IMRT for Prostate Cancer. Robert A. Price Jr., Ph.D. Philadelphia, PA

Transcription

1 IMRT for Prostate Cancer Robert A. Price Jr., Ph.D. Philadelphia, PA

2 Number of Patients IMRT Patients at FCCC Prostate Breast H&N Other 64 Approximately patients per day on 6 linacs ~ 55-6% are treated via IMRT >19 IMRT patients total 2 Treatment Site 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 half-full bladder because during treatment a full bladder is difficult to maintain. foot holder alpha cradle

3 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. Bad rectum 6 cm 4.5 cm Good rectum 3 cm 2.5 cm 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 3 mm slice thickness and 3 mm table increment. All other regions are scanned to result in a 1 cm slice thickness.

4 MR Scans 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..23 T, Philips Medical Systems Retrograde urethrograms are not performed. MRI CT Extracapsular extension Seminal vesicles? Imaging modality may affect treatment regime

5 MRI CT Prostate (CT) Prostate (MR) Imaging artifacts may affect contouring PTV growth = 8mm in all directions except posteriorly where a 5mm margin is typically used A Rt FH Bladder S I CTV P Rectum Lt FH The effective margin is defined by the distance between the posterior aspect of the CTV and the prescription isodose line and typically falls between 3 and 8 mm.

6 Acceptance Criteria DVH Acceptance Criteria PTV 95 % 1% Rx R 65 Gy 17%V R 4 Gy 35%V B 65 Gy 25%V B 4 Gy 5%V FH 5 Gy 1%V Good DVH R 4 = 22.7% PTV 95 = 1% R 65 = 8.3% R 4 = 19% B 65 = 8.4%

7 Good plan example (axial) 1% 9% 8% 7% 6% 5% CTV Effective margin 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 1% 9% 8% 7% 6% 5% Good plan example (sagital) CTV Attempting to get isodose line compression (fast dose fall-off) at the prostate-rectum interface

8 DVH Acceptance Criteria PTV 95 % 1% Rx R 65 Gy 17%V R 4 Gy 35%V B 65 Gy 25%V B 4 Gy 5%V FH 5 Gy 1%V DVH for bad plan (meets DVH criteria) R 4 = 31.5% PTV 95 = 1% R 65 = 13.4% B 4 = 21.3% B 65 = 9% Bad plan example (axial) 1% 9% 8% 7% 6% 5% CTV The 5% isodose line falls outside the rectal contour

9 Bad plan example (sagital) 1% 9% 8% 7% CTV 6% 5% The 5% isodose line falls outside the rectal contour Typical Dose Routine treatments Prostate + proximal sv (76 2. Gy/fx) Distal sv, lymphatics (56 ~1.5 Gy/fx) 38 fractions total Post Prostatectomy Prostate bed ( Gy/fx)

10 Hypofractionation Prostate + proximal sv ( Gy/fx) equivalent to 84.4 Gy in 2Gyfractions assuming an α/β ratio of 1.5. Distal sv, lymphatics (5 ~1.5 Gy/fx) 26 fractions total BED for rectum & bladder R 5 Gy 17%V R 31 Gy 35%V B 5 Gy 25%V B 31 Gy 5%V FH 4 Gy 1%V Number of Beam Directions 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

11 Localization BAT Alignment This has allowed for increased accuracy. Patient scans randomly evaluated; 33 prior to and 31 after technique adopted. Evaluated by same physician. Substandard alignments dropped from 15.1% to 3.5% (p=.6) -McNeeley et al. AAPM 24 Separation of seminal vesicles into proximal and distal

12 CT-on-rails Prostate CT shifts (mm) LAT AP LONG 1σ =2.16mm 2σ =4.32mm Ave=-.62mm BAT shifts (mm) BAT vs. Primatom shifts. Data for 218 alignments are presented (differences between the 2 sets of shifts). The solid line is the line of perfect agreement between the two systems. 1σ =2.14mm 2σ =4.28mm Ave=-.2mm 1σ =2.36mm 2σ =4.72mm Ave=-.32mm Feigenberg et al. (submitted) Prostate Bed Note lack of physical structures for alignment with BAT BAT first, CT second BAT first, CT second (Mon, Thurs, Mon ) Patient #2 (with no template) Patient #7 (w ith tem plate) Residual shift with sign (mm) AP Lat Long Residual shift with sign (mm) Initial Template (CT first and Template forced BAT shift) AP Lat Long -15. Observation number -15. Observation number Paskalev et al. (In Press)

13 Regions for dose constraint Region Limit % volume limit Minimum Maximum 1 9% of target goal 2 45% of target goal Target Max 2 8% 2 4% 9% of target goal 3 7% 2 35% 75% 4 5% 1 25% 55% 5 3% 1 15% 35% 6 2% 1 1% 25% Price et al. IJROBP 23 Region 1 Bladder Region 2 Region 3 CTV Region 6 Rectum Region 5 Region 4 Attempt to assure that PTV will be encompassed by the 1 st region Bladder CTV Region 1 Region 6 Region 2 Region 3 Region 4 Region 5

14 Regions 26 previously treated patients (6 and 1 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 1 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% Price et al. IJROBP 22

15 Bladder Bladder PTV PTV S.V. Rectum S.V. Rectum Direct right lateral Anterior 45 degree oblique Percent Volume Covered IMRT Plan Comparison (Rectum) 5fd ax 7fd ax (non eq) 7fd ax (eq) 9fd ax 5fd xfire 7fd xfire Percent of Delivered Dose

16 Nodal Irradiation JCO 21: , 23 The inclusion of pelvic lymphatic irradiation in the treatment of prostate cancer for some patients has been suggested in RTOG 9413.

17 WP followed by prostate boost Hormonal therapy and WP PSA control Roach et al, RTOG Targeting Progression Intermediate risk (group 1) PTV = prostate + proximal sv High risk (group 2) PTV1 = prostate + proximal sv PTV2 = distal sv (no lymph nodes) High risk (group 3) PTV1 = prostate + proximal sv PTV2 = distal sv PTV3 = periprostatic + peri sv LNs High risk (group 4) PTV1 = prostate + proximal sv PTV2 = distal sv PTV3 = periprostatic + peri sv LNs + LN ext High risk (group 5) PTV1 = prostate + proximal sv PTV2 = distal sv PTV3 = periprostatic + peri sv LNs + LN ext + presacral LN LN ext = external iliac, proximal obturator and proximal internal iliac

18 Prostate Proximal SVs Prostate Proximal SVs Distal SVs

19 Prostate Regional Lymphatics Distal SVs Proximal SVs Extended Lymphatics Prostate Regional Lymphatics Distal SVs Proximal SVs

20 Extended Lymphatics Prostate Rectum Regional Lymphatics Distal SVs Proximal SVs Bladder Prostate Extended Lymphatics No longer a geometry problem; avoidance is only minimally useful Rectum Regional Lymphatics Distal SVs Proximal SVs

21 Bladder Extended Lymphatics Prostate Rectum Regional Lymphatics Distal SVs Proximal SVs Presacral Nodes Lymphatic irradiation study 1 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 Evaluate effect on erectile tissues Treatment time (logistical concerns as well as patient comfort) Physics concerns (dose per fraction vs. cone downs, increased hot spots, PTV growth and localization technique, rectal expansion and inclusion of presacral nodes, etc.)

22 1% 9% 8% 7% 6% 5% Extended Lymphatics (good) 56 Gy 76 Gy 56 Gy 1% 9% 8% 7% 6% 5% Extended Lymphatics (good) B4 = 4.5% R4 = 29.1% B65 = 8.2% R65 = 1.2%

23 1% 9% 8% 7% 6% 5% Extended Lymphatics (bad) 56 Gy 76 Gy 56 Gy 1% 9% 8% 7% 6% 5% Extended Lymphatics (bad) B4 = 74.3% B65 = 35.3% R4 = 34.4% R65 = 12.4%

24 Prostate Proximal SVs Percent Volume Rectal Dose Patient Index Beams = 7.1 (σ = 1.1) R65 R4 R65 limit R4 limit Percent Volume Tx Time ~ 9. min Bladder Dose Patient Index Segments = 54.4 (σ = 13.1) B65 B4 B65 limit B4 limit Prostate Distal SVs Proximal SVs Prostate Distal SVs Proximal SVs Percent Volume Percent Volume Rectal Dose Patient Index Rectal Dose Regional Lymphatics Patient Index Beams = 7. (σ = 1.2) R65 R4 R65 limit R4 limit Percent Volume Tx Time ~ 9.1 min Beams = 8.2 (σ =.9) R65 R4 R65 limit R4 limit Percent Volume Tx Time ~ 12.6 min Bladder Dose Patient Index Bladder Dose Segments = 55.1 (σ = 14.2) Patient Index B65 B4 B65 limit B4 limit Segments = 76.1 (σ = 13.2) Siemens Primus, 1 MV, 1 x 1 mm 2 minimum beamlet B65 B4 B65 limit B4 limit Rectum Extended Lymphtics Percent Volume Rectal Dose Patient Index Beams = 8.7 (σ =.8) R65 R4 R65 limit R4 limit Percent Volume Tx Time ~ 19.3 min Bladder Dose Patient Index Segments = 117 (σ = 14.8) B65 B4 B65 limit B4 limit Bladder Percent Volume Presacral nodes Rectal Dose Patient Index Beams = 9. (σ = ) R65 R4 R65 limit R4 limit Percent Volume Tx Time ~ 23.9 min Bladder Dose Patient Index Segments = (σ = 11.7) Siemens Primus, 1 MV, 1 x 1 mm 2 minimum beamlet B65 B4 B65 limit B4 limit

25 Varian 21 Ex & Siemens Primus 1 cm leaf width vs 5 mm leaf width 1 x 1 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? MSF mod = MU IMRT /MU 3D CRT Price et al. JACMP 23 Bladder Prostate PTV 1 x 5 mm 2 beamlets 5 x 5 mm 2 beamlets Rectum Bladder Prostate PTV Collimator 9 degrees. This places the short axis of the beamlet ~perpendicular to the prostate-rectal interface Rectum Bladder Prostate PTV 1 x 5 mm 2 beamlets Collimator degrees Rectum

26 Mean values 5mm x 5mm (1.1%) 1mm x 5mm coll= (11.5%) 1mm x 5mm coll=9 (1.%) Percent of Rectum at 65 Gy Percentage of Total Rectal Volume Original (5mm x 5 mm) 1mm x 5mm (Coll = ) 1mm x 5mm (Coll = 9) Number of Patients Comparisons 5mm x 5mm to 1mm x 5mm coll= p=.4 (significant) Comparisons 5mm x 5mm to 1mm x 5mm coll=9 p=.85 (NOT significant) Comparisons 1mm x 5mm coll= to 1mm x 5mm coll=9 P<.1 (significant) Mean values 5mm x 5mm (255 MU) 1mm x 5mm coll= (1186 MU) 1mm x 5mm coll=9 (1344 MU) Monitor Units (MU) Comparison of Daily Monitor Units Original 5mm x 5mm 1mm x 5mm (Coll = ) 1mm x 5mm (Coll = 9) Comparisons 5mm x 5mm to 1mm x 5mm coll= P<<.1 (HIGHLY significant) Comparisons 5mm x 5mm to 1mm x 5mm coll=9 P<<.1 (HIGHLY significant) Number of Patients

27 Analysis 5 mm x 5 mm beamlets Average # of segments 386 Average # of MU 255 Average MSF mod 7. 1 mm x 5 mm beamlets (coll 9) Average # of segments 197 (~49 % reduction) Average # of MU 1344 (~34.6 % reduction) Average MSF mod 4.6 (~34.3 % reduction) 5x5 beamlet 5x1 beamlet CTV PTV 1% PTV CTV 1% 5% 5% 5x5 beamlet 1% 5x1 beamlet 1% PTV 5% CTV Reductions Segments from 141 to 81 PTV 5% CTV MU 142 to 886 MSF mod 4.8 to 3.

28 Routine QA Number of Patients Prostate (Measured vs Calculated) 9% 8% 5% 3% [<-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)

29 HooRay!!! Post Docs!!! Zuoqun (Jay) Chen Weijun (Wil) Xiong Freek DuPlessis Wei Luo Jiajin (James) Fan Antonio Leal Plaza Jennifer Zhu Xiu Xu Sotirios Stathakis Copernicus Pollack-nicus