3D Conformal Plans Research Articles

Computed Tomography/Magnetic Resonance Imaging (CT/MRI) Image Registration and Fusion Assessment for Accurate Glioblastoma Radiotherapy Treatment Planning

Background: In this study, computed tomography/magnetic resonance imaging (CT/MRI) image registration and fusion in the 3D conformal radiotherapy treatment planning of Glioblastoma brain tumor was investigated. Good CT/MRI image registration and fusion made a great impact on dose calculation and treatment planning accuracy. Indeed, the uncertainly associated with the registration and fusion methods must be well verified and communicated. Unfortunately, there is no standard procedure or mathematical formalism to perform this verification due to noise, distortion, and complicated anatomical situations. Objectives: This study aimed at assessing the effective contribution of MRI in Glioma radiotherapy treatment by improving the localization of target volumes and organs at risk (OARs). It is also a question to provide clinicians with some suitable metrics to evaluate the CT/MRI image registration and fusion results. Methods: Quantitative image registration and fusion evaluation were used in this study to compare Eclipse TPS tools and Elastix CT/MRI image registration fusion. Thus, Dice score coefficient (DSC), Jaccard similarity coefficient (JSC), and Hausdorff distance (HD) were found to be suitable metrics for the evaluation and comparison of the image registration and fusion methods of Eclipse TPS and Elastix. Results: The programmed tumor’s volumes (PTV) delineated on CT slices were approximately 1.38 times smaller than those delineated on CT/MRI fused images. Large differences were observed for the edema and the brainstem. It was also found that MRI considerably optimized the dose to be delivered to the optic nerve and brainstem. Conclusions: Image registration and fusion is a fundamental step for suitable and efficient Glioma treatment planning in 3D conformal radiotherapy that ensure accurate dose delivery and unnecessary OAR irradiation. MRI can provide accurate localization of targeted volumes leading to better irradiation control of Glioma tumor.

Radio-induced cardiotoxicity: From physiopathology and risk factors to adaptation of radiotherapy treatment planning and recommended cardiac follow-up

Cancer and cardiovascular disease (CVD) are the leading cause of mortality worldwide, and breast cancer (BC) the most common malignancy affecting women worldwide. Radiotherapy is an important component of BC treatment and participates in CVD occurrence. It seems, therefore, crucial to gather both radiation oncology and cardiology medical fields to improve the follow-up quality of our BC patients. This review aims at updating our knowledge regarding cardiotoxicities risk factors, and consequently, doses constraints in case of 3D-conformal and IMRT treatment planning. Then we will develop how to reduce cardiac exposure and what kind of cardiac follow-up we could recommend to our breast cancer patients.

Scattering kernels for fast neutron therapy treatment planning

The University of Washington (UW) Clinical Neutron Therapy System (CNTS) has been used to treat over 3300 patients. Treatment planning for these patients is currently performed using an MV x-ray model in Pinnacle® adapted to fit measurements of fast neutron output factors, wedge factors, depth-dose and lateral profiles. While this model has provided an adequate representation of the CNTS for 3D conformal treatment planning, later versions of Pinnacle did not allow for isocentric gantry rotation machines with a source-to-axis distance of 150 cm. This restriction limited the neutron model to version 9.0 while the photon and electron treatment planning at the UW had moved on to newer versions. Also, intensity modulated neutron therapy (IMNT) is underdevelopment at the UW, and the Pinnacle neutron model developed cannot be used for inverse treatment planning. We have used the MCNP6 Monte Carlo code system to develop Collapsed Cone (CC) and Singular Value Decomposition (SVD) neutron scattering kernels suitable for integration into the RayStation treatment planning system. Kernels were generated for monoenergetic neutrons with energies ranging from 1 keV to 51 MeV, i.e. the energy range most relevant to the CNTS. Percent depth dose (PDD) profiles computed in RayStation for the CC and SVD kernels are in excellent agreement with each other for depths beyond the beam’s dose build-up region (depths greater than about 1.7 cm) for open 2.8 × 2.8 cm2, 10.3 × 10.3 cm2, and 28.8 × 32.8 cm2 fields. Lateral profiles at several depths, as well as the PDD, calculated using the CC kernels in RayStation for the full CNTS energy spectrum pass a 3%/3 mm gamma test for field sizes of 2.8 × 2.8 cm2, 10.0 × 10.3 cm2, and 28.8 × 32.8 cm2.

Functionally weighted airway sparing (FWAS): a functional avoidance method for preserving post-treatment ventilation in lung radiotherapy

Recent changes to the guidelines for screening and early diagnosis of lung cancer have increased the interest in preserving post-radiotherapy lung function. Current investigational approaches are based on spatially mapping functional regions and generating regional avoidance plans that preferentially spare highly ventilated/perfused lung. A potentially critical, yet overlooked, aspect of functional avoidance is radiation injury to peripheral airways, which serve as gas conduits to and from functional lung regions. Dose redistribution based solely on regional function may cause irreparable damage to the ‘supply chain’. To address this deficiency, we propose the functionally weighted airway sparing (FWAS) method. FWAS (i) maps the bronchial pathways to each functional sub-lobar lung volume; (ii) assigns a weighting factor to each airway based on the relative contribution of the sub-volume to overall lung function; and (iii) creates a treatment plan that aims to preserve these functional pathways. To evaluate it, we used four cases from a retrospective cohort of SAbR patients treated for lung cancer. Each patient’s airways were auto-segmented from a diagnostic-quality breath-hold CT using a research virtual bronchoscopy software. A ventilation map was generated from the planning 4DCT to map regional lung function. For each terminal airway, as resolved by the segmentation software, the total ventilation within the sub-lobar volume supported by that airway was estimated and used as a function-based weighting factor. Upstream airways were weighted based on the cumulative volumetric ventilation supported by corresponding downstream airways. Using a previously developed model for airway radiosensitivity, dose constraints were determined for each airway corresponding to a <5% probability of airway collapse. Airway dose constraints, ventilation scores, and clinical dose constraints were input to a swarm optimization–based inverse planning engine to create a 3D conformal SAbR plan (CRT). The FWAS plans were compared to the patients’ prescribed CRT clinical plans and the inverse-optimized clinical plans. Depending on the size and location of the tumour, the FWAS plan showed superior preservation of ventilation due to airflow preservation through open pathways (i.e. cumulative ventilation score from the sub-lobar volumes of open pathways). Improvements ranged between 3% and 23%, when comparing to the prescribed clinical plans, and between 3% and 35%, when comparing to the inverse-optimized clinical plans. The three plans satisfied clinical requirements for PTV coverage and OAR dose constraints. These initial results suggest that by sparing pathways to high-functioning lung subregions it is possible to reduce post-SAbR loss of respiratory function.

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.

P14.80 Advances in radiotherapy for brain tumors (benign, malignant and pediatrics tumors)

Abstract BACKGROUND New techniques in radiation oncology such as VMAT (volumetric modulated arc therapy), IGRT (image guidance radiotherapy) compare 3D-conformal technique offering better coverage of the target and more safety for the organs at risk for brain tumors such as Glioblastomas, low grade gliomas, pediatric tumors, meningiomas, pituitary adenomas, brain metastasis. MATERIAL AND METHODS Compare 3D-conformal treatment plans with VMAT -IGRT plan for Glioblastoma, pituitary adenoma, pediatric tumors, low grade gliomas, brain metastasis. Clinical target definition occur with Fusion of planing-MRI with Planing-CT inclusive preoperative and postoperative MRI to exact delineation of GTV (gross tumor volume), CTV (clinical target definition, PTV (planing tumor volume). contouring of organs at risk such as brainstemm, chiasm, N. opticus right and left, eye right and left, lens right and left, brain, cerebellum, internal ears. RESULTS VMAT treatment plans offer higher coverage of the target, higher homogenize radiation index and less radiation for the organs at risk. Due to the good safety of the organs at risk less toxicity during radiation was mentioned specially for neuroaxisradiation for medulloblastoma in children. The toleration during radiotherapy with VMAT technique is is much better than 3D conformal technique CONCLUSION VMAT technique offers higher radiation dose to the target and less radiation to the organs at risk with better toleration of treatment and less toxicity inclusive late side effects such as radionecrosis.

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.

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.

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

Comparison of an in-house developed monitor unit double-check program for 3D conformal radiation therapy and treatment planning system verification

AbstractAimThe treatment planning system (TPS) plays a key role in radiotherapy treatments; it is responsible for the accurate determination of the monitor unit (MU) needed to be delivered to treat a patient with cancer. The main goal of radiotherapy is to sterilise the tumour; however, any imprecise dose delivered could lead to deadly consequences. The TPS has a quality assurance tool, an independent program to double check the MU, evaluate patient plan correctness and search for any potential error.Materials and methodsIn this work, a comparison was carried out between a MU calculated by TPS and an independent in-house-developed monitor unit calculation program (MUCP). The program, written in Cplusplus (C++ Object-Oriented), requires a database of several measured quantities and uses a recently developed physically based method for field equivalence calculation. The ROOT CERN data analysis library has been used to establish fit functions, to extend MUCP use to a variety of photon beams. This study presents a new approach to checking MU correctness calculated by the TPS for a water-like tissue equivalent medium, using our MUCP, as the majority of previous studies on the MU independent checks were based on the Clarkson method. To evaluate each irradiated region, four calculation points corresponding to relative depths under the water phantom were tested for several symmetric, asymmetric, irregular symmetric and asymmetric field cases. A comparison of MU for each radiation fields from readings of the TPS and the MUCP was undertaken.ResultsA satisfactory agreement has been obtained and within the required standards (3%). Additional experimental measurements of dose deposited in a water phantom showed a deviation of &amp;lt;1·6%.FindingsThe MUCP is a useful tool for basic and complex MU verification for 3D conformal radiation therapy plans.

Assessment of a 2D EPID-based Dosimetry Algorithm for Pre-treatment and In-vivo Midplane Dose Verification

Introduction: The use of electronic portal imaging devices (EPIDs) is a method for the dosimetric verification of radiotherapy plans both pretreatment and in-vivo. The aim of this study was to test a 2D EPID-based dosimetry algorithm for dose verification of some plans inside a homogenous and anthropomorphic phantom and in-vivo, as well. Materials and Methods: Dose distributions were reconstructed from EPID images using a 2D EPID dosimetry algorithm inside a homogenous slab phantom for a simple 10×10 cm2 box technique, the 3D conformal (prostate, head-and-neck and lung) and an IMRT prostate plans inside an anthropomorphic (Alderson) phantom and the patients (one fraction in-vivo) for the 3D conformal plans (prostate, head-and-neck and lung). Results: The Planned and EPID dose difference at isocenter, on average, was 1.7% for the pretreatment verification and was less than 3% for all in vivo plans except a head-and-neck which was 3.6%. The mean γ values for a 7-field prostate IMRT plan delivered to the Alderson phantom varied from 0.28 to 0.65. For 3D conformal plans applied for the Alderson phantom, all γ1% values were within the tolerance level for all plans and in both AP-PA beams. Conclusion: The 2D EPID-based dosimetry algorithm provides an accurate method to verify the dose of a simple 10×10 cm2 fields in two dimensions inside a homogenous slab phantom as well as for IMRT prostate plan and 3D conformal plans (prostate, head-and-neck and lung plans) applied using an anthropomorphic phantom and in-vivo.

Camera based EPID dosimetric verification of radiation treatments

Introduction: Tumor control and treatment quality depend on accuracy of delivered dose. Various methods have been studied for treatment dosimetry verification. Among these methods, the use of electronic portal imaging device (EPID) is highly considered. Many efforts are underway to improve the results of this context. Materials and Methods: In this study, a new method for pretreatment dose verification is reported using the transmitted signal of a camera based EPID. Lateral scatter within imager has been considered as field size dependent additive operation. Lateral scatter description within the imager were obtained from measurements with a 2D array ionization chambers for a set of different field sizes. The water-equivalent thickness of phantom material was defined for dose reconstruction, by means of the treatment planning system, according to the patient's data in CT scans along the beam central axis. Results: The method was tested for pretreatment verification of 3D conformal prostate cancer treatment plans. There are no significant differences between the EPID and ionization chamber responses (P value = 0.37). Conclusion: This study proposes a practical method with easier and less calculations in comparison to the deconvolution approaches that can be applied for overall dosimetric assessments of treatments in every fraction.

A novel dynamic arc treatment planning solution to reduce dose to small bowel in preoperative radiotherapy for rectal cancer

Preoperative radiotherapy or combined chemoradiotherapy for locally advanced rectal cancer (LARC) can cause acute and late gastrointestinal (GI) side-effects. There is thought to be a dose-volume relationship between small bowel irradiation and the development of these effects. A planning study was undertaken to compare small bowel sparing for a range of 3D conformal and dynamic arc planning solutions. A planning study was carried out for 20 LARC patients. Organs at risk (OAR) contoured included bowel loops and peritoneal space (PS). For each of the 20 patients, 5 plans were created: (1) standard 3D conformal plan; (2) standard dual dynamic arc plan; (3) dual dynamic arc plan with 90° avoidance sector through the anterior portion of the patient; (4) dual dynamic arc plan with an anterior avoidance structure in the optimizer; (5) dual dynamic arc plan with both an anterior avoidance structure and an avoidance sector. The prescription was 50.4 Gy in 28 fractions to the planning target volume (PTV). Five Dose Volume Levels (DVLs; V15 Gy, V20 Gy, V25 Gy, V35 Gy, V40 Gy, and V50.4 Gy) for bowel and PS were selected. The DVLs were compared between the plans using Friedman Tests and Wilcoxon Signed Rank Tests. Comparison of the 5 plans revealed that a dual dynamic arc plan containing both an anterior avoidance sector and structure significantly improved the dose to the bowel compared to a standard 3D conformal plan and to a standard dual dynamic arc plan. This improvement was achieved while maintaining PTV coverage. This novel dual dynamic arc planning technique that uses both an avoidance sector and structure reduces the dose to the bowel and PS, which may lead to a reduction in GI toxicity.

Comparison of Treatment Planning Approaches for Spatially Fractionated Irradiation of Deep Tumors

Conventional GRID radiation therapy fractionates radiation in space. Spatially fractionated radiation therapy (SFRT) with a grid block has limitations in the treatment of deep tumors. Other treatment options may better allow for the application of the principles of SFRT to deep tumors. The purpose of this work was to compare the dosimetric and delivery time characteristics of 3D conformal-, volumetric arc therapy (VMAT)-, and TomoTherapy-based approaches for SFRT of deep targets. Two virtual GRID phantoms were created consisting of 7 cylinders (1cm diameter) aligned longitudinally along the tumor in a honey-comb pattern, mimicking a conventional GRID block, with 2cm center-to-center spacing (GRID2cm) and 3cm center-to-center spacing (GRID3cm), all contained within a larger cylinder. These virtual phantoms consisted of: the tumor (the larger cylinder structure), the targets (the cylindrical structures inside the larger cylinder), and an avoidance structure created by extracting the targets from the tumor. The larger cylinder was 8cm and 10cm in diameter for the GRID2cm and GRID3cm, respectively. TomoTherapy, VMAT and multi-multileaf collimator (MLC) segment 3D conformal plans forming the grid pattern were created using commercially available software. The mean dose to the GRID target and the heterogeneity of the dose distribution (peak-to-valley and peak-to-edge dose ratios) inside the GRID target were obtained. The peak-to-valley ratio was determined as the mean dose delivered to the 7 cylinders to the mean dose delivered to the avoidance structure. The peak-to-edge ratio was determined as the mean dose delivered to the 7 cylinders to the mean dose delivered at the edge of the tumor (defined as a 2mm ring encompassing the edge). Prescriptions for all plans were set to deliver a mean dose of 15 Gy to the grid targets in one fraction. The mean doses inside the GRID2cm/GRID3cm target were 16.3±2.0Gy/16.6±2.0Gy, 15.0±0.4Gy/15.0±0.5Gy, and 15.0±0.4Gy/15.0±2.2Gy for the TomoTherapy, VMAT, and 3D conformal plans, respectively. The mean doses at the edge of the GRID2cm/GRID3cm cylinder were 7.0±3.2Gy/6.3±3.3Gy, 6.0±1.3Gy/6.8±0.7Gy, and 5.1±2.2Gy/4.6±2.2Gy for the TomoTherapy, VMAT, and 3D conformal plans, respectively. The peak-to-valley ratios for GRID2cm/GRID3cm were 1.7/1.9, 1.7/1.6, 2.1/2.3 for the TomoTherapy, VMAT, and 3D conformal plans, respectively. The peak-to-edge ratios for GRID2cm/GRID3cm were 2.3/2.6, 2.5/2.2, 2.9/3.3 for the TomoTherapy, VMAT, and 3D conformal plans, respectively. The delivery times for the GRID2cm/GRID3cm were 44min/27.5min, 16.5min/8min, and 15min/21min for TomoTherapy, VMAT, and 3D conformal plans, respectively. Our results demonstrate that 3D conformal planning yield the highest peak-to-valley and peak-to-edge ratios with indication of shorter treatment times for this specific geometry.

Reduction of Heart Dose Using Voluntary Deep Inspiration Breath- Holding Technique in Left Breast Cancer Patients Treated by Hypofractionated Radiation Therapy

This study aims at proving that voluntary Deep Inspiration Breath- Holding (vDIBH) technique lowers radiation exposure to the heart and Left Anterior Descending Artery (LAD) without compromising coverage of left breast or chest wall. Irradiation of a substantial volume of the heart to a sufficiently high dose can damage virtually any component of the heart which can cause significant morbidity or mortality. Sixty-six women with left sided breast cancer requiring post-operative radiotherapy and fulfilling inclusion criteria were accrued from radiotherapy department at a single institution from November 2015 to December 2016. Inclusion criteria comprised patients with non-metastatic left breast cancer who are candidates for post-operative radiotherapy and can hold their breaths for longer than 20 seconds. Informed consent was obtained from all patients who were then coached on proper method of breath holding. 2 sets of CT simulations were done during free breathing and DIBH techniques. The average time for which the patients were asked to hold their breath was between 18 and 23 seconds. Both CT image data serials were then transferred to the treatment planning system where target volume and organs at risk (left lung, heart, and contralateral breast) were delineated according to RTOG protocols. LAD arteries were contoured according to the University of Michigan cardiac atlas. 3D-conformal planning using hypofractionated dose of 40Gy/15 fractions was done in all cases. Dose-Volume Histograms were used to compare between both techniques regarding doses to critical organs at risk (mean heart dose, V10-heart, V20-heart, V25-heart, LAD artery, contralateral breast, and lungs), and planning target volume (PTV). Acceptance was based on RTOG 1005 and University of Michigan protocols. Using vDIBH technique, all patients had lower heart and LAD artery doses. In the free breathing serials, mean heart doses ranged from 99 cGy to 613 cGy with the average being 330 cGy. Based on RTOG 1005 protocol, 3 patients had an unacceptable mean heart dose of more than 500 cGy, while 14 patients had a less than ideal mean heart dose between 400 and 500 cGy. Utilizing vDIBH technique, mean heart doses ranged from 74 cGy to 407 cGy with the average being 210 cGy. This represents a statistically significant difference (p-value <0.001). Patients who received internal mammary nodal irradiation, with wide tangential fields, showed statistically significant lower doses regarding heart and LAD artery between both techniques (p-value <0.05). vDIBH technique was associated with lower radiation dose to the heart, LAD artery and ipsilateral lung without compromising coverage of the breast or chest wall.

Modeling Variability for at Risk Lung Functionality by Location of Esophageal Cancer Radiation Therapy Fields

Dose volume histogram (DVH) parameters are used to assess lung tolerance for esophageal cancer radiotherapy. Although lung functionality is heterogeneous, DVH evaluation treats all lungs as equivalent. We modeled variability of ventilation in lung exposed to radiotherapy by site of esophageal cancer. We developed simulated 3D conformal 4-field radiation treatment plans for gastroesophageal junction and mid-thoracic esophagus patients from 9 individual 4D CT scans. Standard expansions were used (4 cm superiorly/inferiorly and 1cm radially for clinical target volume and then 5mm in all directions for planning target volume (PTV)). Radiation dose was 5,040 cGy in 28 fractions to the PTV. We then determined points in the lung that were at the superior and inferior edges of the radiation fields for each plan and measured the displacement of those points from full exhalation to full inhalation as a surrogate for lung expansion. P-values were determined through the Wilcoxon Rank Sum test and t-tests. Lung displacement as measured by points at the superior and inferior edges of the gastroesophageal and mid-thoracic fields were 12.1 mm (± 6.7), 19.2 mm (± 5.9), 3.8 mm (± 1.3), and 7.1 mm (± 2.5), respectively, between full exhalation and full inhalation. Points in the superior aspect of the gastroesophageal fields moved significantly more than points in the superior aspect of the mid-thoracic fields (p=0.0078). Displacement was generally lateral and caudal in direction. There was a difference in displacement in the simulated tumors as well, with the mid-thoracic tumors moving a mean distance of 6.7 mm caudally and the gastroesophageal tumors moving a mean distance of 10.0 mm ventrally and caudally (p=0.039). There was also a difference in dose to the inferior aspects of the lung that displaced the most during the breathing cycle between the gastroesophageal and mid-thoracic fields, 3,541 cGy and 580 cGy, respectively (p=0.0001). This difference in dose to the most expansive part of the lung was not well expressed through the mean lung dose, V5, V10, or V30. The V5 to the total lung volume was higher for mid-thoracic plans than for gastroesophageal plans (63% vs 43%; p=0.0078) as was V10 (52.2% vs 36.9%; p=0.0039), while V30 was higher for gastroesophageal plans (17% vs 11%; p=0.039). The mean lung dose was numerically higher at 1,540 cGy for mid-thoracic plans versus 1,320 cGy for gastroesophageal plans although not statistically significant (p=0.18). Gastroesophageal junction fields have superior lung DVH parameters but are treating more ventilated lung versus mid-thoracic esophagus fields. Further study of differences in pulmonary outcomes based on location of tumor and ventilation of treated lung are warranted. In conjunction with tumor movement results, gastroesophageal junction tumors would appear to be more amenable to advanced planning techniques managing movement and functional lung avoidance.

Robust Prediction of Isodose Distribution with a Fully Convolutional Networks (FCN)-Based Deep Learning Model

Deep learning excels conventional methods in the domain of image recognition, classification and segmentation. It uses many layered convolution neural network to find hierarchies of representations and abstractions of images through pretraining on a large data set. Dose prediction based on the geometry shape and location of the contours, without relying on time-consuming dose calculations and subsequent optimizations can facilitate clinical decision making and improve efficiency by reducing the back and forth between the planner and the physician. Instead of predicting DVHs with machine learning as is conventionally done, here we propose to predict the isodose in voxel domain with the popular Fully Convolution Networks (FCN). We trained the FCN end-to-end, pixels-to-pixels on over 10,000 input images with artificially generated patient contours and corresponding output images with dose distributions, in a resolution of 512x512. We generate the BODY, PTV and OAR contours randomly to increase the variety of the training set, thus testing the robustness of the method. The location, size and shape of the contours are different from case to case and the body sizes vary from 12 cm to 20 cm. We calculate the dose distribution with a simplified pencil beam algorithm for a generic 6x beam and treating every pixel inside BODY as water. For each case, we optimized a 3D conformal plan by balancing the mean dose to the PTV and the OAR. The generated dose distribution is then converted to 10 isodose lines from 100% to 10% which forms the output image. The FCN, as a popular deep learning structure for segmentation, adapted the state of the art recognition network VGG16 that is pretrained on the ImageNet. The first 5 layers of the VGG16 consist of convolution layer and pooling layer that generate 1d vector representing the image classes. FCN replaced the last three full-connected layers of the VGG16 with deconvolutional layers which up-sample the coarse output to the same resolution as the original input. The network was trained by Stochastic Gradient Descent with momentum 0.9, fixed learning rate of 10ˆ-4, weight decay of 2ˆ-4. The training takes around 40 epochs (one pass through all the training set) on a Titan X video card with 12 GB memory. We used the Caffe framework and MatLab for our deep learning implementation. Mean Intersection over union (MIOU) and pixel accuracy (PA) are used to test the accuracy on a validation set that is generated the same way as the training set with 1000 cases. The MIOU is ∼ 63% and the PA is ∼ 91% on the validation set. It takes around one tenth of a second for the dose prediction. We showed the potential of deep learning method in reliably predicting dose distribution from patient geometries alone. The speed and precision of this method would only improve with the fast advances in the deep learning field. The versatility and speed of this method makes it a valuable tool for any TPS and promises to significantly improve the clinical workflow.

Three-dimensional conformal radiation therapy for the osteoarthritis of knee joint: the radiobiological background, dose distribution analysis

Osteoarthritis (OA) is the most frequent rheumatological pathology of the joints. Standard medical treatment does not always allow to stop the pain syndrome. The alternative method of pain treatment causes by OA is orthovoltage X-ray therapy (OVRT). It was used from 1970. The maximum dose by OVRT lies on the skin surface. Based on the modern methods of diagnosis, choosing the appropriate radiation energy, it is possible to reduce the amount of irradiation of the knee joint.The purpose. Is to present the technique of radiation planning in patients with gonarthritis and compare it with OVRT by dosimetry criteria.Materials and methods. Comparison of dose distribution plans of the orthovoltage beam was carried out according to the two-dimensional axial plan in the area of the isocenter for the energy of 200 kV from two tangential fields and a megavoltage energy beam of 6 MeV for a three-dimensional conformal radiation therapy using 3-and 6-fields isocentric irradiation techniques. To describe amounts of radiation were applied to the CTV (clinical target volume) and PTV (planning target volume). To estimate the volume distribution of the dose, bones forming the knee joint were contoured separately. The indent on the PTV was 3 mm.Results. The application of the 6-fields technique allows achieving 95% dose distribution at 93% of the volume, and 90% of the planned dose of 45 SGR covers 97% of the PTV. The average dose on the skin and the neurovascular bundle are of 150 and 240 cGy, respectively. The average radiation dose per course in critical anatomical areas is 280 cGy and 150 cGy. It can be considered that the target coverage for the compared methods is similar as for OVRT, and for 3D conformal radiation therapy plans for dose distribution of the orthogonal beam in the axial plane in comparison with dose distributions for conformal radiation techniques.Conclusion. The technique of three-dimensional conformal radiation therapy of the knee joint in OA with progressive pain syndrome can potentially lead to an increase in the analgesic effect due to greater coverage with a dose of bone elements of the joint, which are a potential source of pain. Three-dimensional conformal radiotherapy megavoltage beam allows reducing the radiation load on the skin in 2.5 times, which can reduce the frequency of delayed adverse effects.

I091] Clinical deployment of the mridian linac

Purpose The introduction of MR-guided radiotherapy (MRgRT) into clinical practice opens a lot of new possibilities and at the same time presents novel challenges. Funded by the German Research Foundation, a Viewray MRIdian Linac was installed in our department in 2017 with the first patient treatments in April 2018. Methods The Viewray MRIdian Linac combines a 0.345T magnetic resonance imaging system with a 6 MV FFF linac. Fields are shaped by a double-stack, double-focus MLC, enabling the delivery of static conformal beams as well as step-and-shoot IMRT. 3D-MRI scans performed prior to treatment are used for patient positioning as well as adaption of treatment plans. Additionally, single slices of cine MRI can be continuously acquired during treatment and used for gating. Results The commissioning tests can be divided into RT-tests, MR-tests and tests for the combination of both. RT-related tests in general followed existing recommendations for commissioning and quality assurance (QA), but needed to be adapted due to the presence of the magnetic field. For the MR-related tests of the MRIdian system, the customer is presented with a set of MR-phantoms and test recommendations by the vendor. Those verifications comprised tests of field homogeneity, spatial integrity, uniformity and signal-to-noise ratio. Other MR-related tests as the ACR-test may be adapted from diagnostic MRI. Regarding the combination of MR and RT, one important test was for example the coincidence of both isocenters. Furthermore, phantoms for RT-QA with adequate MR imaging contrast were developed and evaluated. Regarding the clinical integration, we follow a step-by-step concept. In the first step, patients with not too complicated, i.e. 3D conformal treatment plans are treated, in order to enable the whole team to get acquainted with the workflow and all novel concepts and processes coming along with daily MR imaging. For the second step, inclusion of IMRT treatments as well as gating are planned, which both should involve additional QA tests. Thirdly, the goal is to implement on-table adaption of treatments, which will also need additional verification. Conclusions Commissioning tests and workflow considerations were presented for the clinical deployment of an MR-Linac.

Radiation treatment planning and delivery strategies for a pregnant brain tumor patient.

The management of a pregnant patient in radiation oncology is an infrequent event requiring careful consideration by both the physician and physicist. The aim of this manuscript was to highlight treatment planning techniques and detail measurements of fetal dose for a pregnant patient recently requiring treatment for a brain cancer. A 27‐year‐old woman was treated during gestational weeks 19–25 for a resected grade 3 astrocytoma to 50.4 Gy in 28 fractions, followed by an additional 9 Gy boost in five fractions. Four potential plans were developed for the patient: a 6 MV 3D‐conformal treatment plan with enhanced dynamic wedges, a 6 MV step‐and‐shoot (SnS) intensity‐modulated radiation therapy (IMRT) plan, an unflattened 6 MV SnS IMRT plan, and an Accuray TomoTherapy HDA helical IMRT treatment plan. All treatment plans used strategies to reduce peripheral dose. Fetal dose was estimated for each treatment plan using available literature references, and measurements were made using thermoluminescent dosimeters (TLDs) and an ionization chamber with an anthropomorphic phantom. TLD measurements from a full‐course radiation delivery ranged from 1.0 to 1.6 cGy for the 3D‐conformal treatment plan, from 1.0 to 1.5 cGy for the 6 MV SnS IMRT plan, from 0.6 to 1.0 cGy for the unflattened 6 MV SnS IMRT plan, and from 1.9 to 2.6 cGy for the TomoTherapy treatment plan. The unflattened 6 MV SnS IMRT treatment plan was selected for treatment for this particular patient, though the fetal doses from all treatment plans were deemed acceptable. The cumulative dose to the patient's unshielded fetus is estimated to be 1.0 cGy at most. The planning technique and distance between the treatment target and fetus both contributed to this relatively low fetal dose. Relevant treatment planning strategies and treatment delivery considerations are discussed to aid radiation oncologists and medical physicists in the management of pregnant patients.