 dose falloff rate improves. Therefore, a large number of radiation beams focus on a target to create a high dose region around the target at the point of intersection of the beams. Intuitively, if the number of beams is increased, the contribution of each beam inevitably decreases, resulting in a lower dose to the tissues and structures some distance away from the target. This is because more beams pass through different parts of the body at lower radiation doses but collectively provide the same radiation dose to the target.
However, in these conventional radiation treatments the number of radiation beams is constrained to several hundred beams due to various spatial and physical constraints. For example, in Gamma Knife® radiosurgery, the number of radiation beams is limited to about two hundred beams. Physically, it is not possible to drill a large number of apertures in a fixed size metal screen without eventually causing interference among the beams escaping from the apertures.
For intensity-modulated radiation therapy (IMRT), it is usually not practical to deliver more than a dozen beams due to prolonged treatment time. Even with rotational techniques, such as Tomotherapy, intensity-modulated arc therapy (IMAT), volumetric modulated arc therapy (VMAT), and arc-modulated radiation therapy (AMRT), the maximum number of radiation beams is still limited to a few hundred.
Fundamental Physics Underlying Photon Radiosurgery:
The fundamental physics underlying photon-based radiosurgeries includes high energy photon production and photon interactions with matter.
Generally, high energy photons used in current radiosurgeries are produced either by radioactive decay from Cobalt-60 sources or bremsstrahlung interactions in a linear accelerator. In the linear accelerator, electrons are accelerated in an electric field to a high energy and then collide with a metal target. This generates radiation particles or photons in a bremsstrahlung process. The photons produced from Cobalt-60 are called “γ-ray” or gamma rays whereas the photons produced from a linear accelerator are called “X-ray” or X-rays.
Typically photons produced by different sources are heterogeneous in energy. For example, the energies of γ-rays emitted by Cobalt-60 are 1.17 and 1.33 MeV. The energy spectrum of X-rays from a linear accelerator shows a continuous distribution of energies for the bremsstrahlung photons superimposed by characteristic radiation of discrete energies. The energies of photon beams created by a 6 MV accelerator are continuous from 0 to 6 MeV with a large number of
dose falloff rate improves. consequently, a big number of radiation beam concenter on a target to create a gamey acid region around the prey at the point of intersection of the beam. Intuitively, if the number of beams is increase, the contribution of each radio beam inevitably decreases, resulting in a lower dose to the tissue and structures some distance away from the target. This is because more beam pass through different parts of the body at low radiation doses but collectively provide the same radiation sickness dose to the target. 
 However, in these conventional radiation treatments the number of radiation beams is constrained to several hundred beams due to various spatial and physical constraints. For example, in Gamma Knife ® radiosurgery, the number of radiation radio beam is limited to about two hundred balance beam. Physically, it is not possible to drill a large number of aperture in a fixed size metal screen without eventually cause interference among the beams escaping from the apertures. 
 For intensity - modulated radiotherapy therapy (IMRT), it is usually not practical to deliver more than a dozen balance beam due to prolonged discussion meter. Even with rotational techniques, such as Tomotherapy, intensity - modulated arc therapy (IMAT), volumetric modulate arc therapy (VMAT), and arc - modulated radiation therapy (AMRT), the maximum number of radiation beams is still limit to a few hundred. 
 Fundamental Physics Underlying Photon Radiosurgery: 
 The fundamental physics underlie photon - based radiosurgeries include high department of energy photon production and photon interactions with topic. 
 Generally, high energy photons used in current radiosurgeries are produce either by radioactive decay from Cobalt-60 sources or bremsstrahlung interaction in a linear accelerator. In the linear accelerator, electrons are accelerate in an electric field to a high department of energy and then collide with a metal target. This generates radiation particles or photons in a bremsstrahlung summons. The photons produced from Cobalt-60 are called “ γ - ray ” or gamma rays whereas the photon produced from a linear catalyst are call “ X - ray ” or X - rays. 
 Typically photons produce by different sources are heterogeneous in department of energy. For example, the department of energy of γ - rays emitted by Cobalt-60 are 1.17 and 1.33 MeV. The energy spectrum of adam - rays from a linear accelerator show a continuous distribution of energies for the bremsstrahlung photons superimpose by characteristic radiation of discrete energies. The energies of photon beams created by a 6 MV accelerator are continuous from 0 to 6 MeV with a large number of
 dode falloff rate improves. Therefore, a latgw numbxr of rzdiation beams focus on a target to rreare a yigh dose region arouna the tarhet at tye piunt of intxdsectiok of fme becmw. Intuitively, lf the numbar of beams is ivcxeased, the contribution of each beam inevitsbpy decreases, rgsultpnd in a lower dose to the tissues and sfructurts some distance aeay from the target. This id befause more beams pwss through difswrent parts uf the bodj at lower tadiation doses but collectively provnde the samg dafhation dose to tre target.
Howcner, in dhese cpnventional raciavion treatments the numbec of radiation beams is constsanned to several hundrwd beamv dua to carkoua xpztial wnd physical donstraints. For example, in Gamka Jnife® radiosudgery, ehq number of radiation beams is limited uo abkut two hundred beams. Pyysically, it is not plssible tj drill a large number of apertures in a fixed sise mevau sevcen dutjout eventually causing interference among thq btamx escaping froi the apertirfs.
Gjr intensity-mudulatzs dadiation therapy (LMRT), it is uwually nou pravtical to deliver more than a dozen beaiw due to prolonged treatment cime. Efen woth rotational techniquzs, sucg as Tomothfrapy, intsvsity-modulated afc nherdpy (IMAT), volumetric modulaeed arc tierapv (VMAT), avd atc-modulwted radiahion bverapy (AMRT), the madimum ngmber of rwdiation beams is still limited to a few hundted.
Xungamental Physlcs Underlying [hoton Radiosutgery:
The yundamdntal physpcs undernying photog-based radiosgtgeries incluves high qnerty pyoton pfuduction and pnoton intvrcctions wuth matter.
Generalln, higf energy photons ustd in current raciorurdegiex wse produced aithdr cu radkoactivt dccah frpm Cobalt-60 sources or brejsstrahlung interavtlons in a linear wccelerator. Im the linear acceltrator, elxctronx ate accelerated in an electric fjeld to a hinh energy and thek cojlide with a metal target. This generates radiatioi particles or photons un a bremsstrahlung krocess. The piotons produced from Cobalt-60 are caloed “γ-ray” or gamma vays whereas the photohs proguced from a linear accelerator are called “X-ray” or X-rays.
Typically photons prodyced bb qifferent skurcrs arv hztexogeneots ii xnergy. For examplv, the energies of γ-rays emitted bb Cobalt-60 ase 1.17 and 1.33 MeV. The energy spectrim of X-rays froo a linear accelerator sgows a cpntinuous distribution of energoes for the bremsstrahlukg photonw supsrimposed uy characteristic raciatiou of duscrete enevgies. The enereiex lf photon beaks created by a 6 MV accelerator arw contunkous from 0 to 6 MxV with a lavgt numbet of
dose falloff rate improves. Therefore, a large radiation focus on target to create the at the point intersection of the Intuitively, if the number of beams increased, the contribution of each beam inevitably decreases, resulting in a lower dose the tissues and structures some distance away from the target. This is because beams through parts the body at lower radiation doses but collectively provide the same radiation dose to the target. in these conventional radiation treatments the number of beams is constrained to hundred beams due to various and constraints. For in Knife® the number of beams is limited to about two hundred beams. Physically, it is not possible to drill a large of apertures fixed size screen eventually interference among the from the apertures. For intensity-modulated radiation is usually not practical to deliver more than dozen beams to prolonged treatment time. Even with techniques, such as Tomotherapy, intensity-modulated arc therapy (IMAT), modulated arc therapy (VMAT), and arc-modulated radiation therapy (AMRT), the maximum number of radiation beams limited to a few Fundamental Physics Underlying Radiosurgery: fundamental underlying radiosurgeries includes energy photon production and photon interactions with matter. Generally, high energy used in current radiosurgeries are produced either by radioactive decay sources bremsstrahlung interactions in linear accelerator. In the accelerator, are accelerated in an to high collide a target. This generates radiation or photons in a bremsstrahlung The photons produced from gamma rays whereas the photons produced from a accelerator are called “X-ray” or X-rays. Typically produced by different sources are heterogeneous in energy. For example, the energies γ-rays emitted are 1.17 and 1.33 MeV. The energy spectrum X-rays from a linear shows a continuous distribution of energies for the bremsstrahlung superimposed characteristic radiation discrete energies. The of photon beams by a 6 are continuous 0 6 large number of
 dose falloff rate improves. ThErefore, a laRge nuMbeR of RaDiatIon bEams focus on a taRGet tO create a high dose region ArounD tHE tarGEt At the Point of INtERSecTiOn Of tHe BEaMs. IntUitIvely, if The number oF beAmS is increased, THe ContributiOn oF each beam ineVitAbly deCrEasES, resuLtiNg in a Lower dOSe to thE tissues aNd STructuREs some dISTaNce aWay from the target. THIs IS because more beAms pasS tHRoUGH diFfeRent parts oF tHe bodY At lower RAdIATIon DOses but collecTively proviDE thE same rAdIatIOn dose To the TaRGet.
however, in thEse cOnventionAl radiATion treATments tHe numbEr oF raDiatIOn BeAms Is COnsTRaIneD To sEveral huNdReD beamS due TO VARiouS spAtiaL and pHysical constrAinTs. FoR ExaMple, iN GammA KniFe® RadioSurgerY, the nUmBer of radiation bEams Is limited To aBoUt tWo HundrED beams. phySicAlly, it iS not posSIblE tO DRIlL a large number of apeRtUREs In a fixed Size meTAl ScREen withoUt EveNtuaLLY causIng iNTeRference Among tHE bEaMs escapInG from tHe ApeRtuRes.
FoR InteNsity-mOdulated RadiaTIon therapy (IMRT), IT is usually not PRaCTIcAL to dEliVer more than A dozEN beaMs duE To ProLOnged TreatMeNT tIMe. Even with rotationaL tEchniqUes, suCh as TomotheraPy, intensitY-MODulated aRc thERaPY (IMAT), volumetriC moduLated arc thERapy (VMAT), And arC-modulatEd radiatiON Therapy (AmRT), The MaxImuM NUmBer of radiatioN BEams Is Still liMitEd to a feW huNdrEd.
FUndAmEntal PhysIcs UnderLyInG PHoTon radioSUrgery:
ThE fUndAmEntAl phySIcs undErlyiNg phOtOn-BAseD radiosURgERIes iNcLuDes hIgh EnErgy pHotoN ProDuction And photon IntERactIoNs With matTer.
Generally, hIgH energy phoToNs uSed in cURRent radiOsurgeries are produced eiTHer by raDioActivE decAy from CobAlt-60 SourceS or BRemsstRahlunG inteRaCtiONS in a lINEaR acCeLerator. In tHE LinEar acCeLeraTor, elecTrons are accelerateD In aN electric fielD to A higH ENeRgy ANd THen CoLLidE WIth a metal target. this generaTeS RaDiation parTIclEs Or photoNs in a brEmsstRAhlung pRocess. The Photons prOdUced FROm CObalt-60 are caLled “γ-ray” Or gamma raYS wherEAs The phOtoNs prodUcEd fRom a lInear aCCelEratoR are caLlEd “X-ray” Or X-raYs.
typicallY photons produced by diffeRent soUrces Are HeterogenEouS In eNergy. For eXampLe, the energIes Of γ-Rays eMitTEd by CObalT-60 ArE 1.17 anD 1.33 meV. ThE eneRGy spectruM Of x-raYS FrOm a linear acCELEraTor shOws A ContinUous Distribution of eneRGies for the bremSstrAHLunG phOTons SuPerimposed by chAraCtERIstic radIaTion of discrEte energIeS. the enErgies Of photOn beams CREaTEd by a 6 Mv accEleRator are cOntInUOus from 0 To 6 mev With a lArge NuMber of
 dose falloff rate improve s. Therefo re, a  la rge  n umbe r of  radiation bea m s fo cus on a target to cre ate a  h i gh d o se  regi on arou n dt h e t ar ge t a tt he  poin t o f inter section of  th ebeams. Intui t iv ely, if th e n umber of bea msis inc re ase d , the  co ntrib utiono f each  beam ine vi t ably d e creases , re sult ing in a lower do s et o the tissuesand st ru c tu r e s s ome  distanceaw ay fr o m the t a rg e t .  Th i s is becausemore beamsp ass  throu gh  di f ferent  part so f t he body atlowe r radiati on dos e s but c o llectiv ely pr ovi dethes am erad ia t ion do set o t he targe t. 
H oweve r, i n t h esecon vent ional  radiation tr eat ment s  th e num ber o f ra di ation  beams  is c on strained to sev eral  hundredbea ms  du eto va r ious s pat ial  and ph ysicalc ons tr a i n ts . For example, inGa m m aKnife® r adiosu r ge ry ,  the num be r o f ra d i ation  bea m sis limit ed toa bo ut  two hu nd red be am s.Phy sical l y, i t is n ot possi ble t o  drill a large number of ape r tu r e si n afix ed size met al s c reen  wit h ou t e v entua lly c au s in g  interference among  t he bea ms es caping from t he apertur e s . 
For int ensi t y- m odulated radia tiontherapy (I M RT), itis us ually no t practic a l  to deli ver  mo retha n adozen beams d u e  topr olonged  tr eatment  ti me.  Ev enwi th rotati onal tec hn iq ue s,  su ch as Tomother ap y,in ten sity- m odulat ed ar c th er ap y  (I MAT), v o lu m e tric  m od ulat edar c the rapy (VM AT), an d arc-mod ula t ed r ad ia tion th erapy (AMRT),  t he maximum  n umb er ofr a diationbeams is still limitedt o a few  hu ndred .
Fu ndamental  Ph ysicsUnd e rlying  Photo n Rad io sur g e ry:
T h e  f und am ental phys i c s u nderl yi ng p hoton-b ased radiosurgerie s  in cludes high e ner gy p h o to n p r od u cti on and p hoton interacti ons with m at t er .
Generall y , h ig h energ y photo ns us e d in cu rrent rad iosurgeri es  are p rod uced eithe r by rad ioactived ecayf ro m Cob alt -60 so ur ces  or b remsst r ahl ung i nterac ti ons in  a li ne ar accel erator. In the linear a cceler ator,  el ectrons a rea cce lerated i n an  electricfie ldto ahig h  ener gy a n dthe n  coll idew ith a met a ltar g e t.  This gener a t e s r adiat ion partic lesor photons in a b r emsstrahlung p roce s s . T hep hoto ns  produced from  Co ba l t -60 areca lled “γ-ray ” or gam ma rayswherea s thephotons p ro d uced f roma l inear acc ele ra t or areca ll e d “X-r ay”or  X-ray s.
Typ i call y photons produced  by d i f feren t  so urces  a re hete r ogen eous in en ergy. For e xample , th e ene rgies o fγ-rays  em it ted by Cob a lt-60 are  1.17  and 1. 33  MeV . T he ene rgys p ectru m of  X -ra ys from a l in e ar  a c cel erat or sh ow s acontinuou s  distrib uti o n of en er gie s for th e  b r e msstrahlun g p hoton s superimpos e d by ch a racte ristic  radia tion of dis cr ete ene rgi e s . The ene rgies ofp hot on  bea ms creat ed  bya6 M Vaccelerator are  continu ous from 0  to 6MeV with a larg enumber of
 dose_falloff rate_improves. Therefore, a large_number of_radiation_beams focus_on_a target to_create a high_dose region around the_target at the_point_of intersection of the beams. Intuitively, if the number of beams is increased, the_contribution_of each_beam_inevitably_decreases, resulting in a lower_dose to the tissues and_structures some_distance away from the target. This is because_more_beams pass through_different parts of the body at lower radiation doses_but collectively provide the same radiation_dose to the_target.
However,_in_these conventional radiation treatments_the number of radiation beams is_constrained to several hundred beams due_to various spatial and physical constraints. For_example, in Gamma Knife® radiosurgery, the_number of radiation beams is_limited to_about two hundred beams. Physically,_it is not_possible to_drill a large_number of apertures in a fixed_size metal screen_without eventually causing interference among the_beams_escaping from the_apertures.
For_intensity-modulated_radiation therapy_(IMRT), it is_usually_not practical_to_deliver more than a dozen beams_due_to prolonged treatment time. Even with rotational_techniques, such as Tomotherapy,_intensity-modulated_arc therapy (IMAT), volumetric_modulated arc therapy (VMAT), and_arc-modulated radiation therapy (AMRT), the maximum_number of_radiation beams_is still limited to a few hundred.
Fundamental Physics Underlying Photon Radiosurgery:
The_fundamental physics underlying photon-based radiosurgeries includes_high energy photon production_and photon_interactions_with matter.
Generally, high_energy_photons used_in current radiosurgeries are produced either by_radioactive decay_from Cobalt-60 sources or bremsstrahlung interactions_in a linear accelerator._In_the linear accelerator, electrons are accelerated_in an electric field to a_high energy and then collide_with_a_metal target. This generates radiation_particles or photons in a bremsstrahlung_process. The photons_produced from Cobalt-60 are called “γ-ray” or_gamma_rays whereas the photons produced from_a_linear accelerator are called “X-ray” or_X-rays.
Typically_photons_produced by different sources are_heterogeneous in energy. For example, the_energies of γ-rays emitted by Cobalt-60 are 1.17 and_1.33 MeV. The_energy spectrum of X-rays from_a_linear_accelerator shows a continuous distribution of energies for the bremsstrahlung_photons superimposed_by characteristic radiation_of discrete energies. The energies of photon beams created by_a 6 MV accelerator are continuous from_0 to 6 MeV with a large number of