Intercenter validation of a knowledge based model for automated planning of volumetric modulated arc therapy for prostate cancer. The experience of the German RapidPlan Consortium.

PURPOSE: To evaluate the performance of a model-based optimisation process for volumetric modulated arc therapy applied to prostate cancer in a multicentric cooperative group. The RapidPlan (RP) knowledge-based engine was tested for the planning of Volumetric modulated arc therapy with RapidArc on prostate cancer patients. The study was conducted in the frame of the German RapidPlan Consortium (GRC). METHODS AND MATERIALS: 43 patients from one institute of the GRC were used to build and train a RP model. This was further shared with all members of the GRC plus an external site from a different country to increase the heterogeneity of the patient's sampling. An in silico multicentric validation of the model was performed at planning level by comparing RP against reference plans optimized according to institutional procedures. A total of 60 patients from 7 institutes were used. RESULTS: On average, the automated RP based plans resulted fully consistent with the manually optimised set with a modest tendency to improvement in the medium-to-high dose region. A per-site stratification allowed to identify different patterns of performance of the model with some organs at risk resulting better spared with the manual or with the automated approach but in all cases the RP data fulfilled the clinical acceptability requirements. Discrepancies in the performance were due to different contouring protocols or to different emphasis put in the optimization of the manual cases. CONCLUSIONS: The multicentric validation demonstrated that it was possible to satisfactorily optimize with the knowledge based model patients from all participating centres. In the presence of possibly significant differences in the contouring protocols, the automated plans, though acceptable and fulfilling the benchmark goals, might benefit from further fine tuning of the constraints. The study demonstrates that, at least for the case of prostate cancer patients, it is possibile to share models among different clinical institutes in a cooperative framework.

Application of a hydrogel spacer for postoperative salvage radiotherapy of prostate cancer.

BACKGROUND: In contrast to primary radiotherapy, no reports are available for a hydrogel spacer application in postoperative salvage radiotherapy for prostate cancer. CASE REPORT: A 77-year-old patient presented 20 years after radical prostatectomy with a digitally palpable local recurrence at the urethrovesical anastomosis (PSA 5.5 ng/ml). The hydrogel spacer (10 ml, SpaceOAR™) was injected between the local recurrence and rectal wall under transrectal ultrasound guidance. Treatment planning was performed with an intensity-modulated technique up to a total dose of 76 Gy in 2-Gy fractions. The same planning was performed based on computed tomography before spacer injection for comparison. RESULTS: The local recurrence, initially directly on the rectal wall, could be displaced more than 1 cm from the rectal wall after hydrogel injection. With a mean total dose of 76 Gy to the planning target volume, rectal wall volumes included in the 70 Gy, 60 Gy, 50 Gy isodoses were 0 cm(3), 0 cm(3), and 0.4 cm(3) with a spacer and 2.9 cm(3), 4.5 cm(3), and 6.2 cm(3) without a spacer, respectively. The patient reported rectal urgency during radiotherapy, completely resolving after the end of treatment. The PSA level was 5.4 ng/ml a week before the end of radiotherapy and dropped to 0.9 ng/ml 5 months after radiotherapy. CONCLUSION: A hydrogel spacer was successfully applied for dose-escalated radiotherapy in a patient with macroscopic local prostate cancer recurrence at the urethrovesical anastomosis to decrease the dose at the rectal wall. This option can be considered in specifically selected patients.

Learning curve in the application of a hydrogel spacer to protect the rectal wall during radiotherapy of localized prostate cancer.

OBJECTIVE: To evaluate the effect of increasing experience on hydrogel dimensions, rectal dose, and acute toxicity, and to discuss important technical issues gained from this experience. METHODS: Sixty-four consecutive patients with prostate cancer were included in this analysis (G1/G2 corresponding to first/second 32 patients) after injection of 10 mL spacer gel. All patients were treated with a 5-field intensity-modulated radiotherapy technique to 76-78 Gy. Treatment toxicity was evaluated with a validated quality of life questionnaire (expanded prostate cancer index composite) before and after radiotherapy. RESULTS: Rectum volume could be entirely excluded from the planning target volume in 31% in G1 vs 56% in G2 (P = .04). Increasing symmetry was detected comparing the first 15 patients to the subsequent rest, with mean differences between right and left of 0.6 cm vs 0.3 cm at the midgland (P = .03). Mean distance between prostate and anterior rectal wall increased from 0.8 cm/1.1 cm/0.8 cm (G1) at the base/middle/apex to 1.3 cm/1.5 cm/1.2 cm (G2), respectively, so that the dose to the rectum decreased significantly (6% vs 2% of the volume inside the 70 Gy isodose; P <.01). Bowel function and bother score changes were smaller comparing baseline with last day of radiotherapy levels (mean 16/18 in G1 vs 9/12 in G2). CONCLUSION: A learning curve could be demonstrated in our patient population, respecting improved and more symmetrical spacer placement, improved treatment planning, and less treatment-related acute toxicity. Several important technical aspects need to be considered.

The reproducibility of landmarks on three-dimensional images of 4- to 6-year-old children.

OBJECTIVE: The objective of this study was to check the reproducibility and influencing parameters of landmarks on three-dimensional images of 4- to 6-year-old Caucasian children. PROBANDS AND METHODS: We examined the reproducibility of 22 landmarks on six three-dimensional facial scans of 4- to 6-year-old randomly-selected kindergarten children. The 3D scans were taken by the digital system faceSCAN II under standardized conditions. One specially-trained investigator marked all landmarks on each of the six 3D scans a total of ten times. Ten different orthodontic residents also placed all landmarks on each of these scans. Standard deviations from the mean were then calculated from the data for each individual landmark on the x-, y- and z-axes. RESULTS: The specially-trained investigator who had placed all landmarks on each of the six 3D scans a total of ten times found 15 of 22 landmarks to be reproducible well to within a standard deviation of less than 1 mm on each spatial plane. For the ten orthodontic residents, only three landmarks were found to be reproducible to within a standard deviation of under 1 mm for each spatial plane. CONCLUSION: Familiarity with 3D facial scans and their corresponding software programs, together with good image quality, improve the reproducibility of the analysis. Landmarks revealing poor reproducibility should be used, if at all, with due caution for analysis. It remains to be seen whether they can be omitted altogether, or whether they should be re-set.