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document
Accuracy of pelvic radiotherapy : prospective analysis of 90 patients in a randomised trial of blocked versus standard radiotherapy . The aim of this study was to assess the accuracy of pelvic radiotherapy during a trial of blocked radiotherapy at the Royal Marsden Hospital , UK . Prospective evaluation was performed on 90 patients receiving CT planned pelvic radiotherapy using weekly anterior-posterior and lateral portal films . Field placement errors ( FPEs ) were calculated by comparing field centres of each film with a designated point of interest . Data was evaluated to calculate the overall treatment simulator differences , the number of error free treatments , and mean treatment-simulator position and to evaluate the role of systematic versus random errors . Age , weight , disease site , position of treatment , fractionation , blocked versus conventional techniques were assessed for their effect on treatment accuracy . The mean absolute error between treatment and simulator films was anterior right-left ( ARL ) 0.25 cm , anterior superior-inferior ( ASI ) 0.32 cm , lateral anterior-posterior ( LAP ) 0.42 cm , and lateral superior-inferior ( LSI ) 0.28 cm . On average the field centre was displaced by 0.66 cm ( standard deviation , S.D . = 0.34 ) from that intended . On each treatment day 29 % of anterior films and 45 % of lateral films had at least one 0.5 cm error . Overall 59 % of treatments had at least one 0.5 cm error and 9 % a 1.0 cm error . The field centre was more than 0.5 cm from the position intended in 66 % of treatments and over 1 cm for 14 % of treatments . Analysis of variance showed that both random and systematic errors occurred in all directions . Though random errors were of similar magnitude in all direction ( variance sigma 2 = 0.06-0.09 cm2 ) ; systematic errors showed a 4-fold variation being greatest in the LAP direction ( sigma 2 = 0.19 cm2 ) and least the ARL direction ( sigma 2 = 0.048 cm2 ) . No factor consistently predicted for worse outcome in all directions . Hypofractionated treatments were less accurate in the LSI direction ( P > 0.05 ) . Systematic errors were associated in the ARL direction with hypofractionation ( P < 0.01 ) and , in the LSI direction with weight ( P < 0.03 ) and age ( P < 0.05 ) . We conclude that significant random and systematic errors can occur during pelvic radiotherapy especially in the LAP direction . These results suggest that in the absence of a customised immobilisation device , to cover 95 % of errors , margins of 0.6 cm for RL and SI directions and 0.9 cm for AP direction should be allowed between the planning and clinical target volumes . However , ideally , each centre should determine their own margin requirements according to local clinical practice .
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Intervention_Physical
radiotherapy
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Intervention_Physical
radiotherapy
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Intervention_Physical
CT planned pelvic radiotherapy
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Intervention_Physical
radiotherapy
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Outcome_Other
accuracy
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Outcome_Mental
Field placement errors ( FPEs )
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Outcome_Mental
overall treatment simulator differences , the number of error free treatments , and mean treatment-simulator position
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Outcome_Mental
evaluate the role of systematic versus random errors .
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Outcome_Other
Age , weight , disease site , position of treatment , fractionation , blocked versus conventional techniques
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Outcome_Mental
mean absolute error
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Outcome_Other
accurate
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Outcome_Mental
Systematic errors
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Participant_Condition
pelvic radiotherapy
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Participant_Sample-size
90
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Participant_Sample-size
90
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Participant_Condition
pelvic radiotherapy