For treating peripheral brain lesions--where proton therapy would be expected to have the greatest depth-dose advantage over photon therapy--the lateral penumbra strongly impacts the SS plan quality relative to photon techniques: proton beamlet sigma at patient surface must be small (<7.1 mm for three-beam single-field optimized SS plans) in order to achieve comparable or smaller brain necrosis NTCP relative to photon radiosurgery techniques. Achieving such small in-air sigma values at low energy (<70 MeV) is a major technological challenge in commercially available proton therapy systems.

Purpose: Many studies of the effects of tissue heterogeneity corrections exist for lung sites, but relatively few have focused on the esophagus. In this study, we characterize the differences between heterogeneity corrected and uncorrected esophageal cancer treatment plans in terms of physical and equivalent uniform dose (EUD). The aim is to provide guidance on prescription formulation when corrections are utilized, in order to connect past observed clinical outcomes to future planning calculation methods. Method and Materials: Seven patients with esophageal tumors superior to the diaphragm and inferior to the carina were evaluated. All plans used a four field 3D conformal technique, with a dose of 50.4 Gy prescribed to cover, at minimum, 93% of the PTV in 28 fractions. Three treatment plan variations were developed for each patient: (1) with heterogeneity correction, (2) without, and (3) with heterogeneity correction, but prescribed such that the monitor units were the same as the uncorrected plan. The corrected plan was taken to reflect the actual delivered dose and utilized as a reference for comparison. Results: The mean dose to the PTV was on average 2.6% higher in the corrected homo plan compared to the uncorrected plan (range: 0.9% to 5.8%). The standard deviation of the mean dose difference was 1.6%. The standard deviation of the PTV dose increased on average by 39.7% and volume of lung receiving 20 Gy increased by an average of 2.2%. The EUD of the PTV increased by an average of 2.2 percent (range: 0.0% to 5.7%). Conclusion: Using a homogeneous model will result in an increase in the EUD to the PTV as well as greater dose inhomogeneity within the PTV, a greater lung volume receiving at least 20 Gy, and a higher uncertainty in the PTV mean dose.

Purpose: To determine how small the lateral width in air of proton spots must be in order for proton spot scanning (SS) plan quality to be superior to x‐ray radiosurgery for peripheral brain lesions. Methods: Single‐beam proton SS plans with sigma (lateral spot intensity standard deviation) values ranging from 1 to 14 mm, x‐ray volumetric modulated arc therapy (VMAT) utilizing a 0.5 cm leaf thickness, and cone‐based x‐ray radiosurgery plans were generated for eleven patients with clinical target volumes ranging from 0.5 cm3 to 25 cm3. Plans were evaluated using brain necrosis normal tissue complication probability (NTCP), high dose conformity index, and integral dose metrics. Results: For proton SS plans, as sigma increased from 1 to 14 mm, integral dose relative to the cone plan increased from an average of 0.10 (range 0.05 to 0.17) to 0.63 (range 0.26 to 0.85) compared an average of 1.49 (range 0.90 to 3.00) for VMAT. As SS sigma increased from 1 mm to 14 mm, NTCP for healthy brain necrosis increased from an average of 0.02 (range 0.01 to 0.07) to 0.08 (range 0.01 to 0.18) compared to the averages of 0.06 (range 0.01 to 0.15) for cone and 0.05 (range 0.01 to 0.11) for VMAT plans. An in‐air sigma of less than 6 mm was required for the SS plans to have a statistically significant (p < 0.05) NTCP reduction relative to the x‐ray techniques. Conclusion: When treating peripheral brain lesions, which are ideal cases for SS since only a single proton beam direction is needed, SS only provides a superior NTCP to x‐ray radiosurgery techniques if the proton therapy system can produce an in‐air sigma of 6 mm or less.

Radiology and Medical Physics reimbursement for Medicare services is constantly changing. In this presentation we will review the proposed reimbursement rules and levels for 2015 and compare them with those currently in effect for 2014. In addition, we will discuss the challenges that may lie ahead for the medical physics profession as the Centers for Medicare and Medicaid Services (CMS) moves away from a fee for service payment model and towards one of prospective payment. Learning Objectives: Understand the differences in the Medicare reimbursement systems for outpatient departments as opposed to physicians and free standing centers. Learn the proposed Medicare rules for 2015 and how they may affect Radiology and Medical Physics revenues. Be aware of possible long term changes in reimbursement and how they may affect our employers, our pocket books and our profession.