Image-guided helical tomotherapy for localized prostate cancer: technique and initial clinical observations

Abstract

The purpose of the present study was to implement a technique for daily computed tomography (CT)-based image-guided radiation therapy and to report observations on treatment planning, imaging, and delivery based on the first 2 years of clinical experience. Patients with previously untreated stage T1-T3 biopsy-proven adenocarcinoma of the prostate were considered eligible for treatment with daily CT-guided helical tomotherapy. The prostate was targeted daily using megavoltage CT (MVCT) images that were fused with treatment-planning CT images based on anatomic alignments. All patients were treated at 2 Gy per fraction to 76-78 Gy (mean: 76.7 Gy). As part of this study, 33 prostate patients were planned, imaged, and treated with a total of 1266 CT-guided fractions. The prostate, rectum, bladder, femoral heads, and pubis symphysis were visible in one or more slices for all 1266 MVCT image sets. The typical range of measured prostate displacement relative to a 3-point external laser setup in this study was 2-10 mm [3.4 mm standard deviation (SD)] in the anterior-posterior direction, 2-8 mm (3.7 mm SD) in the lateral direction, and 1-6 mm (2.4 mm SD) in the superior-inferior direction. The obese patients in this study had a substantially larger lateral variation (8.2 mm SD) attributable to mobility of skin marks. The prostate, seminal vesicles, rectum, and bladder anatomy were used to position the patient relative to the desired treatment position without the use of implanted markers. Acute toxicities were within the expected range given the number of patients treated and the dose level.

Figure 1

Comparison of (A) diagnostic computed tomography (CT) and (B) megavoltage CT images taken on the HI‐ART² system (TomoTherapy, Madison, WI) for axial (left panel) and sagittal (right panel) views. The prostate, rectum, and bladder contours are shown. Note the superior–inferior displacement of the prostate relative to the reference treatment‐planning CT.

Figure 2

The image fusion tool on the TomoTherapy (Madison, WI) operation station is used to register the treatment planning kilovoltage computed tomography (kVCT) images with megavoltage computed tomography (MVCT) images. After an automated CT‐to‐CT fusion, the operator can manually adjust the registration (A) by using a “checkerboard” display or (B) by overlaying the treatment planning contours with the MVCT image. Axial, sagittal, and coronal views are shown for both registration techniques. Arrows in the “checkerboard” display point to anatomic landmarks used in manual adjustments for prostate patients. The prostate (red), planning target volume (pink), rectum (brown), bladder (yellow), and femoral heads (blue) are shown in the contour overlay. $\text{PRO}=\text{prostate}$; $\text{PS}=\text{pubis}\hspace{0.17em}\text{symphysis}$; $\text{CAL}=\text{calcification}$; $\text{PRI}=\text{prostate}-\text{rectal}$; $\text{BLA}=\text{bladder}$.

Figure 3

Dose–volume histograms (solid blue lines) and the standard deviation (light blue lines) for (A) mean planning target volume (PTV), (B) rectum, and (C) bladder for 30 prostate tomotherapy patients. The PTV consists of the prostate with a 5‐mm posterior margin and a 10‐mm margin in all other directions.

Figure 4

Dose–volume histograms of mean (A) rectum and (B) bladder for 30 prostate tomotherapy patients sorted chronologically into groups of ten. The level of rectal and bladder conformal avoidance increased with inverse treatment planning experience.

Figure 5

Dose–volume histograms of mean (A) planning target volume (PTV), (B) rectum, and (C) bladder for 30 prostate tomotherapy patients with the initial clinical target volume (CTV) comprising the prostate and seminal vesicle and for 3 tomotherapy patients whose initial CTV included at‐risk pelvic lymph nodes.

Figure 6

Six random examples of axial megavoltage computed tomography (MVCT)–to–kilovoltage computed tomography (kVCT) registration for prostate patients using the “checkerboard” image fusion tool on the TomoTherapy (Madison, WI) operator station. The right half of each prostate image is the reference kVCT (grayscale), and the left half is the daily MVCT image (yellowscale). Note that the prostatic–rectal interface is visible in each image.

Figure 7

Measured (A) superior‐inferior, (B) anterior‐posterior, and (A,B) lateral patient setup shifts measured from megavoltage computed tomography (MVCT) image fusion for the first 33 prostate patients. Patients were set up based on external laser alignment with skin marks.