Treatment accuracy without rotational setup corrections in intracranial SRT

a Co esponding au ho : Ee a Boman, Depa men o Oncology, Tampe e Uni e si y Hospi al, PO BOX 2000 (Teiskon ie 35), FI-33521 Tampe e, Finland; phone: (+3853) 311 63201; email: [email p o ec ed] T ea men accu acy wi hou o a ional se up co ec ions in in ac anial SRT Ee a Boman,1,2a Mika Kapanen,1,2 Ma ko Laaksomaa,1 Hanna Mäenpää,1 Simo Hyödynmaa,2 and Pi kko-Liisa Kellokumpu-Leh inen1,3 Depa men o Oncology,1 Tampe e Uni e si y Hospi al, Tampe e, Finland; Depa men o Medical Physics,2 Tampe e Uni e si y Hospi al, Tampe e, Finland; School o Medicine,3 Uni e si y o Tampe e, Tampe e, Finland [email p o ec ed] Recei ed 20 Oc obe , 2015; accep ed 22 Feb ua y, 2016 The aim o his s udy was o e alua e he impac o ac ual o a ional se up e o s on dose dis ibu ions in in ac anial s e eo ac ic adio he apy (SRT) wi h di e - en al e na i es o ea men posi ion selec ion. A o al o 38 SRT ac ions om 18 pa ien s we e e ospec i ely e alua ed wi h o a ional se up e o s ob ained om ac ual ea men s. The planning compu ed omog aphy (CT) images we e o a ed acco ding o online cone-beam CT (CBCT) images and he dose dis ibu ion was ecalcula ed o he o a ed CT images using h ee di e en pa ien posi ionings de i ed om: 1) an au oma ic 6D ma ch neglec ing o a ion co ec ion (Au o6D); 2) an au oma ic 3D ma ch (Au o3D); and 3) a manual 3D ma ch om ac ual ea - men (T ea 3D). The mean con o mi y index (CI) was 0.92 o he o iginal plans and 0.91 o he Au o6D plans. The mean CI dec eased signi ican ly (p < 0.01) o 0.78 and 0.80 o he Au o3D and he T ea 3D plans, espec i ely. The mean minimum dose o he planning a ge olume (PTVmin) was 91.9% o he p esc ibed dose o he o iginal plans and 92.1% o he Au o6D plans, while o he Au o3D and he T ea 3D plans PTVmin dec eased signi ican ly (p < 0.01) o 78.9% and 80.2%, espec i ely. No signi ican di e ences we e seen be ween he Au o6D and he o iginal ea men plans in e ms o he dose pa ame e s. Howe e , he Au o3D and he T ea 3D plans we e s a is ically signi ican ly in e io (p < 0.01) o he Au o6D and he o iginal plans. In addi ion, a signi ican nega i e co ela ion (p < 0.01, | | > 0.38) was ound in he Au o3D and he T ea 3D cases be ween he o a ion e o and CI, PTVmin o minimum dose o g oss umou olume. In SRT, a ea men plan o compa able quali y o 6D o a ion co ec ion can be achie ed by using 6D egis a ion wi hou a o a ional co ec ion in he selec ion o pa ien posi ioning. This was demons a ed o ypical o a ion e o s seen in clinical p ac ice. PACS numbe (s): 87.55, 87.57 Key wo ds: SRT, o a ional se up co ec ion, pa ien posi ioning I. INTRODUCTION B ain me as ases occu in 10%–30% o all cance pa ien s.(1) T ea men op ions a e whole b ain adio he apy, local he apies (SRT o su ge y), and s e oids. Se e al ials ha e shown a bene i in local con ol, quali y o li e, and e en imp o ed su i al o single- o oligome as a ic pa ien s ea ed wi h SRT.(2,3,4) In SRT, small b ain lesions a e ea ed wi h small GTV- o-PTV ma gins in a single o ew ac ions. Because o he ela i ely high dose pe ac ion ( ypically 6-21 Gy pe ac ion), s eep dose g adien s a e equi ed a ound he planning a ge olume (PTV) o a oid damage JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS, VOLUME 17, NUMBER 4, 2016 86 86 87 Boman e al.: SRT accu acy wi hou 6DOF co ec ion 87 Jou nal o Applied Clinical Medical Physics, Vol. 17, No. 4, 2016 o su ounding o gans, mainly he cen al ne ous sys em.(5) Ta ge localiza ion unce ain y should be kep e y small ( ypically wi hin 1 mm) in SRT o no comp omise he local con ol o he ea men (6) and o minimize he isk o inju y o he su ounding b ain pa enchyma.(7) SRT p esumes adequa e pa ien immobiliza ion. The moplas ic s e eo ac ic masks a e nowa- days commonly used in SRT ea men s. These ha e been alida ed in many s udies as ul illing he high accu acy s anda d o SRT.(8,9) Image-guidance wi h o hogonal kV-images,(10) oblique images,(11) cone-beam compu ed omog aphy (CBCT) images,(12) e lec ing ma ke s wi h bi e blocks,(13) and, mo e ecen ly, pa ien su ace ma ching sys ems(14) ha e shown o be su icen in pa ien posi ioning in SRT keeping he esidual se up e o s unde he desi ed limi s. In ensi y-modula ed adia ion he apy (IMRT) and olume ic-modula ed a c he apy (VMAT) ha e inc eased he dose con o mi y o PTVs and dec eased he dose o no mal issues when compa ed o adi ional s a ic beams in linea accele a o -based ea men s.(15) The use o VMAT also dec eases he o e all ea men ime, educing he possibili y o in a ac ion mo emen s by he pa ien . The use o la e ing il e - ee (FFF) beams dec eases he ea men ime e en u he in high dose pe ac ion ea men s.(16) To u he inc ease accu acy in c anial SRT, pa ien o a ional se up e o s can be co ec ed using a six deg ees o eedom (6DOF) couch.(17,18,19) In all o hese s udies, he co ec ion o he o a ional se up e o inc eased plan quali y and o gan-a - isk (OAR) spa ing. I is e iden ha in he pa ien se up, he use o he 6DOF couch imp o es ea men quali y. Howe e , he 6DOF couch may no be a ailable in many cance cen e s due o he high cos . Ge ae e al.(18) compa ed he calcula ed dose wi h and wi hou o a ional co ec ions and concluded a loss o 5% dose co e age when o a ional co ec ion was no used, poin ing o a 0.5° o a ion e o as a h eshold angle o co ec ion. The aim o his s udy was o e alua e he added alue o he use o 6DOF egis a ion in ea men wi hou he p esence o he 6DOF couch sys em. Fo his pu pose, only ansla ional co ec ions we e aken om he 6DOF egis a ion and he dose was ecalcula ed using his 6D pa ien posi ioning on o a ed CT images o illus a e he e ec o unco ec ed ac ual o a ions on dose dis ibu ion. The esul ing dose dis ibu ion was compa ed o ha o he o iginal plan and o hose ob ained by accoun ing o esidual posi ion e o s om he 3DOF egis a ion and he ac ual ea men localized by a physician. II. MATERIALS AND METHODS Eigh een single- o oligome as a ic SRT pa ien s wi h a o al o 38 ac ions we e e ospec- i ely e alua ed in his s udy. The numbe o ea ed ac ions anged om a single ac ion o 5 ac ions, depending on he umo size and pa ien -speci ic de ails. Pa ien s we e immobilized using he B ainLab mask sys em (B ainlab AG, Feldki chen , Ge many). A slice hickness o 1 mm was used in he ini ial ea men planning CT (Philips Big Bo e, Philips Medical Sys ems, Fi chbu g, WI). 6D egis a ion was used be ween he ecen MRI and planning CT in Eclipse egis a ion so wa e (A ia 11, Va ian Medical Sys ems, Palo Al o, CA). T ea men con ou ing and planning we e pe o med wi h he Eclipse .11 ea men planning sys em (Va ian Medical Sys ems). GTV- o-PTV ma gins o 1–2 mm we e used. The VMAT echnique (Rapid A c, Va ian Medical Sys ems) wi h noncoplana o coplana suba cs was used in he ea men planning wi h 6 MV o 6 MV la ening il e - ee (6MV-FFF) beams. High de ini ion mul ilea collima ion wi h lea wid h o 2.5 mm was used in he planning. The dose calcula ion was pe o med wi h a g id size o 1 mm using aniso opic analy ical algo i hm .11 (Va ian Medical Sys ems). The ea men s we e deli e ed on a T ueBeam STx 1.6 wi h HD-MLC (Va ian Medical Sys ems). Pa ien posi ioning was based on online CBCT images wi h a slice hickness o 2 mm. The CBCT images we e e ospec i ely analyzed. A schema ic illus a ion o he wo k low and he coo dina e sys em a e p esen ed in Fig. 1. An au oma ic 6D egis a ion based on skull olume was pe o med be ween he CBCT and o iginal planning CT (CTplan) using Eclipse 88 Boman e al.: SRT accu acy wi hou 6DOF co ec ion 88 Jou nal o Applied Clinical Medical Physics, Vol. 17, No. 4, 2016 egis a ion so wa e (Va ian Medical Sys ems). The esul ing o a ional de ia ions in all 3D di ec ions (pi ch, oll, yaw) we e used in he o a ion o he o iginal CT images so ha he esul - ing o a ed CT (CT o ) p esen ed he ac ual ea men o ien a ion. The o a ion isocen e was he cen e o he CT images. The CT o a ion was done using homemade so wa e on Ma lab (The Ma hWo ks, Inc., Na ick, MA). A e o a ion, he new CT o images we e ma ched by au oma ic 6D egis a ion o he CBCT image (CT o -CBCT 6D). No o a ional de ia ions should be seen in his egis a ion. The ac ual ea men posi ion (T ea 3D) ob ained om he oncologis ’s 3D ma ch was ma ked on he CBCT image and copied on o CT o by using an au oma ic 6D egis a ion be ween he CBCT and CT o . Au oma ic 3D/6D egis a ions we e used o copy he ea men posi ion poin s o he Au o3D/Au o6D plans om CTplan o CT o , espec i ely. All he egis a ions we e done using he skull as he olume o in e es . The dose dis ibu ions wi h ac ual o a ions we e calcula ed in CT o o h ee di e en posi ionings o he pa ien — T ea 3D, Au o3D, and Au o6D — and compa ed o he o iginal ea men plan (planned). To e alua e he a ge co e age and plan quali y, he Paddick con o mi y index (CI) and g adien index (GI) we e used.(20,21) CI is de ined as (1) CI = V100 PTV VPTV V100 PTV V100 in which V100PTV is he p esc ibed dose olume in PTV, VPTV is he PTV olume, and V100 is he olume which ecei es he p esc ibed dose. CI =1 means he bes a ge co e age and lowe alues indica e a wo se plan quali y. GI is de ined by (2) GI = V50 V100 in which V50 is he olume which ecei es highe han hal o he p esc ibed dose. GI alue inc eases as he dose g adien ou side he a ge olume becomes shallowe , indica ing wo se plan quali y. Fig. 1. Wo k low o he di e en image egis a ions and de ini ion o o a ions o cons uc he needed CT image se o localiza ions and dose calcula ions. The coo dina e sys em wi h o a ion axes is also p esen ed. 89 Boman e al.: SRT accu acy wi hou 6DOF co ec ion 89 Jou nal o Applied Clinical Medical Physics, Vol. 17, No. 4, 2016 The Wilcoxon ma ched-pai s, signed- ank es (SPSS, 22, IBM Co p., A monk, NY) o nonpa ame ically dis ibu ed da a was pe o med o es he di e ences be ween he g oups. S a is ical signi icance was conside ed a p < 0.01 ( wo- ailed, |Z| > 2.576) including he Bon e oni co ec ion be ween he g oups planned–Au o6D, planned–Au o3D, planned–T ea 3D, Au o6D–Au o3D, and Au o6D–T ea 3D, which was made by di iding 0.05 by numbe o com- pa isons (i.e., by i e). The dose dis ibu ions in ou di e en cases (planned, T ea 3D, Au o3D, and Au o6D) we e s udied o 38 di e en pa ien se ups. The mean PTV ol was 8.0 cm3 (± 7.6 cm3), wi h a maximum olume o 26.6 cm3 and a minimum olume o 0.9 cm3. The loca ions and shapes o he PTVs a e p esen ed in Fig. 2. F om 38 pa ien se ups, he e we e wo pa ien s wi h mo e han one lesion and ea men isocen e was loca ed ou side o he PTV. One pa ien had 1 ac- ion wi h wo lesions and he o he had 3 ac ions wi h h ee lesions esul ing in ou di e en pa ien se ups. To demons a e he use o 6D egis a ion wi hou o a ional co ec ions o complex shaped a ge s o wo sepa a e sphe ical a ge olumes wi h easonably la ge o a ional e o s, wo pa ien examples a e gi en. In he i s example, he PTV is qui e la ge (14.6 cm3) and complex in shape. The ea men plan consis ed o wo sligh ly noncoplana ull a cs. In he second example, wo sphe ical PTVs we e ea ed simul aneously using ou noncoplana hal a cs. The olumes o he PTVs we e 20.1 cm3 and 5.2 cm3. The dis ance be ween he PTVs was 3 cm. The GTV- o-PTV ma gin was 2 mm in bo h examples. III. RESULTS The mean o a ional se up e o s we e -0.29° ± 0.88° ( ange om -2.1° o 1.6°), -0.26° ± 0.95° ( om -2.0° o 2.4°) and -0.47° ± 0.80° ( om -2.7° o 0.8°) o he pi ch, oll and yaw o a ions, espec i ely. The mean dis ance be ween ac ual ea men posi ioning and he posi ion ob ained om Au o6D egis a ion was 1.2 mm (± 0.6 mm), anging om 2.6 mm o 0.1 mm, while he co esponding dis ance be ween ea men posi ion and ha ob ained om he Au o3D was 1.7 mm (± 0.8 mm), al e ing om 3.8 mm o 0.2 mm. CI, GI, maximum, and minimum doses o PTV and GTV (PTVmax, PTVmin, GTVmin) we e in es iga ed o each plan, and he mean, s anda d de ia ion (SD), minimum (Min), and maximum (Max) alues a e p esen ed in Table 1 o each in es iga ed g oup. The Wilcoxon es esul s o he g oups planned–Au o6D, planned–Au o3D, planned–T ea 3D, Au o6D–Au o3D, and Au o6D–T ea 3D a e shown in Table 2. These esul s show ha he plans om he Au o6D g oup ha e almos he same mean CI, PTVmin, and GTVmin alues as he planned g oup and no s a is ically signi ican di e ence was ound be ween hese wo g oups. The mean CI, PTVmin, and GTVmin alues we e educed Fig. 2. Schema ic illus a ion o he in es iga ed PTVs o 18 pa ien s. 90 Boman e al.: SRT accu acy wi hou 6DOF co ec ion 90 Jou nal o Applied Clinical Medical Physics, Vol. 17, No. 4, 2016 signi ican ly (p < 0.01) o he Au o3D and T ea 3D plans when compa ed o he o iginal and Au o6D plans. Only a mino change was seen in he PTVmax among all he in es iga ed g oups. No signi ican di e ence was seen in GI alues be ween he g oups. Signi ican co ela ion (p < 0.01) was ound be ween he squa e oo o he quad a ic sum o he o a ions (quad a ic sum) and CI in he Au o3D g oup, au o3D = -0.46. In he T ea 3D g oup, he co ela ion was nea ly signi ican , ea 3D = -0.38 (p = 0.02). Signi ican co ela ion (p < 0.01) was ound be ween he o a ion and PTVmin, au o3D = -0.54 and ea 3D = -0.52, and be ween o a ion and GTVmin, au o3D = -0.54 and ea 3D = -0.42. The co ela ion was calcula ed o he pe cen age di e ence om he o iginal plan alues o he CI, PTVmin, and GTVmin alues by di iding hose wi h he o iginal plan alues o minimize he e ec o a ia- ion in he o iginal plans. No signi ican co ela ion was ound in he Au o6D case be ween he o a ion and dose pa ame e s ( CI = -0.24 (p = 0.15), PTVmin = -0.33 (p = 0.04), GTVmin = -0.26 (p= 0.11)). CI, PTVmin, and GTVmin scaled o o iginal plan alues wi h espec o quad a ic Table 1. The mean, SD, Min, and Max esul s o CI, GI, PTVmax, PTVmin, and GTVmin o he ou di e en g oups. CI Mean SD Min Max planned 0.92 0.02 0.82 0.94 Au o6D 0.91 0.03 0.82 0.94 Au o3D 0.78 0.12 0.43 0.94 T ea 3D 0.80 0.10 0.62 0.93 GI Mean SD Min Max planned 4.23 0.83 3.14 5.93 Au o6D 4.23 0.82 3.14 5.91 Au o3D 4.24 0.83 3.14 5.94 T ea 3D 4.22 0.83 3.12 5.92 PTVmax Mean SD Min Max planned 119.8 6.5 110.6 136.5 Au o6D 119.8 6.4 110.6 136.4 Au o3D 119.5 6.4 110.5 136.6 T ea 3D 119.9 6.6 110.6 136.8 PTVmin Mean SD Min Max planned 91.9 3.1 84.9 96.4 Au o6D 92.1 4.0 81.8 97.5 Au o3D 78.9 11.7 53.7 97.0 T ea 3D 80.2 10.7 55.1 96.1 GTVmin Mean SD Min Max planned 105.5 3.6 98.2 115.6 Au o6D 105.7 3.4 98.4 115.6 Au o3D 99.9 5.4 82.7 112.8 T ea 3D 101.1 5.7 90.2 115.1 Table 2. The Z- and p- alues om he Wilcoxon signed- ank es o he ela ed samples be ween he g oups (|Z|/p). CI GI PTVmax PTVmin GTVmin planned – Au o6D 1.62/0.11 1.17/0.24 0.30/0.76 2.05/0.04 1.36/0.17 planned – Au o3D 5.29/<0.01a 1.33/0.19 3.10/<0.01a 5.14/<0.01a 5.09/<0.01a planned – T ea 3D 5.34/<0.01a 1.95/0.05 0.76/0.44 5.30/<0.01a 4.30/<0.01a Au o6D – Au o3D 5.29/<0.01a 2.42/0.02 3.09/<0.01a 5.30/<0.01a 5.27/<0.01a Au o6D – T ea 3D 5.30/<0.01a 1.02/0.31 0.23/0.82 5.29/<0.01a 4.67/<0.01a a G oups wi h |Z| > 2.567, p < 0.01 we e conside ed o ha e a signi ican di e ence. 91 Boman e al.: SRT accu acy wi hou 6DOF co ec ion 91 Jou nal o Applied Clinical Medical Physics, Vol. 17, No. 4, 2016 sum o he o a ions a e p esen ed in Fig. 3. The mul iple lesion cases a e shown sepa a ely in Fig. 3. These images show a h eshold o quad a ic sum o he o a ions o a ound 0.5° when all scaled pa ame e s a e unde he limi s o CI < 90%, PTVmin < 90%, and GTVmin < 95% o he Au o3D g oup. Fo he quad a ic sum highe han 0.5°, mos o he scaled pa ame e s a e unde hose limi s. In he i s example, he PTV is nonsphe ical in shape, as seen in Fig. 4(a). The o a ional se up e o s we e 0.9°, -1.6°, and 2.7° o he pi ch, oll, and yaw o a ions, espec i ely. The dis ance om he ea men posi ioning o he pa ien o he posi ioning gi en by Au o6D eg- is a ion was 2.2 mm, and he dis ance om he ea men posi ioning o ha gi en by Au o3D egis a ion was 0.9 mm. In he second example, whe e he e a e wo sepa a e a ge s (Fig. 4(b)), he o a ional se up e o s we e -1.8°, -0.3°, and 0.2°, he pi ch, oll, and yaw o a ions, espec- i ely. The dis ance om he ea men posi ioning o he Au o6D posi ioning was 1.0 mm, and Fig. 3. The pe cen age di e ence om he o iginal plan o he CI, PTVmin, and GTVmin alues wi h espec o he quad a ic sum o he o a ions. Au o6D plans a e indica ed by a squa e (□), Au o3D plans by iangle (∆), and T ea 3D plans by a ci cle (○). S indica es single lesion and M is o mul iple (2–3) lesions. The mul iple lesions a e shown by illed symbols o Au o6D/3D plans and by a line (-) o T ea 3D plans. 92 Boman e al.: SRT accu acy wi hou 6DOF co ec ion 92 Jou nal o Applied Clinical Medical Physics, Vol. 17, No. 4, 2016 he dis ance om he ea men posi ioning o he Au o3D posi ioning was 0.8 mm. The isodose lines o he 100% p esc ip ion isodose and he dose- olume his og ams (DVHs) o PTV and GTV a e shown in Fig. 4 o he di e en cases (planned, Au o6D, Au o3D, T ea 3D). I is e iden om he DVH igu es ha he co e ages o PTV and GTV a e dec eased signi ican ly o he Au o3D and T ea 3D plans, while o Au o6D he co e ages a e almos iden ical o he o iginal plan in bo h examples. IV. DISCUSSION 6DOF couches ha e become a common ool in s e eo ac ic b ain ea men s. P e iously, he 6DOF couch has been shown o imp o e he ea men quali y by aking in o accoun daily o a ional e o s.(18,19) Common o hese s udies is ha hey compa e he 6D egis a ion wi h o a ional co ec ion esul s only o hose o he 3D egis a ion, which is also shown in his s udy o signi ican ly impai he dose dis ibu ion. We ha e shown ha by app op ia e selec ion o he pa ien posi ioning (Au o6D) in b ain SRT ea men s, a compa able ea men quali y is achie ed wi hou he co ec ion o o a ional e o s. The in es iga ed PTVs we e e y di e en in shape, size, and loca ion. Thus, he esul s gi e he imp ession ha he Au o6D me hod wo ks bes , no only o sphe ical PTVs, bu also o mo e complex PTV shapes and e en o se e al simul aneous a ge s ( he amoun o a ge s a ied om one o h ee). This is demons a ed in Fig. 4. The examples o wo pa ien s (A and B) a e shown wi h PTV ou lines ( ed), isodoses o he p esc ip ion dose o 100% o he o iginal plans (o ange), Au o6D plans (cyan), Au o3D plans (b own), and T ea 3D plans (g een). The loca ions o he pa ien posi ionings a e also shown o Au o6D (6D), Au o3D (3D), and T ea 3D (g een +). On he le , he DVHs a e shown o each case’s PTVs and GTVs. 93 Boman e al.: SRT accu acy wi hou 6DOF co ec ion 93 Jou nal o Applied Clinical Medical Physics, Vol. 17, No. 4, 2016 he examples gi en o nonsphe ical PTVs. Al hough he e we e only wo cases and 4 ac ions wi h mul iple a ge s, hei esul s gi e also an imp ession ha he Au o6D me hod is he bes me hod o pa ien posi ioning amongs he s udied me hods also, o mul iple a ge s, and ha a leas i is be e han he Au o3D. Howe e , mo e s udies migh be needed o make any conclusions o he mul iple a ge cases. Ge ae e al.(18) p oposed 0.5° as a h eshold angle o he co ec ion o o a ion e o s o keep he dose co e age o PTV o e 95% wi h he 3D egis a ion. Ou da a sugges ha a 3D ma ch is subop imal in e ms o CI, PTVmin, and GTVmin when he quad a ic sum o he o a ions exceeds 0.5° (scaled pa ame e s CI < 90%, PTVmin < 90%, and GTVmin < 95% in Fig. 3). Fo 6D egis a ion, ou esul s sugges ha he h eshold o o a ions could be e en la ge . The quad a ic sum o o a ion alues o 2°–3° s ill gi e adequa e plan quali y alues o scaled CI < 95%, PTVmin < 95%, and GTVmin < 95%. Al hough he quad a ic sum does no desc ibe physically he ac ual o a ion angle, i s ill seems o p o ide easonable one-numbe measu e o o e all o a ion. These indings a e demons a ed o be alid o b ain me as ases ea ed wi h he SRT. The used ma gins we e 1–2 mm. Fo s e eo ac ic adiosu ge y (SRS), he clinical ole ances and p ac ices a e di e en and hese indings may no be di ec ly alid o SRS ea men s. Besides he se up e o , he o al ea men accu acy depends also on he pa ien in a ac- ion mo emen (18) and machine isocen e accu acy. These a e no conside ed in his wo k, bu should be kep in mind in es ima ion o su icien ma gins o he SRT. Wi h mask ixa ion he in a ac ion mo emen is e y small, bu no negligible. Ve bakel e al.(8) ound ha , o B ainLab mask sys em, he in a ac ion mo ion was andomly dis ibu ed a ound he ze o in e e y di ec ion and ha he maximum de ia ion was 1 mm and 1° when he a e age ea men ime was 16 min. Fo sho e ea men imes he de ia ion migh be less. In his pape , we ha e shown he 6D egis a ion o be supe io o e 3D egis a ion. Howe e , he 6D egis a ion may no be possible in all online egis a ion so wa e, and implemen a ion in daily p ac ice migh be di icul . A leas on he newes e sions o Va ian (Va ian Medical Sys ems) and Elek a (Elek a L d., C awley, UK) accele a o s and in he ExacT ac (B ainlab) sys em his op ion is a ailable. These esul s apply o Va ian 6D egis a ion and need o be con i med be o e adap a ion o he 6D egis a ion sys ems o o he endo s. V. CONCLUSION We conclude ha he ou come o SRT ea men s wi hou he op ion o 6DOF couch could be imp o ed by using 6D egis a ion in he ea men se up. This was demons a ed o ypical ac ual o a ion e o s below 3° seen in ea men si ua ions. ACKNOWLEDGMENTS This s udy was inancially suppo ed by Pi kanmaa Hospi al Dis ic esea ch und (g an numbe 15013). COPYRIGHT This wo k is licensed unde a C ea i e Commons A ibu ion 3.0 Unpo ed License. 94 Boman e al.: SRT accu acy wi hou 6DOF co ec ion 94 Jou nal o Applied Clinical Medical Physics, Vol. 17, No. 4, 2016 REFERENCES 1. DeVi a VT J ., Law ence TS, Rosenbe g SA. DeVi a, Hellman, and Rosenbe g’s cance : p inciples and p ac ice o oncology, en h edi ion. Alphen aan den Rijn, Ne he lands: Wol e s Kluwe ; 2014. 2. And ews DW, Sco CB, Spe du o PW, e al. 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