A randomized crossover study evaluating two immobilization devices for prostate cancer treatment

Image guidance procedures in radiotherapy for prostate cancer and the influence of body mass index

Purpose

To investigate possible optimisation of the image guidance procedure for the prostate cancer patients with respect to imaging frequency and patient body mass index (BMI).

Methods

The 6,085 setup correction shifts and BMI for 216 prostate cancer patients treated on tomotherapy units in two centres were analysed. Margins needed to account for inter-fraction target motion with daily only automatic correction and with automatic and manual corrections during one, three or five first fractions as a reference for further treatment without imaging were calculated.

Results

The planning target volume margin calculated for the daily automatic correction only scheme was significantly lower than the margins calculated for the image guidance limited to a few initial fractions. Manual corrections after automatic fusion were more important for patients with higher BMI. On average, the patients with normal BMI had manual correction shift of 0·7 mm in anterioposterior direction, while overweight and obese patients required, correspondingly, the shifts of 1·3 and 1·4 mm.

Conclusion

Overweight and obese patients require daily imaging with time saving available by performing automatic kV/MV computed tomography registration only. The patients with normal BMI may be treated with imaging guidance during a few initial treatment fractions.

Optimization of tomotherapy treatment planning for patients with bilateral hip prostheses

BACKGROUND

To determine the effect of different imaging options and the most efficient imaging strategy for treatment planning of patients with hip prostheses.

METHODS

The planning kilovoltage CT (kVCT) and daily megavoltage CT (MVCT) studies for three prostate cancer patients with bilateral hip prostheses were used for creating hybrid kVCT/MVCT image sets. Treatment plans were created for kVCT images alone, hybrid kVCT/MVCT images, and MVCT images alone using the same dose prescription and planning parameters. The resulting dose volume histograms were compared. The orthopedic metal artifact reduction (O-MAR) reconstruction tool for kVCT images and different MVCT options were investigated with a water tank fit with double hip prostheses. Treatment plans were created for all imaging options and calculated dose was compared with the one measured by a pin-point ion chamber.

RESULTS

On average for three patients, the D35% for the bladder was 8% higher in plans based on MVCT images and 7% higher in plans based on hybrid images, compared to the plans based on kVCT images alone. Likewise, the D35% for the rectum was 3% higher than the kVCT based plan for both hybrid and MVCT plans. The average difference in planned D99% in the PTV compared to kVCT plans was 0.9% and 0.1% for MVCT and hybrid plans, respectively. For the water tank with hip prostheses phantom, the kVCT plan with O-MAR correction applied showed better agreement between the measured and calculated dose than the original image set, with a difference of -1.9% compared to 3.3%. The measured doses for the MVCT plans were lower than the calculated dose due to image size limitations. The best agreement was for the kVCT/MVCT hybrid plans with the difference between calculated and measured dose around 1%.

CONCLUSION

MVCT image provides better visualization of patient anatomy and hybrid kVCT/MVCT study enables more accurate calculations using updated MVCT relative electron density calibration.

Comparative analysis of image guidance in two institutions for prostate cancer patients

AIM/BACKGROUND

The analysis of systematic and random errors obtained from the pooled data on inter-fraction prostate motion during radiation therapy in two institutions.

MATERIALS AND METHODS

Data of 6085 observations for 216 prostate cancer patients treated on tomotherapy units in two institutions of position correction shifts obtained by co-registration of planning and daily CT studies were investigated. Three independent variables: patient position (supine or prone), target (prostate or prostate bed), and imaging mode (normal or coarse) were analyzed. Systematic and random errors were evaluated and used to calculate the margins for different options of referencing based on the position corrections observed with one, three, or five imaging sessions.

RESULTS

Statistical analysis showed that only the difference between normal and coarse modes of imaging was significant, which allowed to merge the supine and prone position sub-groups as well as the prostate and prostate bed patients. In the normal and coarse imaging groups, the margins calculated using systematic and random errors in the medio-lateral and cranio-caudal directions (5.5 mm and 4.5 mm, respectively) were similar, but significantly different (5.3 mm for the normal mode and 7.1 mm for the coarse mode) in the anterio-posterior direction. The reference scheme based on the first three fractions (R3) was found to be the optimal one.

CONCLUSIONS

The R3 reference scheme effectively reduced systematic and random errors. Larger margins in the anterio-posterior direction should be used during prostate treatment on the tomotherapy unit, as coarse imaging mode is chosen in order to reduce imaging time and dose.

A Retrospective Review of the Effect of a Simple Foot Immobilization Device for the Treatment of Prostate Cancer

BACKGROUND

The goal of radical radiation therapy is to eradicate tumor cells by delivering maximum dose to the target volume. This requires accurate daily positioning of the patient to minimize the chances of a geographical miss of the target and minimize dose to surrounding normal tissue. Numerous studies have been conducted to find the best immobilization device to improve reproducibility and setup of patient positioning for men with prostate cancer with inconclusive results.

OBJECTIVE

The aim of this study was to evaluate retrospectively, the consistency and reproducibility of prostate patient positioning using a simple foot immobilization device compared with patients treated without any immobilization device.

METHODS

A retrospective chart analysis was completed on 40 patients with histopathologically confirmed adenocarcinoma of the prostate between April 2007 and May 2007. Twenty charts were randomly selected for men treated without any immobilization device and 20 charts were randomly selected for men treated with the foot strap immobilization. Incidence and frequency of isocenter shifts were the primary end points of this study. Direction and magnitude of shifts were secondary end points.

RESULTS

The frequency of isocenter shifts were greater in the patients treated without immobilization (35%) than with patients treated with foot strap immobilization (10%). Required shifts were in either the superoinferior direction or in the right/left direction. No shifts were required in the anteroposterior direction. Magnitude of shifts greater than and equal to 1.0 cm in magnitude was seen only in those treated without immobilization.

CONCLUSION

The foot strap is a simple and inexpensive method of improving daily setup reliability and reducing the need for isocenter shifts.