Between January 1991 and October 1995, 99 patients were treated definitively for inoperable NSCLC. Patients were selected for good performance status (96%) and absence of weight loss (82%). All patients had full 3D treatment planning (including total lung dose–volume histograms [DVHs]) prior to treatment delivery. The total lung DVH parameters were compared with the incidence and grade of pneumonitis after treatment.

Results: Univariate analysis revealed the percent of the total lung volume exceeding 20 Gy (V20), the effective volume (Veff) and the total lung volume mean dose, and location of the tumor primary (upper versus lower lobes) to be statistically significant relative to the development of ? Grade 2 pneumonitis. Multivariate analysis revealed the V20 to be the single independent predictor of pneumonitis.

Until further investigations of this nature can be performed, we recommend that the total lung volume DVH be assessed when evaluating the “goodness” of a 3D radiation plan in the treatment of NSCLC patients. In our clinic when the total lung V20 is <25%, we are comfortable with tumor dose escalation and the very low risk of pneumonitis. These plans are considered “acceptable.”

If a plan has a total lung V20 of >25% to 37%, alternative plans are done with an attempt at reducing the V20. This may be achieved by different beam arrangements, noncoplanar beams, less or no elective nodal irradiation, or smaller margins around the target volumes. This last technique is done only as a last resort and should be carried out with great caution as it may decrease the dose delivered to the tumor. There is much uncertainty in dose calculation accuracy at the PTV periphery greater due to the high dose gradient regions at the margin of tumor and low-density lung tissue.

If a treatment plan gives a V20 of >35–40%, we do not use that plan for treatment. All fatal pneumonitis occurred in patients with a V20 >35%. Similarly, all high-grade pneumonitis occurred in patients with a V20 of >32%. The risk of pneumonitis, in our estimation, is too great. Options for treatment then include: (1) changing the plan, as outlined above, (2) administering neoadjuvant chemotherapy in an attempt to reduce the volume of the tumor and treat the postchemotherapy tumor volume, and (3) treating the patient palliatively with lower doses.