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The rules say that plans must pay for a medical service or item if regular Medicare would pay for it in this case. 
You can find this rule at 42 Code of Federal Regulations (CFR) Section 422.101. 
 
  
  The rules say that Proton Beam Therapy (PBT) is a technology for delivering conformal external beam 
radiation with positively charged atomic particles to a well-defined treatment volume. PBT is approved by the 
U.S. Food and Drug Administration. 
 
Due to its unique dose deposition characteristics, PBT can, in certain situations, deliver the prescribed target 
dose while giving a lower dose to normal tissues as compared to photon-based forms of external beam 
radiotherapy. 
 
Photon beams deposit their greatest amount of energy beneath the patient's surface with a gradual reduction in 
energy deposition along the beam path as photons pass through the target and then through an exit point out of 
the body. In contrast, the physical profile of a beam of proton particles allows for the majority of its energy to 
be deposited over a very narrow range of tissue at a depth largely determined by the energy of the proton beam. 
A proton beam deposits relatively less radiation energy upon entering the body compared to a photon beam. 
The energy deposition of the proton beam then rapidly increases over a narrow range of tissue at a desired 
depth to produce an intense dose distribution pattern called the Bragg peak. Beyond the Bragg peak, energy and 
dose deposition rapidly decrease, resulting in the absence of any significant exit dose deposited in normal tissue 
beyond the target. 
 
PBT Treatment Planning 
PBT can allow for radiation treatment plans that are highly conformal to the target volume. PBT planning 
defines the necessary field sizes, gantry angles and beam energies needed to achieve the desired radiation dose 
distribution. 
 
An assessment of patient suitability for PBT is an important step in the process of care. Changes in the density 
and composition of tissues in the path of the beam have much greater impact on the delivered dose for protons 
than photons. Tissue interfaces, especially those with large differences in electron density, can lead to larger or 
unacceptable dosimetric uncertainties in PBT for certain patients. 
 
PBT treatment planning is a multi-step process and shares functions common to other forms of external beam 
radiotherapy planning: 
 
    Simulation and Imaging: Three-dimensional image acquisition of the target region by simulation employing 
CT, CT/ PET and/or MR scanning equipment is an essential prerequisite to PBT treatment planning. If 
respiratory or other normal organ motion is expected to produce significant movement of the target region 
during radiotherapy delivery, the radiation oncologist may additionally elect to order multi-phasic treatment 
planning image sets to account for motion when rendering target volumes. 
    Contouring: Defining the target and avoidance structures is a multi-step process: 
        The radiation oncologist reviews the three-dimensional images and outlines the treatment target on each 
slice of the image set. The summation of these contours defines the Gross Tumor Volume (GTV). 
        The radiation oncologist draws a margin around the GTV to generate a Clinical Target Volume (CTV) 
which encompasses the areas at risk for microscopic disease (i.e., not visible on imaging studies). 
        A final margin is then added to create a Planning Target Volume (PTV). 
        Nearby normal structures that could potentially be harmed by radiation (i.e., "organs at risk'; or OARs) are 
also contoured. 
        Radiation Dose Prescribing: The radiation oncologist assigns specific dose coverage requirements for the 
CTV which will be met even in the presence of expected positional and range uncertainties. A typical 
prescription may define a dose that will be delivered to at least 99% of the CTV. Additionally, PBT 
prescription requirements routinely include dose constraints for the OARs (e.g., upper limit of mean dose, 
maximum allowable point dose, and/or a critical volume of the OAR that must not receive a dose above a 
specified limit). 
        Dosimetric Planning and Calculations: The qualified medical physicist or a supervised dosimetrist 
calculates a treatment plan to deliver the prescribed radiation dose to the CTV and simultaneously satisfy the normal tissue dose constraints by delivering significantly lower doses to nearby organs. Delivery mechanisms 
vary, but regardless of the delivery technique, all delivery parameters and/or field specific hardware are 
developed by a medical physicist or supervised dosimetrist and an expected dose distribution is calculated for 
the treatment plan. 
        Patient Specific Dose Verification: An independent dose calculation and/or measurement should confirm 
that the intended dose distribution for the patient is physically verifiable and feasible. 
 
    Documentation of all aspects of the treatment planning process is essential. 
 
PBT Treatment Delivery 
    Proton delivery methods can be described in one of two forms: scattering or scanning. 
 
        In scattered deliveries, the beam is broadened by scattering devices, beam energies are combined by 
mechanical absorbers and the beam is shaped by placing material such as collimators and compensators into 
the proton path. 
        In scanning deliveries, the beam is swept laterally over the target with magnets instead of with scattering 
devices. Collimators and range compensators are still sometimes used for lateral and distal beam shaping, but 
field specific hardware is not always required because the scanning magnets allow the lateral extent of the 
beam to be varied with each energy level, a technique sometimes called intensity-modulated proton therapy 
(IMPT). 
 
    The basic requirement for all forms of PBT treatment delivery is that the technology must accurately 
produce the calculated dose distribution described by the PBT plan. PBT dose distributions are sensitive to 
changes in target depth and shape and thus, changes in patient anatomy during treatment may require repeat 
planning. Such a change must be documented. 
 
    Precise delivery is vital for proper treatment. Therefore, imaging techniques such as stereoscopic X-ray or 
CT scan (collectively referred to as Image Guided Radiation Therapy or IGRT) should be utilized to verify 
accurate and consistent patient and target setup for every treatment fraction. You can find these rules in the 
Local Coverage Determination (LCD) Proton Beam Therapy L35075. 
 
If you want to read these Medicare rules, you can go to this website www.medicareappeal.com. 
 
The Plan contract says that the Plan covers items and services in accordance with Medicare rules.