IGRT 2016 Madrid

949 (1) . The 5-year BC for the 50 patients with CSA > 12 cm 2 was 93.6%, as compared with 88.6% for those with CSA ! 12 cm 2 ( p Z 0.468). The BC for SVP subgroups ( < 39.5, 39.5 e 53.3, 53.4 e 75.2, > 75.2 mL) was 86.3%, 90.3%, 91.2%, and 88.6%, respectively ( Fig. 4 ; p Z 0.97). The lack of impact of rectal distension on BC was observed in all subgroups stratified by RV, CSA, and SVP. Table 1b is a summary of the above data. Patient #1

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N= 962 GTV=CTV (+/- 2cm SV) No diet modification, laxatives, or rectal enemas were used The quartile values of RV, CSA, and SVP were used to subdivide each risk group. The impact of these volumetric parameters on 5-year biochemical control (BC, Phoenix definition) and chronic Grade ! 2 and 3 GI and GU toxicity were examined. Common Terminology Criteria for Adverse Events V3.0 was used to score toxicity. Statistics Estimated likelihood of events was calculated using the Kaplan- Meier test. The statistical significance of differences between curves was calculated using the log-rank test. The association of categorical variables within treatment groups was analyzed using Fisher’s two-tailed exact test. Differences between two sample means for continuous variables were analyzed using t -tests. A two-tailed p value of 0.05 was considered to be statistically significant for all tests. Statistical analyses were perfor ed using SPSS Statistics version 17.0 (Chicago, IL). 3DCRT plan for 9 fractions (PTV 1cm isotropic) Prostate ITV based on planning CT + 4CBCT Patient, tumor, treatment, and rectal volumetric characteristics Late G≥2 and G3 = 21% and 3% No impact of RV on both late tox and BC Group I patients comprised 41.6% of the cohort. Median ages were 70.2 and 72.1 years for groups I and II, respectively ( p < 0.01). Group I had a significantly lower mean PSA (5.9 vs. 12.1 ng/mL; p < 0.01) and Gleason score (6.1 vs. 7.1; p < 0.01) when compared with group II. The majority of group I patients (77%) were identified by elevated PSA ( " T1c), whereas 44% of group II were ! T2a. IMRT was employed more frequently among group II (47% vs. 33%, p < 0.01). Table 1a summarizes these observations. For the entire cohort, the median (mean) follow-up was 5.5 years. The median prescription dose was 75.6 Gy (minimum dose t cl-PTV), the median isocenter dose was 79.7 Gy, and no statistical difference was noted between the two risk groups. The median values for RV, CSA, and SVP on the planning CT image were 82.8 cm 3 , 5.6 cm 2 , and 53.3 cm 3 , respectively. Offline adaptive IGRT allowed for a mean reduction from the initial PTV to cl-PTV of 74.4 # 30.2 cm 3 . Target margin from the planning CTV to cl-PTV was very heterogeneous with a mean of 8.1 # 3.1 mm (calculated from the middle of the CTV in the anteroposterior 03/01/13 Results

Toxicity outcome

For the entire cohort, any chronic Grade " 2 GI and GU toxicities (maximum toxicity at any time point) were 21.2% and 15.5%, respectively. The respective values for any chronic Grade " 3 GI and GU were 2.9% and 4.3%. No significant differences were noted in chronic Grade " 2 or 3 GI and GU toxicities when the cohort was stratified by RV ( Tables 2a and 2b ).

Tab

Patient #2

RV

6 8

CS

4 5

SV

Fig. 1. Relationship between the initial planning clinical target volume (CTV; red and light blue) and the ITV (purple) for 2 patients.

3 5

use of the planning CTV would have introduced a significant systematic bias as determined from the CTV at the mean position. The mean difference and the standard deviation from the planning CTV center position to the ITV center position were 0.5 # 2.8 mm in the anteroposterior, 0.1 # 2.1 mm in the superoinferior, and $ 0.1 # 0.7 mm in the right-left positions. Again, the systematic bias was larger in the superior portion of the target and smaller in the inferior portion. The volume of the rectal wall and bladder on the initial planning CT was used for both initial planning and adaptive modification. Therefore, their dose-volume histograms Biochemical control (BC) by cross-sectional area (CSA) quartile ( < 4.4, 4.4 e 5.6, 5.7 e 7.9, > 7.9 cm 2 ). Fig. 3.

A area spec pros

Park S. et al., IJROBP 2012