Prostate and rectal volumes, but not bladder volumes, on treatment planning CT influenced prostate position on treatment fractions. Daily image-guided adoptive radiotherapy would be required for patients with distended or empty rectum on planning CT to reduce rectal toxicity in the case of empty rectum and to minimize geometric miss of prostate.

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Purpose: To study the relationship between prostate volume/location, bladder and rectum volumes on treatment‐planning CT‐day and prostate shift in XYZ directions on treatment‐days. Method and Materials: Prostate, SV, bladder and rectum (rectosigmoid‐flexure to anorectal‐verge), were contoured on CT‐images. Isocenter was 6 cm posterior to the tip of pubic‐arch and 1 cm inferior to the pubic‐brim. IMRT plans were prepared. Contours were exported to BAT‐system. Patients were positioned on couch using skin marks. US‐probe was used to obtain US‐images of prostate, bladder and rectum and aligned with CT‐images. Shifts in XYZ directions as recommended by BAT‐system were made and recorded. 4698 couch‐shifts for 42 patients were analyzed to study a correlation between prostate shifts vs. bladder and rectum volumes and prostate volume/location on CT‐day. Spatial location of prostate was defined as distance of prostate base to isocenter. Dose to 50% of bladder vs. volume was also studied. Pearson's correlation coefficient r, and P values were used for statistical analysis. Results: Mean and range of volumes (cc): bladder: 179, 42–582, rectum: 108, 28–223 and prostate: 55, 21–154. Mean prostate shifts (cm, ±SD): R/L (X): −0.047±0.16, AP/PA (Y): 0.14±0.3 and S/I (Z): 0.19±0.26. Lateral, AP/PA and S/I shifts were not correlated with volumes of bladder, rectum and prostate; bladder and prostate; and bladder and rectum, (P>0.2), respectively. Smaller the rectal volume (P<0.001) or diameter (P<0.05) of rectum, larger was the anterior shift and vice‐versa. Smaller the prostate base distance to isocenter or volume, larger was superior shift and vice‐versa (P<0.05). Dose to bladder decreased with increase in volume up to 300cc, reaching a plateau with further increase in volume (P<0.001). Conclusions: Prostate location/volume and rectal‐volume, but not bladder‐volume on CT‐day influence prostate position. Bladder with 200–300cc volume, but not full bladder, would be optimum for patient comfort, minimizing bladder dose and US‐image quality.

binned into 10 respiratory phases based on liver position. For all phases, the binary mask of each volumetric time frame at phase i were summated prior to the normalization to the total number of dynamic volumes at phase i (resulting in a total of 10 probability distribution maps). For each phase i, V 90, i and the SI translational range (R SI, i) of the liver position were evaluated. For each subject, the optimal gating window phase (P w) and the gating window durations (D w) was determined with two approaches based on (1) R SI (P w Z phases with minimum R SI , D w Z neighboring phases of P w with R SI < 2mm); (2) dice similarity coefficient (DSC) (P w Z phase of maximum V 90 (V 90,max), D W Z neighboring phases of P w with DSC > 0.9). The mean R SI of the phase of V 90,max for all VOIs, and the mean minimum R SI (R SI,min) were also reported. Comparison between RSI and DSC approaches was performed using signed rank test. Results: Comparing between approaches, similar P w at exhalation was obtained using R SI (50AE11%) and DSC (LK:46AE24%, pZ1; RK:54AE19%, pZ0.69). The mean V 90,max (LKZ156AE34mm 3 , RKZ149AE26mm 3) was close to the mean organ volume (LKZ160AE34mm 3 ; RKZ154AE27mm 3). The mean R SI of the phase at V 90,max (LKZ2.48AE1.92mm, pZ0.38; RKZ2.41AE1.91mm, pZ1) was similar to R SI,min (2.06AE1.99mm). The choice of gating window using DSC was preferable because a highly repeatable volumetric coverage was obtained, while such volume information cannot be fully revealed by the R SI approach. A smaller D w was obtained using RSI (14AE5%) then DSC (LK:42AE23%, pZ0.016; RK:60AE31%, pZ0.016), though insignificant, might suggest a less effective gated-RT delivery based simply on SI displacement. Conclusion: Larger D w was obtained based on DSC approach allows a more effective gated-RT delivery with the overlapping volume taken into consideration.

Purpose: Major goal of IMRT is to escalate dose to prostate while keeping doses to bladder and rectum equal to or less than that with 3DCRT. This study is to compare 3DCRT and IMRT to evaluate how far this goal has been achieved. Method and Materials: Dosimetry of 6‐field 3DCRT and 5‐field IMRT plans, generated for the same 32 patients, has been compared. With 3DCRT, prescription to SV and prostate was 45 and 75.6 Gy, respectively. With IMRT, prescription to SV and prostate was 45 and 81 Gy, respectively. IMRT required to keep doses to 30%, 50% and 70% of bladder and rectum less than 70%, 60% and 40% of 81 Gy and to cover 95% PTV with 95% isodose. Dose to rectum and bladder were estimated from DVH. Less than 5% difference in rectal and bladder doses between 3DCRT and IMRT was considered insignificant. Results: Higher the dose to rectum and bladder with 3DCRT, higher also was the dose with IMRT (P<0.001). Dose to 50% rectum with IMRT was equal to that with 3DCRT in 15 cases (47%) and more in 17 cases (53%). Dose to 10% of rectum with IMRT was equal to that with 3DCRT in 9 cases (28%) and more in 23 cases (72%). Dose to 50% and 10% bladder with IMRT were equal to that with 3DCRT in 7 cases (22%) and more in 25 cases (78%). Conclusion: Preliminary analysis suggested that the space between rectum and prostate+SV, and the volume of rectum and bladder in beams path are related to doses to these structures. Higher doses to rectum and bladder with IMRT are a result of trade‐off between doses to PTV, rectum and bladder. This may be acceptable because percent dose coverage to 95% PTV is better with IMRT (93–98%) than with 3DCRT (86–93%).