Assessment of radiobiological metrics applied to patient-specific QA process of VMAT prostate treatments.

VMAT is a powerful technique to deliver hypofractionated prostate treatments. The lack of correlations between usual 2D pretreatment QA results and the clinical impact of possible mistakes has allowed the development of 3D verification systems. Dose determination on patient anatomy has provided clinical predictive capability to patient-specific QA process. Dose-volume metrics, as evaluation criteria, should be replaced or complemented by radiobiological indices. These metrics can be incorporated into individualized QA extracting the information for response parameters (gEUD, TCP, NTCP) from DVHs. The aim of this study is to assess the role of two 3D verification systems dealing with radiobiological metrics applied to a prostate VMAT QA program. Radiobiological calculations were performed for AAPM TG-166 test cases. Maximum differences were 9.3% for gEUD, -1.3% for TCP, and 5.3% for NTCP calculations. Gamma tests and DVH-based comparisons were carried out for both systems in order to assess their performance in 3D dose determination for prostate treatments (high-, intermediate-, and low-risk, as well as prostate bed patients). Mean gamma passing rates for all structures were bet-ter than 92.0% and 99.1% for both 2%/2 mm and 3%/3 mm criteria. Maximum discrepancies were (2.4% ± 0.8%) and (6.2% ± 1.3%) for targets and normal tis-sues, respectively. Values for gEUD, TCP, and NTCP were extracted from TPS and compared to the results obtained with the two systems. Three models were used for TCP calculations (Poisson, sigmoidal, and Niemierko) and two models for NTCP determinations (LKB and Niemierko). The maximum mean difference for gEUD calculations was (4.7% ± 1.3%); for TCP, the maximum discrepancy was (-2.4% ± 1.1%); and NTCP comparisons led to a maximum deviation of (1.5% ± 0.5%). The potential usefulness of biological metrics in patient-specific QA has been explored. Both systems have been successfully assessed as potential tools for evaluating the clinical outcome of a radiotherapy treatment in the scope of pretreatment QA.

[Radiotherapy after radical prostatectomy: description, outcome and prognostic factors in and emerging practice]. / Radioterapia tras prostatectomía radical: factores descriptivos, evolutivos y de pronóstico en una práctica asistencial emergente.

OBJECTIVES: Recently it has been reported in the EORTC (European Organisation for Research and Treatment of Cancer) trial 22911 and the SWOG (Southwest Oncology Group) 8794, the evidence that radiotherapy (RT) is an effective treatment after the prostatectomy in patients with high risk of biochemical failure. We analyze predictor factors of biochemical relapse and the potential benefits induced by rescue treatment are the main purposes of our study. METHODS: From 1993 to 2003, 597 prostatectomy were followed at Hospital Universitario Gregorio Marañón de Madrid, identifying 166 patients (p) (28%) of biochemical failure (defined as PSA > or = 0'5 ng/ml, including post-surgical persistent values). 42 p received RT (78% due to delayed PSA relapse). The median total dose was 66 Gy [60-74]. RESULTS: Clinical variables: Median age: 68 years [49-80], median PSA at diagnosis: 29,8 ng/ml [2,6475]; presurgical Gleason > or = 7: 65%. Histological variables: Prostatectomy induces stage migration to superior T (pT3-T4: 95%) and Gleason categories (> or =7: 81%). 83% of relapsed p had positive margins and 90% had pT3-pT4. OUTCOME VARIABLES: median time to biochemical recurrence was 22,2 months. Median time interval between biochemical failure and RT was 10,5 months. Overall survival (5 years) was 86 +/- 6%. Freedom-from-biochemical failure at 5 years was 76 +/- 4%. RT had poor survival in p with PSA > 2 ng/ml pre-RT (p = 0.03), post-prostatectomy persistant disease (p = 0.05) and Gleason score > or = 7 (p = 0.01). No increased grade 3-4 uro-rectal toxicity was observed. CONCLUSIONS: RT after prostatectomy improves freedom-from-biochemical failure in p with PSA values below 2 ng/ml. In our experience, Gleason score > or = 7 is a negative predictor of response. There is no severe toxicity in our series. Improvement of the staging presurgery, the role of the adjuvant androgen deprivation and selection of patients for adjuvant RT focus current studies on treatment after prostatectomy.