### Volume

Calculates the structure's volume at a specified dose on the DVH e.g. Lung V20Gy. Dose can be specified in absolute (cGy/Gy) or relative (%). Volume can be specified in absolute (cc) or relative (%). Constraint allows > or < to determine passing volume value. A range of acceptable volume values may be entered by using a hyphen e.g. V20Gy<33-35%.

### Dose

Calculates the structure's dose at a specified volume on the DVH e.g. D05%<105%. Volume specified in absolute (cc) or relative (%). Dose specified in absolute (cGy/Gy) or relative (%). Constraint allows > or < to determine passing dose value. A range of acceptable dose values may be entered by using a hyphen e.g. D05%<105-108%.

### Max

Calculates the structure's maximum dose on the DVH e.g. Max<110%. Dose specified in absolute (cGy/Gy) or relative (%). Constraint allows < or > to determine passing dose value. A range of acceptable dose values may be entered by using a hyphen e.g. Max<110-115%. Note that many protocols use a max dose to 0.035cc which can be calculated with the dose constraint D0.035cc<110%

### Min

Calculates the structure's minimum dose on the DVH e.g. Min>95%. Dose specified in absolute (cGy/Gy) or relative (%). Constraint allows > to determine passing dose value. A range of acceptable dose values may be entered by using a hyphen e.g. Min>95-93%. Note: When a range is specified for "greater than" constraints, the first value is the ideal goal and the second value is the limit goal. The ideal goal has to be greater than the limit goal.

### Mean

Calculates the structure's mean dose on the DVH e.g. Mean<20Gy. Dose specified in absolute (cGy/Gy) or relative (%). Constraint allows > or < to determine passing Dose value. A range of acceptable dose values may be entered by using a hyphen e.g. Mean<20-21Gy.

### Min Dose Volume

Calculates the structure's minimum dose volume on the DVH e.g. MinD0.03cc>95%. Volume specified in absolute (cc) or relative (%). Dose specified in absolute (cGy/Gy) or relative (%). Constraint allows > to determine passing dose value. A range of acceptable dose values may be entered by using a hyphen e.g. MinD0.03cc>95-93%. Note: When a range is specified for "greater than" constraints, the first value is the ideal goal and the second value is the limit goal. The ideal goal has to be greater than the limit goal.

### Hot Spot Within

Calculates whether or not the global hot spot is within or not within the specified structure e.g. HSW% or HSNW%.

### CI

Calculates the conformity index for a specified structure. Isodose specified in absolute (cGy/Gy) or relative (%). (Isodose volume / structure volume) ratio is specified in the table columns ratio ideal and ratio limit. If ratio ideal column is left empty, a range of acceptable ratio values will not be used. Constraint allows < to determine passing ratio values. Because RTOG "no deviation" and "minor deviation" levels vary with structure target volume, you may enter multiple rows in the look-up table. If specified structure’s volume is not an exact match to values in the table, linear interpolation is used to determine ratio ideal and ratio limit.

where *PIV* is the volume (cc) of the specified dose and *TV* is the volume (cc) of the target structure.

The patient "Body" structure is used to calculate the volume of the specified isodose. If "Select Structure in lieu of Body" is checked, this structure will be used to calculate the volume of the specified isodose. This is useful in brain SRS with multiple targets receiving different prescription doses as PTV expansion structures can be used to calculate CI for each target. **WARNING: dose outside this structure will not be considered in the volume calculation so appropriate expansion sizes are required.**

### GI

Calculates the gradient index for a specified structure. Isodose specified in absolute (cGy/Gy) or relative (%). GI works the same as CI (see above) with definition below.

where *PIV* is the volume (cc) of the specified dose value.

This is commonly used in SRS cases.

### Dose Spill

Calculates the volume of dose outside the specified target structure, e.g. DSV105%<5cc. Dose specified in absolute (cGy/Gy) or relative (%). Volume specified in absolute (cc) or relative (%). Volume that is specified in relative (%) will be relative to the structure plan that is chosen. The structure plan volume will determine the 100% volume. Constraint allows < to determine passing volume value. A range of acceptable Volume values may be entered by using a hyphen DSV105%<5-7cc.

*Dose Spill Volume = PIV - TV*

_{PIV}
where *PIV* is the volume (cc) of the specified dose value and *TV _{PIV}* is the volume (cc) of the specified dose inside the target structure.

### Max Dose Table

Calculates the structure’s maximum dose on the DVH just as the Max Dose Constraint, except that the constraint can vary depending upon the volume of the structure specified in the "Structure for Table Volume Lookup" area. Dose specified in absolute (cGy/Gy) or relative (%) by using MaxDTGy or MaxDT%, respectively. Max dose is specified in the table columns max dose ideal and max dose limit. If max dose ideal column is left empty, a range of acceptable max dose values will not be used. Because RTOG "no deviation" and "minor deviation" levels vary with structure volume, you may enter multiple rows in the look-up table. If specified structure’s volume is not an exact match to values in the table, linear interpolation is used to determine max dose ideal and max dose limit.

### Min Volume Spared

Calculates the structure's minimum volume spared at a specified dose on the DVH e.g. Lung MVS7Gy. Dose can be specified in absolute (cGy/Gy) or relative (%). Volume can be specified in absolute (cc) or relative (%). Constraint allows > to determine passing volume value. A range of acceptable volume values may be entered by using a hyphen e.g. MSV7Gy>1500-1250cc. Note: When a range is specified for "greater than" constraints, the first value is the ideal goal and the second value is the limit goal. The ideal goal has to be greater than the limit goal.

*Min Volume Spared = SV - V*

where *SV* is the volume (cc) of the structure and *V* is the specified volume (cc).

### PCI

Calculates the paddick conformity index for a specified structure. Isodose specified in absolute (cGy/Gy) or relative (%). PCI works the same as CI (see above) except the definition is:

_{PIV})

^{2}TV*PIV

where *PIV* is the volume (cc) of the specified dose value, *TV* is the volume (cc) of the target structure, *TV _{PIV}* is the volume (cc) of the specified dose inside the target structure.

### Volume Table

Calculates the structure’s volume at a specified dose on the DVH just as the Volume Constraint, except that the constraint can vary depending upon the volume of the structure specified in the "Structure for Table Volume Lookup" area. Volume specified in absolute (cGy/Gy) or relative (%) by using VT20Gy<cc or VT20Gy<%, respectively. Volume is specified in the table columns volume ideal and volume limit. If volume ideal column is left empty, a range of acceptable volume values will not be used. Because "no deviation" and "minor deviation" levels might vary with structure volume, you may enter multiple rows in the look-up table. If specified structure’s volume is not an exact match to values in the table, linear interpolation is used to determine volume ideal and volume limit.

### Gradient Measure

Calculates the gradient index for a specified structure. Isodose specified in absolute (cGy/Gy) or relative (%). GI works the same as CI (see above) with definition below.

where *R50%* is the radius(cm) of an equivalent sphere with the same volume as the 50% isodose volume, and *R100%* is the radius(cm) of an equivalent sphere with the same volume as the 100% isodose volume.

This is commonly used in SRS cases.

### ICRU Homogeneity Index

Calculates the ICRU homogeneity index for a specified structure. IHI works the same as CI (see above) with definition below.

_{2%}-D

_{98%}D

_{50%}

where *D _{2%}* is the dose to 2% of the structure volume,

*D*is the dose to 98% of the structure volume, and

_{98%}*D*is the dose to 50% of the structure volume.

_{50%}### RTOG Homogeneity Index

Calculates the RTOG homogeneity index for a specified structure. Dose specified in absolute (cGy/Gy) or relative (%). RHI works the same as CI (see above) with definition below.

_{Max}D

_{Rx}

where *D _{Max}* is the structure max dose,

*D*is the specified dose.

_{Rx}### NTCP

Calculates the NTCP using the LKB model. NTCP is specified in relative (%). Constraints allow < to determine passing value. If α/β and BED Standard Fx are left empty or have a value of zero, no BED calculation is performed. The definition of NTCP is:

where *TD50(1)* (Gy) and *m* are specified by the user. Since the structure doesn't receive
a uniform dose an effective dose is calculated to use in equation (1). The definition of
*D _{eff}* is:

where *v _{i}* is the volume fraction in a
differential DVH dose bin centered on

*D*, and

_{i}*n*is specified by the user.

NTCP can also be calculated to account for Biologically Effective Dose (BED). The user specifies the Alpha
Beta ratio (*α/β*) and Standard Fraction Dose (*SFD*). The differential DVH is then
converted to a Standard BED differential DVH using:

where *N* is the total number of fractions, *d _{i}* is the ith differential DVH dose bin
fraction dose (Gy),

*SFD*is the Standard Fraction Dose (Gy), and

*α/β*is the Alpha Beta ratio. Typically a

*SFD*value of 2Gy is used in which case

*LQED(SFD)*=

*LQED2*.