Focal dose escalation using FDG-PET-guided intensity-modulated radiation therapy boost for postoperative local recurrent rectal cancer: a planning study with comparison of DVH and NTCP

BACKGROUND: To evaluate the safety of focal dose escalation to regions with standardized uptake value (SUV) >2.0 using intensity-modulated radiation therapy (IMRT) by comparison of radiotherapy plans using dose-volume histograms (DVHs) and normal tissue complication probability (NTCP) for postoperative local recurrent rectal cancer METHODS: First, we performed conventional radiotherapy with 40 Gy/20 fr. (CRT 40 Gy) for 12 patients with postoperative local recurrent rectal cancer, and then we performed FDG-PET/CT radiotherapy planning for those patients. We defined the regions with SUV > 2.0 as biological target volume (BTV) and made three boost plans for each patient: 1) CRT boost plan, 2) IMRT without dose-painting boost plan, and 3) IMRT with dose-painting boost plan. The total boost dose was 20 Gy. In IMRT with dose-painting boost plan, we increased the dose for BTV+5 mm by 30% of the prescribed dose. We added CRT boost plan to CRT 40 Gy (summed plan 1), IMRT without dose-painting boost plan to CRT 40 Gy (summed plan 2) and IMRT with dose-painting boost plan to CRT 40 Gy (summed plan 3), and we compared those plans using DVHs and NTCP. RESULTS: D(mean) of PTV-PET and that of PTV-CT were 26.5 Gy and 21.3 Gy, respectively. V50 of small bowel PRV in summed plan 1 was significantly higher than those in other plans ((summed plan 1 vs. summed plan 2 vs. summed plan 3: 47.11 +/- 45.33 cm3 vs. 40.63 +/- 39.13 cm3 vs. 41.25 +/- 39.96 cm3 (p < 0.01, respectively)). There were no significant differences in V30, V40, V60, D(mean) or NTCP of small bowel PRV. CONCLUSIONS: FDG-PET-guided IMRT can facilitate focal dose-escalation to regions with SUV above 2.0 for postoperative local recurrent rectal cancer.