Increase in Dosimetry Calculations Requires Differentiating between Basic and Special
Published on Fri Mar 01, 2002
The emergence of intensity modulated radiation therapy (IMRT) has resulted in the need for more dosimetry calculations 77300 (Basic radiation dosimetry calculation) and 77331 (Special dosimetry).
Radiation oncology practices should code dosimetry calculations based on the number of ports and fields. Dosimetry is used to determine the amount of radiation that needs to be administered to a specific area, including beam or implant orientations and exposures, tissue inhomogeneities, isodose strength, and distribution. It is part of the overall preparation prior to the delivery of radiation, which also includes simulations. Unlike simulations, dosimetry may be repeated during the course of treatment because of changes in tumor volume, for example, and each calculation may be paid separately.
Code 77300 is used more often because it represents a more typical calculation than 77331, which uses special radiation measuring and monitoring devices.
Basic dosimetry includes eight types of dose calculations:
Central axis depth dose
Time dose factor
Nominal standard dose
Gap calculation
Off-axis factor
Tissue inhomogeneity factors
Monitor unit calculation for electron field
Breast angle calculation.
Coding for Simple Dosimetry
Some payers reimburse for 77300 each time the calculation is performed, while others will pay only once per area treated. For example, if two dosimetry calculations are performed on the same port, a payer may allow 77300 to be reported twice.
Generally, however, payers (including Medicare) will reimburse for dosimetry calculations once per port, per treatment setup, says Jim Hugh, vice president of AMAC, a coding consulting firm in Atlanta.
Some practices may cap the number of dosimetry calculations reported to avoid payer scrutiny, but this is not advisable. "The number of times 77300 is performed is the number of times it should be reported, with few exceptions," says Carl Bogardus, MD, president of the Cancer Care Network, an oncology practice management consulting firm in Midwest City, Okla.
To illustrate, dosimetry calculations performed on a brain tumor with nine ports will result in reporting 77300 nine times. In the case of a patient with prostate cancer (185) where two ports are used to deliver radiation, you would report two dosimetry calculations. However, if the ports represent mirror images, such as anterior/posterior, only one can be reported because the images are calculations of the same size field, shape and depth.
If further treatment was required, for instance, after the volume of the tumor had changed, and the same nine ports were used, bill for nine additional basic dosimetry calculations, Hugh says.
Medicare considers 77300 reasonable and necessary for each treatment port. It is also appropriate to report if a patient has off-axis calculations, calculations for different depth doses, different volumes of interest, secondary film dosimetry, abutting volumes of interest, or any other situation requiring individual point calculations of radiation dosage.
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