77300: Basic Radiation Dosimetry Calculation, central axis depth dose, TDF, NSD, gap calculations, off-axis factor, tissue inhomogeneity factors as required during course of treatment.

For external beam treatment, 77300 is used for dosimetry calculations.

This type of calculation is needed to determine the number, or monitor units that the treatment machine is set to deliver the prescribed dose that the Radiation Oncologist orders per area.

For Brachytherapy, the usage of 77300 is to report dwell times & durations of implant time.

Dosimetry is defined as a calculation, ordered by a radiation oncologist, of the radiation dose distribution within an area of interest.

Dosimetry may be obtained either by a hand calculation or computer generated calculation. Each must be documented, signed by the staff member who performed the task, dated, then approved by the physician with his signature!

Basic Dosimetry includes:
* Central axis depth dose
* Time dose factor (TDF)
* Nominal standard dose (NSD)
* Gap calculation
* Off axis factor
* Tissue inhomogeneity factors
* MU calculation for electron field
* Breast angle calculation

The calculation code is usually billed at the beginning of treatment course, when the treatment field shrinks (conedowns), for all other special calculation procedures in Radiation Therapy such as HDR, implants, and stereotactic radiosurgery.

During a typical course of radiation therapy, one to eight calculations may need to be billed depending on the complexity of the case. If there is a excess of this range, Medicare may deny it or request documentation to support the number of times the 77300 is billed.

BILLING TIP

A special dosimetry calc (77300) may be charged for each port being treated as long as it is not a mirror image. What does this mean?

Example I:

Mr. Doe is being treated to his pelvis: 4 fields/day (anterior, posterior, Rt. lateral & Lt. lateral)

A calculation is done for each field. If the anterior/posterior monitor unit is the same, then only 1 calculation would be charged. If the Rt. lateral monitor unit is 57 MU, and the Lt. lateral monitor unit is 59 MU, then each lateral field would be charged a 77300.

AP Pelvis	PA Pelvis	RT LAT Pelvis	LT LAT Pelvis
90 MU	90 MU	57 MU	59 MU

Thus, three units of 77300 would be billed!

Example II:

If a patient were having stereotactic radiosurgery and was being treated to six (6) fields & all six (6) fields had different monitor units calculated, then six (6) 77300 charges would be billed.

Field 1	Field 2	Field 3	Field 4	Field 5	Field 6
70 MU	75 MU	90 MU	85 MU	72 MU	70 MU