Prostate Intensity-modulated Radiation Therapy Research Articles

Experiencing In-Vivo Dosimetry Verification in Malaysia: A Patient-Specific EPID-Based Approach

Real-time dosimetry is crucial for patient-specific quality assurance in radiotherapy facilities across Europe, and the same demand extends to advanced countries like Malaysia. Our study aimed to assess the need for in vitro diagnostic (IVD) testing in Malaysia, exploring the use of Electronic Portal Imaging Device (EPID)-based dose verification to simplify complex methods. In this research, we assessed the accuracy of in-vivo dose reconstruction using EPIgrayTM (DOSIsoft, Cachan, France) for 20 cohorts of patients who underwent breast and prostate Intensity-Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT), and compared the results with the dose calculated by the Treatment Planning System (TPS). Initially, we set a default tolerance level of 7-10% for dose acceptance. Our study found that the majority of patients in the cohort met the 10% tolerance level when validated with EPIgrayTM in vivo dosimetry. Specifically, 12 out of 15 patients who underwent VMAT treatment were within this tolerance range. Additionally, for IMRT treatment, 4 out of 6 patients achieved the 10% tolerance level. These initial findings demonstrate the potential of EPIgrayTM as a valuable tool for verifying in vivo dosimetry for advanced treatment techniques. For VMAT plans, more than 85% of the points were in agreement with the 10% tolerance level for 11 out of 15 patients. For IMRT plans, more than 90% of the points met the set tolerance level for 4 out of 15 patients. By understanding the agreement and variability of EPID-based IVD, we can further refine the utilization of EPID-based IVD as a relevant tool in ensuring accurate and reliable dose delivery during radiotherapy treatments.

Salvage prostate intensity modulated radiation therapy after cryotherapy failure

Cryotherapy is an ablative therapy that can be used to treat localized prostate cancer. In case of recurrence, treatment options are not well-defined, and their outcomes are unknown. We therefore collected all patients treated with radiotherapy after cryotherapy for prostate cancer recurrence in Nantes (France) between 2012 and 2019. We identified ten patients. After a median follow-up of 5 years, two patients presented late grade 3 toxicities; one patient presented a grade 3 rectal hemorrhage, and one had a grade 3 hematuria. Two patients relapsed at 61 and 62 months, and three patients died of other causes. Radiotherapy to treat local prostate cancer recurrence after cryotherapy seems feasible and effective in local control. These results do not allow us to recommend this technique in current practice but are encouraging for the conduct of prospective trials.

Radiological imaging protection: a study on imaging dose used while planning computed tomography for external radiotherapy in Japan.

Previous studies have primarily focused on quality of imaging in radiotherapy planning computed tomography (RTCT), with few investigations on imaging doses. To our knowledge, this is the first study aimed to investigate the imaging dose in RTCT to determine baseline data for establishing national diagnostic reference levels (DRLs) in Japanese institutions. A survey questionnaire was sent to domestic RT institutions between 10 October and 16 December 2021. The questionnaire items were volume computed tomography dose index (CTDIvol), dose-length product (DLP), and acquisition parameters, including use of auto exposure image control (AEC) or image-improving reconstruction option (IIRO) for brain stereotactic irradiation (brain STI), head and neck (HN) intensity-modulated radiotherapy (IMRT), lung stereotactic body radiotherapy (lung SBRT), breast-conserving radiotherapy (breast RT), and prostate IMRT protocols. Details on the use of motion-management techniques for lung SBRT were collected. Consequently, we collected 328 responses. The 75th percentiles of CTDIvol were 92, 33, 86, 23, and 32mGy and those of DLP were 2805, 1301, 2416, 930, and 1158mGy·cm for brain STI, HN IMRT, lung SBRT, breast RT, and prostate IMRT, respectively. CTDIvol and DLP values in institutions that used AEC or IIRO were lower than those without use for almost all sites. The 75th percentiles of DLP in each treatment technique for lung SBRT were 2541, 2034, 2336, and 2730mGy·cm for free breathing, breath holding, gating technique, and real-time tumor tracking technique, respectively. Our data will help in establishing DRLs for RTCT protocols, thus reducing imaging doses in Japan.

Performance assessment of variant UNet-based deep-learning dose engines for MR-Linac-based prostate IMRT plans

Objective. UNet-based deep-learning (DL) architectures are promising dose engines for traditional linear accelerator (Linac) models. Current UNet-based engines, however, were designed differently with various strategies, making it challenging to fairly compare the results from different studies. The objective of this study is to thoroughly evaluate the performance of UNet-based models on magnetic-resonance (MR)-Linac-based intensity-modulated radiation therapy (IMRT) dose calculations. Approach. The UNet-based models, including the standard-UNet, cascaded-UNet, dense-dilated-UNet, residual-UNet, HD-UNet, and attention-aware-UNet, were implemented. The model input is patient CT and IMRT field dose in water, and the output is patient dose calculated by DL model. The reference dose was calculated by the Monaco Monte Carlo module. Twenty training and ten test cases of prostate patients were included. The accuracy of the DL-calculated doses was measured using gamma analysis, and the calculation efficiency was evaluated by inference time. Results. All the studied models effectively corrected low-accuracy doses in water to high-accuracy patient doses in a magnetic field. The gamma passing rates between reference and DL-calculated doses were over 86% (1%/1 mm), 98% (2%/2 mm), and 99% (3%/3 mm) for all the models. The inference times ranged from 0.03 (graphics processing unit) to 7.5 (central processing unit) seconds. Each model demonstrated different strengths in calculation accuracy and efficiency; Res-UNet achieved the highest accuracy, HD-UNet offered high accuracy with the fewest parameters but the longest inference, dense-dilated-UNet was consistently accurate regardless of model levels, standard-UNet had the shortest inference but relatively lower accuracy, and the others showed average performance. Therefore, the best-performing model would depend on the specific clinical needs and available computational resources. Significance. The feasibility of using common UNet-based models for MR-Linac-based dose calculations has been explored in this study. By using the same model input type, patient training data, and computing environment, a fair assessment of the models’ performance was present.

Standard and Hypofractionated Dose Escalation to Intraprostatic Tumor Nodules in Localized Prostate Cancer: 5-Year Efficacy and Toxicity in the DELINEATE Trial

Our purpose was to report 5-year efficacy and toxicity of intraprostatic lesion boosting using standard and hypofractionated radiation therapy. DELINEATE (ISRCTN 04483921) is a single center phase 2 multicohort study including standardly fractionated (cohort A: 74 Gy/37F to prostate and seminal vesicles [PSV]; cohort C 74 Gy/37F to PSV plus 60 Gy/37F to pelvic lymph nodes) and moderately hypofractionated (cohort B: 60 Gy/20F to PSV) prostate intensity-modulated radiation therapy patients with National Comprehensive Cancer Network intermediate/high-risk disease. Patients received an integrated boost of 82 Gy (cohorts A and C) or 67 Gy (cohort B) to multiparametric magnetic resonance imaging identified lesion(s). Primary endpoint was late Radiation Therapy Oncology Group (RTOG) gastrointestinal (GI) toxicity at 1 year. Secondary endpoints were acute and late toxicity (clinician and patient reported) and freedom from biochemical/clinical failure at 5 years. Two hundred and sixty-five men were recruited and 256 were treated (55 cohort A, 153 cohort B, and 48 cohort C). Median follow-up for each cohort was >5 years. Cumulative late RTOG grade 2+ GI toxicity at 1 year was 3.6% (95% confidence interval [CI], 0.9%-13.8%) (cohort A), 7.2% (95% CI, 4%-12.6%) (cohort B), and 8.4% (95% CI, 3.2%-20.8%) (cohort C). Cumulative late RTOG grade 2+ GI toxicity to 5 years was 12.8% (95% CI, 6.3%-25.1%) (cohort A), 14.6% (95% CI, 9.9%-21.4%) (cohort B), and 20.7% (95% CI, 11.2%-36.2%) (cohort C). Cumulative RTOG grade 2+ genitourinary toxicity to 5 years was 12.9% (95% CI, 6.4%-25.2%) (cohort A), 18.2% (95% CI, 12.8%-25.4%) (cohort B), and 18.2% (95% CI, 9.5%-33.2%) (cohort C). Five-year freedom from biochemical/clinical failure was 98.2% (95% CI, 87.8%-99.7%) (cohort A), 96.7% (95% CI, 91.3%- 98.8%) (cohort B), and 95.1% (95% CI, 81.6-98.7%) (cohort C). The DELINEATE trial has shown safety, tolerability, and feasibility of focal boosting in 20 or 37 fractions. Efficacy results indicate a low chance of prostate cancer recurrence 5 years after radiation therapy. Evidence from ongoing phase 3 randomized trials is awaited.

Long-term outcomes of prostate intensity-modulated radiation therapy incorporating a simultaneous intra-prostatic MRI-directed boost.

Purpose/objectivesThis retrospective study demonstrates the long-term outcomes of treating prostate cancer using intensity modulated (IMRT) with incorporation of MRI-directed boost.Materials/methodsFrom February 2009 to February 2013, 78 men received image-guided IMRT delivering 77.4 Gy in 44 fractions with simultaneously integrated boost to 81–83 Gy to an MRI-identified lesion. Patients with intermediate-risk or high-risk prostate cancer were recommended to receive 6 and 24–36 months of adjuvant hormonal therapy, respectively.ResultsMedian follow-up was 113 months (11–147). There were 18 low-risk, 43 intermediate-risk, and 17 high-risk patients per NCCN risk stratification included in this study. Adjuvant hormonal therapy was utilized in 32 patients (41%). The 10-year biochemical control rate for all patients was 77%. The 10-year biochemical control rates for low-risk, intermediate-risk, and high-risk diseases were 94%, 81%, and 88%, respectively (p = 0.35). The 10-year rates of local control, distant control, and survival were 99%, 88%, and 66%, respectively. Of 25 patients who died, only four (5%) died of prostate cancer. On univariate analysis, T-category and pretreatment PSA level were associated with distant failure rate (p = 0.02). There was no grade =3 genitourinary and gastrointestinal toxicities that persisted at the last follow-up.ConclusionsThis study demonstrated the long-term efficacy of using MRI to define an intra-prostatic lesion for SIB to 81–83Gy while treating the entire prostate gland to 77.4 Gy with IMRT. Our study confirms that modern MRI can be used to locally intensify dose to prostate tumors providing high long-term disease control while maintaining favorable long-term toxicity.

Development and dosimetric evaluation of the IMRT prostate at outside-the-irradiated field in a heterogeneity male pelvis phantom

Abstract Background: Intensity-modulated radiation therapy (IMRT) treatment delivery requires pre-treatment patient-specific quality assurance (QA) for the dosimetry verification due to its complex multileaf-collimator movement. The prostate target close position between the bladder and rectum requires a tight margin during planning, and mistreatment would have a huge impact on the patient. A commercially available QA tool consists of a homogeneous medium and does not represent an exact photon interaction on the tumour and also on the nearby healthy organ. Objective: A heterogeneous male pelvis phantom was developed and investigated the efficiency of the treatment planning system (TPS) calculation on the off-axis region. Methods: Polymethyl methacrylate was used for the phantom housing, and the material closed to the bladder, rectum and prostate density was chosen to construct the organ models. The phantom was scanned and validated by the computed tomography number and density. An IMRT treatment was planned in the Monaco TPS, and a thermoluminescent dosimeter (TLD-100) was used to validate the point dosimetry. In addition, an EGSnrc Monte Carlo simulation was carried out to validate the phantom dosimetry. Results & Discussion: The dose measurement between TLD-100, TPS, and EGSnrc was compared and validated in the pelvis phantom. In the prostate region, the dose difference was within ± 5%, and the maximum dose difference outside-the-irradiated field was up to 20·07 % and 47·31 % in TPS and TLD-100, respectively. Meanwhile, the measured dose was lower than the calculated dose, and it was apparent for the dose outside-the-irradiated field. Conclusion: The developed heterogeneity male pelvis phantom was validated and verified to be an important QA device for validating radiation dosimetry in the pelvis region. The dose outside-the-irradiated field was underestimated by both TPS and TLD, respectively.

Dosimetric Effects of Air Cavities for MRI-Guided Online Adaptive Radiation Therapy (MRgART) of Prostate Bed after Radical Prostatectomy.

Purpose: To evaluate dosimetric impact of air cavities and their corresponding electron density correction for 0.35 tesla (T) Magnetic Resonance-guided Online Adaptive Radiation Therapy (MRgART) of prostate bed patients. Methods: Three 0.35 T MRgRT plans (anterior–posterior (AP) beam, AP–PA beams, and clinical intensity modulated radiation therapy (IMRT)) were generated on a prostate bed patient’s (Patient A) planning computed tomography (CT) with artificial rectal air cavities of various sizes (0–3 cm, 0.5 cm increments). Furthermore, two 0.35 T MRgART plans (‘Deformed’ and ‘Override’) were generated on a prostate bed patient’s (Patient B) daily magnetic resonance image (MRI) with artificial rectal air cavities of various sizes (0–3 cm, 0.5 cm increments) and on five prostate bed patient’s (Patient 1–5) daily MRIs (2 MRIs: Fraction A and B) with real air cavities. For each MRgART plan, daily MRI electron density map was obtained by deformable registration with simulation CT. In the ‘Deformed’ plan, a clinical IMRT plan is calculated on the daily MRI with electron density map obtained from deformable registration only. In the ‘Override’ plan, daily MRI and simulation CT air cavities are manually corrected and bulk assigned air and water density on the registered electron density map, respectively. Afterwards, the clinical IMRT plan is calculated. Results: For the MRgRT plans, AP and AP–PA plans’ rectum/rectal wall max dose increased with increasing air cavity size, where the 3 cm air cavity resulted in a 20%/17% and 13%/13% increase, relative to no air cavity, respectively. Clinical IMRT plan was robust to air cavity size, where dose change remained less than 1%. For the MRgART plans, daily MRI electron density maps, obtained from deformable registration with simulation CT, was unable to accurately produce electron densities reflecting the air cavities. However, for the artificial daily MRI air cavities, dosimetric change between ‘Deformed’ and ‘Override’ plan was small (<4%). Similarly, for the real daily MRI air cavities, clinical constraint changes between ‘Deformed’ and ‘Override’ plan was negligible and did not lead to change in clinical decision for adaptive planning except for two fractions. In these fractions, the ‘Override’ plan indicated that the bladder max dose and rectum V35.7 exceeded the constraint, while the ‘Deformed’ plan showed acceptable dose, although the absolute difference was only 0.3 Gy and 0.03 cc, respectively. Conclusion: Clinical 0.35 T IMRT prostate bed plans are dosimetrically robust to air cavities. MRgART air cavity electron density correction shows clinically insignificant change and is not warranted on low-field systems.

Original Knee Fixation Device as a Useful Fixation Method during Prostate Intensity-Modulated Radiation Therapy.

Purpose:The purpose of he study was to reduce setup errors during intensity-modulated radiation therapy (IMRT) with an original knee fixation device (KFD) and evaluate the clinical target volume (CTV) coverage.Methods:Participants were classified into two groups: knee flexion (KF) group (n = 16), wherein participants' knees were fixed in a flexed position using the proposed KFD during planning computed tomography, and knee extension group (KE; n = 15), wherein no KFD was used. We investigated the residual rotational errors and inter-fractional setup errors with or without KFD. Furthermore, inter-fractional margins were calculated using logistic regression analysis, and CTV coverage was evaluated.Results:The residual rotational errors in the yaw and roll directions (P < 0.02) and the inter-fractional error in the anterior-posterior (A-P) direction (P < 0.02) improved significantly in the KF group compared with the KE group. Repeatability was improved for the pitch direction. The inter-fractional margins were 6.68 mm and 4.87 mm in the A-P and superior-inferior (S-I) directions, respectively, in the KF group, representing reductions (mm) of 20.8% and 12.6% compared with the KE group, respectively. The odds ratios for CTV coverage in the KF group compared to the KE group were 2.76 (P < 0.001) and 1.74 (P < 0.05) in the A-P and S-I directions, respectively.Conclusions:The IMRT fixation method using an original KFD improved the residual rotational error in the three directions and the inter-fractional error in the A-P direction, reduced the interfractional margins in the A-P, and S-I directions and improved CTV coverage. Our original KFD may be a useful fixation method during prostate IMRT.

A hierarchical deep reinforcement learning framework for intelligent automatic treatment planning of prostate cancer intensity modulated radiation therapy

Purpose. We have previously proposed an intelligent automatic treatment planning (IATP) framework that builds a virtual treatment planner network (VTPN) to operate a treatment planning system (TPS) to generate high-quality radiation therapy (RT) treatment plans. While the potential of IATP in automating RT treatment planning has been demonstrated, its poor scalability caused by an almost linear growth of network size with the number of treatment planning parameters (TPPs) is a bottleneck, preventing its application in complicate, but clinically relevant treatment planning problems. The decision-making behavior of the trained network is hard to understand. Motivated by the decision-making process of a human planner, this study proposes a hierarchical IATP framework. Methods and materials. The hierarchical VTPN (HieVTPN) consists of three networks, i.e. Structure-Net, Parameter-Net, and Action-Net. When interacting with a TPS, the networks are employed in a sequential order in each step to decide the structure to adjust, the TPP to adjust for the selected structure, and the specific adjustment manner for the parameter, respectively. We developed an end-to-end hierarchical deep reinforcement learning scheme to simultaneously train the three networks. We then evaluated the effectiveness of the proposed framework in the treatment planning problems for prostate cancer intensity modulated RT (IMRT) and stereotactic body RT (SBRT). We benchmarked the performance of our approach by comparing plans made by VTPN of a parallel architecture, and the human plans submitted for competition in the 2016 American Association of Medical Dosimetrist (AAMD)/Radiosurgery Society (RSS) Plan Study. We analyzed scalability of the network size with respect to the number of TPPs. Numerical experiments were also performed to understand the rationale of the decision-making behaviors of the trained HieVTPN. Results. Both HieVTPNs for prostate IMRT and SBRT were trained successfully using 10 training patient cases and 5 validation cases. For IMRT, HieVTPN was able to generate high-quality plans for 59 testing patient cases that were not included in training process, achieving an average plan score of 8.62 (±0.83), with 9 being the maximal score. The score was comparable to that of the VTPN, 8.45 (±0.48). For SBRT planning, HieVTPN achieved an average plan score of 139.07 on five testing patient cases compared to the score of 132.21 averaged over the human plans summited for competition in AAMD/RSS plan study. Different from VTPN with network size linearly scaling with the number of TPPs, the network size of HieVTPN is almost independent of the number of TPPs. It was also observed that the decision-making behaviors of HieVTPN were understandable and generally agreed with the human experience. Conclusions. With the scalability and explainability, the hierarchical IATP framework is more favorable than the previous framework in terms of handling treatment planning problems involving a large number of TPPs.

A comprehensive evaluation of the quality and complexity of prostate IMRT and VMAT plans generated by an automated inverse planning tool

AbstractIntroduction:The Pinnacle3 Auto-Planning (AP) package is an automated inverse planning tool employing a multi-sequence optimisation algorithm. The nature of the optimisation aims to improve the overall quality of radiotherapy plans but at the same time may produce higher modulation, increasing plan complexity and challenging linear accelerator delivery capability.Methods and materials:Thirty patients previously treated with intensity-modulated radiotherapy (IMRT) to the prostate with or without pelvic lymph node irradiation were replanned with locally developed AP techniques for step-and-shoot IMRT (AP-IMRT) and volumetric-modulated arc therapy (AP-VMAT). Each case was also planned with VMAT using conventional inverse planning. The patient cohort was separated into two groups, those with a single primary target volume (PTV) and those with dual PTVs of differing prescription dose levels. Plan complexity was assessed using the modulation complexity score.Results:Plans produced with AP provided equivalent or better dose coverage to target volumes whilst effectively reducing organ at risk (OAR) doses. For IMRT plans, the use of AP resulted in a mean reduction in bladder V50Gy by 4·2 and 4·7 % (p ≤ 0·01) and V40Gy by 4·8 and 11·3 % (p &lt; 0·01) in the single and dual dose level cohorts, respectively. For the rectum, V70Gy, V60Gy and V40Gy were all reduced in the dual dose level AP-VMAT plans by an average of 2·0, 2·7 and 7·3 % (p &lt; 0·01), respectively. A small increase in plan complexity was observed only in dual dose level AP plans.Findings:The automated nature of AP led to high quality treatment plans with improvement in OAR sparing and minimised the variation in achievable dose planning metrics when compared to the conventional inverse planning approach.

Comparison of gamma analysis with using different dosimetric systems for pre-treatment verification of intensity-modulated radiation therapy

The evaluation of the agreement between calculated and measured dose plays an essential role in the quality assurance procedures of intensity-modulated radiation therapy (IMRT). This study aimed to compare gamma analysis using portal dosimetry (PD), Epiqa, and 2D array detector for dose verification of radiotherapy treatment plans. Five field step-and-shoot IMRT plan was performed for 20 prostate IMRT patients using the dual-energy DHX linear accelerator (Varian Medical System, Palo Alto, Calif., USA). The treatment plans were created using Varian DHX Eclipse treatment planning system (TPS) version 15.1. All measurements were performed by aS500 EPID integrated into Varian DHX linear accelerator and 2D array detector. The dose distribution was evaluated with gamma area histograms (GAHs) generated using different γ criteria (1%/1 mm, 2%/2 mm, 3%/2 mm, and 3%/3 mm) for dose agreement and distance to agreement parameters. Statistical analyses were evaluated by using Mann–Whitney U test and Kruskal–Wallis test, and p-value of p &lt; 0.01 was considered to be significant. The average pass rate for 20 IMRT plans was above 95 for all devices with 2%/2 mm, 3%/2 mm, and 3%/3 mm. The mean and standard deviation pass rates (γ ≤ 1) were found to be 99.80 ± 0.19, 99.35 ± 0.34, and 97.53 ± 0.71 for PD, Epiqa, and 2D array, respectively. All IMRT plans passed 2%/2 mm, 3%/2 mm, and 3%/3 mm gamma by more than 95 of three dosimetric systems. They are all in good agreement with the literature. All three devices are acceptable for quality control of IMRT. Due to the simplicity and fast evaluation process, PD can be preferred for quality control.

Pelvic organ motion and dosimetric implications during horizontal patient rotation for prostate radiation therapy.

Gantry-free radiation therapy systems utilizing patient rotation would be simpler and more cost effective than the conventional gantry-based systems. Such a system could enable the expansion of radiation therapy to meet global demand and reduce capital costs. Recent advances in adaptive radiation therapy could potentially be applied to correct for gravitational deformation during horizontal patient rotation. This study aims to quantify the pelvic organ motion and the dosimetric implications of horizontal rotation for prostate intensity-modulated radiation therapy (IMRT) treatments. Eight human participants who previously received prostate radiation therapy were imaged in a clinical magnetic resonance imaging (MRI) scanner using a bespoke patient rotation system (PRS). The patients were imaged every 45 degrees during a full roll rotation (0-360 degrees). Whole pelvic bone, prostate, rectum, and bladder motion were compared to the supine position using dice similarity coefficient (DSC) and mean absolute surface distance (MASD). Prostate centroid motion was compared in the left-right (LR), superior-inferior (SI), and anterior-posterior (AP) direction prior to and following pelvic bone-guided rigid registration. Seven-field prostate IMRT treatment plans were generated for each patient rotation angles under three adaption scenarios: No plan adaption, rigid planning target volume (PTV)-guided alignment to the prostate, and plan re-optimization. Prostate, rectum, and bladder doses were compared for each adaption scenario. Pelvic bone motion within the PRS of up to 53mm relative to the supine position was observed for some participants. Internal organ motion was greatest at the 180-degree PRS couch angle (prone), with prostate centroid motion range<2mm LR, 0mm to 14mm SI, and -11mm to 4mm AP. Rotation with no adaption of the treatment plan resulted in an underdose to the PTV -- in some instances up to 75% (D95%: 78±0.3Gy at supine to 20±15.0Gy at the 225-degree PRS couch angle). Bladder dose was reduced during the rotation by up to 98% (V60Gy: 15.0±9.4% supine to 0.3±0.5% at the 225-degree PRS couch angle). In some instances, the rectum dose increased during rotation (V60Gy: 20.0±4.5% supine to 25.0±15.0% at the 135-degree PRS couch angle). Rigid PTV-guided alignment resulted in PTV coverage which, though statistically lower (P<0.05 for all D95% values), was within 1Gy of the supine plans. Plan re-optimization resulted in a statistically equivalent PTV coverage compared to the supine plans (P>0.05 for all D95% metrics and all within ±0.4Gy). For both rigid PTV-guided alignment and plan re-optimization, rectum dose volume metrics were reduced compared to the supine position between the 90- and 225-degree PRS couch angles (P<0.05). Bladder dose volume metrics were not impacted by rotation. Pelvic bone and internal organ motion are present during patient rotation. Rigid PTV-guided alignment to the prostate will be a requirement if prostate IMRT is to be safely delivered using patient rotation. Plan re-optimization for each PRS couch angle to account for anatomical deformations further improves the PTV coverage.

Verification of IMRT and RapidArc Localized Prostate Cancer Treatment Plans Using EPID and Delta4 in vivo Dosimetry Methods

Background: Quality assurance for intensity modulated radiation therapy (IMRT) depends on the type of dosimetry system and its evaluation procedure. We can check both the intensity and distribution of each field as the required pretreatment verification with dosimetry systems. Method: Treatment verification for different plans (IMRT and RapidArc) applied on localized prostate cancer patients was done with electronic portal imager device (EPID), Delta4). The EPID used was Varian aS1000 mounted on Varian (TrueBeam) Linac with gamma criteria set to ΔD=3% and Δd=3mm. RapidArc plans were designed by arcs (179.0o CCW to 181.0o and 181.0o CW to 179.0o) under the same gamma criteria of (ΔD=3%, DTA=3mm and γ-index ≤1) while the threshold dose was 20%. Results: Evaluation analysis is passed for IMRT prostate plans with the area gamma ˂1.0 which equaled 99.1% (99.1% of the pixels had gamma˂1) within a tolerance of 95.0%, area gamma ˃0.8 (was equal to 2.1%) / area gamma ˃1.2 (was equal to 0.3%) and the average dose difference was 0.42CU. Delta4 dosimetry system was assessed with RapidArc plan; the agreement between the measured and planned doses was ±1% and gamma analysis resulted in 100% data points with the same agreement conditions. Conclusion: Portal dosimetry provided a good verification of the treatment unit ability to deliver doses according to plan. For an IMRT field comprised of several subfields, it could give rise to much more errors. RapidArc plans were verified using Delta4 system, which generated excellent dosimetry results. Periodic calibration was recommended for Delta4 dosimetry system; radiation damage affected sensitivity by ˃1% every 1kGy.

Automatic IMRT planning via static field fluence prediction (AIP-SFFP): a deep learning algorithm for real-time prostate treatment planning

The purpose of this work was to develop a deep learning (DL) based algorithm, Automatic intensity-modulated radiotherapy (IMRT) Planning via Static Field Fluence Prediction (AIP-SFFP), for automated prostate IMRT planning with real-time planning efficiency. The following method was adopted: AIP-SFFP generates a prostate IMRT plan through predictions of fluence maps using patient anatomy. No inverse planning is required. AIP-SFFP is centered on a custom-built deep learning (DL) neural network for fluence map prediction. Predictions are imported to a commercial treatment-planning system for dose calculation and plan generation. AIP-SFFP was demonstrated for prostate IMRT simultaneously-integrated-boost planning (58.8 Gy/70 Gy to PTV58.8 Gy/PTV70 Gy in 28 fx, PTV = Planning Target Volume). Training data was generated from 106 patients using a knowledge-based planning (KBP) plan generator. Two types of 2D projection images were designed to represent structures’ sizes and locations, and a total of eight projections were utilized to describe targets and organs-at-risk. Projections at nine template beam angles were stacked as inputs for artificial intelligence (AI) training. 14 patients were used as independent tests. The generated test plans were compared with the plans from the KBP training plan generator and clinic practice. The following results were obtained: After normalization (PTV70 Gy V70 Gy = 95%), all 14 AI plans met institutional criteria. The coverage of PTV58.8 Gy in the AI plans was comparable to KBP and clinic plans without statistical significance. The whole body (BODY) D1cc and rectum D0.1cc of AI plans were slightly higher (<1 Gy) compared to KBP and clinic plans; in contrast, the bladder D1cc and other rectum and bladder low doses in the AI plans were slightly improved without clinical relevance. The overall isodose distribution in the AI plans was comparable with KBP plans and clinical plans. AIP-SFFP generated each test plan within 20s including the prediction and the dose calculation. In conclusion, AIP-SFFP was successfully developed for prostate IMRT planning. AIP-SFFP demonstrated good overall plan quality and real-time efficiency. Showing great promise, AIP-SFFP will be investigated for immediate clinical application.

Voxel-level biological optimisation of prostate IMRT using patient-specific tumour location and clonogen density derived from mpMRI

AimsThis study aimed to develop a framework for optimising prostate intensity-modulated radiotherapy (IMRT) based on patient-specific tumour biology, derived from multiparametric MRI (mpMRI). The framework included a probabilistic treatment planning technique in the effort to yield dose distributions with an improved expected treatment outcome compared with uniform-dose planning approaches.MethodsIMRT plans were generated for five prostate cancer patients using two inverse planning methods: uniform-dose to the planning target volume and probabilistic biological optimisation for clinical target volume tumour control probability (TCP) maximisation. Patient-specific tumour location and clonogen density information were derived from mpMRI and geometric uncertainties were incorporated in the TCP calculation. Potential reduction in dose to sensitive structures was assessed by comparing dose metrics of uniform-dose plans with biologically-optimised plans of an equivalent level of expected tumour control.ResultsThe planning study demonstrated biological optimisation has the potential to reduce expected normal tissue toxicity without sacrificing local control by shaping the dose distribution to the spatial distribution of tumour characteristics. On average, biologically-optimised plans achieved 38.6% (p-value: < 0.01) and 51.2% (p-value: < 0.01) reduction in expected rectum and bladder equivalent uniform dose, respectively, when compared with uniform-dose planning.ConclusionsIt was concluded that varying the dose distribution within the prostate to take account for each patient’s clonogen distribution was feasible. Lower doses to normal structures compared to uniform-dose plans was possible whilst providing robust plans against geometric uncertainties. Further validation in a larger cohort is warranted along with considerations for adaptive therapy and limiting urethral dose.

Progress towards Patient-Specific, Spatially-Continuous Radiobiological Dose Prescription and Planning in Prostate Cancer IMRT: An Overview.

Advances in imaging have enabled the identification of prostate cancer foci with an initial application to focal dose escalation, with subvolumes created with image intensity thresholds. Through quantitative imaging techniques, correlations between image parameters and tumour characteristics have been identified. Mathematical functions are typically used to relate image parameters to prescription dose to improve the clinical relevance of the resulting dose distribution. However, these relationships have remained speculative or invalidated. In contrast, the use of radiobiological models during treatment planning optimisation, termed biological optimisation, has the advantage of directly considering the biological effect of the resulting dose distribution. This has led to an increased interest in the accurate derivation of radiobiological parameters from quantitative imaging to inform the models. This article reviews the progress in treatment planning using image-informed tumour biology, from focal dose escalation to the current trend of individualised biological treatment planning using image-derived radiobiological parameters, with the focus on prostate intensity-modulated radiotherapy (IMRT).

External beam patient dose verification based on the integral quality monitor (IQM®) output signals

Background: The Integral Quality Monitor (IQM®) can essentially measure the integral fluence through a segment and provide real-time information about the accuracy of radiation delivery based on comparisons of measured segment signals and pre-calculated reference values. However, the present IQM chamber cannot calculate the dose in the patient. Aim: This study aims to make use of IQM field output signals to calculate the number of monitor units (MUs) delivered through an arbitrary treatment field in order to convert Monte Carlo (MC)-generated dose distributions in a patient model into absolute dose. Methods: XiO and Monaco treatment planning systems (TPSs) were used to define treatment beam portals for cervix and esophagus conformal radiotherapy as well as prostate intensity-modulated radiotherapy for the translation of patient and beam setup information from DICOM to DOSXYZnrc. The planned beams were simulated in a patient model built from actual patient CT images and each simulated integral field/segment was weighted with its MUs before summation to get the total dose in the plan. The segment beam weights (MUs) were calculated as the ratio of the open-field IQM measured signal and the calculated signal per MU extracted from chamber sensitivity maps. These are the actual MUs delivered not just MUs set. The beam weighting method was evaluated by comparing weighted MC doses with original planned doses using profile and isodose comparisons, dose difference maps, γ analysis and dose-volume histogram (DVH) data. Results: γ pass rates of up to 98% were found, except for the esophagus plan where the γ pass rate was below 45%. DVH comparisons showed good agreement for most organs, with the largest differences observed in low-density lung. However, these discrepancies can result from differences in dose calculation algorithms or differences in MUs used for dose weighting planned by the TPS and MUs calculated using IQM field output signals. To test this, a 4-field box DOSXYZnrc MC simulation weighted with planned (XiO) MUs was compared with the same simulation weighted with IQM-based MUs. Dose differences of up to 5% were found on the isocentre slice. For XiO versus MC, up to 7% dose differences were found, indicating additional error due to limitations of XiO’s superposition algorithm. Dose differences between MC Monaco and MC EGSnrc were less than 3%. Conclusions: The most valuable comparison was MC versus MC as it eliminated algorithm discrepancies and evaluated dose differences precisely according to beam weighting. For XiO TPS, care must be taken as dose differences may also arise due to limitations in XiO’s planning software, not merely due to differences in MUs. Overall, the IQM was successfully used to compute beam dose weights to accurately reconstruct the patient dose using unweighted MC beams. Our technique can be used for pre-treatment QA provided each segment output is known and an accurate linac source model is available.

Estimation of Dynamic MLC Parameters Using Dynamic MLC Position Accuracy Analysis Software in Prostate IMRT

It is necessary to verify an intensity-modulated radiation therapy (IMRT) plan and to confirm dose error within the tolerance, in order to perform it securely and precisely. IMRT with dynamic multi-leaf collimator (DMLC) requires high DMLC position accuracy. The DMLC position accuracy analysis software DynaLog File Viewer (DFV; Varian Medical Systems, Palo Alto, CA, USA) is used to analyze position errors of DMLC for IMRT plans. We analyzed correlation between DMLC parameters and position error of DMLC obtained from DFV in prostate IMRT. A regression analysis of the position error and the DMLC parameters was performed. As a result, a strong correlation was found between MLC position error and each of the DMLC parameters: leaf speed, gap width, and segment monitor unit (MU). We found the factors for the DMLC position error in this study. DMLC position error could be estimated from leaf speed, gap width, and segment MU when we analyze IMRT cases in the further study.

Evaluation of Dose Distribution and Normal Tissue Complication Probability of a Combined Dose of Cone-Beam Computed Tomography Imaging with Treatment in Prostate Intensity-Modulated Radiation Therapy.

Purpose:The purpose of this study is to evaluate the effects of cone-beam computed tomography (CBCT) on dose distribution and normal tissue complication probability (NTCP) by constructing a comprehensive dose evaluation system for prostate intensity-modulated radiation therapy (IMRT).Methods:A system that could combine CBCT and treatment doses with MATLAB was constructed. Twenty patients treated with prostate IMRT were studied. A mean dose of 78 Gy was prescribed to the prostate region, excluding the rectal volume from the target volume, with margins of 4 mm to the dorsal side of the prostate and 7 mm to the entire circumference. CBCT and treatment doses were combined, and the dose distribution and the NTCP of the rectum and bladder were evaluated.Results:The radiation dose delivered to 2% and 98% of the target volume increased by 0.90 and 0.74 Gy on average, respectively, in the half-fan mode and on average 0.76 and 0.72 Gy, respectively, in the full-fan mode. The homogeneity index remained constant. The percent volume of the rectum and bladder irradiated at each dose increased slightly, with a maximum increase of <1%. The rectal NTCP increased by approximately 0.07% from 0.46% to 0.53% with the addition of a CBCT dose, while the maximum NTCP in the bladder was approximately 0.02%.Conclusions:This study demonstrated a method to evaluate a combined dose of CBCT and a treatment dose using the constructed system. The combined dose distribution revealed increases of <1% volume in the rectal and bladder doses and approximately 0.07% in the rectal NTCP.