Patient positioning variations to reduce dose to normal tissues during 3D conformal radiotherapy for high-risk prostate cancer

Volumetric and dosimetric comparison of organs at risk between the prone and supine positions in postoperative radiotherapy for prostate cancer

Background

The aim of this study was to evaluate the effects of patient positioning on the volume of organs at risk (OARs) in or near the planning target volume (PTV) and the dose distribution in adjuvant or salvage radiotherapy for prostate cancer after prostatectomy.

Methods

Seventeen patients who received intensity-modulated radiation therapy (66 Gy in 33 fractions) as adjuvant or salvage therapy after prostatectomy were evaluated. All patients underwent CT scans in both the prone (on a belly board) and supine positions. The target volumes and OARs were delineated on each CT series. The planning target volume (PTV) was extended in every direction to generate the PTV + 0.5 cm, PTV + 1 cm, PTV + 2 cm, PTV + 3 cm, and PTV + 4 cm values. The volumes of the OARs overlapping with the PTV and the extended target volumes in the prone and supine position were compared using the Wilcoxon signed-rank test. Dose-volume histogram (DVH) parameters in the prone and supine position were compared using the paired t-test.

Results

The mean overlapping volumes of the small intestine for each of the PTV values were as follows (prone position vs. supine position [mean ± SD]): PTV, 1.5 ± 5.5 cm³ vs. 7.9 ± 15.7 cm³ (P = 0.028); PTV + 0.5 cm, 2.6 ± 8.9 cm³ vs. 12.1 ± 22.6 cm³ (P = 0.028); PTV + 1 cm, 3.5 ± 11.4 cm³ vs. 17.1 ± 29.8 cm³ (P = 0.028); PTV + 2 cm, 5.6 ± 14.5 cm³ vs. 26.8 ± 46.9 cm³ (P = 0.028); and PTV + 3 cm, 9.0 ± 17.4 cm³ vs. 36.5 ± 63.2 cm³ (P = 0.019), respectively. Some of the overlapping volumes of the rectum and bladder were significantly smaller in the prone position. On the other hand, when the target volume was extended by ≥2 cm, the overlapping volumes of the femurs were significantly larger in the prone position. V15 of the rectum and mean dose and V65 of the bladder were significantly lower in the prone position.

Conclusions

This study indicated that the volumes of the small intestine, rectum, and bladder in or near the PTV decreased when the patient was placed in the prone position on a belly board in postoperative radiotherapy for prostate cancer. The dose distribution seemed superior in the prone position to the supine position.

Does transperitoneal minimally invasive radical prostatectomy increase the amount of small bowel receiving salvage radiation?

INTRODUCTION

Transperitoneal minimally invasive radical prostatectomy (MIRP) has become first choice for several urologists and patients dealing with localized prostate cancer. We evaluate the effect of postoperative radiation on the small bowel in patients who underwent extraperitoneal open versus transperitoneal MIRP.

METHODS

We reviewed all patients who received postoperative radiation from 2006 to 2010. Planning target volume (PTV) and surrounding organs, including the small bowel, were delineated. The presence of the small bowel in PTV and its volume in receiving each dose level were analyzed.

RESULTS

A total of 122 patients were included: 26 underwent MIRP and 96 underwent open prostatectomy. The median age of patients was 66 years, with median body mass index 27 kg/m(2). The total PTV dose was 66 Gy, with the minimum and maximum doses received by the small bowel 0.4 and 66.4 Gy, respectively. The maximum volume of small bowel that received the safe limit of 40 Gy was 569 cm(3). Of the 26 patients who underwent MIRP, 12 (46%) had small bowel identified inside the PTV compared to 57 (59%) among patients who underwent open prostatectomy (p = 0.228). The mean volume of the small bowel receiving 40 Gy was 26 and 67 cm(3) in open and MIRP groups, respectively (p = 0.006); the incidence of acute complications was the same in both groups.

CONCLUSIONS

Higher volumes of the small bowel are subjected to significant radiation after MIRP procedures compared to open procedures; however, we could not demonstrate any impact on acute complications. Whether there is a difference in late complications remains to be evaluated.

Interfractional variability in intensity-modulated radiotherapy of prostate cancer with or without thermoplastic pelvic immobilization

PURPOSE

To determine the variability of patient positioning errors associated with intensity-modulated radiotherapy (IMRT) for prostate cancer and to assess the impact of thermoplastic pelvic immobilization on these errors using kilovoltage (kV) cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

From February 2012 to June 2012, the records of 314 IMRT sessions in 19 patients with prostate cancer, performed with or without immobilization at two different facilities in the Korea University Hospital were analyzed. The kV CBCT images were matched to simulation computed tomography (CT) images to determine the simulation-to-treatment variability. The shifts along the x (lateral)-, y (longitudinal)- and z (vertical)-axes were measured, as was the shift in the three dimensional (3D) vector.

RESULTS

The measured systematic errors in the immobilized group during treatment were 0.46 ± 1.75 mm along the x-axis, - 0.35 ± 3.83 mm along the y-axis, 0.20 ± 2.75 mm along the z-axis and 4.05 ± 3.02 mm in the 3D vector. Those of nonimmobilized group were - 1.45 ± 7.50 mm along the x-axis, 1.89 ± 5.07 mm along the y-axis, 0.28 ± 3.81 mm along the z-axis and 8.90 ± 4.79 mm in the 3D vector. The group immobilized with pelvic thermoplastics showed reduced interfractional variability along the x- and y-axes and in the 3D vector compared to the nonimmobilized group (p < 0.05).

CONCLUSION

IMRT with thermoplastic pelvic immobilization in patients with prostate cancer appears to be useful in stabilizing interfractional variability during the planned treatment course.

Three-dimensional surface scanning for accurate patient positioning and monitoring during breast cancer radiotherapy

PURPOSE

Clinical evaluation of an optical three-dimensional surface scanning (3D-SS) system for patient positioning and monitoring during radiotherapy (RT) for breast cancer.

MATERIALS AND METHODS

A ceiling-mounted scanner was developed to acquire multiple 3D body surface images and tested in 14 conservatively operated breast cancer patients. A reference skin surface was derived from the planning computed tomography (CT) scan as basis for rigid registration with the surface scans. In addition to electronic portal images (EPIs), optical scans were acquired at three defined time points before and during daily RT. Patient setup was guided by laser alignments and corrected according to EPI findings. The accuracy of the 3D-SS system was validated by comparison of the optical scans to EPIs generated in parallel. Interfraction shifts were investigated by comparison of the first 3D-SS image with the reference body outline. Intrafractional motions were analysed by comparing the three daily surface scans with the first EPI.

RESULTS

Comparison of EPIs and 3D-SS images revealed good accordance (- 0.05±0.94 mm). Analysis of daily patient positions revealed average deviations of 0.4±2.4 mm laterally, 0.3±1.9 mm longitudinally and 0.2±3.3 mm vertically. After 2 weeks, a systematic interfraction shift in patient positioning was noted, particularly in the vertical direction (4.9±0.56 mm), which was attributed to patients progressively relaxing. 3D-SS images showed intrafractional shifts of 1.2±0.7 mm over a time course of 2 min.

CONCLUSION

Optical surface scanning is a simple, fast and reproducible method for breast cancer patient alignment. Particularly for more sophisticated irradiation techniques, it helps to improve accuracy in patient positioning during radiotherapy without the exposure to additional ionizing radiation.