Targeting Issues For Proton Treatments Of The Prostate SJ Rosenthal Ph.D., JA Wolfgang Ph.D., Sashi Kollipara Department of Radiation Oncology Massachusetts General Hospital, Boston MA

History of Proton Prostate Therapy Issue of Proton Scatter Issue of Organ Motion Setting Compensator Smear Patient/Organ Set Up Technique Early Patient Study Range Compensator Strategy

1982 Perineal Proton Boost for Prostate Protocol Up to 75.6 CGE -1992Used 160 MeV Beam at Harvard Cyclotron Laboratory Rectal Probe to Immobilize Prostate Radiographic Set Up 1995Perineal Boost Increased to 79CGE At HCL -2000Boost with Probe Delivered First to Reduce Toxicity 1991LLUMC Proton Only with Lateral Fields Retained Probe for Alignment 2002 NPTC Study of Proton Treatments of the Prostate Lateral Fields Plan Optimized with Pencil Beam Calculation Organ Motion Adjustments - No Probe Digital Radiography for Rapid Set Up and Seed Tracking 2002Prostate Dose Escalation Protocol Up to 84.6 CGE History of Proton Prostate Therapy

Pencil Beam vs. Broad Beam

Pencil Beam Calculation Needed to Insure Distal Coverage Broad Beam Calculation Pencil Beam Calculation Cold Target when Broad Beam Calculation is Used Add 1 cm to Range and Modulation for Good Coverage with Pencil Beam Calculation

Gold Seeds in Prostate

Prostate Seed Daily Motion First Three Patients Patient 1Patient 3 Patient 2

Daily Treatment Set Up 6 Prostate Patients Monitored position of prostate by marking position of seeds relative to original setup simulation position Perform statistical analysis of observed setup error for six patients Take average setup error after N (  total fractions) treatments and apply it to remaining treatments

Setup Error Analysis Standard Deviation averaged about 2 mm per patient Setup error could be as large as 0.5 – 1.0 cm

Increasing the Compensator Smear From 5 to 10 mm 5 mm Smear 10 mm Smear Actually Improves Femoral Head Sparing and Prostate Coverage

Increasing the Compensator Smear From 5 to 10 mm Anterior Rectum 5 mm Smear Anterior Rectum 10 mm Smear Prostate 10 mm Smear Prostate 5 mm Smear Allows for prostate to bony anatomy mis-registration up to 1 cm

Consequences of Prostate Motion and Re -Targeting Create Shifted Prostate Target to Simulate Movement in Treatment Plan GTV Draw by MD GTV with 1cm Shift Inferior GTV with 1cm Shift Inferior GTV Draw by MD Target Beam to Shifted Prostate but Retain Aperture and Compensator designed to Original Target

Minimum Dose To Prostate Shifted Prostate With Tracking As Planned No Shift

Maximum Dose To Femoral Heads With Prostate Tracking As Planned No Shift 40 % Isodose 43 % Isodose

Dose to Femoral Heads and Prostate in Fixed and Shifted Plans Femoral Heads Fixed Plan Femoral Heads Shifted Plan Prostate Fixed Plan Shifted Prostate Shifted Plan