Introduction Technical฀ advances฀ and฀ innovations฀ in฀ computers,฀ 3D฀ imaging฀ and฀ radiation฀ delivery฀ process฀ have฀ made฀ it฀ possible฀ to฀ escalate฀ dose฀ to฀ the฀ prostate.฀ At฀ the฀ same฀ time,฀ the฀ expense฀ of฀ the฀ high฀ tech฀ equipment,฀ such฀ as฀ CTSIM,฀ IMRT฀ and฀ IGRT฀ capable฀ Linacs,฀ have฀also฀escalated฀treatment฀costs.฀Treatment฀planning฀and฀delivery฀costs฀for฀IMRT฀and฀ IGRT฀are฀in฀the฀order฀of฀$100,000,฀while฀those฀for฀3D-CRT฀and฀IGRT฀are฀less฀than฀half฀ of฀that.฀Then,฀if฀it฀were฀shown฀that฀3D฀plan฀dosimetry฀is฀similar฀to฀IMRT฀plan฀dosimetry,฀ considerable฀ time฀ and฀ cost฀ savings฀ could฀ be฀ achieved.฀ This฀ presentation฀ shows฀ that฀ for฀ small฀ to฀ medium฀ size฀ prostate฀ volumes,฀ 3D-CRT฀ plans฀ are฀ dosimetrically฀ equivalent฀ to฀ IMRT฀plans.฀ With฀ IGRT,฀ treatment฀ margins฀ could฀ be฀ reduced฀ for฀ both฀ IMRT฀ and฀ 3D฀ plans฀ while฀ minimizing฀the฀geometric฀miss฀of฀prostate฀and฀limiting฀the฀dose฀to฀bladder฀and฀rectum.฀ Comparison฀ of฀ 3D฀ and฀ IMRT฀ plan฀ dosimetry฀ data฀ for฀ a฀ large฀ group฀ of฀ patients฀ with฀ varying฀ volumes฀ of฀ prostate฀ and฀ seminal฀ vesicles,฀ bladder฀ and฀ rectum฀ have฀ not฀ been฀ reported.฀Such฀data฀would฀be฀needed฀to฀evaluate฀the฀efficacy฀of฀3DCRT฀and฀IMRT฀used฀ with฀ IGRT฀ in฀ terms฀ of฀ dose฀ to฀ prostate฀ and฀ SV,฀ rectum,฀ bladder,฀ femurs,฀ treatment฀ planning฀ and฀ QA฀ time,฀ MUs,฀ body฀ integral฀ dose฀ and฀ treatment฀ cost.฀ A฀ better฀ understanding฀ of฀ the฀ factors฀ governing฀ dose฀ to฀ prostate,฀ SV,฀ PTVs,฀ rectum฀ and฀ bladder฀ with฀ 3DCRT฀ and฀ IMRT฀ might฀ help฀ to฀ make฀ an฀ informed฀ decision฀ whether฀ 3DCRT฀ or฀ IMRT฀with฀image฀guidance฀(IG-3DCRT฀or฀IG-IMRT)฀is฀suitable฀to฀treat฀a฀given฀prostate฀ cancer฀patient.฀ Presented฀at฀the฀50 th ฀Annual฀Meeting฀of฀ASTRO,฀21-25฀September฀2008,฀Boston,฀MA฀ 3D฀Plan฀Dosimetry฀is฀Comparable฀to฀IMRT฀Plans฀for฀Small฀to฀ Medium฀Size฀Prostate฀Cases฀for฀Use฀with฀IGRT฀ Nandanuri M. Reddy, Ph.D 1 , Dattatreyudu Nori, MD, FACR 1,2 , Brij M. Sood, MD 1,2 , Akkamma Ravi, MD 1,2 , Heysook Chang, MD 1,2 ,Christopher S. Lange, D.Phil.,KKOZRP 3 . Departments฀of฀Radiation฀Oncology,฀ 1 NY฀Hospital฀Queens,฀Flushing,฀NY;฀ 2 New฀York฀Presbyterian฀Hospital,฀฀ Weill-Cornell฀Medical฀Center,฀New฀York,NY; ฀ 3 SUNY฀Downstate,฀Brooklyn,฀NY. Purpose ฀To฀ develop฀ 3D฀ plans฀ dosimetrically฀ comparable฀ to฀ IMRT฀ plans฀ for฀ prostate฀ cancer฀ IGRT. ฀Methods฀and฀Materials Dosimetry฀of฀3D฀and฀IMRT฀plans฀for฀48฀patients฀was฀compared.฀Structure฀volumes฀and฀ prescriptions฀were฀the฀same฀for฀both฀plans.฀Prescription฀to฀prostate฀+฀SV฀(PTV)฀was฀45฀ Gy฀and฀36฀Gy฀boost฀to฀prostate฀(CDPTV).฀Varian฀Eclipse฀treatment฀planning฀was฀used.฀ 6MV,฀ 5฀ field,฀ DMLC฀ IMRT฀ plans฀ with฀ 250,฀ 315,฀ 45,฀ 110฀ and฀ 180฀ gantry฀ angles฀ were฀ used.฀IMRT฀plan฀margins฀were:฀0.5฀cm฀post฀and฀superior฀and฀1฀cm฀in฀other฀dimensions฀to฀ P+SV฀ and฀ prostate฀ to฀ create฀ PTV฀ and฀ CDPTV,฀ respectively.฀ Dose฀ volume฀ constraints฀ (DVC)฀were฀required฀to฀deliver฀95%฀of฀81฀Gy฀to฀95฀%฀of฀PTVs฀and฀to฀keep฀dose฀to฀70,฀ 50฀ and฀ 30%฀ of฀ rectum฀ and฀ bladder฀ less฀ than฀ 30,฀ 50฀ and฀ 70%฀ of฀ 81฀ Gy.฀ DVC฀ priority:฀ PTVs฀>฀rectum฀>฀bladder.฀Normalization฀was฀to฀the฀mean฀and฀prescribed฀to฀100%.฀15X,฀ 6฀field฀3D฀plans฀with฀MLC฀blocking฀were฀prepared,฀retrospectively,฀with฀225,฀270,฀315,฀ 45,฀ 90฀ and฀ 135฀ gantry฀ angles,฀ with฀ 0.2,฀ 0.5,฀ 0.3,฀ 0.3,฀ 0.5฀ and฀ 0.2฀ beam฀ weights.฀ 3D฀ margins฀ for฀ P+SV฀ or฀ prostate฀ were:฀ 1฀ cm฀ post฀ and฀ superior฀ and฀ 1.5฀ cm฀ in฀ other฀ dimensions.฀ Normalization฀ was฀ to฀ the฀ isocenter฀ or฀ to฀ a฀ point฀ and฀ prescribed฀ to฀ 98%.฀ Dosimetry฀parameters฀common฀to฀3D฀and฀IMRT฀plans฀were฀used฀for฀comparison: mean฀doses฀to฀prostate,฀CDPTV,฀SV,฀rectum,฀bladder;฀femurs;฀dose฀to฀30%฀of฀rectum฀and฀ bladder฀ and฀ percent฀ of฀ 81฀ Gy฀ delivered฀ to฀ 95%฀ of฀ CDPTV.฀ Pearson’s฀ correlation฀ coefficient r฀and฀paired฀t฀test฀were฀used฀for฀statistical฀analysis.฀ Results Mean฀±฀SD฀and฀range฀of฀structure฀volumes:฀Prostate฀-฀52.4฀±฀24.5฀(17.2฀-฀139.1),฀SV฀-฀ 12.1฀±฀6.6฀(1.5฀-฀28.9),฀CDPTV฀-฀144฀±฀48฀(68฀-฀296),฀rectum฀-฀124฀±฀64฀(51฀-฀351)฀and฀ bladder฀-฀184฀±฀92฀(59฀–฀484,฀Table฀1).฀Larger฀the฀dose฀to฀rectum฀(Fig.฀1A)฀or฀bladder฀ (Fig.฀ 1B)฀ ฀ with฀ 3D฀ plans,฀ larger฀ was฀ also฀ the฀ dose฀ to฀ rectum฀ and฀ bladder฀ with฀ IMRT฀ (P<0.001).฀ Mean฀ dose฀ to฀ CDPTV฀ and฀ prostate฀ (all฀ patients)฀ was฀ higher฀ with฀ 3D฀ than฀ IMRT฀ plans฀ (81.9฀ ±฀ 0.6฀ >฀ 81.2฀ ±฀ 0.09฀ and฀ 83฀ ±฀ 0.61฀ >฀ 81.8฀ ±฀ 0.23฀ (both,฀ P<0.01),฀ respectively฀ (Table฀ 2).฀ Mean฀ dose฀ to฀ 30%฀ rectum฀ with฀ 3D฀ and฀ IMRT฀ plans฀ was฀ comparable฀ (P>0.1,฀ Table฀ 2).฀ Dose฀ to฀ bladder฀ was฀ less฀ with฀ 3D฀ than฀ IMRT฀ plans฀ (P<0.01,฀Table฀2).฀Dose฀to฀femurs฀was฀more฀with฀3D฀than฀IMRT฀plans฀(P<0.01,฀Table฀2).฀ Prostate฀ or฀ P+SV฀ volumes฀ vs.฀ mean฀ dose฀ or฀ dose฀ to฀ 30%฀ rectum฀ (Fig.฀ 2A,฀ 2B,฀ 3A฀ and฀3B)฀and฀bladder฀(Fig.฀4A,฀4B,฀5A฀and฀5B)฀showed฀that฀dose฀to฀these฀structures was฀ less฀ with฀ 3D฀ than฀ IMRT฀ plans฀ when฀ prostate฀ or฀ P+SV฀ volumes฀ were฀ <฀ 65฀ (38/48)฀ and฀ 85฀ cc฀ (39/48)฀ (small฀ to฀ medium฀ size)฀ and฀ vice฀ versa฀ (P<0.01)฀ .฀ With฀ increase฀ in฀ prostate฀ volume,฀ the฀ percent฀ of฀ 81฀ Gy฀ delivered฀ to฀ 95%฀ CDPTV฀ increased฀ with฀ 3D฀ plans฀ (P<0.02),฀ but฀ decreased฀ with฀ IMRT฀ (P<0.01,฀ Fig.฀ 6).฀ IMRT฀ delivered฀ higher฀doses฀to฀rectum฀and฀bladder฀to฀achieve฀better฀dose฀coverage฀to฀CDPTV฀for฀small฀ to฀ medium฀ size฀ prostates฀ and฀ P+SVs฀ but฀ limited฀ the฀ dose฀ to฀ rectum฀ and฀ bladder฀ at฀ the฀ expense฀ of฀ dose฀ coverage฀ to฀ CDPTV฀ in฀ case฀ of฀ large฀ prostates฀ and฀ P+SVs฀ (Figs.฀ 2-6).฀ Mean฀ dose฀ to฀ CDPTV฀ was฀ higher฀ with฀ 3D฀ than฀ IMRT฀ plans,฀ but฀ dose฀ conformity฀ to฀ CDPTV฀was฀better฀with฀IMRT฀than฀3D฀plans฀(Fig.฀7).฀ Conclusions Dosimetrically,฀ 3D฀ and฀ IMRT฀ plans฀ are฀ comparable฀ for฀ patients฀ with฀ small฀ to฀ medium฀ size฀prostate฀and฀P+SV฀volumes.฀After฀completing฀the฀contouring฀of฀structures,฀trial฀runs฀ of฀3D฀and฀IMRT฀plans฀would฀take฀less฀than฀an฀hour฀and฀would฀indicate฀the฀suitability฀of฀ a฀ 3DCRT฀ or฀ advantage฀ of฀ IMRT฀ for฀ a฀ given฀ patient.฀ Tailoring฀ the฀ treatment฀ to฀ the฀ clinical฀condition฀in฀trems฀of฀prostate฀volume฀would฀be฀timely฀and฀reduce฀treatment฀costs฀ in฀ selected฀ cases,฀ without฀ compromising฀ the฀ treatment฀ quality.฀ IGRT฀ with฀ 3D฀ plans฀ would฀not฀only฀reduce฀treatment฀costs฀but฀also฀reduce฀the฀body฀integral฀dose,฀MU,฀ IMRT฀planning฀and฀QA฀time. Table฀1.฀Mean฀and฀range฀of฀structure฀volumes,฀cc,฀n฀=฀48฀ Structure฀ Mean฀volume฀±฀SD฀ ฀ ฀ Range฀of฀volumes฀ Prostate฀ 52.4฀±฀24.5฀฀ ฀ ฀ ฀ 17.2฀-฀139.1฀ SV฀฀ ฀ 12.1฀±฀6.6฀฀ ฀ ฀ ฀ ฀฀1.5฀-฀28.9฀ CDPTV฀฀ 144฀±฀48฀ ฀ ฀ ฀ ฀68฀–฀296฀ Rectum฀ 124฀±฀64฀฀ ฀ ฀ ฀ ฀51฀–฀351฀ Bladder฀฀ 184฀±฀92฀฀ ฀ ฀ ฀ ฀59฀–฀484฀ Femur฀ ฀ ฀201฀±฀11฀฀ ฀ ฀ ฀ 141฀–฀280฀ ------------------------------------------------------------------------------------------------------------ Table฀2.฀Mean฀dose฀and฀dose฀to฀30%฀of฀structures฀with฀3D฀and฀IMRT฀plans฀in฀Gy;฀ prescription฀dose฀was฀81฀Gy,฀n฀=฀48.฀ ฀ Mean฀dose฀±฀SD฀ ฀ ฀ Dose฀to฀30%฀volume฀±฀SD฀ ฀ 3D฀plans฀ IMRT฀plans฀ ฀P฀ 3D฀plans฀ IMRT฀plans฀ ฀฀฀฀฀P฀ ฀ --------------------------------------------------------------------------------------------------- Prostate฀ 83฀±฀0.61฀฀฀฀>฀฀฀81.8฀±฀0.23฀ ฀ -฀ ฀ -฀ ฀฀฀฀฀฀฀฀฀฀฀<0.01฀฀ SV฀ ฀ 66.8฀±฀6.1฀฀฀<฀ 69฀±฀6.6฀ ฀ -฀ ฀ -฀ ฀฀฀฀฀฀฀฀฀฀฀<0.01฀ CDPTV฀ 81.9฀±฀0.6฀฀฀>฀ 81.2฀±฀0.09฀ ฀ -฀ ฀ -฀ ฀ <0.01฀ Femurs฀ 29.6฀±฀4.7฀฀฀>฀ 16.2฀±฀4.4฀ ฀ -฀ ฀ -฀ ฀฀฀฀฀฀฀฀฀฀฀฀<0.01฀ Rectum฀ 29.3฀±฀6.6฀฀฀=฀฀฀30.8฀±฀4.7฀฀฀฀P<0.01฀ 41฀±฀10฀฀฀฀฀฀฀=฀฀฀42.5฀±฀5.3฀ ฀>0.10฀ Bladder฀ 26.1฀±฀9.0฀฀฀<฀฀฀29.5฀±฀7.6฀฀฀฀P<0.01฀33.9฀±฀15.4฀฀฀<฀ 38.5฀±฀11.6฀ ฀<0.01฀ y = 0.4404x + 2441.9 R 2 = 0.6081 P < 0.001 2000 2500 3000 3500 4000 4500 5000 5500 6000 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 Dose to 30% rectum with 3D plans, cGy y G c , s n a l p T R M I h t i w m u t c e r % 0 3 o t e s o D Figure฀ 1A.฀ Dose฀ to฀ 30%฀ of฀ rectum฀ with฀ 3D฀ plans฀ vs.฀ IMRT฀ plans,฀ n฀ =฀ 48.฀ Higher฀ the฀ dose฀to฀rectum฀with฀3D฀plans,฀higher฀was฀also฀the฀dose฀to฀rectum฀with฀IMRT฀plans.฀ R 2 = 0.8846 P < 0.001 y = 0.7057x + 1456.6 0 1000 2000 3000 4000 5000 6000 7000 8000 0 1000 2000 3000 4000 5000 6000 7000 8000 Dose to 30% bladder with 3D plans, cGy y G c , s n a l p T R M I h t i w r e d d a l b % 0 3 o t e s o D Figure฀ 1B.฀ Dose฀ to฀ 30%฀ of฀ bladder฀ with฀ 3D฀ plans฀ vs.฀ IMRT฀ plans,฀ n฀ =฀ 48.฀ Higher฀ the฀ dose฀to฀bladder฀with฀3D฀plans,฀higher฀was฀also฀the฀dose฀to฀bladder฀with฀IMRT฀plans.฀ y = 14.171x + 2182.5 Diamonds, 3D, R 2 = 0.2701, P<0.001 y = 6.7052x + 2723.9 Squares, IMRT, R 2 = 0.1164 P<0.02 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 0 20 40 60 80 100 120 140 160 Prostate volume, cc y G c , m u t c e r o t e s o d n a e M Figure฀2A.฀Prostate฀volume฀vs.฀mean฀dose฀to฀rectum฀with฀3D฀and฀IMRT฀plans.฀Dose฀to฀ rectum฀with฀3D฀plans฀is฀lower฀than฀that฀with฀IMRT฀for฀prostate฀volumes฀less฀than฀<65฀cc.฀ y = 20.377x + 3028.7 Diamonds, 3D, R 2 = 0.2765, P<0.001 y = 8.7534x + 3787.2 Squares, IMRT, R 2 = 0.16, P<0.01 1000 2000 3000 4000 5000 6000 7000 8000 0 20 40 60 80 100 120 140 160 Prostate volume, cc y G c , m u t c e r % 0 3 o t e s o D Figure฀2B.฀Prostate฀volumes฀vs.฀dose฀to฀30%฀rectum฀with฀3D฀and฀IMRT฀plans.฀Dose฀to฀ rectum฀with฀3D฀plans฀is฀lower฀than฀that฀with฀IMRT฀for฀prostate฀volumes฀less฀than฀<65฀cc.฀ y = 13.824x + 2011.7 Diamonds, 3D, R 2 = 0.289, P<0.001 y = 6.3661x + 2654.7 Squares, IMRT, R 2 = 0.118, P<0.05 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 0 20 40 60 80 100 120 140 160 180 P+SV volume, cc y G c , m u t c e r o t e s o d n a e M Figure฀ 3A.฀ Prostate฀ +฀ SV฀ volumes฀ vs.฀ mean฀ dose฀ to฀ rectum฀ with฀ 3D฀ and฀ IMRT฀ plans.฀ Mean฀ dose฀ to฀ rectum฀ with฀ 3D฀ plans฀ is฀ lower฀ than฀ that฀ with฀ IMRT฀ for฀ prostate฀ +฀ SV฀ volumes฀less฀than฀<85฀cc.฀ y = 19.255x + 2824.5 Diamonds, 3D, R 2 = 0.2777, P<0.01 y = 7.3945x + 3757.7 Squares, IMRT, R 2 = 0.1284, P<0.02 1000 2000 3000 4000 5000 6000 7000 8000 0 20 40 60 80 100 120 140 160 180 Volume of P+SV, cc y G c , m u t c e r % 0 3 o t e s o D Figure฀ 3B.฀ Prostate฀ +฀ SV฀ volumes฀ vs.฀ dose฀ to฀ 30%฀ rectum฀ with฀ 3D฀ and฀ IMRT฀ plans.฀ Dose฀ to฀ 30%฀ rectum฀ with฀ 3D฀ plans฀ is฀ lower฀ than฀ that฀ with฀ IMRT฀ for฀ prostate฀ +฀ SV฀ volumes฀less฀than฀<85฀cc.฀ y = 11.826x + 2328.8 Diamonds, 3D, R 2 = 0.1413, P<0.02 y = 15.905x + 1774.8 Squares, IMRT, R 2 = 0.1835, P<0.02 0 1000 2000 3000 4000 5000 6000 0 20 40 60 80 100 120 140 160 Prostate volume, cc y G c , r e d d a l b o t e s o d n a e M Figure฀4A.฀Prostate฀volume฀vs.฀mean฀dose฀to฀bladder฀with฀3D฀and฀IMRT฀plans.฀Dose฀to฀ bladder฀with฀3D฀plans฀is฀lower฀than฀that฀with฀IMRT฀plans.฀ y = 29.561x + 1836.8 Diamonds, 3D, R 2 = 0.2159, P<0.01 y = 21.103x + 2740.2 Squares, IMRT, R 2 = 0.1954, P<0.01 0 1000 2000 3000 4000 5000 6000 7000 8000 0 20 40 60 80 100 120 140 160 Prostate volume, cc y G c , r e d d a l b % 0 3 o t e s o d Figure฀4b.฀Prostate฀volume฀vs.฀dose฀to฀30฀%฀bladder฀with฀3D฀and฀IMRT฀plans.฀Dose฀to฀ bladder฀with฀3D฀plans฀is฀lower฀than฀that฀with฀IMRT฀plans฀for฀prostate฀volumes฀<110cc.฀ y = 14.872x + 1622.2 Diamonds, 3D, R2 = 0.1787, P<0.01 y = 11.516x + 2185 Squares, IMRT, R2 = 0.1493, P<0.02 0 1000 2000 3000 4000 5000 6000 0 20 40 60 80 100 120 140 160 180 P+SV volume, cc y G c , r e d d a l b o t e s o d n a e M Figure฀ 5A.฀ Prostate฀ +฀ SV฀ volumes฀ vs.฀ mean฀ dose฀ to฀ bladder฀ with฀ 3D฀ and฀ IMRT฀ plans.฀ Mean฀dose฀to฀rectum฀with฀3D฀plans฀is฀lower฀than฀that฀with฀IMRT.฀ y = 27.411x + 1568.2 Diamonds, 3D, R 2 = 0.2068, P<0.01 y = 20.052x + 2516.4 Squares, IMRT, R 2 = 0.1965, P<0.01 0 1000 2000 3000 4000 5000 6000 7000 8000 0 20 40 60 80 100 120 140 160 180 Prostate + SV volume, cc y G c , r e d d a l b % 0 3 o t e s o D Figure฀ 5B.฀ Prostate฀ +฀ SV฀ volumes฀ vs.฀ dose฀ to฀ 30%฀ bladder฀ with฀ 3D฀ and฀ IMRT฀ plans.฀฀ Dose฀ to฀ 30%฀ rectum฀ with฀ 3D฀ plans฀ is฀ lower฀ than฀ that฀ with฀ IMRT฀ for฀ prostate฀ +SV฀ volumes฀less฀than฀125฀cc.฀ Diamonds, 3D plans, R2 = 0.1314, P<0.02 y = 0.017x + 94.545 y = -0.0243x + 97.472 Squares, IMRT plans, R 2 = 0.3411, P<0.01 92 93 94 95 96 97 98 99 0 20 40 60 80 100 120 140 160 Prostate volume, cc T R M I d n a D 3 h t i w V T P D C f o % 5 9 o t y G 1 8 f o t n e c r e P s n a l p Figure฀ 6.฀ Percent฀ of฀ prescription฀ dose,฀ 81฀ Gy,฀ to฀ 95%฀ of฀ CDPTV฀ with฀ 3D฀ and฀ IMRT฀ plans฀ vs.฀ prostate฀ volume,฀ n฀ =฀ 48.฀ While฀ the฀ dose฀ to฀ CDPTV฀ with฀ 3D฀ plans฀ increases฀ with฀the฀increase฀of฀prostate฀volume,฀dose฀to฀CDPTV฀and฀rectum฀decreases฀with฀IMRT฀ (see฀Fig.฀2A฀below).฀ y = 14.171x + 2182.5 Diamonds, 3D, R 2 = 0.2701, P<0.001 y = 6.7052x + 2723.9 Squares, IMRT, R 2 = 0.1164, P<0.02 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 0 20 40 60 80 100 120 140 160 Prostate volume, cc y G c , m u t c e r o t e s o d n a e M Figure฀2A.฀Prostate฀volume฀vs.฀mean฀dose฀to฀rectum฀with฀3D฀and฀IMRT฀plans.฀Dose฀to฀ rectum฀with฀3D฀plans฀is฀lower฀than฀that฀with฀IMRT฀for฀prostate฀volumes฀less฀than฀<65฀cc.฀ Shown฀for฀comparison฀with฀figure฀6. Diamonds, 3D, R2 = 0.1521, P<0.05 Sqares, IMRT, R2 = 0.0011, P>0.2 8050 8100 8150 8200 8250 8300 8350 0 50 100 150 200 250 300 350 CD PTV volume, cc y G c , e s o d n a e M Figure฀7.฀Mean฀dose฀to฀CD฀PTV฀in฀cGy฀with฀3D฀and฀IMRT฀plans.฀Although฀the฀percent฀ of฀ prescription฀ dose฀ coveting฀ the฀ 95%฀ of฀ CD฀ PTV฀ with฀ 3D฀ plans฀ is฀ less฀ than฀ that฀ of฀ IMRT฀plans฀for฀prostate฀volumes฀less฀than฀65฀cc฀(Fig.฀6),฀the฀mean฀dose฀to฀CD฀PTV฀with฀ 3D฀plans฀is฀higher฀than฀that฀with฀IMRT฀plans,฀P<0.01฀(Table฀2).฀