IMRT or conformal radiotherapy for adjuvant treatment of retroperitoneal sarcoma?

Purpose: To compare the dose distribution between three-dimensional conformal radiotherapy (3DCRT), intensity modulated radiotherapy (IMRT) with six coplanar beams (6b-IMRT) and IMRT with nine coplanar beams (9b-IMRT) during adjuvant radiotherapy for retroperitoneal sarcoma.

Methods and materials: The 10 most recent patients who had received adjuvant radiotherapy were reviewed. Three different treatment plans were generated (3DCRT, 6b-IMRT and 9b-IMRT) to deliver 50.4 Gy in 28 fractions. The dose delivered to the organs at risk (intestinal cavity (IC), contra- and ipsilateral kidney, liver, stomach and whole body), and the conformity index (CI) were compared.

Results: The integral dose to the intestinal cavity was similar with the three modalities but the dose distribution was different, with a change-over around 25 Gy: the V50 and the V40 were reduced five- and twofold, respectively, with IMRT compared to 3DCRT, and the V20 was increased by about 25% with IMRT. A similar integral dose was delivered to the whole body with the three modalities. The treated volume (V95 body) was approximately halved with IMRT compared to 3DCRT, and the CI was twice as good with IMRT than with 3DCRT. As expected, the V5 (body) was higher with IMRT compared to 3DCRT (p<0.0001) (a 12% increase with 6b-IMRT and a 21% increase with 9b-IMRT). Compared to 3DCRT, the mean dose delivered to the contralateral kidney increased from 1.5 to 4-4.4 Gy with IMRT. The number of monitor units was increased with IMRT, especially when nine beams were used instead of six.

Conclusions: As expected, IMRT greatly reduced the high-dose irradiated volume and increased the low-dose exposure of the intestinal cavity, with a change-over around 25 Gy, compared to 3DCRT. The conformity index was compellingly better with IMRT. The integral dose delivered to the whole body was conserved with both 3DCRT and IMRT. Longer follow-up is needed to assess late toxicities to the small bowel, contralateral kidney and the risk of second cancers.