Influence of intrafraction motion on margins for prostate radiotherapy

PURPOSE: To assess the impact of intrafraction intervention on margins for prostate radiotherapy. METHODS AND MATERIALS: Eleven supine prostate patients with three implanted transponders were studied. The relative transponder positions were monitored for 8 min and combined with previously measured data on prostate position relative to skin marks. Margins were determined for situations of (1) skin-based positioning, and (2) pretreatment transponder positioning. Intratreatment intervention was simulated assuming conditions of (1) continuous tracking, and (2) a 3-mm threshold for position correction. RESULTS: For skin-based setup without and with inclusion of intrafraction motion, prostate treatments would have required average margins of 8.0, 7.3, and 10.0 mm and 8.2, 10.2, and 12.5 mm, about the left-right, anterior-posterior, and cranial-caudal directions, respectively. Positioning by prostate markers at the start of the treatment fraction reduced these values to 1.8, 5.8, and 7.1 mm, respectively. Interbeam adjustment further reduced margins to an average of 1.4, 2.3, and 1.8 mm. Intrabeam adjustment yielded margins of 1.3, 1.5, and 1.5 mm, respectively. CONCLUSION: Significant reductions in margins might be achieved by repositioning the patient before each beam, either radiographically or electromagnetically. However, 2 of the 11 patients would have benefited from continuous target tracking and threshold-based intervention.     

Prostate localization using transabdominal ultrasound imaging

PURPOSE: Adding margin around a target is done in an attempt to ensure complete coverage of the target. The B-mode acquisition and targeting (BAT) system allows ultrasound imaging of the prostate in patients with a full bladder. This provides a setup tool for patients with localized prostate cancer that takes into account real-time prostate position and may make it possible to decrease tumor margins. Prostate localization using the conventional setup verification method and daily isocenter shifts recommended by the ultrasound imaging system (BAT) were compared and analyzed. METHODS AND MATERIALS: Daily treatment isocenter shifts for patients with localized adenocarcinoma of the prostate, obtained from two different imaging modalities, electronic portal imaging (EPI) and BAT, were calculated. We studied the difference in patient setup error calculated using BAT contour alignment and measured from EPI; the reproducibility of BAT contour alignment; intrafraction prostate motion; and how the BAT imaging procedure itself affected the prostate position. Prostate motion relative to its position during simulation was calculated by subtracting the EPI-measured isocenter shifts from the corresponding BAT-defined isocenter shifts. BAT reproducibility was measured by taking a verification BAT image after the patient was moved according to the initial BAT-defined isocenter shifts. Intrafraction prostate motion was measured by repeating BAT imaging at the end of a treatment fraction. The BAT imaging effect on prostate position was studied by examining the effect of suprapubic pressure on seed position in patients after a seed implant. RESULTS: The mean BAT isocenter shifts for prostate motion were 0.32 +/- 0.46 cm in the lateral, 0.31 +/- 0.73 cm in the superoinferior, and 0.32 +/- 0.56 cm in the AP directions. Isocenter shifts obtained from EPI measurements were significantly smaller, with a mean of 0.05 +/- 0.24 cm in the lateral, 0.01 +/- 0.11 cm in the superoinferior and -0.11 +/- 0.29 cm in the AP directions. This larger shift seen by BAT was due to prostate motion. For BAT reproducibility, the results showed that for BAT verification images, 90% of the lateral shifts were <0.2 cm, 93% of the superoinferior shifts were <0.3 cm, and 83% of the AP shifts were <0.2 cm. The mean isocenter shift (intrafraction localization error) during patient treatment fraction was 0.02 +/- 0.28 cm in the lateral, 0.04 +/- 0.48 cm in the superoinferior, and 0.0 +/- 0.32 cm in the AP direction. The BAT procedure itself induced an average motion of 1 mm in the AP and superoinferior directions. CONCLUSIONS: Prostate patient setup verification on the basis of bony anatomy position does not reflect the actual prostate position. BAT ultrasound target alignment provides a real-time prostate localization system that may make it possible to measure prostate position variations and reduce margins.     

Initial experience with ultrasound localization for positioning prostate cancer patients for external beam radiotherapy

: Transabdominal ultrasound localization of the prostate gland and its immediate surrounding anatomy has been used to guide the positioning of patients for the treatment of prostate cancer. This process was evaluated in terms of (1) the reproducibility of the ultrasound measurement; (2) a comparison of patient position between ultrasound localization and skin marks determined from a CT treatment planning scan; (3) the predictive indicators of patient anatomy not well suited for ultrasound localization; (4) the measurement of prostate organ displacement resulting from ultrasound probe pressure; and (5) quality assurance measures.

: The reproducibility of the ultrasound positioning process was evaluated for same-day repeat positioning by the same ultrasound operator (22 patients) and for measurements made by 2 different operators (38 patients). Differences between conventional patient positioning (CT localization with skin markings) and ultrasound-based positioning were determined for 38 patients. The pelvic anatomy was evaluated for 34 patients with pretreatment CT scans to identify predictors of poor ultrasound image quality. The displacement of the prostate resulting from pressure of the ultrasound probe was measured for 16 patients with duplicate CT scans with and without a simulated probe. Finally, daily, monthly, and semiannual quality assurance tests were evaluated.

: Self-verification tests of ultrasound positioning indicated a shift of <3 mm in approximately 95% of cases. Interoperator tests indicated shifts of <3 mm in approximately 80–90% of cases. The mean difference in patient positioning between conventional and ultrasound localization for lateral shifts was 0.3 mm (SD 2.5): vertical, 1.3 mm (SD 4.7 mm) and longitudinal, 1.0 mm (SD 5.1). However, on a single day, the differences were >10 mm in 1.5% of lateral shifts, 7% of longitudinal shifts, and 7% of vertical shifts. The depth to the isocenter, thickness of tissue overlying the bladder, and position of the prostate relative to the pubic symphysis, but not the bladder volume, were significant predictive indicators of poor ultrasound imaging. The pressure of the ultrasound probe displaced the prostate in 7 of the 16 patients by an average distance of 3.1 mm; 9 patients (56%) showed no displacement. Finally, the quality assurance tests detected ultrasound equipment defects.

: The ultrasound positioning system is reproducible and may indicate the need for significant positioning moves. Factors that predict poor image quality are the depth to the isocenter, thickness of tissue overlying the bladder, and position of the prostate relative to the pubic symphysis. The prostate gland may be displaced a small amount by the pressure of the ultrasound probe. A quality assurance program is necessary to detect ultrasound equipment defects that could result in patient alignment errors.     

Assessment of residual error for online cone-beam CT-guided treatment of prostate cancer patients

PURPOSE: Kilovoltage cone-beam CT (CBCT) implemented on board a medical accelerator is available for image-guidance applications in our clinic. The objective of this work was to assess the magnitude and stability of the residual setup error associated with CBCT online-guided prostate cancer patient setup. Residual error pertains to the uncertainty in image registration, the limited mechanical accuracy, and the intrafraction motion during imaging and treatment. METHODS AND MATERIALS: The residual error for CBCT online-guided correction was first determined in a phantom study. After online correction, the phantom residual error was determined by comparing megavoltage portal images acquired every 90 degrees to the corresponding digitally reconstructed radiographs. In the clinical study, 8 prostate cancer patients were implanted with three radiopaque markers made of high-winding coils. After positioning the patient using the skin marks, a CBCT scan was acquired and the setup error determined by fusing the coils on the CBCT and planning CT scans. The patient setup was then corrected by moving the couch accordingly. A second CBCT scan was acquired immediately after the correction to evaluate the residual target setup error. Intrafraction motion was evaluated by tracking the coils and the bony landmarks on kilovoltage radiographs acquired every 30 s between the two CBCT scans. Corrections based on soft-tissue registration were evaluated offline by aligning the prostate contours defined on both planning CT and CBCT images. RESULTS: For ideal rigid phantoms, CBCT image-guided treatment can usually achieve setup accuracy of 1 mm or better. For the patients, after CBCT correction, the target setup error was reduced in almost all cases and was generally within +/-1.5 mm. The image guidance process took 23-35 min, dictated by the computer speed and network configuration. The contribution of the intrafraction motion to the residual setup error was small, with a standard deviation of +/-0.9 mm. The average difference between the setup corrections obtained with coil and soft-tissue registration was greatest in the superoinferior direction and was equal to -1.1 +/- 2.9 mm. CONCLUSION: On the basis of the residual setup error measurements, the margin required after online CBCT correction for the patients enrolled in this study would be approximatively 3 mm and is considered to be a lower limit owing to the small intrafraction motion observed. The discrepancy between setup corrections derived from registration using coils or soft tissue can be due in part to the lack of complete three-dimensional information with the coils or to the difficulty in prostate delineation and requires further study.     

Intrafraction prostate motion during IMRT for prostate cancer

PURPOSE: Although the interfraction motion of the prostate has been previously studied through the use of fiducial markers, CT scans, and ultrasound-based systems, intrafraction motion is not well documented. In this report, the B-mode, Acquisition, and Targeting (BAT) ultrasound system was used to measure intrafraction prostate motion during 200 intensity-modulated radiotherapy (IMRT) sessions for prostate cancer. METHODS AND MATERIALS: Twenty men receiving treatment with IMRT for clinically localized prostate cancer were selected for the study. Pre- and posttreatment BAT ultrasound alignment images were collected immediately before and after IMRT on 10 treatment days for a total of 400 BAT alignment procedures. Any ultrasound shifts of the prostate borders in relation to the planning CT scan were recorded in 3 dimensions: right-left (RL), anteroposterior (AP), and superior-inferior (SI). Every ultrasound procedure was evaluated for image quality and alignment according to a 3-point grading scale. RESULTS: All the BAT images were judged to be of acceptable quality and alignment. The dominant directions of intrafraction prostate motion were anteriorly and superiorly. The mean magnitude of shifts (+/-SD) was 0.01 +/- 0.4 mm, 0.2 +/- 1.3 mm, and 0.1 +/- 1.0 mm in the left, anterior, and superior directions, respectively. The maximal range of motion occurred in the AP dimension, from 6.8 mm anteriorly to 4.6 mm posteriorly. The percentage of treatments during which prostate motion was judged to be 5 mm. The extent of intrafraction motion was much smaller than that of interfraction motion. Linear regression analysis showed very little correlation between the two types of motion (r = 0.014, 0.029, and 0.191, respectively) in the RL, AP, and SI directions. CONCLUSION: Using an ultrasound-based system, intrafraction prostate motion occurred predominantly in the anterior and superior directions, but was clinically insignificant. Intrafraction motion was much smaller than interfraction motion, and the two types of movement did not correlate.     

Accuracy of ultrasound-based (BAT) prostate-repositioning: a three-dimensional on-line fiducial-based assessment with cone-beam computed tomography

PURPOSE: To assess the accuracy of ultrasound-based repositioning (BAT) before prostate radiation with fiducial-based three-dimensional matching with cone-beam computed tomography (CBCT). PATIENTS AND METHODS: Fifty-four positionings in 8 patients with 125I seeds/intraprostatic calcifications as fiducials were evaluated. Patients were initially positioned according to skin marks and after this according to bony structures based on CBCT. Prostate position correction was then performed with BAT. Residual error after repositioning based on skin marks, bony anatomy, and BAT was estimated by a second CBCT based on user-independent automatic fiducial registration. RESULTS: Overall mean value (MV+/-SD) residual error after BAT based on fiducial registration by CBCT was 0.7+/-1.7 mm in x (group systematic error [M]=0.5 mm; SD of systematic error [Sigma]=0.8 mm; SD of random error [sigma]=1.4 mm), 0.9+/-3.3 mm in y (M=0.5 mm, Sigma=2.2 mm, sigma=2.8 mm), and -1.7+/-3.4 mm in z (M=-1.7 mm, Sigma=2.3 mm, sigma=3.0 mm) directions, whereas residual error relative to positioning based on skin marks was 2.1+/-4.6 mm in x (M=2.6 mm, Sigma=3.3 mm, sigma=3.9 mm), -4.8+/-8.5 mm in y (M=-4.4 mm, Sigma=3.7 mm, sigma=6.7 mm), and -5.2+/-3.6 mm in z (M=-4.8 mm, Sigma=1.7 mm, sigma=3.5 mm) directions and relative to positioning based on bony anatomy was 0+/-1.8 mm in x (M=0.2 mm, Sigma=0.9 mm, sigma=1.1 mm), -3.5+/-6.8 mm in y (M=-3.0 mm, Sigma=1.8 mm, sigma=3.7 mm), and -1.9+/-5.2 mm in z (M=-2.0 mm, Sigma=1.3 mm, sigma=4.0 mm) directions. CONCLUSIONS: BAT improved the daily repositioning accuracy over skin marks or even bony anatomy. The results obtained with BAT are within the precision of extracranial stereotactic procedures and represent values that can be achieved with several users with different education levels. If sonographic visibility is insufficient, CBCT or kV/MV portal imaging with implanted fiducials are recommended.     

A moving target: Image guidance for stereotactic body radiation therapy for early-stage non-small cell lung cancer

PurposePrecise patient positioning is critical due to the large fractional doses and small treatment margins employed for thoracic stereotactic body radiation therapy (SBRT). The goals of this study were to evaluate the following: (1) the accuracy of kilovoltage x-ray (kV x-ray) matching to bony anatomy for pretreatment positioning; (2) the magnitude of intrafraction tumor motion; and (3) whether treatment or patient characteristics correlate with intrafraction motion.Methods and MaterialsEighty-seven patients with lung cancer were treated with SBRT. Patients were positioned with orthogonal kV x-rays matched to bony anatomy followed by cone-beam computed tomography (CBCT), with matching of the CBCT-visualized tumor to the internal gross target volume obtained from a 4-dimensional CT simulation data set. Patients underwent a posttreatment CBCT to assess the magnitude of intrafraction motion.ResultsThe mean CBCT-based shifts after initial patient positioning using kV x-rays were 2.2 mm in the vertical axis, 1.8 mm in the longitudinal axis, and 1.6 mm in the lateral axis (n = 335). The percentage of shifts greater than 3 mm and 5 mm represented 39% and 17%, respectively, of all fractions delivered. The mean CBCT-based shifts after treatment were 1.6 mm vertically, 1.5 mm longitudinally, and 1.1 mm laterally (n = 343). Twenty-seven percent and 10% of shifts were greater than 3 mm and 5 mm, respectively. Univariate and multivariable analysis demonstrated a significant association between intrafraction motion with weight and pulmonary function.ConclusionsKilovoltage x-ray matching to bony anatomy is inadequate for accurate positioning when a conventional 3-5 mm margin is employed prior to lung SBRT. Given the treatment techniques used in this study, CBCT image guidance with a 5-mm planning target volume margin is recommended. Further work is required to find determinants of interfraction and intrafraction motion that may help guide the individualized application of planning target volume margins.     

The reproducibility of organ position using active breathing control (ABC) during liver radiotherapy

Purpose: To evaluate the intrafraction and interfraction reproducibility of liver immobilization using active breathing control (ABC).

Methods and Materials: Patients with unresectable intrahepatic tumors who could comfortably hold their breath for at least 20 s were treated with focal liver radiation using ABC for liver immobilization. Fluoroscopy was used to measure any potential motion during ABC breath holds. Preceding each radiotherapy fraction, with the patient setup in the nominal treatment position using ABC, orthogonal radiographs were taken using room-mounted diagnostic X-ray tubes and a digital imager. The radiographs were compared to reference images using a 2D alignment tool. The treatment table was moved to produce acceptable setup, and repeat orthogonal verification images were obtained. The positions of the diaphragm and the liver (assessed by localization of implanted radiopaque intra-arterial microcoils) relative to the skeleton were subsequently analyzed. The intrafraction reproducibility (from repeat radiographs obtained within the time period of one fraction before treatment) and interfraction reproducibility (from comparisons of the first radiograph for each treatment with a reference radiograph) of the diaphragm and the hepatic microcoil positions relative to the skeleton with repeat breath holds using ABC were then measured. Caudal-cranial (CC), anterior-posterior (AP), and medial-lateral (ML) reproducibility of the hepatic microcoils relative to the skeleton were also determined from three-dimensional alignment of repeat CT scans obtained in the treatment position.

Results: A total of 262 fractions of radiation were delivered using ABC breath holds in 8 patients. No motion of the diaphragm or hepatic microcoils was observed on fluoroscopy during ABC breath holds. From analyses of 158 sets of positioning radiographs, the average intrafraction CC reproducibility (σ) of the diaphragm and hepatic microcoil position relative to the skeleton using ABC repeat breath holds was 2.5 mm (range 1.8–3.7 mm) and 2.3 mm (range 1.2–3.7 mm) respectively. However, based on 262 sets of positioning radiographs, the average interfraction CC reproducibility (σ) of the diaphragm and hepatic microcoils was 4.4 mm (range 3.0–6.1 mm) and 4.3 mm (range 3.1–5.7 mm), indicating a change of diaphragm and microcoil position relative to the skeleton over the course of treatment with repeat breath holds at the same phase of the respiratory cycle. The average population absolute intrafraction CC offset in diaphragm and microcoil position relative to skeleton was 2.4 mm and 2.1 mm respectively; the average absolute interfraction CC offset was 5.2 mm. Analyses of repeat CT scans demonstrated that the average intrafraction excursion of the hepatic microcoils relative to the skeleton in the CC, AP, and ML directions was 1.9 mm, 0.6 mm, and 0.6 mm respectively and the average interfraction CC, AP, and ML excursion of the hepatic microcoils was 6.6 mm, 3.2 mm, and 3.3 mm respectively.

Conclusion: Radiotherapy using ABC for patients with intrahepatic cancer is feasible, with good intrafraction reproducibility of liver position using ABC. However, the interfraction reproducibility of organ position with ABC suggests the need for daily on-line imaging and repositioning if treatment margins smaller than those required for free breathing are a goal.     

A randomized comparison of interfraction and intrafraction prostate motion with and without abdominal compression

BACKGROUND AND PURPOSE: To quantify inter- and intrafraction prostate motion in a standard VacLok (VL) immobilization device or in the BodyFix (BF) system incorporating a compression element which may reduce abdominal movement. MATERIALS AND METHODS: Thirty-two patients were randomly assigned to VL or BF. Interfraction prostate motion >3 mm was corrected pre-treatment. EPIs were taken daily at the start and end of the first and last treatment beams. Interfraction and intrafraction prostate motion were measured for centre of mass (COM) and individual markers. RESULTS: There were no significant differences in interfraction (p0.002) or intrafraction (p0.16) prostate motion with or without abdominal compression. Median intrafraction motion was slightly smaller than interfraction motion in the AP (7.0 mm vs. 7.6 mm) and SI direction (3.2 mm vs. 4.7 mm). The final image captured the maximal intrafraction displacement in only 40% of fractions. Our PTV incorporated >95% of total prostate motion. CONCLUSIONS: Intrafraction motion became the major source of error during radiotherapy after online correction of interfraction prostate motion. The addition of 120 mbar abdominal compression to custom pelvic immobilization influenced neither interfraction nor intrafraction prostate motion.     

Reproducibility of liver position using active breathing coordinator for liver cancer radiotherapy

PURPOSE: To measure the intrabreath-hold liver motion and the intrafraction and interfraction reproducibility of liver position relative to vertebral bodies using an active breathing coordinator (ABC) in patients with unresectable liver cancer treated with hypofractionated stereotactic body radiation therapy (SBRT). METHODS: Tolerability of ABC and organ motion during ABC was assessed using kV fluoroscopy in 34 patients. For patients treated with ABC, repeat breath-hold CT scans in the ABC breath-hold position were acquired at simulation to estimate the volumetric intrafraction reproducibility of the liver relative to the vertebral bodies. In addition, preceding each radiation therapy fraction, with the liver immobilized using ABC, repeat anteroposterior (AP) megavoltage verification images were obtained. Off-line alignments were completed to determine intrafraction reproducibility (from repeat images obtained before one treatment) and interfraction reproducibility (from comparisons of the final image for each fraction with the AP) of diaphragm position relative to vertebral bodies. For each image set, the vertebral bodies were aligned, and the resultant craniocaudal (CC) offset in diaphragm position was measured. Liver position during ABC was also evaluated from kV fluoroscopy acquired at the time of simulation, kV fluoroscopy at the time of treatment, and from MV beam's-eye view movie loops acquired during treatment. RESULTS: Twenty-one of 34 patients were screened to be suitable for ABC. The average free breathing range of these patients was 13 mm (range, 5-1 mm). Fluoroscopy revealed that the average maximal diaphragm motion during ABC breath-hold was 1.4 mm (range, 0-3.4 mm). The MV treatment movie loops confirmed diaphragm stability during treatment. For a measure of intrafraction reproducibility, an analysis of 36 repeat ABC computed tomography (CT) scans in 14 patients was conducted. The average mean difference in the liver surface position was -0.9 mm, -0.5 mm, and 0.2 mm in the CC, AP, and medial-lateral (ML) directions, with a standard deviation of 1.5 mm, 1.5 mm, and 1.5 mm, respectively. Ninety-five percent of the liver surface had an absolute differences in position between repeat ABC CT scans of less than 4.1 mm, 3.3 mm, and 3.3 mm in the CC, AP, and ML directions, respectively. Analysis of 257 MV AP images from patients treated using ABC revealed an average intrafraction CC reproducibility (sigma) of diaphragm relative to vertebral bodies of 1.5 mm (range, 0.6-3.9 mm). The average interfraction CC reproducibility (sigma) was 3.4 mm (range, 1.5-7.9 mm), indicating less day-to-day reproducibility of diaphragm position relative to vertebral bodies. The average absolute intra and interfraction CC offset in diaphragm position relative to vertebral bodies was 1.7 and 3.7 mm, respectively, with 86% of intrafraction and 54% of interfraction absolute offsets 3.0 mm or less. CONCLUSIONS: Intrafraction reproducibility of liver position using ABC is good in the majority of screened patients. However, interfraction reproducibility is worse, suggesting a need for image guidance.     

Short-course intensity-modulated radiotherapy for localized prostate cancer with daily transabdominal ultrasound localization of the prostate gland

PURPOSE: To present our initial observations on the clinical feasibility of the technique of short-course intensity-modulated radiotherapy (SCIM-RT) in the treatment of localized prostate cancer coupled with daily transabdominal ultrasound localization of the prostate. The proposed regimen consists of a hypofractionated course delivering 70.0 Gy in 28 fractions. METHODS AND MATERIALS: The treatment data of the first 51 patients treated with SCIM-RT at the Cleveland Clinic Foundation are presented in this report. The technique consisted of intensity-modulated radiotherapy using 5 static fields (anterior, 2 laterals, and 2 anterior obliques). Inverse plans were generated by the Corvus treatment-planning system. The treatment delivery was performed with a Varian Dynamic Multileaf Collimator. The target was the prostate only in patients with low-risk disease (stage T1-T2, pretreatment PSA < or =10, and biopsy Gleason < or =6). The target was the prostate and seminal vesicles in patients with high-risk disease (stage T3 or pretreatment PSA > 10 or biopsy Gleason > or =7). In the Corvus planning system, the margins for the planning target volume (PTV) were 4 mm posteriorly, 8 mm laterally, and 5 mm in all other directions. A total of 70.0 Gy (mean prostate dose approximately 75 Gy) was prescribed in all cases at 2.5 Gy per fraction to be delivered in 28 fractions over 5 1/2 weeks. Prior to treatment delivery, the patients were minimally immobilized on the treatment table, only using lasers and skin marks. The location of the prostate gland was verified daily with the BAT transabdominal ultrasound system and patient position adjustments were performed accordingly. Fifty-one patients completed therapy between October 1998 and May 1999. RESULTS: The dose was prescribed to an isodose line ranging from 82.0% to 90.0% (mean: 87.2%). The range of the individual prostate mean doses was 73.5 to 78.5 Gy (average: 75.3 Gy). The range of the maximum doses was 77.4 to 84.5 Gy (average: 80.2 Gy). The range of the minimum doses was 64.3 to 69.2 Gy (average: 67.5 Gy). The average time for the prostate position verification and alignment of the prostate using the BAT system was 5 minutes. The entire localization/alignment process was performed by the radiation therapists. The daily alignment images were automatically saved and reviewed by the radiation oncologist, a process similar to port film checks. The total treatment (beam-on) time was around 6 minutes using the 5 static intensity-modulated fields. The mean and standard deviation (SD) of bladder volumes irradiated to 50, 60, and 70 Gy were as follows: 24 +/- 11 cc, 16 +/- 8 cc, and 8 +/- 6 cc. The mean and SD of rectal volumes irradiated to 50, 60, and 70 Gy were as follows: 22 +/- 11 cc, 15 +/- 8 cc, and 7 +/- 5 cc. The RTOG acute bladder toxicity scores were as follows: 0 in 3 (6%), 1 in 38 (74%), and 2 in 10 (20%). The RTOG acute rectal toxicity scores for SCIM-RT cases were as follows: 0 in 10 (20%), 1 in 33 (65%), and 2 in 8 (16%). No Grade 3 or 4 acute toxicities were observed. CONCLUSION: The delivery of our proposed hypofractionated-schedule SCIM-RT in combination with daily target localization/alignment with the BAT transabdominal ultrasound system is clinically feasible. It is an alternative method of dose escalation in the treatment of localized prostate cancer. The proposed schedule would significantly increase convenience to patients due to the decrease in overall treatment time. Preliminary acute toxicity results are extremely encouraging. Long-term follow-up is needed to assess late complications and treatment efficacy.     

Measurements and clinical consequences of prostate motion during a radiotherapy fraction

PURPOSE: Here we study the magnitude of prostate motion during the delivery of a radiotherapy fraction. These motions have clinical consequences for on-line position verification and the choice of margins around the target volume. METHODS AND MATERIALS: We studied the motion of the prostate for 10 patients during 251 radiotherapy treatment fractions by assessing the position of implanted gold markers. Gold markers of 1 mm diameter and 5 mm length were implanted in the prostate before the start of the radiotherapy. We obtained movies during each fraction using an a-Si flat-panel imager. The markers could be detected in separate frames using a marker extraction kernel. RESULTS: Marker displacements as large as 9.5 mm were detected in one fraction. The motion of the prostate is greatest in the caudal-cranial and the anterior-posterior directions. Within a time window of 2 to 3 min, deviations from the initial marker position, averaged over all patients, are 0.3 +/- 0.5 mm and -0.4 +/- 0.7 mm in the anterior-posterior and caudal-cranial directions, respectively. CONCLUSIONS: It appeared that on average, the intrafraction prostate motions did not result in margins larger than 1 mm, provided that the position verification is performed at time intervals of 2 to 3 min. Only for some patients performing more frequent position verification or adding extra margins of 2 to 3 mm is required to account for intrafraction prostate motions.     

早期乳腺癌保乳术后不同固定装置下全乳照射的摆位误差分析

背景与目的：准确的靶区位置是乳腺癌精确放疗的重要影响因素。本研究利用电子射野影像系统(electronic portal imaging device,EPID)测量乳腺托架和手臂托架两种不同体位固定状态下全乳放疗前、后的摆位误差,并对比其差别。方法：选择12例接受保乳术后调强放疗的乳腺癌患者,6例体位固定装置使用乳腺托架,6例使用手臂托架,在患者分次放疗前、后拍摄切线野的电子射野影像片(electronic portal imaging,EPI),将得到的EPI和数字重建图像(digitally reconstructed radiograph,DRR)进行配准,计算摆位误差,并进行比较。结果：手臂托架组的水平与垂直方向的位移分布分别为>5 mm：0和0;3~5 mm：6.6%和4.9%;<3 mm：93.4%和95.1%。乳腺托架组的水平与垂直方向的位移分布分别为>5 mm：6.7%和3.3%;3~5 mm：45.0%和23.3%;<3 mm：48.3%和73.3%。手臂托架组在放疗前EPI得到的水平与垂直方向的平均位移值小于乳腺托架组,差异有统计学意义(P=0.000,P=0.006)。两组放疗前、后分次内均存在位移,水平方向的差异有统计学意义(P=0.003,P=0.008),且手臂托架组在放疗前、后分次内的位移差值优于乳腺托架组,水平方向的差异有统计学意义(P=0.000)。结论：乳腺托架、手臂托架均有较好的全乳放疗摆位重复性和准确性,手臂托架在放疗前及分次内的位移优于乳腺托架,更适宜全乳放射治疗的体位固定。     

Evaluation of respiratory movement during gated radiotherapy using film and electronic portal imaging

PURPOSE: To evaluate the effectiveness of a commercial system(1) in reducing respiration-induced treatment uncertainty by gating the radiation delivery. METHODS AND MATERIALS: The gating system considered here measures respiration from the position of a reflective marker on the patient's chest. Respiration-triggered planning CT scans were obtained for 8 patients (4 lung, 4 liver) at the intended phase of respiration (6 at end expiration and 2 at end inspiration). In addition, fluoroscopic movies were recorded simultaneously with the respiratory waveform. During the treatment sessions, gated localization films were used to measure the position of the diaphragm relative to the vertebral bodies, which was compared to the reference digitally reconstructed radiograph derived from the respiration-triggered planning CT. Variability was quantified by the standard deviation about the mean position. We also assessed the interfraction variability of soft tissue structures during gated treatment in 2 patients using an amorphous silicon electronic portal imaging device. RESULTS: The gated localization films revealed an interfraction patient-averaged diaphragm variability of 2.8 +/- 1.0 mm (error bars indicate standard deviation in the patient population). The fluoroscopic data yielded a patient-averaged intrafraction diaphragm variability of 2.6 +/- 1.7 mm. With no gating, this intrafraction excursion became 6.9 +/- 2.1 mm. In gated localization films, the patient-averaged mean displacement of the diaphragm from the planning position was 0.0 +/- 3.9 mm. However, in 4 of the 8 patients, the mean (over localization films) displacement was >4 mm, indicating a systematic displacement in treatment position from the planned one. The position of soft tissue features observed in portal images during gated treatments over several fractions showed a mean variability between 2.6 and 5.7 mm. The intrafraction variability, however, was between 0.6 and 1.4 mm, indicating that most of the variability was due to patient setup errors rather than to respiratory motion. CONCLUSIONS: The gating system evaluated here reduces the intra- and interfraction variability of anatomy due to respiratory motion. However, systematic displacements were observed in some cases between the location of an anatomic feature at simulation and its location during treatment. Frequent monitoring is advisable with film or portal imaging.     

Clinical use of stereoscopic X-ray positioning of patients treated with conformal radiotherapy for prostate cancer

PURPOSE: To evaluate accuracy and time requirements of a stereoscopic X-ray-based positioning system in patients receiving conformal radiotherapy to the prostate. METHODS AND MATERIALS: Setup errors of the isocenter with regard to the bony pelvis were measured by means of orthogonal verification films and compared to conventional positioning (using skin drawings and lasers) and infrared marker (IR) based positioning in each of 261 treatments. In each direction, the random error represents the standard deviation and the systematic error the absolute value of the mean position. Time measurements were done in 75 treatments. RESULTS: Random errors with the X-ray positioning system in the anteroposterior (AP), lateral, and longitudinal direction were (average +/- 1 standard deviation) 2 +/- 0.6 mm, 1.7 +/- 0.6 mm, and 2.4 +/- 0.7 mm. The corresponding values of conventional as well as IR positioning were significantly higher (p < 0.01). Systematic errors for X-ray positioning were 1.1 +/- 1.2 mm AP, 0.6 +/- 0.5 mm laterally, and 1.5 +/- 1.6 mm longitudinally. Conventional and IR marker-based positioning showed significantly larger systematic errors AP and laterally, but longitudinally, the difference was not significant. Depending on the axis looked at, errors of >or=5 mm occurred in 2%-14% of treatments after X-ray positioning, 13%-29% using IR markers, and 28%-53% with conventional positioning. Total linac time for one treatment session was 14 min 51 s +/- 4 min 18 s, half of which was used for the X-ray-assisted positioning procedure. CONCLUSION: X-ray-assisted patient positioning significantly improves setup accuracy, at the cost of an increased treatment time.     

Intrafraction motion of the prostate during external-beam radiation therapy: analysis of 427 patients with implanted fiducial markers

PURPOSE: To analyze the intrafraction motion of the prostate during external-beam radiation therapy of patients with prostate cancer. METHODS AND MATERIALS: Between August 2001-December 2005, 427 patients with Stage T3Nx/0Mx/0 prostate carcinoma received intensity-modulated radiation therapy treatment combined with position verification with fiducial gold markers. For a total of 11,426 treatment fractions (average, 27 per patient), portal images were taken of the first segment of all five beams. The irradiation time of the technique varied between 5-7 min. From these data, the location of gold markers could be established within every treatment beam under the assumption of minimal marker movement. RESULTS: In 66% of treatment fractions, a motion outside a range of 2 mm was observed, with 28% outside a range of 3 mm. The intrafraction marker movements showed that motion directions were often reversed. However, the effect was small. Even with perfect online position-correction at the start of irradiation, intrafraction motion caused position uncertainty, but systematic errors (Sigma) were limited to <0.6 mm, and random errors (sigma) to <0.9 mm. This would result in a lower limit of 2 mm for margins, in the absence of any other uncertainties. CONCLUSIONS: Intrafraction motion of the prostate occurs frequently during external-beam irradiation on a time scale of 5-7 min. Margins of 2 mm account for these intrafraction motions. However, larger margins are required in practice to accommodate other uncertainties in the treatment.     

主动呼吸控制用于原发性肝癌放射治疗肝脏位置重复性的研究

背景与目的：呼吸运动能造成肝癌放疗靶区的扩大,限制了放疗剂量的增加.主动呼吸控制（active breathing control,ABC）提供了一种减少呼吸运动的简便方法,肝脏位置重复性较好是使用ABC技术减少靶区边界外放的一个重要前题,然而对使用该技术放疗过程中深吸气后肝脏位置的重复性目前尚不明确,因此本研究对ABC用于原发性肝癌放疗肝脏位置的重复性进行了测量.方法：入组本研究的患者共20人,其中16例肝癌碘油沉积良好.所有的患者进行了ABC呼吸训练和ABC控制下的放射治疗.在常规模拟机透视下测量一次屏气过程肝脏位置的稳定性和通过5次反复屏住吸气表示的一次放疗中肝脏位置的重复性.每周用兆伏级X线电子射野影像仪拍摄验证片与放疗计划生成的数字重建图像（digital reconstruction radiograph,DRR）比较测量分次放疗间肝脏位置在头脚方向上的重复性,通过每周在模拟机下体模固定在治疗体位拍摄正、侧位X线片,测量碘油在前后和左右位置上距离脊柱垂直距离的变化值,计算肝脏位置在这两个方向上的重复性.结果：所有患者配合良好,均能全程耐受ABC放疗屏气,没有1例因为不能耐受中断放疗.在平静呼吸状态下,患者膈在头脚方向上运动幅度平均为1.6 cm（范围：1.0～2.6 cm）.在透视下测得一次屏气过程中肝脏上下移动幅度平均为1.3 mm（范围：0.0～2.9 mm）.使用ABC放疗时一次放疗中和分次放疗间肝脏位置在头脚方向上的重复性（标准差）分别为1.6 mm和6.6 mm,前后方向上的重复性分别为0.9 mm和4.2 mm,左右方向上的重复性分别为0.7 mm和5.5 mm.结论：应用主动呼吸控制技术对入选的原发性肝癌患者放疗时肝脏的位置重复性良好.分次放疗间的重复性要差于一次放疗中的.安全的减少计划靶区的外扩需要结合影像引导的放疗并且要考虑肝脏位置的重复性.     

Intrafraction variations in linac-based image-guided radiosurgery of intracranial lesions

PurposeThis study investigated image-guided patient positioning during frameless, mask-based, single-fraction stereotactic radiosurgery of intracranial lesions and intrafractional translational and rotational variations in patient positions.Patients and methodsA non-invasive head and neck thermoplastic mask was used for immobilization. The Exactrac/Novalis Body system (BrainLAB AG, Germany) was used for kV X-ray imaging guided positioning. Intrafraction displacement data, obtained by imaging after each new table position, were evaluated.ResultsThere were 269 radiosurgery treatments performed on 190 patients and a total of 967 setups within different angles. The first measured error after each table rotation (mean 2.6) was evaluated (698 measurements). Intrafraction translational errors were (1 standard deviation [SD]) on average 0.8, 0.8, and 0.7 mm for the left–right, superior–inferior, and anterior–posterior directions, respectively, with a mean 3D-vector of 1.0 mm (SD 0.9 mm) and a range from –5 mm to +5 mm. On average, 12%, 3%, and 1% of the translational deviations exceeded 1, 2, and 3 mm, respectively, in the three directions.ConclusionThe range of intrafraction patient motion in frameless image-guided stereotactic radiosurgery is often not fully mapped by pre- and post-treatment imaging. In the current study, intrafraction motion was assessed by performing measurements at several time points during the course of stereotactic radiosurgery. It was determined that 12% of the intrafraction values in the three dimensions are above 1 mm, the usual safety margin applied in stereotactic radiosurgery.     

Three-dimensional intrafractional motion of breast during tangential breast irradiation monitored with high-sampling frequency using a real-time tumor-tracking radiotherapy system

PURPOSE: To evaluate the three-dimensional intrafraction motion of the breast during tangential breast irradiation using a real-time tracking radiotherapy (RT) system with a high-sampling frequency. METHODS AND MATERIALS: A total of 17 patients with breast cancer who had received breast conservation RT were included in this study. A 2.0-mm gold marker was placed on the skin near the nipple of the breast for RT. A fluoroscopic real-time tumor-tracking RT system was used to monitor the marker. The range of motion of each patient was calculated in three directions. RESULTS: The mean +/- standard deviation of the range of respiratory motion was 1.0 +/- 0.6 mm (median, 0.9; 95% confidence interval [CI] of the marker position, 0.4-2.6), 1.3 +/- 0.5 mm (median, 1.1; 95% CI, 0.5-2.5), and 2.6 +/- 1.4 (median, 2.3; 95% CI, 1.0-6.9) for the right-left, craniocaudal, and anteroposterior direction, respectively. No correlation was found between the range of motion and the body mass index or respiratory function. The mean +/- standard deviation of the absolute value of the baseline shift in the right-left, craniocaudal, and anteroposterior direction was 0.2 +/- 0.2 mm (range, 0.0-0.8 mm), 0.3 +/- 0.2 mm (range, 0.0-0.7 mm), and 0.8 +/- 0.7 mm (range, 0.1-1.8 mm), respectively. CONCLUSION: Both the range of motion and the baseline shift were within a few millimeters in each direction. As long as the conventional wedge-pair technique and the proper immobilization are used, the intrafraction three-dimensional change in the breast surface did not much influence the dose distribution.     

Precise positioning of patients for radiation therapy

We have developed a number of immobilization schemes which permit precise daily positioning of patients for radiation therapy. Pretreatment and post-treatment radiographs have been taken with the patient in the treatment position and analyzed to determine the amount of intratreatment movement. Studies of patients in the supine, seated and decubitus positions indicate mean movements of less than 1 mm with a standard deviation of less than 1mm. Patients immobilized in the seated position with a bite block and a mask have a mean movement of about 0.5 mm +/- 0.3 mm (s.d.), and patients immobilized in the supine position with their necks hyperextended for submental therapy evidence a mean movement of about 1.4 mm +/- 0.9 mm (s.d.). With the exception of those used for the decubitus position, the immobilization devices are simply fabricated out of thermoplastic casting materials readily available from orthopedic supply houses. A study of day-to-day reproducibility of patient position using laser alignment and pretreatment radiographs for final verification of position indicates that the initial laser alignment can be used to position a patient within 2.2 mm +/- 1.4 mm (s.d.) of the intended position. These results indicate that rigid immobilization devices can improve the precision of radiotherapy, which would be advantageous with respect to both tumor and normal tissue coverage in certain situations.