COMPARISON OF 2 REPOSITIONING DEVICES USED DURING RADIATION-THERAPY FOR HODGKINS-DISEASE

Purpose: Patients irradiated for Hodgkin's disease are fixed in an imm obilization cradle to improve repositioning. In the early 1990s, we ch anged our cradle system from a ''short'' upper torso cradle to an exte nded near-total body cradle that also includes the lower torso and thi ghs. In this study, we assess the impact of the extended cradle on the reproducibility of patient repositioning during irradiation of Hodgki n's disease. Methods and Materials: A total of 782 port films of 56 pa tients treated immediately before and after the changeover were studie d to assess positioning reproducibility. Patients treated prior to 199 3 were positioned in the short cradle, while those treated 1993 and la ter were positioned in the extended cradle. All treatment were deliver ed via anterior and posterior fields and treatment areas above and bel ow the diaphragm mere considered separately and together. All treatmen t fields were simulated and the field shape was designed on anterior a nd posterior radiographs. Discrepancies in field placement between the simulation radiographs and subsequent port films were noted by a radi ation oncologist and requests for position adjustment (both translatio nal and rotational shifts) were noted. The number, magnitude, and dire ction of any physician-requested position adjustment on port films wer e retrospectively reviewed. For the purpose of scoring the frequency o f field misplacements, when an adjustment was noted on two port films taken during the same treatment session (i.e., a left shift on both an anterior and a posterior port film), it was scored as only one event. A two-tailed chi-square test was used to compare the differences in r equested shifts in the two patient groups. Results: The study populati on consisted of 56 patients (31 short and 25 extended cradle) represen ting 92 treatment sites. A total of 782 port films representing 450 tr eatment setups were analyzed (292 above and 158 below the diaphragm). When all port films above the diaphragm (mostly mantle fields) are con sidered, position adjustments were requested in 13.4% (21 out of 157) of treatment setups with the upper torso cradle and in 5.9% (8 out of 135) of treatment setups with the extended cradle (p = 0.054). When al l port films below the diaphragm (mostly paraaortic/spleen and pelvic fields) are considered, position adjustments were requested in 33.8% ( 27 out of 80) of treatment setups with the upper torso cradle and in 1 6.7 % (13 out of 78) of treatment setups with the extended cradle (p = 0.056). A reduction in the frequency of both translational and rotati onal adjustments were seen. When both treatment sites are combined, po sition adjustments were requested in 20.3% (48 out of 237) of treatmen t setups with the upper torso cradle and in 9.9% (21 out of 213) of tr eatment setups when the extended cradle was used (p = 0.0086). Conclus ions: The extended cradle provides superior repositioning of patients undergoing radiation therapy for Hodgkin's disease. Differences observ ed in setup accuracy in this study underscore the importance of aggres sive immobilization of patients with Hodgkin's disease. Increased accu racy of daily setup may provide an opportunity to improve the therapeu tic ratio both by increased likelihood of tumor control and decreased risk of normal tissue complications. (C) 1997 Elsevier Science Inc.