The backscatter from the DFM for a single, parallel-opposed fields, and RapidArc treatment technique was found significant. The application of mask in replacing streaking artifacts can be useful in improving dose homogeneity in the PTV. The use of a virtual filter around the teeth during the planning phase reduces the target underdosage issue in the phantom. Furthermore, a reduction in mucositis is observed in the head and neck patients with the use of PDM.

Proton therapy is increasingly used in medical treatments for cancer patients due to the sharp dose conformity offered by the characteristic Bragg peak. Proton beam interactions with the eye will be simulated using the MCNPX Monte Carlo code and available nuclear cross-section data to calculate the dose distribution in the eye gel and surrounding organs. A high-resolution eye model will be employed using a 3D geometrical voxel-based anthropomorphic head phantom obtained from the Visible Human Project (female data). Manual segmentation of the eye, carried out by the Medical Physics group at the University of Surrey resulted in 15 identified structures. This work emphasizes the use of a realistic phantom for accurately predicting dose deposition by protons.

In this study, we investigate the effect of dental filling materials (DFM) on RapidArc TM treatment plans and delivery in a patient undergoing radiotherapy treatment. The presence of DFM creates uncertainties in CT number and causes long streaking artifacts in the reconstructed images which greatly affect the dose distribution inside the oral cavity. The influence of extensive dental filling artifacts on dose distribution was performed using a geometrically well defined head and neck IMRT verification phantom (PTW, Freiburg, Germany) together with inserts from DFM (Amalgam, 11.3 g/cm 3 ). The phantom was scanned using Siemens SOMATOM Sensation CT simulator (Siemens AG, Germany) under standard head and neck imaging protocol (120 kV, 120 mAs, voxel size 1×1×2 mm 3 ). Three RapidArc™ plans were created in the Varian Eclipse treatment planning System (TPS) to treat oral cavity using the same CT dataset including; 1) raw CT image, 2) streaking artifacts replaced with a mask of 10 HU and 3) 2 cm thick 6000 HU virtual filter (a volume around the teeth in TPS to mimic extra attenuation). The virtual filter thickness optimization was purely based on measured PDD data acquired with DFM and the calculation in Eclipse Planning System using direct beam. The dose delivery and distribution for the three plans was verified using Gafchromic EBT2 (International Specialty Product, Wayne, NJ, USA) film measurements. The artifact mask and virtual filter around the teeth in the planning was found very useful to reduce the discrepancies between the dose plan and delivery. From clinical point of view, these results can be helpful to understand the increase of mucositis in patient having DFM, and further investigation is underway for clinical solution.

Purpose/Objective(s): Curative radiation therapy (RT) for locally advanced nasopharyngeal carcinoma (NPC) is based on the gross tumor volume (GTV), but the magnitude and timing of GTV changes during combined modality therapy remain unclear. This study analyzes GTV changes at phases of induction chemotherapy and sequential concurrent chemoradiation therapy (CRT) in patients with locally advanced NPC. Materials/Methods: Subjects included 13 patients with newly diagnosed stage III-IV NPC who underwent treatment between 2011 and 2014. Criteria for eligibility included 2 cycles of neoadjuvant chemotherapy, at least 5 cycles of concurrent chemotherapy and 3 magnetic resonance imaging (MRI) scans at specific phases of treatment (T0: before treatment, T1: postinduction, and T3: 3 months after CRT). The induction phase consisted of 2 cycles of gemcitabine and cisplatin. The CRT phase consisted of weekly cisplatin and RT delivered using volumetric modulated arc therapy (VMAT). The total dose was 70 Gy over 35 daily fractions administered 5 days/week. A subset of 3 patients received an additional MRI 4 to 5 weeks into CRT (T2). Primary gross tumor volume (GTVp) was defined as the GTV and adjacent involved retropharyngeal lymph nodes. Tumor volumes were delineated on gadolinium-enhanced fatsaturation T1 weighted MRIs by 2 observers. Mean values are reported +/one standard deviation. Results: Preliminary analysis included 6 (out of 13) subjects. The mean initial GTVp was 62.7 +/-32.8 mL. The mean GTVp response after induction phase was 21.4% +/-12.3% with a mean rate of volume change of 0.31 +/-0.19 mL/day which corresponded to a 0.56% +/-0.35% daily reduction in tumor volume. The total mean GTVp response after completion of treatment (T3) was 77.6% AE 21.6%. Subgroup analysis of subjects who underwent an additional MRI showed a mean GTVp reduction of 42.5% AE 22.6% and a mean rate of volume change of 0.87 AE 0.08 mL/day which corresponded to a 1.7% AE 0.93% daily reduction in tumor volume (from T1 to T2). Conclusion: Preliminary results suggest that the GTVp progressively diminishes following both induction chemotherapy and CRT. The mean GTVp response after 4 to 5 weeks of CRT exceeded the response observed after induction chemotherapy by a factor of 2. The mean rate of volume change at 4 to 5 weeks of CRT was threefold the rate seen during induction chemotherapy. These observations may support the optimal timing of imaging for replanning in the context of adaptive field RT. Analysis of the full NPC patient dataset is ongoing and will be reported.

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