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Multi-Leaf Collimator Leaf Open Time Sinogram (LOTS) Based Patient Specific Quality Assurance: A Novel Approach for Total Marrow Irradiation

Rajesh T1*, Dayananda S1, G Krishnan1, A Manikandan1, M Noufal1, K Patro1, A Nambiraj N2, S Kaushik1, R Jalali1, (1) Apollo Proton Cancer Centre, Chennai, Tamil Nadu, India, (2) Vit University, Vellore India

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
There is no commercial detector-phantom combination to perform patient specific quality assurance (PSQA) for total marrow irradiation (TMI) plan delivered inhelical tomotherapy (HT). In this study, multi-leaf collimator leaf open time sinogram(LOTS) was investigated for PSQA of TMI patients.

Methods:
The LOTS based PSQA relies on radiation measurement using mega voltage computed tomography (MVCT) detectors available in RadiXact HT. The feasibility of this method was first validated for ten non-TMI patients, having complex treatment plan, by comparing reconstructed absolute dose (RAD) with ion-chamber and helical detector array (ArcCheck) measurement results. The RAD from LOTS was also compared with treatment planning system (TPS) calculated dose distribution using 3D gamma (?) analysis and dose volume histogram (DVH). The same comparison was extended for four TMI patients.

Results:
In all non-TMI patients both TPS calculated and LOTS RAD were within ±1.8% compared to ion chamber measurement, whereas TPS calculated absolute dose were within ±1.2% of LOTS RAD. The ArcCheck measured and LOTS reconstructed 2D/3D dose distribution also agrees with TPS calculation with mean (SD) 2D? of 99.28% (1.39%) and 3D?of 98.97% (1.36%) respectively for 3%,3mm criteria. The target DVH data from TPS and LOTS reconstruction agrees within 1.71% (0.47 ± 0.90%) for D99%.In the case of eight treatment plans of four TMI patients, the measured and TPS calculated absolute dose agrees within ±1.5%. The agreement between TPS calculated and LOTS RAD at eleven organs of each patient agrees with mean (SD) of 1.08%(0.51).The 3D? analysis between TPS calculated and LOTS reconstructed dose agrees above 92.0% with mean (SD) of 93.80±1.67 %.

Conclusion:
LOTS based PSQA is accurate and robust. It serves as an effective and efficient method of PSQA for HT treatment plans including very large volume TMI. This method is easily implemented in any busy radiation oncology facility without additional logistics

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Keywords

TBI, Tomotherapy, Quality Assurance

Taxonomy

TH- External Beam- Photons: tomotherapy

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