Adjuvant external beam radiotherapy after therapeutic groin lymphadenectomy for patients with melanoma: a dosimetric comparison of three-dimensional conformal and intensity-modulated radiotherapy techniques.

Radiotherapy after lymph node dissection is recommended in high-risk melanoma cases. The aim of this study is to assess whether intensity-modulated radiotherapy (IMRT) offers advantages over three-dimensional conformal radiotherapy (3DCRT) in the groin nodal basin. Fifteen consecutively treated patients (5 3DCRT and 10 IMRT) were selected. Optimized theoretical plans using the other modality were created - enabling direct comparisons of 3DCRT and IMRT. Target volume and organs at risk constraints were assessed as achieved or as having minor (≤5%) or major (>5%) deviations. The Wilcoxon signed-rank test was used to compare the dose received from each patient plan (3DCRT vs. IMRT), whereas the Mann-Whitney U-test was used to compare clinical plans with theoretical plans. Fisher's exact test was used to compare categorical data. Target coverage was achievable in most patients (major deviations - 1 IMRT and 3 3DCRT). Conformity index improved with IMRT - median 0.65, range 0.48-0.81, versus median 0.44, range 0.29-0.60 for 3DCRT; P value less than 0.001. All 3DCRT plans had major deviations for femoral head/neck constraints. Twelve and 13 IMRT plans achieved the high (V42<5%) and low (V36<35%) constraints; P value less than 0.001. IMRT delivered statistically significant lower doses to small bowel volumes up to 40 ml. There were no differences in beam numbers used nor dosimetric endpoints measured when clinical plans were compared with theoretical plans. IMRT appears to allow superior conformity of dose to the target volume while relatively sparing the adjacent the bowel and femoral head/neck. This may reduce toxicity while maintaining control rates.