Program Information
Adaptive Radiotherapy for Local-Regionally Advanced Nasopharyngeal Carcinoma - A Dosimetric Comparison Between IMRT and VMAT Planning
J Hu1*, J Wee1 , Z Master1 , A Hussain1 , P Haring2 , J Lee1 , (1) National Cancer Center Singapore, Singapore, Singapore,(2) German Cancer Research Center, Heidelberg, Heidelberg,
Presentations
SU-H4-GePD-J(B)-6 (Sunday, July 30, 2017) 4:30 PM - 5:00 PM Room: Joint Imaging-Therapy ePoster Lounge - B
Purpose: To investigate if IMRT planning is more sensitive to changes in anatomy and will require more frequent re-planning than VMAT for local-regionally advanced Nasopharyngeal Carcinoma (NPC), as IMRT has smaller MLC segments than VMAT plans.
Methods: Five patients undergoing concurrent chemo-radiotherapy were recruited for weekly CT simulation. Both IMRT and VMAT plans were generated on initial CT using the Eclipse TPS. IMRT plans were optimized using Dose Volume Optimizer and Progressive Resolution optimizer was used for VMAT plans. Initial plans were then re-calculated on the weekly CT data. Re-planning was initiated if evaluation plans failed the NPC planning evaluation criteria. A total of 86 plans were evaluated for dose and volumes changes for both targets and organs at risk (OARs).
Results: There is no difference in terms of frequency of re-planning required for IMRT or VMAT plans, despite a reduction in volume of up to 34.66% for the target volumes and 32.31% for parotids. PTV coverage for both IMRT and VMAT plans were comparable in all the recalculated plans. VMAT showed better homogeneity for the primary PTV 70Gy volume in the original plans as well as all the evaluation plans. 5 out of 39 OARs parameters showed increased doses in the evaluation plans using VMAT, but the mean increase in dose was only 0.29Gy (0.12-0.63Gy). For both IMRT and VMAT, most OARs showed a small trend of dose increase of not more than 5% from baseline value. However, the spinal cord and parotid had dose increments ranging between 5.26% and 58.89% towards the end of treatment.
Conclusion: Although IMRT plans are slightly more sensitive towards inter-fraction anatomic changes for PTV and OAR doses, the difference may be clinically insignificant and there is no difference between the requirement for adaptive re-planning across VMAT and IMRT plans.
Funding Support, Disclosures, and Conflict of Interest: The author have received research funding from National Medical Research Council of Singapore (NMRC)
Contact Email: