Abstract of Talk :
Proton beam Therapy (PBT) is increasingly adopted as a superior radiotherapy technique owing to its Bragg Peak characteristics, which allows sparing of surrounding normal tissue more effectively than modern photon radiotherapy techniques. PBT can potentially enhance clinical outcomes, quality of life, and prevent/reduce the radiation induced secondary cancers. However, only 2-3% of radiotherapy patients, currently receive PBT due to limited proton therapy (PT) facilities and cost-benefit justification. Nevertheless, over the last decade, the number of PT facilities have increased significantly, primarily due the technological development which have focussed on making cost effective, compact (single-room) PT facility rather than usual capital-intensive multi-room facility, to serve a broader group of oncology patients. Currently, more than 110 PT facilities are operational across the world and many more are under construction and planning stage. Apollo Proton cancer centre is the first multi-room PT facility in South-East Asia and Middle East which was clinically commissioned in Jan 2019.
In PBT, a narrow proton beam (70-250 MeV) accelerated either by cyclotron or synchrotron, is transported through a beam-line to the treatment room. Depending on the design of the “nozzle”, last part of the beam-line just before the beam enters the patient, a therapeutic dose can be delivered precisely to the tumour by spreading out the Bragg peaks of multiple proton energies either by using double scattering (DS) or pencil-beam scanning (PBS) techniques. During the process, proton interact with various materials while accelerating inside the cyclotron, transferring through the beam-line, treatment nozzle, patient specific beam shaping and range modulating devices and finally to patient. As a consequence, secondary stray radiations predominantly prompt neutron having wide energy spectrum ranging from thermal up to 230-250 MeV and photon up to ≈ 10 MeV are produced through intra nuclear cascade and evaporation. This causes a concern for radiation protection of staff and public.
A massive shielding barrier is therefore required to stop secondary radiations, especially high energy neutron for protection of occupational workers and general public from unwanted radiation. The shielding thickness can be calculated using analytical methods or more accurately using Monte Carlo (MC) codes [FLUCKA, MCNPX, GEANT 4] and computational models. However, designing the neutron radiation shielding for a PT facility presents several major challenges due to the uncertainties in the estimation of proton beam lost, neutron production and attenuation calculations. Even with the best available predictive tools, it remains large and difficult to estimate. Therefore, a detail measurement of total ambient dose equivalent H*(10) need to be carried out around the PT facility so as to ensure that the dose limit of radiation professional and public are within the stipulated limit.
Unwanted irradiation of patient from stray radiation is another concern of radiation protection while treating a clinical indication and it depend on proton delivery technique. In DS technique, beside two metal scatterers and range modulator present in nozzle, patient specific beam shaping devices made up of brass and 3D Tissue compensators are used resulting in production of secondary radiation sources in close proximity to the patient. In PBS technique, all these devices are replaced by a pair of scanning magnets resulting in a considerably lower stray radiation (neutron) compared with DS.
PBT of a patient entails a carefully orchestrated series of steps that include the following: a) preparation of customized patient immobilization device, b) 3D imaging (CT, MRI, PETCT), c) multi-modality image registration in the treatment planning system (TPS), d) delineation of tumour and critical organs in TPS, e) 3D modelling, simulation and dose computation of intended treatment plan using sophisticated dose calculation algorithms, f) seamless transfer of all treatment planning parameters from TPS to treatment delivery machine through oncology information system (OIS), g) assurance that planed dose in TPS is delivered in treatment machine, h) target localization on treatment delivery machine using on-bord imaging and i) treatment delivery. Any weak link in any of the stage may lead to compromise in treatment outcome and hence stringent quality assurance (QA) program must be design and implemented to guarantee that the intended dose is exclusively given to the tumour while maintaining the dose to the surrounding critical organs. The QA program must ensure that all the a) electro-mechanical, b) safety interlock, c) proton beam characteristics, d) integration of multi-modality equipment are functional and within their tolerance limit. In this talk, every facet of radiation safety concerning to general public, professionals, and patients will be discussed in a proton therapy facility.
Profile :
He has completed his Ph.D from Mumbai University. He has professional experience as chief medical physicist for last 15 years in his career of 25 years. Currently, he is Professor and Head Department of Medical Physics. Radiation Safety Officer (RSO) at Apollo Proton Cancer Center, Chennai.
He is the first Physicist to clinically commissioned the first Proton therapy Facility in South East Asia and Middle East. Recipient of many best paper awards in different international and national conferences. He is authored several papers in peer reviewed journals.