Simultaneously integrated boost (SIB) spares OAR and reduces treatment time in locally advanced cervical cancer

We performed a dosimetric comparison of sequential IMRT (sIMRT) and simul-taneously integrated boost (SIB) IMRT to boost PET-avid lymph nodes while concurrently treating pelvic targets to determine the potential of SIB IMRT to reduce overall treatment duration in locally advanced cervical cancer. Ten patients receiving definitive radiation therapy were identified retrospectively. RTOG consensus guidelines were followed to delineate the clinical target volume and organs at risk (OAR), which were then expanded per IMRT consortium guidelines to yield the planning target volume (PTV). Dosimetric parameters for PTVs and OAR including conformity (CI95%) were collected and compared using Wilcoxon signed-rank tests with Bonferroni correction. The median PTV volume was 1843 cc (1088-2225 cc) and the median boost volume was 43 cc (15-129 cc). Comparable target volume coverage was achieved with sIMRT and SIB plans, while hot spots were significantly reduced using SIB. SIB plans improved sparing for all OAR, though only rectum and small bowel doses were statistically significant. Comparing sIMRT and SIB plans averaged over all patients, rectal doses were V45: 70.8% vs. 64.5% (p = 0.002) and 0.1 cc: 50.7 Gy vs. 48.7 Gy (p = 0.006). For small bowel, sIMRT and SIB IMRT plans yielded V45: 13.4% vs. 11.4% (p = 0.006) and 1 cc: 54.4 Gy vs. 52.6 Gy (p = 0.006), respectively. Doses to femoral heads and blad-der trended towards significance in favor of SIB plans. The mean treatment time was 25 versus 29 days for SIB and sIMRT plans, respectively. When compared to sIMRT, SIB for treatment of nodal targets provides a significant, but small, dose reduction (3.8%-4.4%) to OAR, which leads to comparable biological dose despite higher fractional doses. Furthermore, SIB IMRT reduces overall treatment time and simplifies the planning process, and should be considered for targeting PET-positive nodal disease in patients with locally advanced cervical cancer.