Dosimetric and volumetric changes in the rectum and bladder in patients receiving CBCT-guided prostate IMRT: analysis based on daily CBCT dose calculation.

Delivered dose can be calculated by transferring the planned treatment beams onto the daily CBCT. Bladder and rectum volumetric doses were calculated and cor-related to the daily bladder and rectum fullness. Patients for this study underwent hypofractionated prostate IMRT to 70 Gy in 28 fractions. Daily CBCT was utilized for image guidance. A clinically acceptable plan was created using a CTV-to-PTV uniform margin of 5 mm. Image fusion was performed to transfer the bladder and rectum contours onto each CBCT. Contours were then edited to match the anatomy of each CBCT. Using the daily treatment isocenter, the planned beams were transferred onto the CBCT and daily and cumulative DVHs calculated. For the results a total of 168 daily CBCTs were evaluated. The bladder was found to be smaller for 74.7% of the 168 daily CBCTs accessed in this study. This reduction in volume correlated to an increase in the cumulative bladder V70 Gy from 9.47% on the planning CT to 10.99% during treatment. V70Gy for the rectum was 7.27% on the planning CT, when all six patients were averaged, and increased to 11.56% on the average of all daily treatment CBCTs. Increases in volumetric rectum dose correlated with increases in rectal volume. For one patient, the rectum and blad-der absolute V70 Gy, averaged over the course of treatment, increased by 295% and 61%, respectively. Larger variations in the daily bladder and rectal volume were observed and these correlated to large deviations from the volumetric dose received by these structures. In summary, bladder and rectum volume changes during treatment have an effect on the cumulative dose received by these organs. It was observed that the volumetric dose received by the bladder decreases as the volume of the bladder increases. The inverse was true for the rectum.

Pearson D ，Gill SK ，Campbell N ，Reddy K ... -  《Journal of Applied Clinical Medical Physics》

Determination of optimal PTV margin for patients receiving CBCT-guided prostate IMRT: comparative analysis based on CBCT dose calculation with four different margins.

Gill SK ，Reddy K ，Campbell N ，Chen C ，Pearson D ... -  《Journal of Applied Clinical Medical Physics》

Associations between volume changes and spatial dose metrics for the urinary bladder during local versus pelvic irradiation for prostate cancer.

Casares-Magaz O ，Moiseenko V ，Hopper A ，Pettersson NJ ，Thor M ，Knopp R ，Deasy JO ，Muren LP ，Einck J ... -  《-》

Evaluation of online/offline image guidance/adaptation approaches for prostate cancer radiation therapy.

To evaluate online/offline image-guided/adaptive treatment techniques for prostate cancer radiation therapy with daily cone-beam CT (CBCT) imaging. Three treatment techniques were evaluated retrospectively using daily pre- and posttreatment CBCT images on 22 prostate cancer patients. Prostate, seminal vesicles (SV), rectal wall, and bladder were delineated on all CBCT images. For each patient, a pretreatment intensity modulated radiation therapy plan with clinical target volume (CTV) = prostate + SV and planning target volume (PTV) = CTV + 3 mm was created. The 3 treatment techniques were as follows: (1) Daily Correction: The pretreatment intensity modulated radiation therapy plan was delivered after online CBCT imaging, and position correction; (2) Online Planning: Daily online inverse plans with 3-mm CTV-to-PTV margin were created using online CBCT images, and delivered; and (3) Hybrid Adaption: Daily Correction plus an offline adaptive inverse planning performed after the first week of treatment. The adaptive plan was delivered for all remaining 15 fractions. Treatment dose for each technique was constructed using the daily posttreatment CBCT images via deformable image registration. Evaluation was performed using treatment dose distribution in target and critical organs. Treatment equivalent uniform dose (EUD) for the CTV was within [85.6%, 100.8%] of the pretreatment planned target EUD for Daily Correction; [98.7%, 103.0%] for Online Planning; and [99.2%, 103.4%] for Hybrid Adaptation. Eighteen percent of the 22 patients in Daily Correction had a target dose deficiency >5%. For rectal wall, the mean ± SD of the normalized EUD was 102.6% ± 2.7% for Daily Correction, 99.9% ± 2.5% for Online Planning, and 100.6% ± 2.1% for Hybrid Adaptation. The mean ± SD of the normalized bladder EUD was 108.7% ± 8.2% for Daily Correction, 92.7% ± 8.6% for Online Planning, and 89.4% ± 10.8% for Hybrid Adaptation. Both Online Planning and Hybrid Adaptation can achieve comparable target coverage and normal tissue sparing and are superior to the Daily Correction technique. The Daily Correction technique using a 3-mm target margin in the pretreatment plan is not appropriate to compensate for residual variations in CBCT image-guided prostate cancer radiation therapy.

Qin A ，Sun Y ，Liang J ，Yan D ... -  《-》

Megavoltage cone beam computed tomography dose and the necessity of reoptimization for imaging dose-integrated intensity-modulated radiotherapy for prostate cancer.

Megavoltage cone beam computed tomography (MV-CBCT) dose can be integrated with the patient's prescription. Here, we investigated the effects of imaging dose and the necessity for additional optimization when using intensity-modulated radiotherapy (IMRT) to treat prostate cancer. An arc beam mimicking MV-CBCT was generated using XiO (version 4.50; Elekta, Stockholm, Sweden). The monitor units (MU) for dose calculation were determined by conforming the calculated dose to the dose measured using an ionization chamber. IMRT treatment plans of 22 patients with prostate cancer were retrospectively analyzed. Arc beams of 3, 5, 8, and 15 MU were added to the IMRT plans, and the dose covering 95% of the planning target volume (PTV) was normalized to the prescribed dose with (reoptimization) or without optimization (compensation). PTV homogeneity and conformality changed negligibly with MV-CBCT integration. For critical organs, an imaging dose-dependent increase was observed for the mean rectal/bladder dose (D(mean)), and reoptimization effectively suppressed the D(mean) elevations. The bladder generalized equivalent uniform dose (gEUD) increased with imaging dose, and reoptimization suppressed the gEUD elevation when 5- to 15-MU CBCT were added, although rectal gEUD changed negligibly with any imaging dose. Whereas the dose elevation from the simple addition of the imaging dose uniformly increased rectal and bladder dose, the rectal D(mean) increase of compensation plans was due mainly to low-dose volumes. In contrast, bladder high-dose volumes were increased by integrating the CBCT dose, and reoptimization reduced them when 5- to 15-MU CBCT were added. Reoptimization is clearly beneficial for reducing dose to critical organs, elevated by addition of high-MU CBCT, especially for the bladder. For low-MU CBCT aimed at bony structure visualization, compensation is sufficient.

Akino Y ，Koizumi M ，Sumida I ，Takahashi Y ，Ogata T ，Ota S ，Isohashi F ，Konishi K ，Yoshioka Y ... -  《-》