Room: Karl Dean Ballroom C
Purpose: TBI treatment at our institution has moved from traditional hand calculation to CT-based planning to incorporate dose heterogeneities and organs at risk dose limits. The main objective of this work is to report our institutional experience with CT-based TBI and to show a comparison with the traditional approach.
Methods: Ten patients were CT simulated supine with arms immobilized for lung shielding. Legs are separated to achieve a width similar to umbilicus separation; rice bags were placed between the legs for compensation. Four plans (P1, P2, P3 and P4) were created for each patient, all prescribed at midplane-umbilicus. The first three plans use lateral 15X beams, with head compensation. P1 was planned using a hand calculation. P2 includes heterogeneity corrections and inferior subfield to improve coverage. P3 includes heterogeneity corrections, inferior subfield, and adjustment of field weights to maintain coverage while keeping mean lung doses below 10.5Gy (prescription dose 12Gy). P4 uses AP-PA 6X beams. Dose to target (mean, max, D98%, D95%, min), mean lung and liver doses are calculated for all plans; reported doses when unitless and normalized to prescription dose.
Results: Coverage of the target (Body-2cm), indicated by D98% was 84.1Â±2.8, 84.7Â±3.9, 81.0Â±1.8, and 92.2Â±1.9 whereas the maximum doses were 123Â±5, 135Â±4, 129Â±4, and 124Â±5 for P1, P2, P3, and P4 respectively. The mean relative lung and liver doses were lowest for P3 with values of 87.8Â±0.5 and 89.8Â±3.4. The largest mean lung dose (12.5Gy) was observed for P4 plan as expected, showing the necessity of using lung shielding.
Conclusion: We are able to achieve target coverage of D98%>80%, keeping the mean lung and liver doses <90% of prescription using optimal arm positioning and subfields. This approach is easy to implement without the complexity of introducing lung shielding required with the use of 6X AP-PA beams.
Not Applicable / None Entered.