Radiation Physics

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TU_14_3256 - The Efficiency of Adaptive Intensity Modulated Radiation Therapy Treatment (IMRT) Planning in Nasopharyngeal Carcinoma (NPC) Using Deformable Auto-Segmentation (AS) and Knowledge-Based Planning (KBP)

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

The Efficiency of Adaptive Intensity Modulated Radiation Therapy Treatment (IMRT) Planning in Nasopharyngeal Carcinoma (NPC) Using Deformable Auto-Segmentation (AS) and Knowledge-Based Planning (KBP)
W. M. Hung, C. K. Sze, T. C. Fung, C. Y. Wong, M. C. H. Lee, and W. T. Ng; Pamela Youde Nethersole Eastern Hospital, Chai Wan, Hong Kong

Purpose/Objective(s): Significant anatomic changes as well as tumour shrinkage are not uncommon in radiation treatment of NPC. Timely adaptive planning is essential to correct for the resultant dose discrepancy from the original IMRT plan. However the re-planning process is time consuming and the correction would be delayed. This study compared the efficiency of re-planning using deformable auto-segmentation (AS) and Knowledge-Based Planning (KBP) with re-planning using conventional means.

Materials/Methods: A total of 20 consecutive NPC patients who had undergone adaptive re-planning for IMRT treatment between Nov 2016 and Aug 2017 were retrospectively studied. The re-planning usually took place in the 4th week of the 7-week treatment. For the conventional planning process, the organs-at-risk (OAR) and pseudo-structures (for IMRT optimization) were produced manually. The plans were optimized using universal template of dose constraints with, if necessary, manual editing of beam fluence afterwards. The re-planning was then repeated with OARs produced by an imaging informatics system by deforming those in the initial plan, and the optimization performed with the KBP system RapidPlan (Varian Medical Systems). Target volumes were all contoured by clinicians manually in both cases. Plan optimization was only stopped when the plans were deemed clinically acceptable. Times for structure contouring and IMRT planning were recorded for both the conventional process and re-planning employing AS and KBP. Student t-test was used to compare the performance of the two processes with significance level at p = 0.05.

Results:
Mean time (min) for: Conventional process Using AS and KBP
GTV and CTV contouring 48.5
OARs contouring 173.5 20.5
IMRT Planning 231.45 138.5
Total time of re-planning 453.45 207.5
All the plans were deems acceptable by a qualified oncologist. Using AS shortened the OAR contouring time significantly (p<0.05) although the target volumes were still contoured manually. Using KBP shortened the IMRT planning process significantly too (p<0.05). Hence, the time for the entire re-planning process can be reduced significantly with AS and KBP (p<0.05).

Conclusion: Our results showed that the whole re-planning process could be speeded up by more than 2 fold with the use of AS and KBP without jeopardizing the planning quality.

Author Disclosure: W. Hung: None. C. Sze: None. M.C. Lee: None. W. Ng: None.

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TU_14_3256 - The Efficiency of Adaptive Intensity Modulated Radiation Therapy Treatment (IMRT) Planning in Nasopharyngeal Carcinoma (NPC) Using Deformable Auto-Segmentation (AS) and Knowledge-Based Planning (KBP)



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