A comparison of dosimetric and clinical parameters between different IMRT boost techniques in preoperative rectal...

In this study we compared the clinical and dosimetric outcomes of simultaneous integrated boost intensity modulated radiation therapy (SIB-IMRT) and sequential boost (SEQ-IMRT) techniques in preoperative rectal cancer (RC).

We analyzed 67 preoperative RC patients who received RT with Helical TomoTherapy (HT) device. 27 of patients were irradiated with SEQ-IMRT and 40 were irradiated with SIB-IMRT technique. The primary tumor and involved lymph nodes were simultaneously treated using the SIB-IMRT (50.4Gy/25 fraction). SEQ-IMRT delivered 45Gy/25 fractions to primary tumor (involved lymph nodes) and 5.4Gy/3fractions to boost volume. Dosimetric parameters, acute toxicities and 5year overal survival (OS), disease-free survival (DFS) and local control (LC) between two techniques were compared.

In the SIB-IMRT group planning treatment volume (PTV) homogeneity index (HI) was better than in the SEQ-IMRT group. PTV doses of Dmax for SEQ-IMRT group were higher than the SIB-IMRT group (p<0.05). The bladder doses of Dmax in the SIB-IMRT group were higher than SEQ-IMRT group (p<0.005). There were no significant differences in other dosimetric parameters between groups. Median follow up was 29.06 months (range 4.3-92.07) and 36.46 months (range 8.7-79.6) in the SIB-IMRT and SEQ-IMRT groups, respectively. No significant difference was found between the SIB-IMRT and SEQ-IMRT groups in acute toxicity (p=0,909). Five-year OS, DFS and LC were 73.15%, 66.75% and 75.55% in SIB-IMRT group and 65.19%, 55.53% and 60.22% in the SEQ-IMRT group, respectively. No statically significant differences were found between the two groups regarding 5-year OS, DFS and LC.

SIB-IMRT and SEQ-IMRT tecniques provided similar outcomes for dosimetric and clinical results for RC in HT treatment.