Dosimetric verification of treatment plans for TBI/TMI on helical tomotherapy.
PO-1886
Abstract
Dosimetric verification of treatment plans for TBI/TMI on helical tomotherapy.
1The Maria Sklodowska-Curie Greater Poland Cancer Centre, Department of Radiotherapy , Poznań, Poland
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Purpose or Objective
The aim of the study was to perform dosimetric verification with measurement array ArcCHECK® Sun Nuclear of 10 patients underwent the total body irradiation (TBI). Retrospective analysis included 10 plans created at helical Tomotherapy in Tomotherapy Planing System (TTPS), Precison Accuray .
Material and Methods
The 10 treatment plans of total body irradiation on helical Tomotherapy were prepared. Main assumption was to create treatment plans using <1000 number of iteration in TTPS. Subgroups stratified based on gender, age and body size were analyzed. For dosimetric purpose 9 independent verification plans for 3 random patients (child, adult women and adult man) were performed. Dosimetric verification plans were created for 3 regions of the body - H&N, thorax and pelvis - for each of 3 representative patients. All dosimetric verification plans were measured using measurement array ArcCHECK® - Sun Nuclear and evaluated with gamma index. In this study was used standard quality assurance criteria for IMRT. DTA (distance-to-agreement) and dose-difference criteria was setup as <3% for each measured point. The number of measured points in one verification plan was 1386.The threshold was determined as 5%. The number of points that meet assumption was determined as 95% of total measured points. The analyse was performed in global shift.
Results
Coverage of target by isodose 95% of prescribed dose were achieved for all 10 prepared treatment plans. At 8 from 10 treatment plans isodose 107% of prescribed dose cover less than 2% of irradiated volume. The initial criteria of mean dose in lungs less than 9 Gy were archived in all 10 treatment plans. Results of dosimetric verification was acceptable in six of nine treatment plans. During the verification with measurement array ArcCHECK® - Sun Nuclear only for 1 patient plan failed.
Conclusion
The method of dosimetric verification with measurement array ArcCHECK® - Sun Nuclear for total body irradiation plans at helical Tomotherapy (TTBI) can be use as reference’s method in in vitro dosimetry at helical Tomotherapy.