Prostate Intensity-modulated Radiation Therapy Research Articles

Sexual quality of life following prostate intensity modulated radiation therapy (IMRT) with a rectal/prostate spacer: Secondary analysis of a phase 3 trial

BackgroundWe previously reported the results of a phase 3 trial evaluating a prostate/rectal hydrogel spacer during prostate intensity modulated radiation therapy, which resulted in decreased rectal dose and toxicity and less decline in bowel quality of life (QOL). A secondary analysis was performed to correlate penile bulb dose and sexual QOL. Methods and materialsSexual QOL was measured with the Expanded Prostate Cancer Index Composite (EPIC) by mean scores, the proportion of patients with a minimal clinically important difference (MID), and analyses of the different items composing the sexual domain. ResultsA total of 222 men enrolled with median follow-up of 37 months. Hydrogel reduced penile bulb mean dose, maximum dose, and percentage of penile bulb receiving 10 to 30 Gy (all P < .05) with mean dose indirectly correlated with erections sufficient for intercourse at 15 months (P = .03). Baseline EPIC was low (53 [standard deviation ± 24]) with no difference between arms (P > .1). A total of 41% (88/222) of men had adequate baseline sexual QOL (EPIC >60 (mean, 77 [± 8.3]). This subgroup at 3 years had better sexual function (P = .03) with a spacer with a smaller difference in sexual bother (P = .1), which resulted in a higher EPIC summary on the spacer arm (58 [±24.1] vs control 45 [± 24.4]) meeting threshold for MID without statistical significance (P = .07). There were statistically nonsignificant differences favoring spacer for the proportion of men with MID and 2× MID declines in sexual QOL with 53% vs 75% having an 11-point decline (P = .064) and 41% vs 60% with a 22-point decline (P = .11). At 3 years, more men potent at baseline and treated with spacer had “erections sufficient for intercourse" (control 37.5% vs spacer 66.7%, P = .046) as well as statistically higher scores on 7 of 13 items in the sexual domain (all P < .05). ConclusionsThe use of a hydrogel spacer decreased dose to the penile bulb, which was associated with improved erectile function compared with the control group based on patient-reported sexual QOL.

Effect of modern, high-quality prostate intensity-modulated radiation therapy on outcome: Evidence from a community radiation oncology program.

Radiation technique for prostate cancer has continuously evolved over the past several decades. The aim of the present study was to describe the effects of implementing modern prostate intensity-modulated radiation therapy (M-IMRT) on dosimetry and outcome. Between January 2010 and April 2012, 48 consecutive patients were treated with conventional prostate IMRT (C-IMRT) to a dose of 81 Gy. Between May 2012 and April 2015, 50 consecutive patients were treated with M-IMRT to the entire prostate to a dose of 75.6-79.2 Gy, while using prostate magnetic resonance imaging fusion, dose-volume constraints prioritizing normal tissue avoidance above planning target volume coverage, and boosting any dominant intraprostatic masses to 79.2-81 Gy. Rectal Dmax, V75, V60, V65 and V50, bladder Dmax, V75, V70 and V65, and acute and late toxicities were compared between the C-IMRT and M-IMRT groups. The median follow-up for the C-IMRT and M-IMRT groups was 61 vs. 26 months, respectively (P<0.001). M-IMRT resulted in a significant reduction in median rectal Dmax, rectal V75, rectal V70, rectal V65, bladder Dmax, bladder V75, bladder V70 and bladder V65 (P<0.01 for all). There was no significant difference in rectal V50. The 2-year rate of late grade ≥2 rectal bleeding was 13% with C-IMRT vs. 3% with M-IMRT (P=0.03). The 2-year rate of late grade ≥2 genitourinary toxicity was 11% for C-IMRT vs. 5% for M-IMRT (P=0.21). There were no significant differences in acute toxicity, biochemical control or overall survival. Therefore, compared with C-IMRT, M-IMRT was associated with reduced rectal toxicity without compromising disease control.

MEASUREMENT OF ABSORPTION DOSE OUTSIDE IRRADIATION FIELD IN IMRT.

The absorption dose outside the irradiation field for prostate intensity-modulated radiation therapy was measured and evaluated by comparison with calculated values of radiation treatment planning system (TPS). The values of TPS calculated were using Varian CLINAC21EX/Eclipse and TomoTherapy Planning System for constant irradiation time. The absorption dose was measured by placing a glass-element dosemeter in a human-bone enclosure phantom with a planning target volume inside the irradiation field. The organs at risk were the rectum, spinal cord, thyroid, eyeball and the left lung. The calculated values of TPS, Varian CLINAC21EX/Eclipse and TomoTherapy Planning System were calculated, up to 17 and 55 cm from the isocenter, respectively. The absorbed dose outside the irradiation field diverged with increased distance from the isocenter (Varian/Eclipse: p = 0.03, TomoTherapy Planning System: p = 0.25). The calculated values for the absorbed dose outside the irradiation field were underestimated.

Uncertainties of cumulative dose assessment for prostate IMRT

Intensity-modulated radiation therapy (IMRT) is capable of providing conformal doses to the target volume while minimizing doses to nearby normal tissue for radiotherapy of localized prostate cancer (1). However, the clinical gains of prostate IMRT may be limited by geometric uncertainties of a patient. The prostate movement between fractions, i.e., inter-fractional motion, is associated with patient setup uncertainty as well as internal organ displacement between fractions. The inter-fractional motion contributes to the deviation in the delivered doses to the target volume and organs at risk (OARs) (2). Depending on the filling state of the rectum and bladder, the prostate can move by more than 1 cm (3,4). Image guidance before each fraction can reduce these errors and deliver a precise prescription dose to the target volume while sparing doses to OARs. On the other hand, intra-fractional motion refers to the external patient movement as well as internal organ motion during the actual treatment. The major intra-fractional motion of the prostate gland is generally due to changes of gas in the rectum and surrounding digestive track (5). This temporal behavior of prostate motion can vary rapidly and substantially, which could result in large discrepancies between planned doses and actually delivered doses to a patient.

Can a peri-rectal hydrogel spaceOAR programme for prostate cancer intensity-modulated radiotherapy be successfully implemented in a regional setting?

The aim of this study was to investigate whether the implementation of a hydrogel spacer (SpaceOAR) programme for patients treated with 81Gy prostate intensity-modulated radiotherapy (IMRT) in a regional setting can reduce rectal doses and toxicity. In this retrospective study, 125 patients with localised prostate cancer treated between April 2014 (programme commencement) and June 2015 were compared: 65 with SpaceOAR (inserted by five different urologists) and 60 patients treated over the same time period without SpaceOAR. Patients were treated with 81Gy in 45Fx of IMRT over 9weeks. Planning aims included restricting rectal doses to V40Gy<35%, V65Gy<17%, V75Gy<10%. Acute toxicity was assessed weekly during radiotherapy and at 12weeks. Rectal volume parameters were all significantly lower in the SpaceOAR group, with an associated reduction in acute diarrhoea (13.8% vs 31.7%). There were no significant differences in the very low rates of acute and late faecal incontinence or proctitis, however, there was a trend towards increased haemorrhoid rate in the SpaceOAR group (11.7% vs 3.1%, P=0.09). A SpaceOAR programme in a regional setting with urologists performing low volumes of insertions (<1 per month on average) is of clinical benefit, and was associated with significantly lower radiation doses to the rectum and lower rates of acute diarrhoea.

Development and verification of a time delivery model for prostate intensity modulated radiotherapy using a Siemens® Artiste™ 160 Multi-leaf Collimator Linac.

Time delivery models thus far proposed for prediction of radiotherapy delivery times are not applicable to all makes of Linac. Our purpose was to develop a time delivery model, which would also be applicable for a Siemens® ARTISTE™ 160 Multi-leaf Collimator (MLC) linear accelerator (Linac) and validate the model using prostate Intensity Modulated Radiation Therapy (IMRT) treatment plans. To our knowledge, a time delivery model has not yet been proposed for a Siemens® ARTISTE™ 160 MLC Linac. We used the principles of the time delivery model created for a Varian® Linac and added the radio frequency (RF) wave component, and the MLC delay time to the MLC travel time component. Machine input parameters were confirmed using a WIN® stopwatch. We tested our derived model by selecting ten random 15 MV prostate IMRT treatment plans from our clinic. The delivery time was measured three times, once per day on three different days. The calculated and measured times were compared by means of correlation. The time delivery ranged between 314 and 480s. The largest percentage difference was 3.3% (16s) and the smallest 0.2% (1s); the mean percentage difference was 1.9%. MLC delay and MLC speed, representing segment delivery, had the greatest uncertainties. From the successfully verified time delivery model created, it is concluded that the inter-segmental component of the process is most time-consuming. In order to decrease delivery time it is proposed that the total segments of a treatment plan be decreased.

Three-dimensional quality assurance of IMRT prostate plans using gel dosimetry

Intensity modulated radiotherapy (IMRT) is one of the most modern radiation therapy treatment techniques. Although IMRT can deliver high and complex conformational doses to the tumor volume, its implementation requires rigorous quality assurance (QA) procedures that include a dosimetric pre-treatment verification of individual patient planning. This verification usually involves measuring a small volume of absolute dose with an ionization chamber and checking bi-dimensional fluency with an array of detectors. The planning technique has tri-dimensional characteristics, but no tridimensional dosimetry has been established in the clinical routine. One strategy to perform three-dimensional dosimetry is to use polymeric gels associated with magnetic resonance imaging to evaluate dose distribution. Here, we have compared the results of conventional QA procedures involving one- and two-dimensional dosimetry to the results of three-dimensional dosimetry conducted with MAGIC-f gel in 10 cases of prostate cancer IMRT planning. More specifically, we used the gamma index (3%/3mm) to compare the results of three-dimensional dosimetry to the expected dose distributions obtained with the treatment planning system. Except for one IMRT treatment plan, the gel dosimetry results agreed with the conventional quality control and provided an overview of dose distribution in the target volume.

The impact of intensity-modulated radiation therapy plan normalization in the postprostatectomy setting—does it matter?

The International Commission on Radiation Units & Measurements -83 recommends prescribing intensity-modulated radiation therapy (IMRT) in a dose-volume manner. Despite this, clinical variation still exists in how prostate IMRT plans are prescribed. This study aims to investigate the impact of different plan normalization methods for postprostatectomy IMRT.IMRT treatment plans were created retrospectively for 20 postprostatectomy patients. These were normalized such that the dose received by 98% (D98) of the planning target volume (PTV) was equal to 100% of the prescribed dose. All plans were individually optimized to achieve target coverage and organ at risk (OAR) dose constraints. Each patient's plan was then copied and normalized such that the mean dose (Dmean) received by the PTV was equal to 100% of the prescribed dose. The International Commission on Radiation Units & Measurements -83 recommended dosimetric end points were extracted for targets and Quantitative Analyses of Normal Tissue Effects in the Clinic or Radiation Therapy Oncology Group 0534 end points extracted for OARs. Statistical analysis using the Wilcoxon signed-rank test to measure the difference between data from plans normalized to D98 and Dmean was conducted.Extracted dosimetric end points of the targets and OARs were significantly higher in plans normalized to D98 than Dmean (p < 0.05) with the exceptions of D2 of the rectum and right femoral head.Normalization impacts on dosimetric end points of a plan. Hence, reporting the normalization method used is necessary to allow for meaningful interpretation of IMRT dosimetric studies.

Dose-volume consistency and radiobiological characterization between prostate IMRT and VMAT plans

Purpose: Dose-volume consistency of the planning target volume (PTV) and rectum for the prostate intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) plans were evaluated and compared. Dependences of radiobiological parameters of the prostate and rectum on the PTV and rectal volume were also investigated. Methods: From 40 prostate IMRT and 50 VMAT patients treated with the same prescription (78 Gy per 39 fractions) and dose-volume criteria in the inverse planning, the prostate tumour control probability (TCP), rectal equivalent uniform dose (EUD) and rectal normal tissue complication probability (NTCP) were calculated. The dose-volume consistency of the PTV and rectum, demonstrating the variability of dose-volume histogram (DVH) among patients, was defined and calculated as per the deviation between the corresponding and mean DVH. Results: For the IMRT plans, the prostate TCP was found increasing with the PTV with a rate equal to 1.05 × 10 -3 % cm -3 , which was lower than 1.11 × 10 -3 % cm -3 for the VMAT plans. Both the rectal EUD and rectal NTCP were found decreasing with the rectal volume. The decrease rates for the IMRT plans (EUD = 0.47 × 10 -3 Gy cm -3 and NTCP = 3.94 × 10 -2 % cm -3 ) were higher than those for the VMAT (EUD = 0.28 × 10 -3 Gy cm -3 and NTCP = 2.61 × 10 -2 % cm -3 ). Conclusion: For the dose-volume consistency, small prostate TCP variation could be achieved by decreasing the dose-volume variability among the IMRT and VMAT plans. However, dependences of the rectal EUD and rectal NTCP on the dose-volume variability were not significant. It is concluded that maintaining a good dose-volume consistency in prostate plans can decrease the prostate TCP variation among the IMRT and VMAT patients. However, dose-volume variability is not affected by variations of the rectal EUD and rectal NTCP.

The benefit of using bladder sub-volume equivalent uniform dose constraints in prostate intensity-modulated radiotherapy planning.

BackgroundTo assess the benefits of bladder wall sub-volume equivalent uniform dose (EUD) constraints in prostate cancer intensity-modulated radiotherapy (IMRT) planning.MethodsTwo IMRT plans, with and without EUD constraints on the bladder wall, were generated using beams that deliver 80 Gy to the prostate and 46 Gy to the seminal vesicles and were compared in 53 prostate cancer patients. The bladder wall was defined as the volume between the external manually delineated wall and a contraction of 7 mm apart from it. The bladder wall was then separated into two parts: the internal-bladder wall (bla-in) represented by the portion of the bladder wall that intersected with the planning target volume (PTV) plus 5 mm extension; the external-bladder wall (bla-ex) represented by the remaining part of the bladder wall. In the IMRT plan with EUD constraints, the values of “a” parameter for the EUD models were 10.0 for bla-in and 2.3 for bla-ex. The plans with and without EUD constraints were compared in terms of dose–volume histograms, 5-year bladder and rectum normal tissue complication probability values, as well as tumor control probability (TCP) values.ResultsThe use of bladder sub-volume EUD constraints decreased both the doses to the bladder wall (V70: 22.76% vs 19.65%, Dmean: 39.82 Gy vs 35.45 Gy) and the 5-year bladder complication probabilities (≥LENT/SOMA Grade 2: 20.35% vs 17.96%; bladder bleeding: 10.63% vs 8.64%). The doses to the rectum wall and the rectum complication probabilities were also slightly decreased by the EUD constraints compared to physical constraints only. The minimal dose and the V76Gy of PTVprostate were, however, slightly decreased by EUD optimization, nevertheless without significant difference in TCP values between the two plans, and the PTV parameters finally respected the Groupe d’Etude des Tumeurs Uro-Génitales recommendations.ConclusionSeparating the bladder wall into two parts with appropriate EUD optimization may reduce bladder toxicity in prostate IMRT. Combining biological constraints with physical constraints in the organs at risk at the inverse planning step of IMRT may improve the dose distribution.

Application programming in C# environment with recorded user software interactions and its application in autopilot of VMAT/IMRT treatment planning.

An autopilot scheme of volumetric‐modulated arc therapy (VMAT)/intensity‐modulated radiation therapy (IMRT) planning with the guidance of prior knowledge is established with recorded interactions between a planner and a commercial treatment planning system (TPS). Microsoft (MS) Visual Studio Coded UI is applied to record some common planner‐TPS interactions as subroutines. The TPS used in this study is a Windows‐based Eclipse system. The interactions of our application program with Eclipse TPS are realized through a series of subroutines obtained by prerecording the mouse clicks or keyboard strokes of a planner in operating the TPS. A strategy to autopilot Eclipse VMAT/IMRT plan selection process is developed as a specific example of the proposed “scripting” method. The autopiloted planning is navigated by a decision function constructed with a reference plan that has the same prescription and similar anatomy with the case at hand. The calculation proceeds by alternating between the Eclipse optimization and the outer‐loop optimization independent of the Eclipse. In the C# program, the dosimetric characteristics of a reference treatment plan are used to assess and modify the Eclipse planning parameters and to guide the search for a clinically sensible treatment plan. The approach is applied to plan a head and neck (HN) VMAT case and a prostate IMRT case. Our study demonstrated the feasibility of application programming method in C# environment with recorded interactions of planner‐TPS. The process mimics a planner's planning process and automatically provides clinically sensible treatment plans that would otherwise require a large amount of manual trial and error of a planner. The proposed technique enables us to harness a commercial TPS by application programming via the use of recorded human computer interactions and provides an effective tool to greatly facilitate the treatment planning process.PACS number(s): 87.55.D‐, 87.55.kd, 87.55.de

An Accuracy Assessment of Exit-Fluence–Based Dose Recalculation for Prostate Intensity Modulated Radiation Therapy

An Accuracy Assessment of Exit-Fluence–Based Dose Recalculation for Prostate Intensity Modulated Radiation Therapy

Prostate intensity-modulated radiotherapy planning in seven mouse clicks: Development of a class solution for cancer

AimThe aim of the retrospective study was to develop a planning class solution for prostate intensity-modulated radiotherapy (IMRT) that achieved target and organs-at-risk (OAR) doses within acceptable departmental protocol criteria using the Monaco treatment planning system (Elekta-CMS Software, MO, USA). BackgroundAdvances in radiation therapy technology have led to a re-evaluation of work practices. Class solutions have the potential to produce highly conformal plans in a time-efficient manner. Materials and MethodsUsing data from intermediate and high risk prostate cancer patients, a stepwise quality improvement model was employed. Stage 1 involved the development of a broadly based treatment template developed across 10 patients. Stage 2 involved template refinement and clinical audit (n=20); Stage 3, template review (n=50) and Stage 4 an assessment of a revised template against the actual treatment plan involving 72 patients. ResultsThe computer algorithm that comprised the Stage 4 template met clinical treatment criteria for 82% of patients. Minor template changes were required for a further 13% of patients. Major changes were required in 4%; one patient could not be assessed. The average calculation time was 13min and involved seven mouse clicks by the planner. Thus, the new template met treatment criteria or required only minor changes in 95% of prostate patients; this is an encouraging result suggesting improvements in planning efficiency and consistency. ConclusionIt is feasible to develop a class solution for prostate IMRT using a stepwise quality improvement model which delivers clinically acceptable plans in the great majority of prostate cases.

Investigation of a real-time EPID-based patient dose monitoring safety system using site-specific control limits.

PurposeThe aim of this study is to investigate the performance and limitations of a real-time transit electronic portal imaging device (EPID) dosimetry system for error detection during dynamic intensity modulated radiation therapy (IMRT) treatment delivery. Sites studied are prostate, head and neck (HN), and rectal cancer treatments.MethodsThe system compares measured cumulative transit EPID image frames with predicted cumulative image frames in real-time during treatment using a χ comparison with 4 %, 4 mm criteria. The treatment site-specific thresholds (prostate, HN and rectum IMRT) were determined using initial data collected from 137 patients (274 measured treatment fractions) and a statistical process control methodology. These thresholds were then applied to data from 15 selected patients including 5 prostate, 5 HN, and 5 rectum IMRT treatments for system evaluation and classification of error sources.ResultsClinical demonstration of real-time transit EPID dosimetry in IMRT was presented. For error simulation, the system could detect gross errors (i.e. wrong patient, wrong plan, wrong gantry angle) immediately after EPID stabilisation; 2 seconds after the start of treatment. The average rate of error detection was 7.0 % (prostate = 5.6 %, HN= 8.7 % and rectum = 6.7 %). The detected errors were classified as either clinical in origin (e.g. patient anatomical changes), or non-clinical in origin (e.g. detection system errors). Classified errors were 3.2 % clinical and 3.9 % non-clinical.ConclusionAn EPID-based real-time error detection method for treatment verification during dynamic IMRT has been developed and tested for its performance and limitations. The system is able to detect gross errors in real-time, however improvement in system robustness is required to reduce the non-clinical sources of error detection.

SpaceOAR Hydrogel in Dose-escalated Prostate Cancer Radiotherapy: Rectal Dosimetry and Late Toxicity

AimTo investigate the feasibility, dosimetric benefits and late toxicity of a temporary hydrogel spacer between the rectum and the prostate for prostate intensity-modulated radiotherapy. Materials and methodsThirty patients with prostate cancer were enrolled on a phase I/II study. All patients underwent magnetic resonance imaging before and after placement of 10 cm3 of hydrogel. The first 10 patients had an additional magnetic resonance imaging after the completion of radiation treatment. SpaceOAR hydrogel was injected under general anaesthetic using a transperineal approach with transrectal ultrasound guidance. Primary end points were perioperative toxicity and comparison of rectal dosimetry. Secondary end points included cute and late radiation toxicity. All patients were planned on both pre- and post-hydrogel scans to a D95 of 80 Gy in 40 fractions. A contemporary control group of 110 prostate cancer patients treated with the same prescription was identified for comparison. ResultsThere were no perioperative complications. Rectal doses were significantly lower for the post-hydrogel plans, especially above 65 Gy (V82 = 0.2% versus 1.3%; V80 = 0.8% versus 5.3%; V75 = 2.2% versus 9.5%; V70 = 3.7% versus 12.3%; V65 = 5.4% versus 14.7%; V40 = 22.9% versus 32% and V30 = 42.7% versus 49.4%). There was no significant difference in acute grade 1 and 2 gastrointestinal toxicity, which was 43% versus 51% and 0% versus 4.5% in the hydrogel and control groups, respectively. Late grade 1 was significantly less frequent in the hydrogel group (16.6% versus 41.8%, P = 0.04). ConclusionSpaceOAR hydrogel was inserted with minimal side-effects. Dosimetric benefits were greatest at higher rectal doses (V65 to V82). Late grade 1 gastrointestinal toxicity was significantly lower than that seen in patients treated without hydrogel.

SU-F-T-378: Evaluation of Dose-Volume Variability and Parameters Between Prostate IMRT and VMAT Plans

Purpose: This study compared the rectal dose-volume consistency, equivalent uniform dose (EUD) and normal tissue complication probability (NTCP) in prostate intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). Methods: For forty prostate IMRT and fifty VMAT patients treated using the same dose prescription (78 Gy/39 fraction) and dose-volume criteria in inverse planning optimization, the rectal EUD and NTCP were calculated for each patient. The rectal dose-volume consistency, showing the variability of dose-volume histogram (DVH) among patients, was defined and calculated based on the deviation between the mean and corresponding rectal DVH. Results: From both the prostate IMRT and VMAT plans, the rectal EUD and NTCP were found decreasing with the rectal volume. The decrease rates for the IMRT plans (EUD = 0.47 × 10−3 Gy cm−3 and NTCP = 3.94 × 10−2 % cm−3) were higher than those for the VMAT (EUD = 0.28 × 10−3 Gy cm−3 and NTCP = 2.61 × 10−2 % cm−3). In addition, the dependences of the rectal EUD and NTCP on the dose-volume consistency were found very similar between the prostate IMRT and VMAT plans. This shows that both delivery techniques have similar variations of the rectal EUD and NTCP on the dose-volume consistency. Conclusion: Dependences of the dose-volume consistency on the rectal EUD and NTCP were compared between the prostate IMRT and VMAT plans. It is concluded that both rectal EUD and NTCP decreased with an increase of the rectal volume. The variation rates of the rectal EUD and NTCP on the rectal volume were higher for the IMRT plans than VMAT. However, variations of the rectal dose-volume consistency on the rectal EUD and NTCP were found not significant for both delivery techniques.

Analysis and Management of Rectal Gas with Kampo Formulas During Intensity-Modulated Radiotherapy of Prostate Cancer: A Case Series Study

During intensity-modulated radiation therapy (IMRT) for prostate cancer, the target, bladder, and rectum positions should be kept constant to reduce adverse events, such as radiation proctitis, and to increase local tumor control. For this purpose, decreasing the rectal contents as much as possible is important. Daisaikoto (DST) and bukuryoingohangekobokuto (BIHKT) are traditional Japanese herbal (Kampo) formulas that have been used to treat patients with abdominal bloating or constipation. This study investigated the effect of DST and BIHKT on the rectal gas volume during prostate IMRT according to Kampo diagnosis. Five patients were treated with DST or BIHKT at a dose of 5.0 or 7.5 g/d. The volume of rectal gas in 189 megavoltage computed tomographic images taken before each treatment session and the frequency of rectal gas drainage were evaluated before and after DST or BIHKT administration. After DST or BIHKT treatment, the mean volume of rectal gas was reduced from 6.4 to 2.1 mL, and the mean frequency of gas drainage decreased from 43% to 9%. DST and BIHKT appear to be useful in reducing rectal gas, which would help prevent radiation proctitis and improve the local control of prostate cancer with IMRT.

Dosimetric comparison between the prostate intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans using the planning target volume (PTV) dose–volume factor

AbstractBackgroundWe demonstrated that our proposed planning target volume (PTV) dose–volume factor (PDVF) can be used to evaluate the PTV dose coverage between the intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) plans based on 90 prostate patients.PurposePDVF were determined from the prostate IMRT and VMAT plans to compare their variation of PTV dose coverage. Comparisons of the PDVF with other plan evaluation parameters such as D5%, D95%, D99%, Dmean, conformity index (CI), homogeneity index (HI), gradient index (GI) and prostate tumour control probability (TCP) were carried out.Methods and materialsProstate IMRT and VMAT plans using the 6 MV photon beams were created from 40 and 50 patients, respectively. Dosimetric indices (CI, HI and GI), dose–volume points (D5%, D95%, D99% and Dmean) and prostate TCP were calculated according to the PTV dose–volume histograms (DVHs) of the plans. All PTV DVH curves were fitted using the Gaussian error function (GEF) model. The PDVF were calculated based on the GEF parameters.ResultsFrom the PTV DVHs of the prostate IMRT and VMAT plans, the average D99% of the PTV for IMRT and VMAT were 74·1 and 74·5 Gy, respectively. The average prostate TCP were 0·956 and 0·958 for the IMRT and VMAT plans, respectively. The average PDVF of the IMRT and VMAT plans were 0·970 and 0·983, respectively. Although both the IMRT and VMAT plans showed very similar prostate TCP, the dosimetric and radiobiological results of the VMAT technique were slightly better than IMRT.ConclusionThe calculated PDVF for the prostate IMRT and VMAT plans agreed well with other dosimetric and radiobiological parameters in this study. PDVF was verified as an alternative of evaluation parameter in the quality assurance of prostate treatment planning.

MRI-based IMRT planning for MR-linac: comparison between CT- and MRI-based plans for pancreatic and prostate cancers**This work was present in part at the 2014 ASTRO annual meeting.

The treatment planning in radiation therapy (RT) can be arranged to combine benefits of computed tomography (CT) and magnetic resonance imaging (MRI) together to maintain dose calculation accuracy and improved target delineation. Our aim is study the dosimetric impact of uniform relative electron density assignment on IMRT treatment planning with additional consideration given to the effect of a 1.5 T transverse magnetic field (TMF) in MR-Linac.A series of intensity modulated RT (IMRT) plans were generated for two representative tumor sites, pancreas and prostate, using CT and MRI datasets. Representative CT-based IMRT plans were generated to assess the impact of different electron density (ED) assignment on plan quality using CT without the presence of a 1.5 T TMF. The relative ED (rED) values used were taken from the ICRU report 46. Four types of rED assignment in the organs at risk (OARs), the planning target volumes (PTV) and in the non-specified tissue (NST) were considered. Dose was recalculated (no optimization) using a Monaco 5.09.07a research planning system employing Monte Carlo calculations with an option to include TMF. To investigate the dosimetric effect of different rED assignment, the dose-volume parameters (DVPs) obtained from these specific rED plans were compared to those obtained from the original plans based on CT.Overall, we found that uniform rED assignment results in differences in DVPs within 3% for the PTV and 5% for OAR. The presence of 1.5 T TMF on IMRT DVPs resulted in differences that were generally within 3% of the Gold St for both the pancreas and prostate. The combination of uniform rED assignment and TMF produced differences in DVPs that were within 4–5% of the Gold St. Larger differences in DVPs were observed for OARs on T2-based plans.The effects of using different rED assignments and the presence of 1.5 T TMF for pancreas and prostate IMRT plans are generally within 3% and 5% of PTV and OAR Gold St values. There are noticeable dosimetric differences between the CT- and MRI-based IMRT plans caused by a combination of anatomical changes between the two image acquisition times, uniform rED assignment and 1.5 T TMF.

Clinical Experience and Evaluation of Patient Treatment Verification With a Transit Dosimeter

To prospectively evaluate a protocol for transit dosimetry on a patient population undergoing intensity modulated radiation therapy (IMRT) and to assess the issues in clinical implementation of electronic portal imaging devices (EPIDs) for treatment verification. Fifty-eight patients were enrolled in the study. Amorphous silicon EPIDs were calibrated for dose and used to acquire images of delivered fields. Measured EPID dose maps were back-projected using the planning computed tomographic (CT) images to calculate dose at prespecified points within the patient and compared with treatment planning system dose offline using point dose difference and point γ analysis. The deviation of the results was used to inform future action levels. Two hundred twenty-five transit images were analyzed, composed of breast, prostate, and head and neck IMRT fields. Patient measurements demonstrated the potential of the dose verification protocol to model dose well under complex conditions: 83.8% of all delivered beams achieved the initial set tolerance level of ΔD of 0±5cGy or %ΔD of 0%±5%. Importantly, the protocol was also sensitive to anatomic changes and spotted that 3 patients from 20 measured prostate patients had undergone anatomic change in comparison with the planning CT. Patient data suggested an EPID-reconstructed versus treatment planning system dose difference action level of 0%±7% for breast fields. Asymmetric action levels were more appropriate for inversed IMRT fields, using absolute dose difference (-2±5cGy) or summed field percentage dose difference (-6%±7%). The invivo dose verification method was easy to use and simple to implement, and it could detect patient anatomic changes that impacted dose delivery. The system required no extra dose to the patient or treatment time delay and so could be used throughout the course of treatment to identify and limit systematic and random errors in dose delivery for patient groups.