool & Technology LLC. J.C. Park: None. J.G. Li: None. C. Liu: None. B. Lu: None. 336 A New Microbeam Scanned Proton Therapy Option and Example CNS Germ Cell Tumor Treatment Planning Exercise With Improved Cognitive Sparing J.B. Farr, 1 J.M. Gray, 2 R.C. Lukose, 1 C.H. Hua, 1 H.M. Conklin, 1 and T.E. Merchant 1 ; 1 St. Jude Children’s Research Hospital, Memphis, TN, 2 St. Jude Children’s Research Hospital, Memphis, TN Purpose/Objective(s): To compare potential cognitive and dose sparing using new intensity modulated microbeam proton therapy (IMmPT) versus intensity modulated x-ray therapy (IMXT) and conventional intensity modulated proton therapy (IMPT) with the treatment of CNS germ cell tumors (CNS GCT) used as example. Materials/Methods: Three CNS GCT patients, representing the three most common tumor treatment scenarios, were selected from the institution’s current IMXT practice for IMPT and IMmPT replanning. The IMXT and IMPT plans were optimized for 4p available beam geometry; whereas, the IMmPT was restricted to fixed horizontal beam (FHB) delivery. Based on specification and modeling the IMPT and IMmPT beam-lets compared as 4.0 mm and 1.5 mm (sigma), respectively in air at 220 MeV. The CNS GCT scenarios investigated were: whole-ventricle + pineal (WVP), whole- ventricle + pineal + suprasellar (WVPS), and whole-ventricle + suprasellar (WVS). Using comparative average dose based on a WV irradiation of 30.6 Gy, and boost irradiation to 23.4 Gy volume receiving less than or equal to, Oral Scientific Abstracts 336; Table 1 Target-Modality IQ Benefit Brain 25%j Mean ST25%j Mean IT25%j Mean LT25%j Mean RT25%j Mean LH25%jMean RH25%jMean WVP-IMXT Ref. 30j20 28j20 38j23 37j24 34j23 87j35 79j36 WVP-IMPT 11.3 17j12 17j12 20j12 12j8 12j8 19j13 28j14 WVP-IMmPT 12.7 14j9 14j9 15j9 9j5 9j5 15j9 18j11 WVPS-IMXT Ref. 32j22 31j26 39j25 29j21 30j21 100j37 100j36 WVPS-IMPT 4.2 22j15 22j15 26j15 20j12 21j12 100j31 100j31 WVPS- IMmPT 6.4 19j12 19j12 18j11 16j8 17j8 100j31 100j31 WVS-IMXT Ref. 32j21 32j21 30j21 33j22 33j23 92j30 79j29 WVS-IMPT 10.1 21j14 21j15 20j12 13j9 13j9 19j14 7j10 WVS-IMmPT 10.4 17j11 18j12 14j9 11j7 12j7 31j15 9j7 Volume 93  Number 3S  Supplement 2015 Oral Scientific Sessions S147