Preoperative helical tomotherapy and megavoltage computed tomography for rectal cancer: impact on the irradiated volume of small bowel.
OBJECTIVE
Preoperative (chemo)radiotherapy is considered to be standard of care in locally advanced rectal cancer, but is associated with significant small-bowel toxicity. The aim of this study was to explore to what extent helical tomotherapy and daily megavolt (MV) CT imaging may reduce the irradiated volume of small bowel.


METHODS
A 3D-conformal radiotherapy (3D-CRT) plan with CTV-PTV margins adjusted for laser-skin marks (15, 15, and 10 mm for X, Y, and Z directions, respectively) was compared with helical tomotherapy (IMRT) using the same CTV-PTV margins, and to helical tomotherapy with margins adapted to daily MV-CT imaging (IMRT/IGRT; 8, 11, 7, and 10 mm for X, Y(ant), Y(post) and Z resp.) for 11 consecutive patients. The planning goals were to prescribe 43.7 Gy to 95% of the PTV, while minimizing the volume of small bowel receiving more than 15 Gy (V(15 SB)).


RESULTS
The mean PTV was reduced from 1857.4 +/- 256.6 cc to 1462.0 +/- 222.3 cc, when the CTV-PTV margins were adapted from laser-skin marks to daily MV-CT imaging (p < 0.01). The V(15 SB) decreased from 160.7 +/- 102.9 cc to 110.9 +/- 74.0 cc with IMRT and to 81.4 +/- 53.9 cc with IMRT/IGRT (p < 0.01). The normal tissue complication probability (NTCP) for developing Grade 2+ diarrhea was reduced from 39.5% to 26.5% with IMRT and to 18.0% with IMRT/IGRT (p < 0.01).


CONCLUSIONS
The combination of helical tomotherapy and daily MV-CT imaging significantly decreases the irradiated volume of small bowel and its NTCP.
Engels
Benedikt
B
Department of Radiation Oncology, Oncologisch Centrum UZ Brussel, Brussels, Belgium.
De Ridder
Mark
M
Tournel
Koen
K
Sermeus
Alexandra
A
De Coninck
Peter
P
Verellen
Dirk
D
Storme
Guy A
GA
D003967:Diarrhea / Q000209:etiology / Q000517:prevention & control*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D007421:Intestine, Small / Q000000981:diagnostic imaging / Q000528:radiation effects*; D008297:Male; D011832:Radiation Injuries / Q000150:complications; D011835:Radiation Protection; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000009:adverse effects / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects / Q000379:methods*; D012004:Rectal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden