Considerations and current status of treatment planning for proton FLASH radiotherapy
Radiation therapy(RT)plays an important role in tumor treatment.How to balance the tradeoff between tumor control probability and normal tissue complication probability is an important issue in radiotherapy.With a higher fractional dose,the normal tissue complication probability will increase;with a lower fractional dose,the tumor control probability will decrease.Recently,several studies have shown that the RT delivered at an ultra-high dose rate,e.g.,＞40 Gy/s,could potentially improve normal tissue sparing while maintaining tumor control,the so-called"FLASH effect".The FLASH effect makes it possible to improve the fractional dose to kill the tumor more efficiently while controlling the normal tissue complication probability.Moreover,the ultra-fast dose delivery of FLASH-RT makes it easier for intra-fractional motion management.Although the FLASH effect has been demonstrated in the irradiation of cells and animals,e.g.,mice,zebrafish,and pigs,there still are some obstacles to the clinical translation of the FLASH effect.One of the biggest problems is how to realize the ultra-high dose rate treatment planning with current machine capabilities.The photon,electron,and proton beams have demonstrated the FLASH effect.However,the clinical photon beam is hard to reach the dose rate threshold of FLASH-RT.While the clinical electron beam has shown the capability to deliver dose at an ultra-high dose rate,however,it is limited to treating the tumor located at a shallow depth.The proton has the dosimetric advantages to treat the tumor in-depth and eliminate the exit dose.Moreover,compared to electrons and photons,the proton has higher relative biological effectiveness and linear energy transfer,resulting in more efficient tumor killing.Most importantly,the proton beam is easy to deliver dose at an ultra-high dose rate with the current beamline.Hence,how to design the proton FLASH treatment plan has been drawing attention in radiotherapy.To provide available evidence for proton FLASH treatment planning comprehensively and systematically,this review summarized the relative articles searched from the year 2014-2023 in databases.This review first summarized the requirements to trigger the FLASH effect,which indicated the additional considerations for proton FLASH treatment plans,compared to conventional treatment plans.Then we focused on the capability of existing accelerators,including the accelerators that have been used in clinical treatment,i.e.,cyclotron and synchrotron,and other accelerators that have shown the potential to be used in clinical treatment.The beamlines of different dose delivery technologies were also discussed.Both the accelerators and beam lines determine whether it is possible to realize the ultra-high dose rate treatment plan delivery.As the dose rate is the main factor to trigger the FLASH effect and has not been defined clearly in proton FLASH-RT,we summarized the proposed definitions of dose rate for proton fields and discussed the characters of these definitions.And we summarized the proposed treatment planning strategies for proton FLASH-RT and discussed the prospects in clinical applications and existing shortcomings for clinical usage.We also summarized the pre-clinical experiments using proton beams.In the end,we prospected the future development of FLASH-RT.
万方数据
维普
