Is there any impact of PET/CT on radiotherapy planning in rectal cancer patients undergoing preoperative IMRT?

BACKGROUND/AIM To investigate the effect of positron emission tomography-computed tomography (PET/CT)-based contouring on dosimetric parameters in rectal cancer patients undergoing preoperative intensity-modulated radiation therapy (IMRT). MATERIALS AND METHODS Preoperative radiation therapy plans with conformal radiotherapy (CRT) or IMRT were created and examined according to the CT- and PET/CT-based contouring of 20 rectal cancer patients, retrospectively. RESULTS The target volumes delineated with PET/CT were significantlylarger than the volumes created by CT (P= 0.043). Dose delivered to 98% of the planning target volume was high in IMRT planning contouring with CT and PET/CT compared with CRT planning, but the difference was not statistically significant (P = 0.056). Percent volumes receiving 105% of dose and 110% of dose were low in IMRT planning when compared with CRT (P < 0.0001 and P = 0.044, respectively). The volumes receiving 45 Gy for the small intestine, femur heads, and bladder and the maximum dose received by the bladder were significantly lower in IMRT. CONCLUSION We showed that the target volumes created with PET/CT are significantly larger than the target volumes created with CT and that IMRT provides lower radiation exposure to the tumor-free tissues compared to the CRT planning. The dosimetric results primarily favor IMRT planning in rectal cancer patients and consequently present the significant alteration in target volumes.