Comparison of Thermoplastic Cast Versus Knee Wedge/Foot Rest Immobilization Technique in the Treatment of Carcinoma Cervix with Conformal Radiation Therapy

A total of 58 patients who underwent concurrent chemo-radiation for carcinoma cervix were analyzed for magnitude of variation in daily treatment position with two immobilization methods, and its impact on the dose delivered to the organs at risk. Assessment was done with the help electronic portal imaging devices (EPID). The main endpoints of the study were to quantify and compare the total isocentric displacement among the knee rest foot rest and thermoplastic cast groups, and to correlate the effect of isocentric displacement with dose volume changes. The EPIDs were compared with the DRR and set-up errors were noted in X (medio-lateral) Y (antero- posterior) and Z (cranio-caudal) axes. Any variations above the prescribed limits were corrected accordingly before treatment and variations were noted. The root mean square variation in thermoplastic cast group ranged from 0.93 mm to 4.61 mm in X axis, 1.28 mm to 8.07 mm in Y axis, 1.19 mm to 9.49 mm in Z axis. In knee rest foot rest arm these variations are 1.27 mm to 6.05 mm in X axis, 0.91 mm to 4.8 mm in Y axis and 1.09 mm to 5.3 mm in Z axis respectively. P value was significant in Y direction. The total vector error in thermoplastic cast group is 6.308 ± 2.17, and for the knee rest foot rest group was 4.67 ± 1.48. The p value obtained was 0.002, which was statistically significant in favor of knee rest foot rest arm. The bladder, rectum, bowel dose mean differences after isocenter displacement were not statistically significant in both arms.