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					                   Is the Dose We See the Dose We Get? Analysis of DVHs using Daily Tomotherapy Based MVCT
                 Deformation of Prostate, Bladder and Rectum, to Assess the Actual Dose Received during Treatment
                                          C. Small, R. Chowdhury, R. Rivest, M. Mackenzie, G. Fallone, R. Pearcey, N. Pervez
                                                                                  Cross Cancer Institute, Edmonton, Canada

                                                                                 Bladder Deformation
  Introduction                                                                                                                                                                             Results

• Radiotherapy toxicity in the treatment of prostate cancer can be in
  part attributed to the dose received by the organs at risk (OAR),
  namely the bladder and rectum                                                                                                                                                                  Average Planned Dose Versus Treatment Dose (N=5)
• Dose volume constraints for the OARs have been based on the
                                                                                                                                                                                                                           Plan           Treatment
  correlation between the Dose Volume Histograms (DVH) generated
  from the a single planning CT and observed toxicity                                                                                                                                              Bladder
• It is well recognized that there can be significant day-to-day variation
  in the size and position of the OARs. This has been shown for both                                                                                                                                     Median          48.27Gy          52.93Gy
  the rectum and bladder                                                                                                                                                                                 V65Gy           18.64%           22.75%
                                                                             a                                   b                                         c
• The true dose received by the OAR can only be accurately                       Prostate Deformation
  determined by daily imaging of the treatment area in combination                                                                                                                                 Rectum
  with a record of the dose received to create a treatment specific DVH
  for each day                                                                                                                                                                                           Median          42.77Gy          46.82Gy
• The variation in size, shape and position of the bladder means that                                                                                                                                    V60Gy           14.37%           21.37%
  any one point on the organ can be in a different position each day. A
  simple summation of the daily DVH will mis-represent the dose                                                                                                                                    Prostate
  received by that organ. For example summing the Dmax each day
                                                                                                                                                                                                         D99%(min)       67.91 Gy         69.26Gy
  will not reveal the maximum dose a particular point of the organ
  received, as the Dmax point may delivered to different areas of the                                                                                                                                    D1%(max)        69.29 Gy         73.52Gy
  organ each day
• Daily deformable registration of the OARs is required to enable                                                                                                                          • Treatment dose in general is hotter than the planned dose except in
  summation of the daily DVH’s to enable a single actual dose                a                                   b                                         c                                 one patient were the rectum received a lower dose than planned
  received DVH
                                                                                 Rectal Deformation                                                                                        • The treatment dose received still met all study dose volume
                                                                                                                                                                                             constraints in all cases for the rectum
  Methods                                                                                                                                                                                  • In one patient the bladder treatment dose was higher than both study
                                                                                                                                                                                             dose volume constraints (i.e. Median and V65Gy)
• 60 patients with high risk prostate adenocarcinoma, underwent                                                                                                                            • Number of patients (n=5) is too small to detect any significant
  hypofractionated RT on a phase II clinical trial                                                                                                                                           differences
• RT prescription was 68Gy in 25 fractions (2.72 Gy per fraction) to
  the prostate and proximal seminal vesicles
• The pelvic lymph nodes and distal SV concurrently received 45Gy in                                                                                                                       Conclusions
  25 fractions.
• Dose volume constraints- Bladder: V65Gy ≤ 30%, median dose ≤
  60Gy. Rectum: V60Gy ≤ 30% and median dose ≤ 55Gy                           a                                   b                                         c                               • Treatment dose in general is hotter than planned dose
• Treated with Helical Tomotherapy (TomoTherapy Inc., Madison, WI,           a = Planning KVCT                                                                                             • All warped images for each organ must be manually checked to
  USA) based IMRT and underwent daily megavoltage CT (MVCT) for              b = Treatment MVCT with contour from planning CT                                                                ensure accuracy, currently some MVCT’s require modification of
  image guided verification prior to each treatment. There was an            c = Organ deformed to shape of planning CT contour                                                              default parameters before an accurate deformation is achieved
  initial automatic bone alignment performed each day, this was the                                                                                                                        • Large variations in rectal volumes are the main cause of initial
  followed by a manual 3D matching of the prostate-rectal interface                                                                                                                          inaccurate deformation and the efforts are continuing in order to
  prior to the treatment being delivered. The x, y and z offsets were            Results
                                                                                                                                                                                             improve this
  recorded.
                                                                                                                                                                                           • Standard DVH’s based on the planning CT are not an accurate
• 5 patients were selected                                                                                                                                                                   reflection of the dose received by the OARs during treatment
                                                                                       100%
• Each daily treatment sinogram (a record of the dose delivered) was
  then applied to that days MVCT and a verification isodose                            90%                                                                                                 • This may be the cause of poor correlations between DVH’s and
  distribution was generated for that MVCT                                             80%
                                                                                                                                                                                             toxicity
• The planning CT slices, the prostate, rectal, bladder and femoral                    70%
                                                                                                                                                                                           • All 60 patients need to be analysed and deformed cumulative DVH
  head contours, and the 25 daily MVCT’s and verification isodoses                                                                                                        Prostate Treat     correlated with acute and late toxicity
                                                                                       60%                                                                                Bladder Treat
  were then exported to DoseWarp. This is an in-house deformable                                                                                                          Rectum Treat     • Individual variations in toxicity may be due to variations in actual
                                                                                       50%
  registration software package                                                                                                                                           Prostate Plan      dose received to the OARs
                                                                                       40%                                                                                Bladder Plan
• The prostate, bladder, rectum and femoral heads from the MVCT                                                                                                           Rectum Plan
  were then warped to match their respective shapes and positions on                   30%

  the planning CT                                                                      20%
                                                                                                                                                                                            Acknowledgements
• The MVCT isodoses were then warped using the data generated                          10%
  from the warping of the organs. A DVH could then be generated for                     0%
  each organ                                                                                  0   5   10   15   20   25   30      35   40   45   50   55   60   65   70

• Each 25 daily DVH’s were then summed and the process was                                                                     Dose Gray
                                                                                                                                                                                           Albert Cancer Board for Bridge and Pilot Funding
  repeated for each patient                                                            Dose planned versus actual dose received for patient 1

				
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