**7. Summary**

**5.8. Criteria on plan change**

58 Radiotherapy

function such as COPD?

**6. Future directions**

decision‐making.

adaptation at all for the rest of treatment.

The criteria on when and how to adapt a plan can differ from institution to institution and depend on the attending physician and/or individual patient. There are several consider‐ ations during QA plan evaluations including: (1) Is there noticeable anatomic change? How will the anatomy change affect the dose? (2) How much does the PTV coverage change compared to the initial plan? Is the target coverage still acceptable? (3) How much does the normal tissue dose change? Is the normal tissue dose within tolerance? (4) How much is the dose deviation from the original plan? Will a re‐planning improve the dose distribution significantly? (5) How long does it take to have the revised plan ready for treatment? Will a treatment break be needed before the new plan becomes available? (6) How much are the cost and effort for a plan adaptation (e.g., whether new hardware fabrication was involved, or just some parameter change)? How many fractions are left? Is it worthwhile to make a plan change for the remainder of treatment? (8) Are there any special consideration for the patients, for example, does the patient need more sparing in lung due to pre‐existing lung

Change *et al.* reported that the main criteria for plan adaptation was whether CTV or GTV receives <95% of dose and whether doses for normal tissues such as heart and cord dose were out of tolerance [6]. At our center, in addition to looking into dosimetric effect such as the tar‐ get coverage and normal tissue dose, we take into account the potential clinical gain as well as the cost and time associated with plan adaptation to decide on whether and how to adapt a plan. For example, if the patient is close to the end of treatment and the clinical impact of plan adaptation is low, we may use a simple adaptation strategy like range adjustment or no

The technology of proton therapy is evolving very quickly, and many progresses are being made toward more accurate and efficient adaptive planning. Currently, only offline adap‐ tion has been reported in proton therapy due to the lack of accurate in‐room imaging system and long turnaround of manufacturing patient specific hardware for both PSPT and USPT. However, PBS has been increasingly used for lung cancer treatment, and CBCT and other in‐ room CT have become available. The advancement of both PBS and in‐room CT makes online adaptive planning possible in proton therapy in the future. Before online proton adaptive planning becomes a reality, many challenges need to be addressed. Better tools are needed for automatic image registration and dose accumulation, the dose calculation accuracy of in‐ room CT such as CBCT needs to be improved, and automatic and fast robust re‐planning and QA with IMPT should be developed. In addition, criteria on plan adaptation based on both dosimetric parameters and clinic outcome should be developed for quick and accurate

While adaptive planning is needed for proton therapy of lung cancer, it is time and effort consuming, and not every patient can benefit from this process. It would be helpful to be able to predict when adaptive planning is needed and for which patients. This would allow Adaptive planning is necessary for proton therapy treatment of lung cancer to maintain opti‐ mal dosimetric distribution when patient anatomy changes. To achieve optimal adaptive planning process and clinical outcome, we need to consider not only the benefits from the improved dosimetric distribution and potential clinical outcome with plan adaptation but also its cost and limitations, available resources, and potential risks associated with plan change. Better tools for image registration, dose accumulation, and plan automation are desired to make the plan adaption process more efficient and accurate. The plan adaptation process, for instances, the frequency of repeated CT scanning and the criteria for plan adaptation, needs to be adapted with institutional resource and experience. Online adaption in proton therapy can be feasible with the advancement of pencil beam scanning and in‐room CT, but many challenges, such as the limitation of the in room CT image quality, efficient robust proton re‐planning and quality assurance, need to be addressed before its clinical use.
