Simultaneous integrated boost (SIB) of the parametrium and cervix in radiotherapy for uterine cervical carcinoma: a dosimetric study using a new alternative approach.

Objective: To compare the dose distributions of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) using the simultaneous integrated boost (SIB) technique with that of the traditional midline block (MB) technique for boosting the parametrium in patients with cervical cancer. Methods: Treatment plans using VMAT or IMRT with the SIB technique (VMAT-SIB and IMRT-SIB) and IMRT followed by the MB technique (IMRT-MB) were generated for each of the 10 patients with cervical cancer. For the SIB plans, 45-Gy and 50-Gy dose levels in 25 equal fractions were set for the pelvis planning target volume 45 (PTV45) and the parametrial boost volume (PTV50), respectively. For the IMRT-MB plans, the parametrium was sequentially boosted with the MB technique (5.4Gy in three fractions) after pelvic IMRT (PTV45). Results: Volume receiving 100% of the prescribed dose or more coverage of the PTV50 was significantly better for VMAT-SIB and IMRT-SIB than that for IMRT-MB (99.08 and 99.31% compared with 91.79%, respectively; p < 0.05). VMAT-SIB and IMRT-SIB both generated significantly greater doses to the organs at risk (OARs) except for the volume receiving 50Gy or more doses, which were significantly lower for the bladder and bowel. Comparable results were achieved with VMAT-SIB and IMRT-SIB. Conclusion: The VMAT-SIB and IMRT-SIB techniques are promising in terms of dose distributions and tumour coverage, although these approaches might result in slightly higher doses of radiation to the OARs. Advances in knowledge: This is the first study to examine the feasibility of the SIB technique using IMRT or VMAT to boost the parametrium. The techniques dosimetrically produced better target coverage but resulted in slightly higher doses to the OARs.