IMRT for Prostate Cancer

Transcription

1 IMRT for Cancer All patients are simulated in the supine position. Reproducibility is achieved using a custom alpha cradle cast that extends from the mid-back to mid-thigh. The feet are positioned in a custom plexiglas foot-holder. The patient is told to have a 1/2-3/4 bladder because during treatment a full bladder is difficult to maintain. foot holder Robert A. Price Jr., Ph.D. Philadelphia, PA AAPM Minneapolis, July 24, 27 alpha cradle Simulation (Positioning and Immobilization ) The patient is asked to empty the rectum using an enema prior to simulation. Also, a low residue diet the night before simulation is recommended to reduce gas. If at simulation the rectum is >3 cm in width due to gas or stool, the patient is asked to try to expel the rectal contents. 6 cm 3 cm Bad rectum 4.5 cm Good rectum CT Scans Scans are acquired from approximately 2 cm above the top of the iliac crest to approximately mid-femur. This scan length will facilitate the use of noncoplanar beams when necessary. Scans in the region beginning 2 cm above the femoral heads to the bottom of the ischial tuberosities are acquired using a 2.5 mm slice thickness and 2.5 mm table increment. All other regions may be scanned to result in a 1 cm slice thickness. 2.5 cm 1

2 MR Scans MRI CT All prostate patients also undergo MR imaging within the department, typically within one half hour before or after the CT scan. Scans are obtained without contrast media. The resultant images are processed using a gradient distortion correction (GDC) algorithm. CT and MR (after GDC) images are fused according to bony anatomy using either chamfer matching or maximization of mutual information methods. All soft tissue structures are contoured based on the MR information while the external contour and bony structures are based on CT. 1.5 T, GE Medical Systems Retrograde urethrograms are not performed. Extracapsular extension Seminal vesicles? Imaging modality may affect treatment regime MRI CT growth = 8mm in all directions except posteriorly where a 5mm margin is typically used A Rt FH Bladder (CT) S (MR) I P Lt FH Imaging artifacts may affect contouring The effective margin is defined by the distance between the posterior aspect of the and the prescription isodose line and typically falls between 3 and 8 mm. 2

3 The effective margin is defined as: 1. The distance between the posterior aspect of the and the anterior rectal wall 2. The distance between the posterior aspect of the and the prescription isodose line 3. The distance between the posterior aspect of the and the posterior rectal wall 4. The average 3D margin 5. The difference between take-home pay and what your better half allows you to spend Regions Number of Beam Directions 26 previously treated patients (6 and MV) The average number of beam directions decreased by 1.62 with a standard error (S.E.) of.12. The average time for delivery decreased by 28.6% with a S.E. of 2. decreasing from 17.5 to 12.3 minutes The amount of nontarget tissue receiving D decreased by 15.7% with a S.E. of 2.4% Non-target tissue receiving D 95, D 9, D 5 decreased by 16.3, 15.1, and 19.5%, respectively, with S.E. values of approximately 2% In the interest of delivery time we typically begin with 6 and progress to 9 Simpler plans such as prostate only or prostate + seminal vesicles typically result in fewer beam directions than with the addition of lymphatics 3

4 Typical Dose Routine treatments + proximal sv (8 2. Gy/fx) Distal sv, lymphatics (56 ~1.4 Gy/fx) Post ctomy bed ( Gy/fx) Acceptance Criteria What is a good plan? When can I stop planning? DVH Acceptance Criteria 95 % Rx R 65 Gy 17%V R 4 Gy 35%V B 65 Gy 25%V B 4 Gy 5V Good DVH 95 = Good plan example (axial) FH 5 Gy 1V R 4 = 22.7% Effective margin R 4 = 19% R 65 = 8.3% B 65 = 8.4% The 5 isodose line should fall within the rectal contour on any individual CT slice The 9 isodose line should not exceed ½ the diameter of the rectal contour on any slice 4

5 DVH Acceptance Criteria 95 % Rx R 65 Gy 17%V R 4 Gy 35%V B 65 Gy 25%V B 4 Gy 5V FH 5 Gy 1V DVH for bad plan (meets DVH criteria) R 4 = 31.5% 95 = R 65 = 13.4% Bad plan example (axial) The 5 isodose line falls outside the rectal contour B 4 = 21.3% B 65 = 9% Routine prostate IMRT plan acceptance criteria at FCCC include all of the following except: Localization 1. The volume of either femoral head receiving 5 Gy 2 2. The volume of bladder receiving 65 Gy 25% 3. The 5 isodose line should fall within the rectal contour on each individual CT slice 4. The 9 isodose line should not exceed ½ the rectal diameter on any CT slice 5. The volume of rectum receiving 65 Gy 17% Gold Seed and CBCT BAT Alignment CT-on-rails Calypso (localization & tracking) 5

6 Average Motion >5mm (from Calypso beacons) 7 Time (sec) Overall Average = 12 sec Average Maximum = 2 sec Nodal Irradiation Patient Index Targeting Progression Intermediate risk (group 1) = prostate + proximalsv High risk (group 2) 1 = prostate + proximalsv 2 = distal sv (no lymph nodes) High risk (group 3) 1 = prostate + proximal sv 2 = distal sv 3 = periprostatic + peri sv LNs High risk (group 4) High risk (group 5) 1 = prostate + proximal sv 2 = distal sv 3 = periprostatic + peri sv LNs + LN ext 1 = prostate + proximal sv 2 = distal sv 3 = periprostatic + peri sv LNs + LN ext + presacral/perirectal LN LN ext = external iliac, proximal obturator and proximal internal iliac 6

7 Distal SVs Regional Distal SVs Extended Extended Regional Distal SVs Regional Distal SVs 7

8 Bladder Extended No longer a geometry problem; avoidance is only minimally useful Bladder Extended Regional Distal SVs Regional Distal SVs Presacral Nodes Lymphatic irradiation study patient data sets Generate plans for each stage in targeting progression Evaluate effect of nodal irradiation on our routine prostate IMRT plan acceptance criteria Evaluate effect on bowel Treatment time (logistical concerns as well as patient comfort) Physics concerns (dose per fraction vs. cone downs, increased hot spots, growth and localization technique, rectal expansion and inclusion of presacral nodes, etc.) Price et al. IJROBP 26 Volume (%) Rectal Dose 4 R65s R65v 35 R4s R4v 3 R65 limit R4 limit Patient Index Ln ext 8

9 Extended (good) Bladder Dose B65s B65v B4s B4v B65 limit B4 limit Gy Volume (%) failure 76 Gy Patient Index Ln ext 56 Gy Extended (good) Extended (bad) 56 Gy B4 = 4.5% 76 Gy R4 = 29.1% R65 =.2% B65 = 8.2% 56 Gy

10 Extended (bad) Bowel Dose 45 x 4 x5 x B4 = 74.3% B65 = 35.3% Volume of Bowel at 4Gy (cc) x5 x x5 x x5 x x5 6 failure R4 = 34.4% R65 = 12.4% Targeting Group Bowel Dose (ext LN treatment) Bowel4 (ext LN lat ) Bowel4 (no growth) Bowel4 limit What if we limit nodal growth laterally with a corresponding limit in the lateral shift based on daily localization? Bladder Dose (Ext LN treatment) B65 (ext LN lat ) B65 (no lat growth) B4 (ext LN lat B4 (no lat growth B65 limit B4 limit Volume (cc) Patient Index Only 4 failure Volume (%) Patient Index Only ~3 failure

11 Varian 21 Ex & Siemens Primus Bladder 1 cm leaf width vs 5 mm leaf width x mm 2 minimum beamlet vs 5 x 5 mm 2 We limit to 6-9 beam directions (primarily due to treatment time) Corvus treatment planning Increased MU Increase leakage secondary malignancies?, shielding concerns? 5 x 5 mm 2 beamlets Bladder x 5 mm 2 beamlets Collimator 9 degrees. This places the short axis of the beamlet ~perpendicularto the prostate-rectal interface Bladder MSF mod = MU IMRT /MU 3D CRT x 5 mm 2 beamlets Collimator degrees Price et al. JACMP 23 5 mm x 5 mm beamlets Analysis mm x 5 mm beamlets (coll 9) 5x5 beamlet 5x beamlet Average # of segments 386 Average # of MU 255 Average MSF mod 7. Average # of segments 197 (~49 % reduction) Average # of MU 1344 (~34.6 % reduction) Average MSF mod 4.6 (~34.3 % reduction) 5x5 beamlet 5 5 5x beamlet 5 Reductions Segments from 141 to 81 5 MU 142 to 886 MSF mod 4.8 to 3. 11

12 Significantly increased MU may result in all of the following except: 1. Increased leakage radiation 2. Potential increase in the occurrence of secondary malignancies 3. Shielding concerns 4. Increased treatment time 5. A decrease in beam stability Number of Patients Routine QA (Measured vs Calculated) [<-3.5] [-2.5,-3.5] [-1.5,-2.5] [-.5,-1.5] [-.5,.5] [.5,1.5] [1.5,2.5] [2.5,3.5] [>3.5] Frequency Bins (% difference).125 cc ion chamber HooRay!!! Post Docs!!! Teh Lin Ahmed Eldib Qianyi Xu Lihui Jin Post Docs Rule!!! 12