Abstract
ObjectivesTo compare treatment plans for helical tomotherapy (TOMO), volumetric modulated arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) for locally advanced rectal cancer (LARC).Materials and MethodsThis retrospective study from December 2010 to June 2013 included 20 patients with LARC who received neoadjuvant concurrent chemoradiotherapy (CCRT) with radiation doses of greater than 50.4 Gy. Dosimetric quality was evaluated based on doses to organs at risk (OARs), including small bowel, urinary bladder and bilateral femoral head, over the same coverage of the clinical target volume (CTV).ResultsIn supine comparison of IMRT with VMAT, VMAT treatment plan had a lower hot spot dose (p=0.0154) and better conformity index (CI, p=0.0036) and homogeneity index (HI, p=0.0246). Lower bladder V34.98 (p=0.0008), V40 (p=0.0058), mean dose (p<0.0001), femoral head mean dose (p=0.0089), V30 (p<0.0001), V40 (p=0.0013) and better CI (p<0.0001) and HI (p=0.0001) were observed for TOMO compared with IMRT. Patients with LARC receiving TOMO planning had lower bladder V34.98 (p=0.0021), V40 (p=0.0055), mean dose (p=0.0039), femoral head mean dose (p=0.0060), V30 (p<0.0001), and V40 (p=0.0044) and better CI (p=0.0157) and HI (p=0.0292) than VMAT. Comparing prone and supine position image planning, there were no significant differences, including in OARs in the three planning systems, except for lower bladder V34.98 (p=0.0403) in the supine position using TOMO.ConclusionsUsing modern radiation techniques, neither prone nor supine positions provide better values for OARs. TOMO was superior to IMRT and VMAT in sparing OARs and planning quality parameters.
Highlights
In Taiwan, preoperative chemoradiotherapy (CCRT) has become a widely accepted treatment modality for locally advanced rectal cancer (LARC)
Lower bladder V34.98 (p=0.0008), V40 (p=0.0058), mean dose (p
TOMO was superior to IMRT and volumetric modulated arc therapy (VMAT) in sparing organs at risk (OARs) and planning quality parameters
Summary
In Taiwan, preoperative chemoradiotherapy (CCRT) has become a widely accepted treatment modality for locally advanced rectal cancer (LARC). Other groups have revealed that preoperative CCRT is associated with significantly less acute and chronic toxicity, a lower local recurrence rate and a higher organ preservation rate than postoperative CCRT [1]. Patients with rectal carcinoma should be treated in the prone position to reduce the volume of the small bowel within the pelvis [4]. Due to the use of modern RT techniques, patients with LARC can be maneuvered to decrease the volume of the small bowel in the radiation field and to treat with a full bladder in the supine position with the use of bowel-displacement tools such as a foam board mound designed to push the full bladder posteriorly and cephalad. Acute and chronic small bowel and rectal toxicities may limit further dose escalation or lead to premature termination of the radiation course, potentially decreasing therapy effectiveness
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