How much Radiation is Safe to the Other Structures in the Chest

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Obviously when radiating the tumor the beams should be targeted as precisely as possible to minimize the amount of radiation to normal structures, the Wash U group limits the V20 (percent of the lung receiving 20Gy) to 25% see data, and the MD Anderson group in chemoradiation limits the V10 to 40% (see data and table here).

The Michigan group said that high doses can be used as long as the MLD (mean lung dose) is < 20Gy and the V20 less than 30% (go here). There are other data relating V20 and mean lung dose (see data).


Some guidelines from RTOG protocols are noted below and the normal tissue table for RTOG 93-11 and RTOG 0412 and NCCN Guidelines here and here.
 

RTOG L-0117 A PHASE I/II DOSE INTENSIFICATION STUDY USING THREE DIMENSIONAL CONFORMAL RADIATION THERAPY AND CONCURRENT CHEMOTHERAPY FOR PATIENTS WITH INOPERABLE, NON-SMALL CELL LUNG CANCER

6.6 Normal Tissue Volume and Tolerances

6.6.1 The normal organs, including skin, lungs (either as total, or contra lateral and ipsilateral), esophagus, heart, liver, spinal cord, shall be contoured in their entirety.

6.6.2 The tolerance of the lungs are related to the volume of the organ(s) irradiated. Data from the Washington University2 reported that high-grade acute pneumonitis did not occur when the V20 was < approximately 30%. The incidence and the grade or severity of pneumonitis was clearly related to the V20. In the Washington University data, maximum dose (with conventional fractionation) was not related to acute pneumonitis. For this protocol all eligible patients must have the V20 < 30%.

6.6.3 The esophagus volume (outer muscular contour) must be contoured from the level of just below the larynx to the gastro-esophageal juncture. Oral contrast at the time of scanning is necessary to delineate the esophagus. The percentage of the esophageal volume exceeding 55 Gy shall be < 30% and the mean esophageal dose shall be < 34 Gy. If the esophageal dose exceeds this with the best plan possible, then the patient should not be treated on this protocol.

6.6.4 The maximum spinal cord (point) dose should not exceed 45 Gy.

6.6.5 Partial volume tolerance data for heart is not available. The heart dose should be kept as low as possible. Whole heart dose should not exceed 40 Gy.

6.6.6 The liver dose should be kept to a minimum. Half the liver should not exceed 35 Gy. The whole liver should not exceed 30 Gy.