Purpose of the study was to evaluate adequacy of target volume coverage with conventional two-dimensional radiotherapy; and to estimate potential of three-dimensional conformal radiotherapy for increasing dose to the target.
Material and methods: Analysis was performed for 34 lung cancer patients referred for curative intend two-dimensional radiation therapy. For the same patients two independent specialist teams created conventional two-dimensional plans according to "gold standard" radiotherapy and three-dimensional conformal plans. Evaluation of target coverage adequacy and normal tissue complication probability parameters was performed on two-dimensional isodose distributions overlay over outlined clinical target volumes. Maximum total dose for three-dimensional conformal radiotherapy was estimated keeping normal tissue complication probability on the same level as for two-dimensional plans. Conformity was evaluated.
Results: For two-dimensional planning maximum target dose was on average 52 Gy (3 Gy 1 standard deviation). Clinical target volumes coverage was poor for most plans; 95% isodose surface covers 57%. This percentage was consistent with 1 standard deviation of 10-17%. Minimum target dose was low - 5-10% of prescribed dose. Three-dimensional conformal radiotherapy allows increasing dose to clinical target volume with elective nodes irradiation up to 68-72 Gy and up to 78-90 Gy without it. Conformity of clinical target volume coverage was acceptable for all patients; 95% isodose surface covered on average 95% of target.
Conclusion: Three-dimensional conformal radiotherapy allows increasing of total dose to the target keeping tolerable dose to functional tissues for most patients. However, only combinations of modern imaging, planning and delivery techniques enable providing adequate and homogeneous clinical target volume coverage with therapeutically significant dose for lung tumors.