The utility of multimodality imaging with CT and MRI in defining rectal tumour volumes for radiotherapy treatment planning: a pilot study

• Published in: Journal of medical imaging and radiation oncology Vol. 54; no. 6; pp. 562 - 568
• Main Authors: Tan, J, Lim Joon, D, Fitt, G, Wada, M, Lim Joon, M, Mercuri, A, Marr, M, Chao, M, Khoo, V
• Format: Journal Article
• Language: English
• Published: Melbourne, Australia Blackwell Publishing Asia 01.12.2010
• Subjects: Adult; Aged; Contrast Media; Female; GTV; Humans; Image Enhancement - methods; Magnetic Resonance Imaging - methods; Male; Middle Aged; MRI; Pilot Projects; Prospective Studies; radiotherapy; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Conformal - methods; rectal cancer; Rectal Neoplasms - diagnostic imaging; Rectal Neoplasms - pathology; Rectum - diagnostic imaging; Rectum - pathology; target volume; Tomography, X-Ray Computed - methods; treatment planning; Tumor Burden
• ISSN: 1754-9477; 1754-9485
• DOI: 10.1111/j.1754-9485.2010.02212.x

Aims: This study compares the volumetric and spatial relationships of gross tumour volume (GTV) derived from CT (CT‐GTV) and GTV derived from MRI (MR‐GTV) to determine the utility of multi‐modality imaging for radiotherapy treatment planning in rectal cancer. Methods and Materials: Fifteen patients with T3 rectal cancer were accrued over 18 months. The male : female ratio was 2:1. The average age was 60.3 years (range 38–79). All patients underwent a diagnostic MRI and CT and MRI simulation. Data sets were co‐registered. A site specialised diagnostic radiologist contoured all volumes in consultation with a radiation oncologist. CT‐GTV was contoured while blinded to MR data sets. MR‐GTV was contoured independently 2–4 weeks later whilst blinded to its respective CT‐GTV data. Tumour volumes were analysed for three anatomical subregions (sigmoid, rectal and anal). Reference points on tumour volumes were used for spatial comparison and analysis. Results: The mean CT‐GTV/MR‐GTV ratio was 1.2 (range 0.5–2.9). The tumour volume ratios for the rectal subregion were well correlated. CT‐GTV provided adequate spatial coverage of tumour in reference to MR‐GTV with the average mean discrepancy of 0.12 (range −0.08–0.38) or a maximum discrepancy of <0.4 cm (1.54 standard deviation). CT‐GTV coverage was inadequate for tumours with MRI evidence of anal and sigmoid invasion. Conclusions: Conventional simulation CT imaging provided a reasonable estimate of the GTV. Multi‐modality imaging with staging MRI can assist target volume definition where there is involvement of the sigmoid and anorectal region and avoid geographic misses. The role of a simulation MRI may aid in this process but remains investigational.