Intensity-modulated radiation therapy (IMRT) vs. 3D conformal radiotherapy (3DCRT) in locally advanced rectal cancer (LARC): dosimetric comparison and clinical implications

Abstract

PurposeTo compare target dose distribution, comformality, normal tissue avoidance, and irradiated body volume (IBV) in 3DCRT using classic anatomical landmarks (c3DCRT), 3DCRT fitting the PTV (f3DCRT), and intensity-modulated radiation therapy (IMRT) in patients with locally advanced rectal cancer (LARC).Materials and methodsFifteen patients with LARC underwent c3DCRT, f3DCRT, and IMRT planning. Target definition followed the recommendations of the ICRU reports No. 50 and 62. OAR (SB and bladder) constraints were D5 ≤ 50 Gy and Dmax < 55 Gy. PTV dose prescription was defined as PTV95 ≥ 45 Gy and PTVmin ≥ 35 Gy. Target coverage was evaluated with the D95, Dmin, and Dmax. Target dose distribution and comformality was evaluated with the homogeneity indices (HI) and Conformity Index (CI). Normal tissue avoidance of OAR was evaluated with the D5 and V40. IBV at 5 Gy (V5), 10 Gy (V10), and 20 Gy (V20) were calculated.ResultsThe mean GTV95, CTV95, and PTV95 doses were significantly lower for IMRT plans. Target dose distribution was more inhomogeneous after IMRT planning and 3DCRTplans had significantly lower CI. The V40 and D5 values for OAR were significantly reduced in the IMRT plans .V5 was greater for IMRT than for f3DCRT planning (p < 0.05) and V20 was smaller for IMRT plans(p < 0.05).ConclusionsIMRT planning improves target conformity and decreases irradiation of the OAR at the expense of increased target heterogeneity. IMRT planning increases the IBV at 5 Gy or less but decreases the IBV at 20 Gy or more.

The Impact of Novel Radiation Treatment Techniques on Toxicity and Clinical Outcomes in Rectal Cancer

“…Female gender was an independent factor associated with IMRT use, possibly explained by the large volume of small bowel in the pelvis among female patients who have undergone hysterectomy (15). Several retrospective dosimetric studies have compared 3DCRT to IMRT in patients treated with preoperative chemoradiation (16-21). IMRT significantly improved the OAR sparing while preserving excellent planning target volume coverage and conformity compared to 3DCRT (17-21).…”

“…IMRT was associated with a reduction in the volume of small bowel irradiated at levels ranging from 15 to 50 Gy (16-21). While some studies reported a reduction in the small bowel V15 with IMRT (17, 18, 20, 21), others did not find a difference compared to 3DCRT (19).…”

“…While some studies reported a reduction in the small bowel V15 with IMRT (17, 18, 20, 21), others did not find a difference compared to 3DCRT (19). As for the homogeneity index, some studies suggested that achieving high target dose conformity with IMRT could be at the expense of more dose inhomogeneity (16-18), while others reported an improvement in target dose homogeneity with IMRT (19-21). The latter could be explained by the various definitions of homogeneity index used throughout the different studies.…”

Feasibility of Image-Guided Radiotherapy for Elderly Patients with Locally Advanced Rectal Cancer

“…Less aggressive treatment in elderly rectal cancer patients has been reported to increase their cancer-specific mortality even though they may be diagnosed in less advanced stages [4]. New modalities of radiation treatment such as intensity-modulated radiotherapy (IMRT) may potentially decrease the rates of grade 3–4 acute toxicity and improve patient tolerance to chemoradiation by generating a steep dose gradient [5]. Preliminary results with IMRT are encouraging with fewer treatment breaks, less serious toxicities, and less hospitalization in patients with rectal cancer undergoing chemoradiation with various chemotherapy regimens [6].…”

Why and How Should We Measure the Long-Term Consequences of Rectal Cancer Treatment?

“…The use of adjuvant radiation with or without chemotherapy will only benefit a minority of patients yet expose many more to the risk of late treatment-related toxicity. Current areas of research include the intensification of concomitant chemotherapy with additional drugs [1][2][3] or biological agents [4] and the use of intensity-modulated radiotherapy [5] and intraluminal brachytherapy [6,7], all which require a meaningful assessment of their impact on both efficacy and long-term toxicity.…”