Gj. Frykholm et al., PREOPERATIVE RADIOTHERAPY IN RECTAL-CARCINOMA - ASPECTS OF ACUTE ADVERSE-EFFECTS AND RADIATION TECHNIQUE, International journal of radiation oncology, biology, physics, 35(5), 1996, pp. 1039-1048
Citations number
40
Categorie Soggetti
Oncology,"Radiology,Nuclear Medicine & Medical Imaging
Purpose: To explain a possible association between treatment technique
and postoperative mortality after preoperative radiotherapy of rectal
carcinoma, the dose distributions were compared in model experiments.
Methods and Materials: Preoperative radiotherapy with a three-beam te
chnique delivered in five fractions to 25 Gy (5 Gy/daily for 5 or 7 da
ys) was given to patients with primary resectable rectal carcinoma. Th
e adverse effects of this treatment, both acute and late, have been lo
w. In a parallel trial using an identical fractionation schedule and t
otal dose but with a two-beam technique, the postoperative mortality w
as higher. Two-, three-, and four-beam techniques were analyzed in 20
patients with computed tomography based, three-dimensional dose planni
ng. Dose distributions and dose-volume histograms in the planning targ
et volume (PTV) and in the organs at risk were considered. A numerical
''biological'' model was used to compare the techniques. Results: The
two-beam and the four-beam box techniques give the most homogeneous d
ose distributions in the PTV, although all techniques result in dose d
istributions that would be considered adequate, provided 16 MV or high
er photon energies are used. Three- and four-beam techniques show adva
ntages over the two-beam technique with respect to organs at risk, par
ticularly the small bowel. With the two-beam technique and the upper b
eam limit at mid-IA, the volume of the bowel that receives >95% of the
prescribed dose, and hence, is included in the treated volume (TV), i
s more than twice as large as that with three- and four-beam technique
s, and that of the total body between 1.5 and 2 times as large. The re
sults of the analyses using the biological model indicate that the thr
ee- and four-beam techniques result in less small bowel complication r
ates than the two-beam technique. The integral energy to the total bod
y is similar for all treatment modalities compared. Conclusions: The v
olume of bowel included in the TV, rather than the energy imparted to
the body, influences postoperative mortality, and emphasizes the impor
tance of precise radiotherapy planning to minimize normal tissue toxic
ity.