Impact of treatment acceleration and its timing on the response of the rhabdomyosarcoma R1H of the rat to fractionated irradiation.
OBJECTIVE
In clinical practice a concomitant boost is usually given as a second daily dose to a reduced field. The question arises which part of treatment should be accelerated to achieve optimal tumor control. An experiment was performed on tumor bearing rats to determine the optimal timing of treatment acceleration for this experimental tumor system.


METHODS
Rhabdomyosarcoma R1H of the rat were treated applying 30 fractions in an overall treatment time of 40-42 days, up to total doses ranging from 67.5 to 97.5 Gy were administered. For control a standard treatment was given as continuous treatment applying one fraction per day. A boost of five additional fractions was given as a second fraction during 5 days. Three experimental arms received a boost either in the 1st, 4th, or in the last week of treatment. Treatment outcome was assessed using tumor control as endpoint.


RESULTS
All experimental arms proved more effective than the standard treatment. Treatment was most effective when the boost was administered in the 1st week of treatment. A TCD37% of 87.1 Gy (95% CI: 82.8 ... 92.7 Gy), 96.5 Gy (89.9 ... 107.1), and 107.3 Gy (97.2 ... 131.0) was determined, when the boost was given in the 1st, 4th, or last week of treatment, respectively. The observed difference between the experimental arms was statistically significant (p = 0.004).


CONCLUSIONS
Initially accelerated treatment schedules were found to be more effective for tumor control in an experimental tumor system.
Raabe
A
A
Abteilung für Strahlentherapie und Radioonkologie, Universität Hamburg, Germany. araabe@uke.uni-hamburg.de
Quaester
S
S
Dubben
H H
HH
Zieron
J O
JO
Krüll
A
A
Alberti
W
W
Beck-Bornholdt
H P
HP
D000818:Animals; D002455:Cell Division / Q000528:radiation effects; D002470:Cell Survival / Q000528:radiation effects; D019583:Dose Fractionation, Radiation; D004307:Dose-Response Relationship, Radiation; D008297:Male; D009368:Neoplasm Transplantation / Q000473:pathology; D051381:Rats; D011919:Rats, Inbred Strains; D012208:Rhabdomyosarcoma / Q000473:pathology / Q000532:radiotherapy*; D012983:Soft Tissue Neoplasms / Q000473:pathology / Q000532:radiotherapy*