Conformal Plans Research Articles

The Role of Virtual Environment for Radiotherapy Training (VERT) in Medical Dosimetry Education

Medical dosimetry is an important component in training of radiation therapist, yet it is not easy for student to understand the principle of treatment planning and to be familiar with the relationship of the clinical target volume (CTV), planned target volume (PTV), and the nearby organs at risk (OARs) by just imagination. This study is conducted to evaluate whether using VERT in teaching medical dosimetry can help student to improve their learning experience. Students of cohort 2015 and 2016 were taught under TPS mode and TPS + VERT mode respectively. Direct comparison was conducted through self-evaluation survey, between two groups of students, in terms of their understanding of the concept of medical dosimetry and their level of confidence in completing different types of plans after the course. Both groups of students were able to understand the concept of medical dosimetry and able to complete 3D conformal plans after taking the course. Though, the students received TPS mode reported that they had lower level of confidence in completing the planning and required longer time for self-study and practice compared to the students who received the TPS + VERT mode. This study demonstrated that including VERT into medical dosimetry education can improve students’ learning experience, by improving their self-confidence, as well as reducing time required for their self-study and practice.

Extended CT density range: Acuros XB algorithm performance

Modern treatment planning systems (TPS) offer photon algorithms capable of enhanced performance in heterogeneous media and high density materials, such as metal implants. Acuros XB was implemented by Varian Medical Systems in their Eclipse TPS. Computed tomography (CT) reconstruction can be performed in two ways: a 16 bits depth for HU or 12 bits. A 12 bit study would have a reduced HU scale, describing normal tissues accurately, but underestimating metal objects. Whenever metal objects can be found in the images, 16 bits are needed to have a realistic estimate of their densities. This work addresses the calculation differences between Acuros XB 13.6 using these two CT configurations. A Philips Brilliant Big Bore CT scanner has been used to scan phantoms with different inserts mimicking different metal implants and both configurations. Head and Neck VMAT and conformal plans (two full arc plans, as per local protocol) were prepared and optimized in Eclipse v13.6. Coverage and dose figures of merit were assessed, and DVH curves compared. Dose to water was used throughout this study. Acuros XB results show an increase in maximum dose for distributions obtained in 16 bits image sets: for instance, from 111.0% (12 bits) to 138.2% for PTV60, in a phantom with Ti dental implants (insert) along the mandible. Differences between Accuros XB results with 12 or 16 bits reconstructions are statistically significant (Student’s T test, p = 0.05). Therefore, the use of extended HU ranges helps address the effect of metal objects inside a patient.

MRI-guided proton therapy planning: accounting for an inline MRI fringe field

MRI-guided proton therapy is being pursued for its promise to provide a more conformal, accurate proton therapy. However, the presence of the magnetic field imposes a challenge for the beam delivery as protons are deflected due to the Lorenz force. In this study, the impact of realistic inline MRI fringe field on IMPT plan delivery is investigated for a water phantom, liver tumor and prostate cancer differing in target volume, shape, and field configuration using Monte Carlo simulations. A method to correct for the shift of the beam spot positions in the presence of the inline magnetic field is presented. Results show that when not accounting for the effect of the magnetic field on the pencil beam delivery, the spot positions are substantially shifted and the quality of delivered plans is significantly deteriorated leading to dose inhomogeneities and creation of hot and cold spots. However, by correcting the pencil beam delivery, the dose quality of the IMPT plans is restored to a high degree. Nevertheless, adaptation of beam delivery alone is not robust regarding different treatment sites. By fully accounting during plan optimization for the dose distortions caused by the fringe and imaging fields, highly conformal IMPT plans are achieved. These results demonstrate proton pencil beam scanning and treatment planning can be adapted for precise delivery of state-of-the-art IMPT plans in MR-guided proton therapy in the presence of an inline MRI fringe field.

Trimmer sequencing time minimization during dynamically collimated proton therapy using a colony of cooperating agents

The dynamic collimation system (DCS) can be combined with pencil beam scanning proton therapy to deliver highly conformal treatment plans with unique collimation at each energy layer. This energy layer-specific collimation is accomplished through the synchronized motion of four trimmer blades that intercept the proton beam near the target boundary in the beam’s eye view. However, the corresponding treatment deliveries come at the cost of additional treatment time since the translational speed of the trimmer is slower than the scanning speed of the proton pencil beam. In an attempt to minimize the additional trimmer sequencing time of each field while still maintaining a high degree of conformity, a novel process utilizing ant colony optimization (ACO) methods was created to determine the most efficient route of trimmer sequencing and beamlet scanning patterns for a collective set of collimated proton beamlets. The ACO process was integrated within an in-house treatment planning system optimizer to determine the beam scanning and DCS trimmer sequencing patterns and compared against an analytical approximation of the trimmer sequencing time should a contour-like scanning approach be assumed instead. Due to the stochastic nature of ACO, parameters where determined so that they could ensure good convergence and an efficient optimization of trimmer sequencing that was faster than an analytical contour-like trimmer sequencing. The optimization process was tested using a set of three intracranial treatment plans which were planned using a custom research treatment planning system and were successfully optimized to reduce the additional trimmer sequencing time to approximately 60 s per treatment field while maintaining a high degree of target conformity. Thus, the novel use of ACO techniques within a treatment planning algorithm has been demonstrated to effectively determine collimation sequencing patterns for a DCS in order to minimize the additional treatment time required for trimmer movement during treatment.

Simulated real-time dose reconstruction for moving tumors in stereotactic liver radiotherapy.

In radiotherapy, tumor motion may deteriorate the planned dose distribution. However, the dosimetric consequences of the motion are normally unknown for individual treatments. We here present a method for real-time motion-including tumor dose reconstruction and demonstrate its use for simulated stereotactic body radiotherapy (SBRT) of patients with liver cancer previously treated with Calypso-guided gating. Real-time motion-including dose reconstruction was performed using in-house developed software, DoseTracker, on offline replays of previous clinical treatments. The patient cohort consisted of fifteen patients previously treated in our clinic with three-fraction SBRT to the liver using conformal or IMRT plans. The tumor motion at treatment was monitored with implanted electromagnetic transponders. The dose reconstruction was performed for both the actual gated treatments and simulated nongated treatments using a 21Hz data stream containing accelerator parameters and the recorded motion. The dose was reconstructed in the same calculation points within the planning target volume (PTV) as used by the treatment planning system (TPS). The reconstructed doses were compared with calculations performed in the TPS, in which the motion was modeled as a series of isocenter shifts. The comparison included point doses as a function of treatment time and the dose volume histogram (DVH) for the clinical target volume (CTV). The motion-induced reduction in the dose to 95% of the CTV, , and in the mean CTV dose, ΔDMean , was compared between DoseTracker and the TPS for each simulated fraction. DoseTracker currently assumes water density within the patient contour, so for comparison, the TPS calculations were performed with both CT density and water density. The calculation times were additionally analyzed. Dose reconstruction was carried out for ninety SBRT sessions with calculation volumes ranging from 9.9 to 366.4cm3 and median calculation times of 55-155ms (equivalent to 18.2-6.5Hz). Time-resolved trends of doses to a single calculation point in the patient were well replicated and dose differences between actual and planned calculations matched well. ΔDMean had a range of -0.1%-30.7%-points and was estimated by DoseTracker with a root-mean-square deviation (RMSD) to the TPS calculations of 0.43%-points (water density) and 0.79%-points (CT density). Similarly, had a range of 0.0%-35.2%-points and was estimated by DoseTracker with an RMSD of 0.80%-points (water density) and 1.33%-points (CT density). DoseTracker predicted losses in tumor dose coverage above 5%-points with high sensitivity (91.7%) and specificity (97.6%). Real-time dose reconstruction to moving tumors was demonstrated on offline replays of previous clinical treatments. DVHs of actually delivered dose are made available immediately after the end of treatment fractions. It shows promising results for liver SBRT with accurate estimation of CTV dose deteriorations caused by motion during treatment.

Dosimetric comparison of inverse optimisation methods versus forward optimisation in HDR brachytherapy of breast, cervical and prostate cancer

ObjectiveDosimetric comparison of HIPO (hybrid inverse planning optimisation) and IPSA (inverse planning simulated annealing) inverse and forward optimisation (FO) methods in brachytherapy (BT) of breast, cervical and prostate cancer.MethodsAt our institute 38 breast, 47 cervical and 50 prostate cancer patients treated with image-guided interstitial high-dose-rate BT were selected. Treatment plans were created using HIPO and IPSA inverse optimisation methods as well as FO. The dose–volume parameters of different treatment plans were compared with Friedman ANOVA and the LSD post-hoc test.ResultsIPSA creates less dose coverage to the target volume than HIPO or FO: V100 was 91.7%, 91% and 91.9% for HIPO, IPSA and FO plans (p = 0.1784) in breast BT; 90.4%, 89.2% and 91% (p = 0.0045) in cervical BT; and 97.1%, 96.2% and 97.7% (p = 0.0005) in prostate BT, respectively. HIPO results in more conformal plans: COIN was 0.72, 0.71 and 0.69 (p = 0.0306) in breast BT; 0.6, 0.47 and 0.58 (p < 0.001) in cervical BT; and 0.8, 0.7 and 0.7 (p < 0.001) in prostate BT, respectively. In breast BT, dose to the skin and lung was smaller with HIPO and FO than with IPSA. In cervical BT, dose to the rectum, sigmoid and bowel was larger using IPSA than with HIPO or FO. In prostate BT, dose to the urethra was higher and the rectal dose was smaller using FO than with inverse methods.ConclusionIn interstitial breast and prostate BT, HIPO results in comparable dose–volume parameters to FO, but HIPO plans are more conformal. In cervical BT, HIPO produces dosimetrically acceptable plans only when more needles are used. The dosimetric quality of IPSA plans is suboptimal and results in unnecessary larger active lengths.

Can Dosimetry Affect Overall Survival in Patients with Medically Inoperable Peripheral Early Stage Lung Cancer Treated with Stereotactic Ablative Radiotherapy (SABR)? An Analysis of 1300 Patients

SABR is an established treatment option for early stage medically inoperable peripheral lung cancer. Recent studies have shown that tight conformity of radiotherapy plans i.e., reducing the radiation dose outside the target volume might worsen loco-regional control and can predict more distant metastases. The aim of the study is to report overall survival and dosimetry of early stage peripheral lung cancer patients treated with SABR and to try to explore if any dosimetric parameters can predict overall survival. Patients treated with SABR in a single institute in UK between May 2009 and August 2018 were included. Electronic medical records were reviewed for baseline characteristics, treatment details and outcomes. Dosimetric data was extracted from software. For the planning target volume (PTV), plan conformity was assessed using three indices, i.e., R100-volume receiving the 100% dose /volume (PTV), R50- volume receiving the 50% dose/volume (PTV), and maximum dose to >2 cm of PTV(D2cm). Patients were treated according to the UK SABR consortium guidelines. Kaplan Meier survival analysis was done for univariate analysis and Cox regression model was used for multivariate analysis, using IBM software. 1300 patients received SABR treatment for 1357 tumors. Median age of the patients were 75 years (range 38-97 years). Median follow up was 26 months. Median overall survival was 37 months with 1,2,3,4 and 5 years survival rates of 84.4%, 65%, 50.7%, 39.5% and 30.8%, respectively. Median PTV volume was 30 cc ((range 5.5-213.4 cc, Inter quartile range (IQR)-29.6). Median values of R100, R50 and D2cm were 1.1(range 0.68-3.19, IQR-0.08), 5.6(range 2.2-16.2, IQR- 2.08), 32.7Gy (range 9.3-56.3Gy, IQR-5.9Gy). Median value of mean lung dose, V20 and V12.5 were 3.9Gy (range 0.6-11.5Gy, IQR-2Gy), 5 %( range 0.2-19.3%, IQR-3.4%) and 9.3% (range 1.4-30.8%, IQR-5.4%). On univariate analysis, only R100 of ≤ 1.10 was found to be significantly associated with improved survival (median survival 40 months vs 33 months, hazard ratio 0.85, 95% confidence interval 0.73-0.98) which was also confirmed in multivariate cox regression analysis. Although treatments with R50 of ≤ 6 have shown to have better survival (38 months vs 35 months) but that was not significant in univariate or multivariate analysis. A more conformal plan with high dose matching to the PTV with R100 of < 1.10 is associated with improved survival in medically inoperable early stage lung cancer patients treated with SABR, which emphasizes the importance of plan conformity. However, this data needs to be interpreted cautiously taking into account other possible confounding variables, particularly higher dose to heart +/- lung with less conformal SABR plans.

Vinorelbine as a radiosensitizer in Pakistani patients with locally advanced unresectable head &amp; neck cancer (HNC) in tertiary care hospital of Pakistan

Background: Head and neck cancer (HNC) is one of the most common cancers in Pakistan. Disease free survival in HNC remains poor due to inefficient loco-regional disease control. The aim of the present study was to assess the response rate and toxicity of concomitant vinorelbine and External radiation therapy (ERT) in advanced Head and Neck cancer in local Pakistani population. The study as per Good Clinical Practice (GCP) guidelines was conducted at the oncology department of Nishat hospital Multan from 2015 to 2017. &#x0D; Methodology: An observational, prospective study with enrollment of 50 patients of advanced head and neck cancer was followed to analyze the outcome for radiosensitization. Primary tumor sites were tongue in 15 (30%) patients; lower lip in 6 (12%); buccal cavity in 5 (10%); cheek in 5 (10%); tonsil in 4 (8%); larynx in 6 (12%); hypopharynx in 5 (10%); and parotid in 4 (8%) patients. Initial clinical stage was: IV in 23 (46%) patients and III in 27 (54%) patients. Vinorelbine (VNB) was given at dose of 10 mg i.v. infusion weekly with ERT (3D conformal radiation plan). Response rate was evaluated after at least 8 doses. Response evaluation criteria in Solid Tumors (RECIST) was used to assess complete response (CR) and partial response (PR); progressive disease (PD) and stable disease (SD). Toxicity was assessed using common toxicity criteria version 3.0 (CTCV3.0).&#x0D; Results: 44 out of 50 patients were evaluable for response rate and toxicity. Immediate response was 90% CR. After 24 months of followup CR, PR, SD, and PD were seen in 26 (59%), 6 (13%), 7 (15%) and 6 (13%) patients respectively. Grade III mucositis and dysphagia were observed in 19 (43%) and 8 (18%) patients respectively, grade III skin rash in 14 (30%) patients, grade-II peripheral neuropathy was seen in 3 (6%) patients.&#x0D; Conclusion: The study showed that vinorelbine as a radiosensitizer in advanced HNC is a feasible option with acceptable toxicities. A large study is required to define its definite role.

Single-Isocenter/Multi-Lesion Synchronous Lung Stereotactic Body Radiation Therapy (SBRT): Plan Quality, Treatment Efficiency and Clinical Outcomes

Patients with multiple primary or metastatic lung lesions may not well tolerate relatively longer SBRT treatments due to distress or shortness of breath, with traditional treatment planning and delivery with individual isocenter per lesion. Treating lesions synchronously with a single-isocenter volumetric modulated arc therapy (VMAT) plan with flattening filter free (FFF) beam will decrease treatment time and improve patient comfort. We report dosimetry, treatment efficiency and early clinical outcomes of oligometastases (< 5 lesions) lung cancer patients who underwent synchronous single-isocenter/multiple-lesions VMAT lung SBRT. Fourteen patients with multiple peripherally located non-small-cell-lung cancer (NSCLC) lesions (two n = 12, three n = 1, five n = 1, total 32 lesions) were treated synchronously with highly conformal single-isocenter non-coplanar VMAT-SBRT plan (bilateral lesions n = 6, right lesions n = 5, left lesions n = 3). Single-isocenter was placed between or in the middle of all lesions. Doses were 54 Gy/50 Gy in 3/5 fractions prescribed to 70-80% isodose line. Plans were generated with Acuros-based algorithm and 6MV-FFF beam following RTOG criteria. Plan quality and delivery efficiency were reported. Outcomes evaluated include local control rates, radiation pneumonitis and rib toxicity. Kaplan-Meier (KM) estimates of time-to-local failure were investigated. Median follow-up time was 5 ± 5 months (range 1 to 15 months). Mean isocenter to tumor distance was 5.6 ± 1.9 cm. Mean combined planning target volume (PTV) was 38.7 ± 22.7 cc. All plans were accepted by treating physicians and met RTOG criteria for target coverage and organs at risk (OAR) dose. Average values of conformity index, gradient index, maximum dose at 2 cm away from the PTV and normal lung V20 were 1.05 ± 0.1, 5.1 ± 0.8, 50.1 ± 5.2% and 6.4 ± 3.1%, respectively. All OAR doses were well below RTOG criteria. Additionally, normal lung V10, V5 and mean lung dose were 18.2%, 31.0 % and 5.4 Gy, on average, respectively. Average beam on time was 3.4 ± 1.4 min. One patient died before follow up and one was lost to follow up. Of twelve patients, eleven achieved complete response to treatment with one lesion of one patient progressing. KM estimated 1-year actuarial tumor local control rate was 100%; however, 50% of the patients developed distant metastases. During the follow-up period, no patient had adverse pulmonary effects, developed grade+2 pneumonitis or had chest wall pain/rib fracture. However, four patients developed radiographic changes that were asymptomatic. Synchronous SBRT treatment to oligometastases lung lesions was fast, effective and safe, with promising early clinical outcomes in terms of local control rates and no adverse side effects to lung or ribs. Although six patients had distant failure, the local control of treated lesions could preserve the patient’s quality of life or delay chemotherapy treatment. Longer follow up of these patients is warranted.

Towards the Clinical Implementation of Pencil Beam Scanned Proton Therapy (PBS-PT) for Thoracic Indications: A Comprehensive 4D Robustness Evaluation Based on Patient and Machine Specific Information

Due to anticipated clinical benefits, thoracic tumors are potential future indications for PBS-PT. However, the concern of plan robustness as a result of motion hamper its clinical implementation. Here we present a comprehensive evaluation of different planning strategies based on patient and machine specific data in order to define optimal PBS-PT protocols for lung and esophageal tumors. This study includes 3 non-small cell lung and 3 esophageal cancer patients with a planning as well as 5 weekly repeated 4DCTs available. For all patients, the CTV volume and motion were monitored throughout the treatment course. Layered rescanned (5 times) 3D and 4D robust optimized PBS-PT plans were created, and approved clinically. These plans were then delivered in dry runs at our proton facility to obtain machine log files, and subsequently evaluated through our 4D robustness evaluation method (4DREM). The 4DREM assesses the plan robustness for the combination of (1) setup and range errors, (2) machine errors, (3) anatomy changes, (4) breathing motion, and (5) interplay effects. The disturbing effects (2), (3), (4), (5) are considered by calculating subplan doses on particular 4DCT phases and performing 4D dose accumulation in all 4DCTs. The subplans were split from the nominal plan by retrieving log files information. For each evaluated plan, 14 4D accumulated scenario dose distributions were obtained, representing 14 possible full fractionated treatment courses. Only small differences in V95(CTV) between nominal and voxel-wise worst-case dose distributions were observed for all 3D / 4D robust optimized plans (consistently ≥ 99.89 %). Similarly, averaged Dmean(lungs-GTV) over all scenarios considered within the 4DREM changed only slightly (Table 1). For 6 patients with lung / esophageal cancer, our 3D / 4D PBS-PT planning protocol showed to be clinically suitable. After confirming these results in an extended patient cohort, we will proceed to investigate less conservative, more conformal planning strategies. The experience gained through comprehensive robustness evaluations based on patient and machine specific data is essential for the definition of optimal PBS-PT protocols for patients with thoracic tumors.Abstract 3762; Table 1Patient characteristics (mean ± SD volume and motion variations) and plan statisticsLungPt. 1Pt. 2Pt. 3Volume [cm3]108.2 ± 16.254.6 ± 5.755.6 ± 2.9Motion [mm]3.9 ± 0.84.6 ± 1.43.8 ± 1.23D4D3D4D3D4DDmean(lungs-GTV) [GyRBE] Nominal9.4010.478.497.359.078.47 Scenarios9.8310.688.617.598.927.96EsophagusPt. 4Pt. 5Pt. 6Volume [cm3]367.4 ± 14.0133.6 ± 10.3209.9 ± 2.6Motion [mm]6.5 ± 0.96.5 ± 0.73.1 ± 0.63D4D3D4D3D4DDmean(lungs-GTV) [GyRBE] Nominal4.304.281.381.411.911.98 Scenarios4.354.531.521.641.972.00 Open table in a new tab

Validation of Dolphin dosimetry in three dimensional patient-specific quality assurance programme.

The aim of this study is to commission and validate Dolphin-Compass dosimetry as a patient-specific Quality Assurance (QA) device. The advancement of radiation therapy in terms of highly conformal delivery techniques demands a novel method of patient-specific QA. Dolphin-Compass system is a dosimetry solution capable of doing different QA in radiation therapy. Dolphin, air-vented ionization detector array mounted on Versa-HD Linear Accelerator (LINAC) was used for measurements. The Compass is a dose computation algorithm which requires modelling of LINAC head similar to other Treatment Planning Systems (TPS). The dosimetry system was commissioned after measuring the required beam data. The validation was performed by comparison of treatment plans generated in Monaco TPS against the measurement data. Different types of simple, complex, static and dynamic radiation fields and highly conformal treatment plans of patients were used in this study. For all field sizes, point doses obtained from Dolphin-Compass dosimetry were in good agreement with the corresponding TPS calculated values in most of the regions, except the penumbra, outside field and at build-up depth. The results of gamma passing rates of measurements by using different Multi-leaf Collimator patterns and Intensity Modulated Radiation Therapy fluence were also found to be in good correlation with the corresponding TPS values. The commissioning and validation of dosimetry was performed with the help of various fields, MLC patterns and complex treatment plans. The present study also evaluated the efficiency of the 3D dosimetry system for the QA of complex treatment plans.

Treatment planning for proton therapy: what is needed in the next 10 years?

Treatment planning is the process where the prescription of the radiation oncologist is translated into a deliverable treatment. With the complexity of contemporary radiotherapy, treatment planning cannot be performed without a computerized treatment planning system. Proton therapy (PT) enables highly conformal treatment plans with a minimum of dose to tissues outside the target volume, but to obtain the most optimal plan for the treatment, there are a multitude of parameters that need to be addressed. In this review areas of ongoing improvements and research in the field of PT treatment planning are identified and discussed. The main focus is on issues of immediate clinical and practical relevance to the PT community highlighting the needs for the near future but also in a longer perspective. We anticipate that the manual tasks performed by treatment planners in the future will involve a high degree of computational thinking, as many issues can be solved much better by e.g. scripting. More accurate and faster dose calculation algorithms are needed, automation for contouring and planning is required and practical tools to handle the variable biological efficiency in PT is urgently demanded just to mention a few of the expected improvements over the coming 10 years.

Conformity of 3-dimensional Surgical Plans With Actual Results: A Comparison of Virtual Surgical Planning Accuracy Between 5 Different Craniofacial Procedures

Conformity of 3-dimensional Surgical Plans With Actual Results: A Comparison of Virtual Surgical Planning Accuracy Between 5 Different Craniofacial Procedures

Dosimetric comparison of different algorithms in stereotactic body radiation therapy (SBRT) plan for non-small cell lung cancer (NSCLC).

PurposesThe main aim of the study was to investigate the dosimetric difference between acuros XB algorithm (AXB), anisotropic analytic algorithm (AAA), and pencil beam convolution (PBC) algorithm in stereotactic body radiation therapy (SBRT) plan for non-small cell lung cancer (NSCLC).Patients and MethodsThirty-eight NSCLC patients were included. GTV, PTV, and organs at risk were delineated by the radiation oncologists. Three optimized SBRT plans for each patients were gained using three algorithms of AXB, AAA, and PBC with the identical plan parameters. Dosimetric endpoints were collected and compared among the three plans, including dosimetric criteria: V100%, V90%, PTV Dmin, Dmax, Dmean, homogeneity index (HI), and Paddick conformity index (CI).ResultsAXB plan resulted in decreased V100% with a mean difference 6.14% compared with PBC plan (For V100%, AXB vs AAA vs PBC=93.44% vs 95.54% vs 99.58%, P<0.05). Three plans showed no significant difference as to the parameter V90%. AXB plan leaded to reduced Dmin of PTV compared with other two algorithms (For Dmin of PTV, AXB vs AAA vs PBC=4048cGy vs 4365Gy vs 4873Gy, P<0.05). PBC induced the enhanced trend of Dmax of PTV compared with other two algorithms (Dmax among three algorithms, P>0.05); and increased the Dmean of PTV in three algorithms with significant difference (For Dmean of PTV, AXB vs AAA vs PBC=5332cGy vs 5330Gy vs 5785Gy, P<0.05). AXB algorithm achieved a similar plan conformity with other two algorithms (For CI, AXB vs AAA vs PBC=0.80 vs 0.85 vs 0.71, P>0.05).ConclusionFor SBRT plan of NSCLC, AAA and PBC algorithms overestimate target coverage, AXB algorithm is recommended for the SBRT plan of NSCLC.

Dose perturbation by metallic biliary stent in external beam radiotherapy of pancreato-biliary cancers

This study aims to investigate dose perturbations caused by a metallic biliary stent (MBS) in patients undergoing external beam radiotherapy for cancers in the pancreato-biliary region. Four MBSs with nitinol mesh were examined in the EasyCube® phantom including a custom stent holder fabricated by a 3D printer. For experimental models, three-dimensional conformal radiotherapy plans using a single anterior-posterior (AP) and four-field box (4FB) as well as volumetric modulated arc therapy (VMAT) plan were prepared to deliver the photon beam of 8Gy to the stent holder. EBT3 film was used to measure dose distributions at four sides surrounding MBS. All MBSs in the AP beam demonstrated mean dose enhancements of 2.3-8.2% at the proximal, left, and right sides. Maximum dose enhancements of 12.3-19.5% appeared at regions surrounding the radiopaque markers. At the location distal to the source, there were mean dose reductions of -3.6 to -10.9% and minimum doses of - 11.1 to - 9.5%. The mean and maximum doses with the 4FB plan were in the ranges of - 0.1 to 3.6% and 6.7-14.9%, respectively. The VMAT produced mean doses of - 0.9 to 4.8% and maximum doses of 6.0-15.3%. Dose perturbations were observed with maximum and minimum spots near the stent surface. The use of multiple beams including parallel-opposed pairs reduced dose perturbations caused by the nitinol and radiopaque components within the stent. Special attention is required for patients in whom the radiopaque markers are closely located near critical structures or the target volume.

Conformity of the Actual to the Planned Result in Orthognathic Surgery.

Virtual surgical planning has facilitated preoperative planning, splint accuracy, and intraoperative efficiency in orthognathic surgery. The translation of the virtual surgical plan to the actual result has not been adequately examined. The authors examined the conformity of the virtual surgical plan to the postoperative result. They hypothesize that the greatest conformity exists in the anteroposterior dimensions. The authors examined patients who underwent Le Fort I maxillary advancement, bilateral sagittal split osteotomy, and genioplasty. The preoperative virtual surgical planning file and postoperative cone beam computed tomographic scan were registered in Mimics using unchanged landmarks. The conformity to the virtual surgical plan was quantified using linear and angular measurements between bone surface landmarks. Results were compared using t tests, with p < 0.05 considered statistically significant RESULTS:: One hundred patients who underwent Le Fort I maxillary advancement, bilateral sagittal split osteotomy, and genioplasty were included. Three-dimensional analysis showed significant differences between the plan and outcome for the following landmarks: A point (y, p = 0.04; z, p = 0.04), B point (y, p = 0.02; z, p = 0.02), pogonion (y, p = 0.04), menton (x, p = 0.02; y, p = 0.01; z, p = 0.03), and anterior nasal spine (x, p = 0.04; y, p = 0.04; z, p = 0.01). Angular measurements sella-nasion-A point, sella-nasion-B point, and A point-nasion-B point were not statistically different. There is a high degree of conformity comparing the orthognathic virtual surgical plan to the actual postoperative result. However, some incongruency is seen vertically (maxilla) and sagittally (mandible, chin). Departures of the actual position compared with the plan could be the result of condylar position changes, osteotomy locations, aesthetic intraoperative decisions, and/or play in the system.

Deep inspiration breath-hold for left-sided breast irradiation: Analysis of dose-mass histograms and the impact of lung expansion

BackgroundThe aim of this study was to compare dose-volume histogram (DVH) with dose-mass histogram (DMH) parameters for treatment of left-sided breast cancer in deep inspiration breath-hold (DIBH) and free breathing (FB). Additionally, lung expansion and anatomical factors were analyzed and correlated to dose differences.MethodsFor 31 patients 3D conformal radiation therapy plans were retrospectively calculated on FB and DIBH CTs in the treatment planning system. The calculated doses, structures and CT data were transferred into MATLAB and DVHs and DMHs were calculated. Mean doses (Dmean), volumes and masses receiving certain doses (Vx, Mx) were determined for the left lung and the heart. Additionally, expansion of the left lung was evaluated using deformable image registration. Differences in DVH and DMH dose parameters between FB and DIBH were statistically analyzed and correlated to lung expansion and anatomical factors.ResultsDIBH reduced Dmean (DVH) and relative V20 (V20 [%]) of the left lung in all patients, on average by − 19 ± 9% (mean ± standard deviation) and − 24 ± 10%. Dmean (DMH) and M20 [%] were also significantly reduced (− 12 ± 11%, − 16 ± 13%), however 4 patients had higher DMH values in DIBH than in FB. Linear regression showed good correlations between DVH and DMH parameters, e.g. a dosimetric benefit smaller than 8.4% for Dmean (DVH) in DIBH indicated more irradiated lung mass in DIBH than in FB. The mean expansion of the left lung between FB and DIBH was 1.5 ± 2.4 mm (left), 16.0 ± 4.0 mm (anterior) and 12.2 ± 4.6 mm (caudal). No significant correlations were found between expansions and differences in Dmean for the left lung. The heart dose in DIBH was reduced in all patients by 53% (Dmean) and this dosimetric benefit correlated to lung expansion in anterior.ConclusionsTreatment of left-sided breast cancer in DIBH reduced dose to the heart and in most cases the lung dose, relative irradiated lung volume and lung mass. A mass related dosimetric benefit in DIBH can be achieved as long as the volume related benefit is about ≥8–9%. The lung expansion (breathing pattern) showed no impact on lung dose, but on heart dose. A stronger chest breathing (anterior expansion) for DIBH seems to be more beneficial than abdominal breathing.

Quantitative metrics for assessing IMRT plan conformity: A virtual phantom study

Intensity Modulated Radiation Therapy (IMRT) is a complex form of radiation delivery for the treatment of malignant tumours and other diseases. In IMRT treatment planning, quantitative assessment is crucial to measure and improve the plan quality and treatment delivery. The search for simple and universal quantitative metrics to assess IMRT treatment plan quality has been identified as important, but as yet not entirely successful. The aim of this study was to assess the IMRT treatment plan quality from the perspective of planning conformity. Conformity index (CI) was adopted to quantify the plan conformity. Virtual phantoms were developed for the initial conformity assessment, in order to form a basis for treatment plan inter-comparisons amongst the different IMRT techniques. A series of multi organs at risk (OARs) phantoms was developed to simulate the planning target volume (PTV) and OARs for different configurations. Conformity assessments were undertaken on all the IMRT plans generated using the virtual phantoms. This study has demonstrated the successful development of virtual phantoms to assess objectively and systematically the IMRT treatment plan conformity.

High Dose 3D Conformal Radiotherapy of Prostate Cancer Using Spaceoar Gel

The aim of this study was to investigate the applicability of high dose radiation therapy following the administration of SpaceOar Hydrogel to decrease rectal toxicity in patients with prostate cancer who had received definitive three-dimensional conformal radiation therapy. Seven patients with a diagnosis of prostate cancer received, under general anesthesia, 10 ml of prostate SpaceOar hydrogel injections transperineally into the space between the prostate and the rectal front wall under the guidance of transrectal ultrasonography. Abdominal tomography and magnetic resonance images of the patients were taken before and after the application of hydrogel. Using both imaging sets and similar algorithms, 3D conformal radiotherapy plans were made that aided in making the calculations. The radiation dose to be applied was calculated from the dose-volume histograms of the target and at risk organs of the patients with tailor-made plans. In the treatment of prostate cancer patients with and without hydrogel plans, there was a statistically significant difference between the rectal V70 and V50 doses, which were 20% ± 14.9 vs 11% ± 2.2 ( p:0.002), and 34 ± 7.9 vs 28.2 ± 11 (p: 0.048), respectively. The D95 and D5 values were similar in all patients with and without hydrogel plans. Rectal toxicity decreased in patients with a distance of >15 mm (p=0.053). Consequently 3D conformal radiotherapy can be successfully and safely applied at high dose with low toxicity to prostate cancer patients after placing hydrogel between the rectum and prostate. Keywords : Prostate cancer, radiotherapy, spaceoar hydrogel, rectal toxicity DOI : 10.7176/JSTR/5-6-08

Automated intensity modulated treatment planning: The expedited constrained hierarchical optimization (ECHO) system.

To develop and implement a fully automated approach to intensity modulated radiation therapy (IMRT) treatment planning. The optimization algorithm is developed based on a hierarchical constrained optimization technique and is referred internally at our institution as expedited constrained hierarchical optimization (ECHO). Beamlet contributions to regions-of-interest are precomputed and captured in the influence matrix. Planning goals are of two classes: hard constraints that are strictly enforced from the first step (e.g., maximum dose to spinal cord), and desirable goals that are sequentially introduced in three constrained optimization problems (better planning target volume (PTV) coverage, lower organ at risk (OAR) doses, and smoother fluence map). After solving the optimization problems using external commercial optimization engines, the optimal fluence map is imported into an FDA-approved treatment planning system (TPS) for leaf sequencing and accurate full dose calculation. The dose-discrepancy between the optimization and TPS dose calculation is then calculated and incorporated into optimization by a novel dose correction loop technique using Lagrange multipliers. The correction loop incorporates the leaf sequencing and scattering effects into optimization to improve the plan quality and reduce the calculation time. The resultant optimal fluence map is again imported into TPS for leaf sequencing and final dose calculation for plan evaluation and delivery. The workflow is automated using application program interface (API) scripting, requiring user interaction solely to prepare the contours and beam arrangement prior to launching the ECHO plug-in from the TPS. For each site, parameters and objective functions are chosen to represent clinical priorities. The first site chosen for clinical implementation was metastatic paraspinal lesions treated with stereotactic body radiotherapy (SBRT). As a first step, 75 ECHO paraspinal plans were generated retrospectively and compared with clinically treated plans generated by planners using VMAT (volumetric modulated arc therapy) with 4 to 6 partial arcs. Subsequently, clinical deployment began in April, 2017. In retrospective study, ECHO plans were found to be dosimetrically superior with respect to tumor coverage, plan conformity, and OAR sparing. For example, the average PTV D95%, cord and esophagus max doses, and Paddick Conformity Index were improved, respectively, by 1%, 6%, 14%, and 15%, at a negligible 3% cost of the average skin D10cc dose. Hierarchical constrained optimization is a powerful and flexible tool for automated IMRT treatment planning. The dosimetric correction step accurately accounts for detailed dosimetric multileaf collimator and scattering effects. The system produces high-quality, Pareto optimal plans and avoids the time-consuming trial-and-error planning process.