Treatment planning study to determine potential benefit of intensity-modulated radiotherapy versus conformal radiotherapy for unresectable hepatic malignancies.
OBJECTIVE
To compare intensity-modulated radiotherapy (IMRT) with conformal RT (CRT) for hypofractionated isotoxicity liver RT and explore dose escalation using IMRT for the same/improved nominal risk of liver toxicity in a treatment planning study.


METHODS
A total of 26 CRT plans were evaluated. Prescription doses (24-54 Gy within six fractions) were individualized on the basis of the effective liver volume irradiated maintaining < or =5% risk of radiation-induced liver disease. The dose constraints included bowel (0.5 cm(3)) and stomach (0.5 cm(3)) to < or =30 Gy, spinal cord to < or =25 Gy, and planning target volume (PTV) to < or =140% of the prescribed dose. Two groups were evaluated: (1) PTV overlapping or directly adjacent to serial functioning normal tissues (n = 14), and (2) the liver as the dose-limiting normal tissue (n = 12). IMRT plans using direct machine parameter optimization maintained the CRT plan beam arrangements, an estimated radiation-induced liver disease risk of 5%, and underwent dose escalation, if all normal tissue constraints were maintained.


RESULTS
IMRT improved PTV coverage in 19 of 26 plans (73%). Dose escalation was feasible in 9 cases by an average of 3.8 Gy (range, 0.6-13.2) in six fractions. Three of seven plans without improved PTV coverage had small gross tumor volumes (< or =105 cm(3)) already receiving 54 Gy, the maximal prescription dose allowed. In the remaining cases, the PTV range was 9.6-689 cm(3); two had overlapped organs at risk; and one had four targets. IMRT did not improve these plans owing to poor target coverage (n = 2) and nonliver (n = 2) dose limits.


CONCLUSIONS
Direct machine parameter optimization IMRT improved PTV coverage while maintaining normal tissue tolerances in most CRT liver plans. Dose escalation was possible in a minority of patients.
Eccles
Cynthia L
CL
Department of Radiation Oncology, Princess Margaret Hospital, University of Toronto, Toronto, ON, Canada.
Bissonnette
Jean-Pierre
JP
Craig
Tim
T
Taremi
Mojgan
M
Wu
Xia
X
Dawson
Laura A
LA
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006528:Carcinoma, Hepatocellular / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D007422:Intestines / Q000528:radiation effects; D008099:Liver / Q000528:radiation effects; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D020714:Maximum Tolerated Dose; D008875:Middle Aged; D011836:Radiation Tolerance; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013116:Spinal Cord / Q000528:radiation effects; D013270:Stomach / Q000528:radiation effects; D047368:Tumor Burden