Interfraction Prostate Motion Research Articles

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

Proceedings to the 7th Annual Conference of the Particle Therapy Cooperative Group North America (PTCOG-NA)

Preliminary analysis of prostate positional displacement using hydrogel spacer during the course of proton therapy for prostate cancer.

In recent years, a novel technique has been employed to maintain a distance between the prostate and the rectum by transperineally injecting a hydrogel spacer (HS). However, the effect of HS on the prostate positional displacement is poorly understood, despite its stability with HS in place. In this study, we investigated the effect of HS insertion on the interfraction prostate motion during the course of proton therapy (PT) for Japanese prostate cancer patients. The study population consisted of 22 cases of intermediate-risk prostate cancer with 11 cases with HS insertion and 11 cases without HS insertion. The irradiation position and preparation were similar for both groups. To test for reproducibility, regular confirmation computed tomography (RCCT) was done four times during the treatment period, and five times overall [including treatment planning CT (TPCT)] in each patient. Considering the prostate position of the TPCT as the reference, the change in the center of gravity of the prostate relative to the bony anatomy in the RCCTs of each patient was determined in the left–right (LR), superior–inferior (SI) and anterior–posterior (AP) directions. As a result, no significant difference was observed across the groups in the LR and SI directions. Conversely, a significant difference was observed in the AP direction (P < 0.05). The proportion of the 3D vector length ≤5 mm was 95% in the inserted group, but 55% in the non-inserted group. Therefore, HS is not only effective in reducing rectal dose, but may also contribute to the positional reproducibility of the prostate.

Dosimetric Impact of Prostate Interfraction Motion and Image Guidance Strategies on Proton PBS Plans treating Prostate with Pelvic Lymph Nodes

Dosimetric Impact of Prostate Interfraction Motion and Image Guidance Strategies on Proton PBS Plans treating Prostate with Pelvic Lymph Nodes

Fiducial markers in prostate cancer image-guided radiotherapy.

Background: Image-guided radiotherapy (IGRT) is recommended to reduce the risk of geometrical miss when modern radiotherapy technologies with high grades of conformity are used. The purpose of this study was to evaluate the efficacy of fiducial markers (FMs) for electronic portal imaging in prostate cancer radiotherapy in term of evaluating the complications associated with FMs implantation, quantifying inter-fraction prostate motion, and determination of optimal planning target volume (PTV) margins. Methods: In this single institution, prospective, consecutive study, 27 patients underwent implantation of three-gold seed FMs into the prostate gland before prostate radiotherapy. Prior to computed tomography planning, all patients were asked to report any complication associated with FMs implantation that have experienced to date. Daily pre-treatment electronic portal images were captured, and prostate position errors were corrected if they were greater than 2 mm along three translational directions. Optimal PTV expansions were computed using van Herk formula [PTV-margin= 2.5Σ + 0.7σ]. Results: FMs implantation was successful with an acceptable toxicity profile in all patients. Without IGRT, margins of 5.4 mm, 5.8 mm and 5.5 mm, in vertical, longitudinal and lateral directions, respectively, are needed for a 95% confidence level of complete clinical target volume (CTV) coverage in each treatment session. The PTV margins of 3.0 mm, 3.3 mm and 4.0 mm in corresponding directions were calculated when FMs based electronic portal imaging was applied. Conclusion: FMs based electronic portal imaging is an effective tool for prostate cancer IGRT.

Interfraction prostate displacement during image-guided radiotherapy using intraprostatic fiducial markers and a cone-beam computed tomography system: A volumetric off-line analysis in relation to the variations of rectal and bladder volumes.

Prostate motion during the radiotherapy course is an important issue. This study investigated the inter-fraction prostate motion in controlled rectal filling condition. 10 prostate cancer patients underwent image-guided radiotherapy (IGRT) using a cone-beam computed tomography (CBCT) system, after the insertion of fiducial markers (FMs). The planning CT was the reference CT (CTref) used to estimate the reference intermarker distances, and CBCTs were used for off-line comparison with CTref. We evaluated the influence of rectal and bladder volume on prostate shifts. We calculated the required planning target volume (PTV) margins in this patient population. 120 CBCTs were analyzed. Mean prostate displacements (± SD) along the 3 axes (x, y, z) averaged over the 10 patients, were: 0.90 ± 0.84 mm in x, 0.00 ± 2.07 mm in y, -0.80 ± 1.28 mm in z. There is a statistically significant anti-correlation between prostate displacements and: bladder volume variations (P < 0.001) in the y-axis, and rectal volume variations (P < 0.05) in the z-axis. PTV margins obtained for the directions x, y and z are respectively 2.5, 5.6 and 3.9 mm. IGRT in reproducible empty rectum condition allow a high reduction of daily treatment uncertainties.

P181] Establishing margins from clinical to planning target volume for low-risk prostate cancer radiotherapy: A multi institutional study

Purpose The aim of this study was to determine the appropriate margins from clinical target volume (CTV) to planning target volume (PTV) in low risk prostate cancer irradiation, in terms of image guided radiotherapy (IGRT) protocol from three radiotherapy (RT) centers. Methods Twenty patients with low risk prostate cancer were selected from each RT center for retrospective review. Prescribed dose of 78 Gy in 39 fractions was delivered with volumetric modulated arc therapy (VMAT). Pretreatment preparation was applied in accordance with institutional protocol. Cone beam computed tomography (CBCT) was daily co-registered with planning Computed Tomography (CT), using two registration protocols: bone match and prostate (soft tissue) match. Based on this data, set up errors and inter-fraction prostate motion were calculated in three RT centers. Literature data for delineation errors and intra-fraction motions were used to determine CTV-PTV margins for different imaging protocols (online 2D/2D bone match and online CBCT or 2D/2D prostate fiducial markers match). Results The standard deviation of the systematic set up errors was in the range of 1.6–3.0 mm and for random set up errors 1.8–3.0 mm. The overall mean prostate movement, relative to bone anatomy, in anterior/posterior (A/P), inferior/superior (I/S), and left/right (L/R) direction, respectively was for: 1st RT center 0.5 ± 1.9 (1 SD), 0.1 ± 0.8 and 0.1 ± 0.7 mm, 2nd RT center 0.1 ± 1.4 (1 SD), 0.1 ± 1.4 and 0.1 ± 1.5 mm, and. 3rd RT center 0.6 ± 2.2 (1 SD), 0.6 ± 2.2 and 0.3 ± 1.3 mm. According to the IGRT modalities and frequency of use, the calculated CTV-PTV margins of A/P, I/S and L/R directions, respectively were in the range of: -for online 2D/2D bone match 7.4–9.1, 7.4–10.1 and 5.5–7.0 mm, respectively, -for online CBCT or 2D/2D prostate fiducial markers matching: 5.7, 7.0 and 5.0 mm, respectively. Conclusions In low risk prostate cancer irradiation, CTV-PTV margins less than 10 mm could not be used safely without daily CBCT prostate based soft tissue matching, due to the increased risk of missing the CTV. Generally smaller, precise margins followed with daily IGRT and online corrections, may influence the local control and lower toxicity rates.

Dosimetric Comparison between Bone and Target Matching Considering Interfractional Prostate Motion in Volumetric Modulated Arc Therapy

Adequate matching methods are critical for accurate volumetric-modulated arc therapy (VMAT). We investigated the dosimetric differences in the target and organs at risk (OARs) between bone matching and target matching in patients with prostate cancer treated with VMAT. The relationship between the dosimetric differences and interfractional motion of the prostate was also evaluated. Forty patients with prostate cancer classified as intermediate risk were enrolled in a study to assess the differences in dosimetry between two matching methods. These patients were treated with VMAT and prescribed dose was 78 Gy. The dose distribution was calculated using cone-beam computed tomography (CBCT) for this study. We selected clinical target volume (CTV) as the target, and the rectum and bladder as the OARs. The Dmean, D98, D95, and D2 to the target and V10-V70 to the OARs were calculated as different dose from target matching value minus bone matching value. Multiple regression analysis was used to evaluate the effect of interfractional motion of the prostate on the differences in dose. The CTV D95 values differed by -0.22 ± 1.01 Gy (mean ± standard deviation). Rectum and bladder V70 values differed by 4.6% ± 7.2% and -2.6% ± 7.2%, respectively. There was a correlation between interfractional motion of the prostate and the dose differences to OARs (R2 = 0.73 - 0.94). The dose differences to OARs also varied depending on the direction of the prostate’s motion. We found that bone matching resulted in an increased rectal dose and high risk of decreasing dose to the CTV.

Interfractional Rectal Displacement Requiring Repeated Precaution Did Not Correlate to Biochemical Control and Rectal Toxicity in Patients with Prostate Cancer Treated with Image-guided Intensity-modulated Radiation Therapy

To investigate the correlation between frequency of action level of interfractional rectal displacement requiring repeated precaution in patients with prostate cancer and late toxicity from image-guided intensity-modulated radiation therapy (IG-IMRT) using helical tomotherapy. We examined 264 patients who underwent IG-IMRT during 2007-2011. Megavoltage computed tomographic (MVCT) images were acquired before radiation therapy and was examined with soft-tissue matching by comparing treatment planning images within 9,345 fractions. Displacement of the anterior rectal region larger than 5 mm, requiring repeated precaution, was defined as the level of rectal displacement requiring action (ARD). ARD was identified in 815 (7.7%) out of 9,345 fractions and at least once in 82% (216/264) of patients. The highest incidence of ARD (11%) was found during the initial week of treatment (first five and next five fractions), after which the incidence decreased to 6% (p<0.0001). Patients with lean body (lower body mass index (BMI) tended to have a higher incidence of ARD. We identified 16 (6%) cases of gastrointestinal toxicity and 12 (4.5%) genitourinary toxicities as a late adverse reaction (3 months or later after IG-IMRT). There was no correlation between ARD and late toxicity. Prostate-specific antigen (PSA) control was also similar (p=0.12) between those with ARD (96% at 5 year) and those without ARD (88%). ARD occurred predominantly in lean patients, during the initial week of treatment and became less likely over time. ARD was not correlated to late toxicity and PSA control, therefore, IG-IMRT technique was able to adequately control error due to interfractional prostate and rectal motion.

An analysis of interfractional and intrafractional prostate motion in hypofractionated precise radiotherapy for prostate cancer

Objective To investigate the interfractional and intrafractional prostate motion during hypofractionated precise radiotherapy for prostate cancer. Methods From 2013 to 2016, twenty-eight patients who received 5 Gy radiotherapy in 9 fractions for prostate cancer were enrolled as subjects. Every patient had three gold fiducials implanted into the prostate by transrectal ultrasound guidance two weeks before computed tomography (CT) simulation. All patients underwent CT scans in the supine position with full bladders and rectal balloons filled with 60 ml air. The Pinnacle planning system was used to design the treatment plans. Twenty-three patients were treated with a Synergy accelerator. Those patients underwent cone-beam CT (CBCT) scans prior to treatment. The set-up error was recorded by bone alignment between CBCT images and planning CT images. The prostate displacement was then recorded by gold fiducial alignment. The interfraction prostate displacement was defined by the difference between the above two parameters. The other 5 patients were treated with a Novalis accelerator. Based on gold fiducial alignment, the real-time tracking of gold fiducials was carried out by the ExacTrac system to evaluate the intrafractional prostate displacement. Results A total of 207 measurements of interfractional prostate displacement were made in the 23 patients before treatment. The mean interfractional prostate displacements in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) directions were (0.05±0.10), (0.20±0.22), and (0.19±0.18) cm, respectively. The displacements larger than 0.3 cm in the above three directions were observed in 1, 52, and 49 measurements, respectively, while the displacements larger than 0.5 cm in the three directions were observed in 1, 29, and 16 measurements, respectively. A total of 225 measurements of gold fiducial displacement were made in the 5 patients during treatment. The mean intrafractional prostate displacements in LR, SI, and AP directions were (0.61±0.50), (0.68±0.69), and (0.70±0.67) mm, respectively. The displacements larger than 3 mm in the three directions were observed in 0, 1, and 1 measurement, respectively. Conclusions In hypofractionated precise radiotherapy for prostate cancer, the interfractional prostate displacement is significantly larger than the intrafractional prostate displacement. The interfractional prostate displacement must be corrected before radiotherapy. In order to avoid off-target irradiation due to postural changes in patients, the tracking of the intrafractional prostate displacement is still necessary although the displacement is relatively small. The rectal balloon can help immobilize the prostate. Key words: Prostate motion; Interfraction; Intrafraction; Prostate neoplasms/hypofraction-ated radiotherapy

Does body mass index or subcutaneous adipose tissue thickness affect interfraction prostate motion in patients receiving radical prostate radiotherapy?

AbstractAimIt is unclear whether body mass index (BMI) is a useful measurement for examining prostate motion. Patient’s subcutaneous adipose tissue thickness (SAT) and weight has been shown to correlate with prostate shifts in the left/right direction. We sought to analyse the relationship between BMI and interfraction prostate movement in order to determine planning target volume (PTV) margins based on patient BMI.Materials and methodsIn all, 38 prostate cancer patients with three implanted gold fiducial markers in their prostate were recruited. Height, mass and SAT were measured, and the extent of interfraction prostate movement in the left/right, superior/inferior and anterior/posterior directions was recorded during each daily fiducial marker-based image-guided radiotherapy treatment. Mean corrective shift in each direction for each patient, along with BMI values, were calculated.ResultsThe median BMI value was 28·4 kg/m2 (range 21·4–44·7). Pearson’s product-moment correlation analysis showed no significant relationship between BMI, mass or SAT and the extent of prostate movement in any direction. Linear regression analysis also showed no relationship between any of the patient variables and the extent of prostate movement in any direction (BMI: R2=0·006 (ρ=0·65), 0·002 (ρ=0·80) and 0·001 (ρ=0·86); mass: R2=0·001 (ρ=0·87), 0·010 (ρ=0·54) and 0·000 (ρ=0·99); SAT: R2=0·012 (ρ=0·51), 0·013 (ρ=0·50) and 0·047 (ρ=0·19) for shifts in the X, Y and Z axis, respectively). Patients were grouped according to BMI, as BMI&lt;30 (n=25, 65·8%) and BMI≥30 (n=13, 34·2%). A two-tailed t-test showed no significant difference between the mean prostate shifts for the two groups in any direction (ρ=0·320, 0·839 and 0·325 for shifts in the X, Y and Z axis, respectively).FindingsBMI is not a useful parameter for determining individualised PTV margins. Gold fiducial marker insertion should be used as standard to improve treatment accuracy.

SU‐G‐BRA‐17: Tracking Multiple Targets with Independent Motion in Real‐Time Using a Multi‐Leaf Collimator

Purpose:Multiple targets with large intrafraction independent motion are often involved in advanced prostate, lung, abdominal, and head and neck cancer radiotherapy. Current standard of care treats these with the originally planned fields, jeopardizing the treatment outcomes. A real‐time multi‐leaf collimator (MLC) tracking method has been developed to address this problem for the first time. This study evaluates the geometric uncertainty of the multi‐target tracking method.Methods:Four treatment scenarios are simulated based on a prostate IMAT plan to treat a moving prostate target and static pelvic node target: 1) real‐time multi‐target MLC tracking; 2) real‐time prostate‐only MLC tracking; 3) correcting for prostate interfraction motion at setup only; and 4) no motion correction. The geometric uncertainty of the treatment is assessed by the sum of the erroneously underexposed target area and overexposed healthy tissue areas for each individual target. Two patient‐measured prostate trajectories of average 2 and 5 mm motion magnitude are used for simulations.Results:Real‐time multi‐target tracking accumulates the least uncertainty overall. As expected, it covers the static nodes similarly well as no motion correction treatment and covers the moving prostate similarly well as the real‐time prostate‐only tracking. Multi‐target tracking reduces &gt;90% of uncertainty for the static nodal target compared to the real‐time prostate‐only tracking or interfraction motion correction. For prostate target, depending on the motion trajectory which affects the uncertainty due to leaf‐fitting, multi‐target tracking may or may not perform better than correcting for interfraction prostate motion by shifting patient at setup, but it reduces ∼50% of uncertainty compared to no motion correction.Conclusion:The developed real‐time multi‐target MLC tracking can adapt for the independently moving targets better than other available treatment adaptations. This will enable PTV margin reduction to minimize health tissue toxicity while remain tumor coverage when treating advanced disease with independently moving targets involved.The authors acknowledge funding support from the Australian NHMRC Australia Fellowship and NHMRC Project Grant No. APP1042375.

Impact of hydrogel spacer injections on interfraction prostate motion during prostate cancer radiotherapy

Background The dosimetric advantage of prostate-rectum spacers to displace the anterior rectal wall outside of the high-dose radiation regions has been clearly established in prostate cancer radiotherapy (RT). The aim of this study was to assess the impact of hydrogel spacer (HS) in the interfraction prostate motion in patients undergoing RT for prostate cancer.Material and methods Twenty prostate cancer patients implanted with three fiducial markers (FM) with (n = 10) or without (n = 10) HS were analyzed. Displacements between the prostate isocenter based on the FM’s position and the bony anatomy were quantified in the left-right (LR), anterior-posterior (AP), superior-inferior (SI) axes by offline analyses of 122 cone beam computed tomography scans. Group systematic (M), systematic (Σ) and random (σ) setup errors were determined.Results In patients with or without HS, the overall mean interfraction prostate displacements were 0.4 versus −0.4 mm (p = 0.0001), 0.6 versus 0.6 mm (p = 0.85), and −0.6 mm versus −0.3 mm (p = 0.48) for the LR, AP, and SI axes, respectively. Prostate displacements >5 mm in the AP and SI directions were similar for both groups. No differences in M, Σ and σ setup errors were observed in the three axes between HS + or HS- patients.Conclusions HS implantation does not significantly influence the interfraction prostate motion in patients treated with RT for prostate cancer. The major expected benefit of HS is a reduction of the high-dose levels to the rectal wall without influence in prostate immobilization.

Nature of intrafractional and interfractional prostate motion during stereotactic radiation.

152 Background: To characterize the intra-fraction and inter-fraction prostate motion as tracked by the X-ray images of the implanted gold fiducials during stereotactic radiotherapy with CyberKnife. The published data have analysed the linear and angular prostate motion intrafraction and interfraction prostate motion among patients. We sought to quantify the same within each patient. Methods: Twenty Five patients with localized prostate cancer treated with CyberKnife radiosurgery between January 2013 and August 2015 were studied retrospectively. A data set constitutes the deviations derived from X-ray images obtained between two consecutive couch motions. Results: Included in the analysis were 3926 data sets. A total of 210 non-coplanar fields were used per fraction. The mean total treatment time for all fields per fraction was 36.13 minutes. The detected and corrected movements over all were in a range of ± 10.1 mm in linear direction (Right: mean 1.1±0.4 mm; Left: mean 1.0±0.6 mm; Superior: mean 0.7±0.3 mm; Inferior: mean 1.6±0.6 mm; Anterior: mean 1.6±0.7 mm; Posterior: mean 0.5±0.3 mm with maximum (max) movement range of Right max 9.9±6.4 mm, Left max 7.1±3.4 mm, Superior max 8.6±5.4 mm, Inferior max 10.1±8.5 mm, Anterior max 9.2±6.5 mm, Posterior max 8.4±2.9 mm) and angular movements were in a range of ± 6.7 deg in all directions (Right Angle: mean 0.6±0.3 deg; Left Angle: mean 0.6±0.3 deg; Head Up(H-U): mean 1.3±0.6 deg; Head Down(H-D): mean 1.4±0.6 deg; Counter-Clockwise movement (CCW): mean 0.7±0.3 deg; Clockwise movement (CW): mean 0.5±0.3 deg with max rotation range of Right angle max 2.4±2 deg, Left angle max 2.7±2 deg, H-U max 10.2±3.5 deg, H-D max 6.7±4.8 deg, CCW 4±2.9 deg, CW max 2.8±2.4 deg). There was an unpredictable change in prostate motion inter-fraction in each patient. But, a unique observation is that a predictable pattern exists for prostate motion intra-fraction within a patient. Change in the linear or angular prostate motion intra-fraction in any direction is not erratic. Conclusions: The linear and rotational prostate motion intra-fraction in any direction has a predictable pattern and any change is gradual and not erratic. The motion shows secular trend during the course of treatment.

How can the aetiological factors of rectal distension be managed to reduce interfraction prostate motion during a course of radiotherapy treatment

AbstractAimDuring radiotherapy of the prostate it is important to minimise interfraction prostate motion to allow dose escalation and reduce normal tissue damage. Rectal volume has been identified as playing a significant role in prostate motion with various methods used to reduce it. The aim was to systematically review published literature to allow evidence based recommendations to be made to current practice to reduce interfraction prostate motion.Materials and methodsA systematic search of CINAHL, Medline, PubMed, Science Direct, NHS Evidence and The Cochrane Library was performed. Limited searches of The Society of Radiographers website, OpenGrey and COPAC were undertaken, alongside manual searches of cross references of eligible articles. The quality of included papers was measured using a pre-existing tool. The causes, consequences and solutions to manage rectal volume and its effect on prostate position were extracted, compared and evaluated to extract solutions to be implemented into clinical practice.ResultsOf the 2,339 unique articles systematically retrieved, 23 met the inclusion criteria, 15 of which discuss radiotherapy, five constipation and three flatulence.FindingsA combined medicinal and dietary approach adaptable to departmental workflow is required to manage rectal volume, with special consideration to patients with pre-existing extrinsic factors.

Magnitude of observer error using cone beam CT for prostate interfraction motion estimation: effect of reducing scan length or increasing exposure.

Objective:Cone beam CT (CBCT) enables soft-tissue registration to planning CT for position verification in radiotherapy. The aim of this study was to determine the interobserver error (IOE) in prostate position verification using a standard CBCT protocol, and the effect of reducing CBCT scan length or increasing exposure, compared with standard imaging protocol.Methods:CBCT images were acquired using a novel 7 cm length image with standard exposure (1644 mAs) at Fraction 1 (7), standard 12 cm length image (1644 mAs) at Fraction 2 (12) and a 7 cm length image with higher exposure (2632 mAs) at Fraction 3 (7H) on 31 patients receiving radiotherapy for prostate cancer. Eight observers (two clinicians and six radiographers) registered the images. Guidelines and training were provided. The means of the IOEs were compared using a Kruzkal–Wallis test. Levene's test was used to test for differences in the variances of the IOEs and the independent prostate position.Results:No significant difference was found between the IOEs of each image protocol in any direction. Mean absolute IOE was the greatest in the anteroposterior direction. Standard deviation (SD) of the IOE was the least in the left–right direction for each of the three image protocols. The SD of the IOE was significantly less than the independent prostate motion in the anterior–posterior (AP) direction only (1.8 and 3.0 mm, respectively: p = 0.017). IOEs were within 1 SD of the independent prostate motion in 95%, 77% and 96% of the images in the RL, SI and AP direction.Conclusion:Reducing CBCT scan length and increasing exposure did not have a significant effect on IOEs. To reduce imaging dose, a reduction in CBCT scan length could be considered without increasing the uncertainty in prostate registration. Precision of CBCT verification of prostate radiotherapy is affected by IOE and should be quantified prior to implementation.Advances in knowledge:This study shows the importance of quantifying the magnitude of IOEs prior to CBCT implementation.

SU‐E‐J‐164: Estimation of DVH Variation for PTV Due to Interfraction Organ Motion in Prostate VMAT Using Gaussian Error Function

Purpose:We developed a method to predict the change of DVH for PTV due to interfraction organ motion in prostate VMAT without repeating the CT scan and treatment planning. The method is based on a pre‐calculated patient database with DVH curves of PTV modelled by the Gaussian error function (GEF).Methods:For a group of 30 patients with different prostate sizes, their VMAT plans were recalculated by shifting their PTVs 1 cm with 10 increments in the anterior‐posterior, left‐right and superior‐inferior directions. The DVH curve of PTV in each replan was then fitted by the GEF to determine parameters describing the shape of curve. Information of parameters, varying with the DVH change due to prostate motion for different prostate sizes, was analyzed and stored in a database of a program written by MATLAB.Results:To predict a new DVH for PTV due to prostate interfraction motion, prostate size and shift distance with direction were input to the program. Parameters modelling the DVH for PTV were determined based on the pre‐calculated patient dataset. From the new parameters, DVH curves of PTVs with and without considering the prostate motion were plotted for comparison. The program was verified with different prostate cases involving interfraction prostate shifts and replans.Conclusion:Variation of DVH for PTV in prostate VMAT can be predicted using a pre‐calculated patient database with DVH curve fitting. The computing time is fast because CT rescan and replan are not required. This quick DVH estimation can help radiation staff to determine if the changed PTV coverage due to prostate shift is tolerable in the treatment. However, it should be noted that the program can only consider prostate interfraction motions along three axes, and is restricted to prostate VMAT plan using the same plan script in the treatment planning system.

Impact of Intrafraction and Residual Interfraction Effect on Prostate Proton Pencil Beam Scanning

To quantitatively evaluate the impact of interplay effect and plan robustness associated with intrafraction and residual interfraction prostate motion for pencil beam scanning proton therapy. Ten prostate cancer patients with weekly verification CTs underwent pencil beam scanning with the bilateral single-field uniform dose (SFUD) modality. A typical field had 10-15 energy layers and 500-1000 spots. According to their treatment logs, each layer delivery time was <1 s, with average time to change layers of approximately 8 s. Real-time intrafraction prostate motion was determined from our previously reported prospective study using Calypso beacon transponders. Prostate motion and beam delivering sequence of the worst-case scenario patient were synchronized to calculate the "true" dose received by the prostate. The intrafraction effect was examined by applying the worst-case scenario prostate motion on the planning CT, and the residual interfraction effect was examined on the basis of weekly CT scans. The resultant dose variation of target and critical structures was examined to evaluate the interplay effect. The clinical target volume (CTV) coverage was degraded because of both effects. The CTV D99 (percentage dose to 99% of the CTV) varied up to 10% relative to the initial plan in individual fractions. However, over the entire course of treatment the total dose degradation of D99 was 2%-3%, with a standard deviation of <2%. Absolute differences between SFUD, intensity modulate proton therapy, and one-field-per-day SFUD plans were small. The intrafraction effect dominated over the residual interfraction effect for CTV coverage. Mean dose to the anterior rectal wall increased approximately 10% because of combined residual interfraction and intrafraction effects, the interfraction effect being dominant. Both intrafraction and residual interfraction prostate motion degrade CTV coverage within a clinically acceptable level. One-field-per-day SFUD delivered twice is as robust as the bilateral SFUD plan treated daily over the course of treatment.

Clinical use of electronic portal imaging to analyse tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers

Purpose: To evaluate the daily treatment setup variation and the interfraction and intrafraction prostate motion with portal imaging and implanted fiducial markers during irradiation with a 3D conformal radiotherapy for localized prostate cancer patients. Methods : By remote verification, shifts from isocenteric positioning and inter/intra-fraction prostate motion were investigated for 34 patients treated supine with escalated dose conformal radiotherapy. To limit the effect of inter-fraction prostate motion, patients were planned and treated with an empty rectum and a comfortably full bladder. Daily pre-therapy and treatment electronic portal images were obtained for anterior and lateral treatment fields according to an on-line target localization protocol using three gold markers. From these images, random and systematic set-up errors were measured by matching corresponding patients’ gold markers on reference digitally reconstructed radiographs (DRR). Superior-inferior, anterior-posterior and lateral motions were measured from the displacement of the gold markers implanted into the prostate before planning. A planning target volume (PTV) was derived to account for the measured prostate motion and field placement deviations. Results: Analysis of 1,278 portal images to determine changes in the radiation field during the course of treatment. From the data, random isocenter positioning deviations were 2.66 mm, 2.78 mm and 2.59 mm for vertical, lateral and longitudinal movements respectively. The systematic deviations were 3.15 mm, 3.09 mm and 2.52 mm for vertical, lateral and longitudinal movements respectively. From the verification process, it was realized that 44.7%, 42.8% and 31.4% of the vertical, lateral and longitudinal prostate migrations respectively needed correction/shift. Conclusion : Random set-up errors were small using real-time isocenter placement corrections. Inter-fraction prostate motion remained the largest source of treatment error, and observed motion was greatest at the laterals. In the absence of real-time pre-treatment imaging of the prostate position, using sequential portal films of implanted gold markers, portions of the PTV is missed and surrounding tissues not spared. This research improves quality assurance by confirming the prostate position within the treatment field over the course of therapy. ----------------------------- Cite this article as : Acquah GF, Gustavsson M, Doudoo CO, Agbeve RK, Schiestl B. Clinical use of electronic portal imaging to analyze tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers. Int J Cancer Ther Oncol 2014; 2 (4):02044. DOI : 10.14319/ijcto.0204.4

Erratum to: Effect of magnesium oxide on interfraction prostate motion and rectal filling in prostate cancer radiotherapy: analysis of a randomized clinical trial

To investigate whether magnesium oxide reduces the interfraction motion of the prostate and the amount of rectal filling and rectal gas, which influences prostate position during radiotherapy for prostate cancer.From December 2008 to February 2010, 92 prostate cancer patients scheduled for intensity-modulated radiotherapy (77 Gy in 35 fractions) using fiducial marker-based position verification were randomly assigned to receive magnesium oxide (500 mg twice a day) or placebo during radiotherapy. In a previous study, we investigated the effect on intrafraction motion and did not find a difference between the treatment arms. Here, we compared the interfraction prostate motion between the two treatment arms as well as the amount of rectal filling and rectal air pockets using pretreatment planning computed tomography and magnetic resonance imagingscans.There was no statistically significant difference between the treatment arms in translation and rotation of the prostate between treatment fractions, except for the rotation around the cranial caudal axis. However, the difference was less than 1° and therefore considered not clinically relevant. There was no significant difference in the amount of rectal filling and rectal air pockets between the treatment arms.Magnesium oxide is not effective in reducing the interfraction prostate motion or the amount of rectal filling and rectal gas during external-beam radiotherapy. Therefore, magnesium oxide is not recommended in clinical practice for these purposes.

Effect of magnesium oxide on interfraction prostate motion and rectal filling in prostate cancer radiotherapy: analysis of a randomized clinical trial.

To investigate whether magnesium oxide reduces the interfraction motion of the prostate and the amount of rectal filling and rectal gas, which influences prostate position during radiotherapy for prostate cancer. From December 2008 to February 2010, 92 prostate cancer patients scheduled for intensity-modulated radiotherapy (77 Gy in 35 fractions) using fiducial marker-based position verification were randomly assigned to receive magnesium oxide (500 mg twice a day) or placebo during radiotherapy. In a previous study, we investigated the effect on intrafraction motion and did not find a difference between the treatment arms. Here, we compared the interfraction prostate motion between the two treatment arms as well as the amount of rectal filling and rectal air pockets using pretreatment planning computed tomography and magnetic resonance imagingscans. There was no statistically significant difference between the treatment arms in translation and rotation of the prostate between treatment fractions, except for the rotation around the cranial caudal axis. However, the difference was less than 1° and therefore considered not clinically relevant. There was no significant difference in the amount of rectal filling and rectal air pockets between the treatment arms. Magnesium oxide is not effective in reducing the interfraction prostate motion or the amount of rectal filling and rectal gas during external-beam radiotherapy. Therefore, magnesium oxide is not recommended in clinical practice for these purposes.