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The Application of Fallback Planning in IMPT for Head and Neck Cancers

Haijiao Shang/ RaySearch Labs; Yuenan Wang/ CAMS Shenzhen Cancer Hospital


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Fallback planning FP is a tool for creating additional plans to be used in a contingency situation, enabling a patient to be treated on another machine, possibly with a different modality and/or treatment technique.Many studies have proved that it is very useful in different treatment technique for photon therapy.However,limited studies have been conducted on FP between different modalities.The purpose of this study is to investigated the feasibility of FP by transferring three-filed IMPT plan to helical tomotherapy (HT) plan automatically for nasopharynx carcinoma (NPC)patients.

Methods: Five NPC patients were randomly and retrospectively selected for this study and approved by the local ethics committee.CTV-based robust IMPT plans are created in Raystation for each patient .For all plans,>=95% of clinical tumor volume(CTV) receive the prescribed 70.4 Gy(RBE) in 32 fractions.A standard set of 3 coplanar angles are selected (40°,180°,320°),which are adapted to the individual patients anatomy. Worst-case robust optimization are used to account for uncertainties in setup(±3mm)and beam range(±3%).The Monte Carlo(MC) algorithm is used to calculate the plan dose and perturbed dose. HT plans are generated atomically on FP with basic plan setting, such as dynamic jaw selection, 2.5 cm filed width, 0,287 pitch factors and so on.The feasibility with FP is proved by plan comparison respect to plan quality and plan robustness.

Results: For plan quality, HT plans presented similar target coverage and similar dose delivered to the Organ of risk, but increasing the low dose area.For plan robustness,IMPT led to more robust plans for both targets and organs.

Conclusion: FP can help to generate HT plans who have similar plan quality as IMPT,thus,can be a useful tool for patient treatment backup in the clinic where there is limited proton resource. However,the practicality of FP in NPC deserves further exploration when considering high low dose area and bad plan robustness.


Tomotherapy, Monte Carlo, Optimization


TH- External Beam- Particle therapy: Proton therapy - Development (new technology and techniques)

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