3D Conformal Treatment Plans Research Articles

Establishment of local diagnostic reference levels for breast cancer CT protocols in radiotherapy in a single Moroccan center

The objective of this study was to establish local diagnostic reference levels (LDRLs) for breast cancer computed tomography imaging in radiotherapy (CT-RT) at a single hospital in Morocco. Data were collected from 106 adult breast cancer patients aged between 33 and 78 yr during five months. Data were obtained using a Hitachi Supria 16-slice CT simulator at a regional oncology center in Morocco. CT-RT images are intended for 3D conformal radiotherapy treatment planning. Dose length product (DLP) and volumetric computed tomography dose index (CTDIvol) were evaluated by determining the 75th percentile as diagnostic reference levels for CT-RT breast cancer. LDRLs for CT-RT breast cancer have been determined in terms of DLP and CTDIvol, and they were 330.4 mGy.cm and 6.8 mGy, respectively. The DRLs were compared with other Europeans study. DRLs for this study were lower than those for the United Kingdom (UK), Croatia and Slovenia. The results of this study can be a reference for the establishment of local and national DRLs in Morocco and the optimization of CT-RT breast cancer procedures.

Different meaning of the mean heart dose between 3D-CRT and IMRT for breast cancer radiotherapy.

Previous studies in 2D and in 3D conformal radiotherapy concludes that the maximal heart distance and the mean heart dose (MHD) are considered predictive of late cardiac toxicities. As the use of inverse-planned intensity modulated radiation therapy (IMRT) is increasing worldwide, we hypothesized that this 3D MHD might not be representative of heart exposure after IMRT for breast cancer (BC). Patients with left-sided BC and unfavorable cardiac anatomy received IMRT. Their treatment plan was compared to a virtual treatment plan for 3D conformal radiotherapy with similar target volume coverage (study A). Then, a second 3D conformal treatment plan was generated to achieve equivalent individual MHD obtained by IMRT. Then the heart and left anterior descending (LAD) coronary artery exposures were analyzed (study B). Last, the relationship between MHD and the heart volume or LAD coronary artery volume receiving at least 30Gy, 40Gy and 45Gy in function of each additional 1Gy to the MHD was assessed (study C). A significant decrease of heart and LAD coronary artery exposure to high dose was observed with the IMRT compared with the 3D conformal radiotherapy plans that both ensured adequate target coverage (study A). The results of study B and C showed that 3D MHD was not representative of similar heart substructure exposure with IMRT, especially in the case of high dose exposure. The mean heart dose is not a representative dosimetric parameter to assess heart exposure following IMRT. Equivalent MHD values following IMRT and 3DRT BC treatment do not represent the same dose distribution leading to extreme caution when using this parameter for IMRT plan validation.

Verification of monitoring unit calculations for the 3D conformal radiotherapy treatment planning system

The present work aims to validate an Independent Calculation of Monitoring Units (ICMU) software developed to accurately calculate the number of Monitoring Units (MU) used in radiation treatment. The calculation was performed for the photon beam with a variety of nominal energies (6 MV − 18 MV) and filed size ranging from 3 × 3 cm2 to 40 × 40 cm2. Two set-up conventions of treatment techniques were tested, a constant source to surface distance (SSD) and an isocentric set-up with a constant source to axis distance (SAD). The ICMU software was written in C-sharp (C #), using the equivalent square field size concept to calculate the radiation field quantities and connects to a database containing measurements quantities such as Tissue Phantom ratio (TPR) and Output Factors (OFs). The ICMU was successfully validated by comparing it to the Treatment Planning System (TPS) or CMS Monitor Unit Calculations (CMS_MU). The required standards were satisfactorily met (5.0%).

Precision radiotherapy by SPECT lung functional imaging in NSCLC

Background: Single Photon Emission Computed Tomography (SPECT) could be used to avoid the non-affected perfusion areas in patients with non-small-cell lung cancer (NSCLC) and to potentially reduce lung toxicity. The aim of this study is to compare dosimetric differences between two different 3D-conformal treatment plans, with and without CT/SPECT contribution. Methods: Simulation Computed tomography (CT) scans were accurately co-registered with SPECT scans and three different areas, based on SPECT intensity perfusion, were contoured: low perfusion (LP), medium perfusion (MP) and high perfusion (HP). Two different 3D-conformal plans, with co-planar and nonco-planar fields, were generated; one without SPECT information (anatomic plan), and one using the perfusion area identified with functional imaging (functional plan). Results: 9 patients were planned and a total of 18 plans were available for analysis. Anatomical and functional plans resulted in comparable planning target volume (PTV) coverage. In the functional plans, a significant reduction of dose in high perfusion areas was reported. The reduction of HP-V20 Gy values ranged from 15% to 8% (p = 0.046), the ipsiHP-V20 Gy from 38% to 22% (p = 0.028) and ipsiHP-Dmean reduction from 16 Gy to 12 Gy (p = 0.039). No significant differences in other organs at risk (OARs) metrics were reported between anatomical and functional plans. Conclusions: Despite the few cases reported, the strength of our study lies in the reported benefit of functional lung information in 3D conformal radiation planning, without compromising target coverage or worsening dose distribution to the OARs. There is an urgent need for prospective clinical and randomized trials in order to define the role of lung functional imaging in reducing toxicity in clinical practice.

Secondary cancer risk after radiotherapy of seminoma stage one

Background: In radiation treatment of stage one seminoma (SOS) induced secondary cancer in organs at risk (OARs), located in or out of the radiation fields, is a late toxicity of major concern. This study aimed to compare the secondary cancer risk in radiotherapy of SOS in two-dimensional conventional radiation therapy (2D) and three-dimensional conformal radiation therapy (3DCRT). Materials and Methods: CT scan images of 10 patients with SOS were used to design 2D conventional and 3D conformal treatment plans using 25 Gy in 20 sessions. The life attributable risk (LAR) of liver, stomach, and colon were calculated using the organ equivalent dose (OED) model for organs in radiation field and Biologic Effects of Ionizing Radiation VII (BEIR VII) model for organs out of field. Results: LAR of OARs in radiation field such as, liver and stomach was obtained 40% higher in the 2D treatment than in the 3D treatment, while as for the colon, it was 17% lower in the 2D treatment than in the 3D treatment. The LAR values of kidneys located outside the radiation field in the 2D treatment were calculated 0.04%. Conclusion: Increasing the prescribed dose (25 vs. 20) as well as the number of treatment sessions (20 vs. 10) resulted in increasing in the LAR of at-risk organs such as liver, stomach, colon. Therefore, estimating cancer risk of critical organs exposed to radiation through examining the effects of dose fractionation and prescribed doses can be used in optimizing of treatment plan for seminoma, selection of a better treatment method by oncologists, and patient follow-up.

Dosimetry comparison and evaluation of 3D and IMRT for left breast cancer radiotherapy techniques treated at ain wazein medical village hospital in Lebanon

Breast cancer patients undergoing radiation therapy can be treated using the 3D conformal or VMAT techniques. For both plans, the doses received by the target and the organs at risk are determined and compared with protocols recommended for the safety of the patients. CT simulations of 10 women with left breast cancer were used for a 3D conformal and VMAT treatment plans in the radiotherapy department of Ain Wazein Medical Village Hospital (AWMV) utilizing Monaco Treatment Planning system using Collapsed-cone and Monte Carlo algorithms respectively. The total prescribed dose to the PTV was 50 Gy in 25 fractions each 2 Gy. The dosimetric parameters obtained were mean, D95%, and homogeneity index for PTV; mean dose and max doses for the heart; the V20% for the left and the right lungs. All values of this retrospective study were analysed and compared to the normal tissue maximum dose tolerance. VMAT plans resulted in significantly better coverage for the target volume concepts as compared with 3D-CRT (D95: 97% vs. 82%, p-value = 0.002; Dmean 4953 cGy in 3D-CRT vs. 5093 cGy in VMAT, p-value = 0.01). The left lung (V20:28.44% with 3D-CRT vs. 21.93 with VMAT, p-value = 0.02). For the heart (Dmax = 4919 cGy in 3D-CRT vs. 4617 cGy in VMAT, p-value = 0.07). For the right lung (V20 was 0.12% in 3D-CRT vs. 0.52% in VMAT with p-value = 0.008). Even though the p-value was significant for the 3D conformal technique, the dose for both techniques was very low and non-significant to have a risk in the organ. The VMAT technique with correct target volume delineation allowed a significant dose escalation and an increase in Tumor Control Probability (TCP). VMAT resulted in an improved sparing of OARs as compared with 3D-CRT at equivalent dose levels.

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.

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.

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.

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.

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.

Development and Preliminary Evaluation of a Murine Model of Chronic Radiation-Induced Proctitis

Radiotherapy (RT) is commonly used to treat most pelvic malignancies. While treatment is often effective, curative radiation doses to the rectum can result in chronic radiation-induced proctitis, which is characterized by diarrhea, tenesmus, and/or rectal bleeding, recently termed pelvic radiation disease. An animal model of chronic radiation-induced proctitis would be useful to test both preventative and therapeutic strategies to limit this morbidity but has been elusive because of the high rodent mortality associated with acute bowel RT injury. The objective of this research was to develop a novel mouse model of chronic radiation-induced proctitis using advanced technology. Using an X-RAD 225-Cx (Precision X-Ray) small animal irradiator, multiple plan configurations were evaluated for planning treatment volume and organ-at-risk avoidance to deliver a 15Gy 3D conformal treatment plan. The final plan was verified by high resolution 3D dosimetry (PRESAGE/optical-CT), and delivered using a single arc. Mice were monitored for mortality for 250days, followed by histopathological correlates including mucicarmine, Masson's trichrome, and fecal pellet length. Six beam arrangements were considered: single and parallel-opposed fields with whole-pelvis coverage, and collimated fields in parallel-opposed, 3-field, 4-field, and arc geometries. A collimated arc plan offered superior planning treatment volume coverage and organ-at-risk avoidance compared to whole-pelvis irradiation. Treatment verification with PRESAGE 3D dosimetry (Heuris Inc) showed >99% of voxels passing gamma analysis with 2%/2mm criteria. Our treatment resulted in no acute mortality and 40% mortality at 250days. Histopathological analysis showed increased mucous production and fibrosis of the irradiated colon, but no change in fecal pellet length. Our model was able to target successfully lower colon and rectum with lower mortality than other published models. This permitted measurement of late effects that recapitulate some features of rectal damage in humans.

Definitive radiotherapy for locally advanced squamous cell carcinoma of the vulva and technical issues: a case report

This case report describes a complex radical 3D-Conformal Radiotherapy treatment planning, dosimetric issues and outcome of definitive treatment of un-resectable carcinoma of the vulvar in a 42-year old lady. The patient presented with large fungating mass of the vulva which was biopsy confirmed as Keratinizing Squamous Cell Carcinoma. Further staging investigation revealed locally advanced disease (T4), with bilateral inguinal lymph nodes involvement. There is no systemic metastasis or intra-pelvic nodes. The patient was seen by Gynae-Oncology team and the disease was deemed un-resectable without significant morbidity. She was treated to a total dose of 64.8Gy in 36 fractions over 7 weeks with concurrent weekly Cisplatinum in 2 phases. 3D-Conformal radiotherapy technique using the modified segmental boost technique (MSBT, large PA and small AP photon fields with inguinal electron matching) was used. TLD chips were used for in-vivo dose verification in phase 1 and 2 of the treatment. At completion of planned radiotherapy, patient had a complete clinical response, grade 2-3 skin toxicity, grade 2 rectal toxicity, and grade 2 dysuria Vulval Squamous Cell Carcinomas are very radiosensitive tumours and the skills of the treating Radiation Oncologist, Dosimetrists, Physicist, Radiation Therapist and also nurses is of foremost importance is ensuring good clinical outcomes.

O12. Monitor units comparison between TPS and independent software verification system

Introduction In radiation therapy, the treatment planning system (TPS) is used to calculate the monitor units (MUs) needed to deliver a prescribed dose. To avoid any potential errors prior to the start of treatment, quality assurance is performed to verify the MUs with an independent verification system. Commercial MU independent check software such as RadCalc (Lifeline Software Inc., v6.2 Build 5.3) can be used to perform independent MU checks for TPS plans. In this study, we compared MUs calculated with the CMS XiO TPS (v5.1) to the MUs calculated by commercial software RadCalc. Materials and methods 3D conformal photon beam treatment plans were created for 4 ELEKTA linear accelerator machines (SL15, Precise, Platform and Synergy with Agility head) using the CMS XiO TPS and imported into RadCalc. TPS and independent MU verification system percentage differences were calculated for 3064 fields from a total of 679 patient treatment plans. For integrity, plans were checked for prescribed dose, dose per fraction, number of fractions, machine names and energies, correct MLC shapes, jaws, calculation SSD, depth and MU percentage differences between TPS plan and RadCalc calculations. Results 679 patient plans were reviewed for a period of five months, calculated MUs were within 10% MU difference limit. For each linac, the average percentage differences were 0.1, −0.9, 0.5 and 0.8% with standard deviations of 2.2, 1.3, 1.8 and 2.0% for SL15, Precise, Platform, and Synergy with Agility head respectively. MUs calculated by RadCalc were comparable to the MUs of the TPS. Conclusion MUs between the TPS and Independent verification system were well within acceptable tolerances. RadCalc is good enough to perform 3D conformal treatment planning system verification.

Comparison of the effects of two different dose algorithms in cardiac dose parameters for hodgkin lymphoma patients receiving mediastinal radiotheraphy

Objective: This study aimed to compare pencil beam (PB) and convolution superposition (CS) dose calculation algorithms with respect to cardiac dose-volume parameters V5, V25, V30 and MHD (median heart dose) in Hodgkin lymphoma (HL) patients who received mediastinal radiotherapy (RT). Material and Methods: Ten eligible cases with the diagnosis of HL who completed mediastinal RT at Dokuz Eylul University Department of Radiation Oncology before 01.01.2011 formed the study population. Related 3D conformal RT treatment plans were obtained from the Treatment Planning System (TPS) (Nucletron Oncentra Master Plan Version 3.3 SP3 program). Calculations were done for 6 and 18 MV-X beam energy, respectively by using PB and CS algorithms in the TPS. Two algorithms were compared in terms of cardiac dose-volume parameters (V5, V25, V30 and MHD). Results: Mean relative difference for both V25 and V30 was found to be significantly higher in favor of PB algorithm in both 6 MV-X and 18 MV-X photon energy. Mean relative differences were 1.75% (p=0.012) and 6.76% (p=0.028) for the V25 and V30 parameters, respectively in 6 MV-X and 3.25% (p=0.021) and 13.95% (p=0.007) for the V25 and V30 parameters, respectively in 18 MV-X energy. Conclusion: When PB algorithm is used in RT treatment planning of HL patients for the mediastinal region where tissue inhomogeneity is relatively high, heart V25 and V30 parameters were shown to result in higher values compared to CS algorithm in our study. It is more appropriate to prefer CS algorithm instead of PB algorithm since it increases accuracy of calculations in the treatment planning of mediastinal RT.

TH‐EF‐BRB‐04: 4π Dynamic Conformal Arc Therapy Dynamic Conformal Arc Therapy (DCAT) for SBRT

Purpose:To develop an efficient and effective trajectory optimization methodology for 4π dynamic conformal arc treatment (4π DCAT) with synchronized gantry and couch motion; and to investigate potential clinical benefits for stereotactic body radiation therapy (SBRT) to breast, lung, liver and spine tumors.Methods:The entire optimization framework for 4π DCAT inverse planning consists of two parts: 1) integer programming algorithm and 2) particle swarm optimization (PSO) algorithm. The integer programming is designed to find an optimal solution for arc delivery trajectory with both couch and gantry rotation, while PSO minimize a non‐convex objective function based on the selected trajectory and dose‐volume constraints. In this study, control point interaction is explicitly taken into account. Beam trajectory was modeled as a series of control points connected together to form a deliverable path. With linear treatment planning objectives, a mixed‐integer program (MIP) was formulated. Under mild assumptions, the MIP is tractable. Assigning monitor units to control points along the path can be integrated into the model and done by PSO. The developed 4π DCAT inverse planning strategy is evaluated on SBRT cases and compared to clinically treated plans.Results:The resultant dose distribution of this technique was evaluated between 3D conformal treatment plan generated by Pinnacle treatment planning system and 4π DCAT on a lung SBRT patient case. Both plans share the same scale of MU, 3038 and 2822 correspondingly to 3D conformal plan and 4π DCAT. The mean doses for most of OARs were greatly reduced at 32% (cord), 70% (esophagus), 2.8% (lung) and 42.4% (stomach).Conclusion:Initial results in this study show the proposed 4π DCAT treatment technique can achieve better OAR sparing and lower MUs, which indicates that the developed technique is promising for high dose SBRT to reduce the risk of secondary cancer.

EPID based in vivo dosimetry system: clinical experience and results.

Mandatory in several countries, in vivo dosimetry has been recognized as one of the next milestones in radiation oncology. Our department has implemented clinically an EPID based in vivo dosimetry system, EPIgray, by DOSISOFT S.A., since 2006. An analysis of the measurements per linac and energy over a two‐year period was performed, which included a more detailed examination per technique and treatment site over a six‐month period. A comparison of the treatment planning system doses and the doses estimated by EPIgray shows a mean of the differences of 1.9% (±5.2%) for the two‐year period. The 3D conformal treatment plans had a mean dose difference of 2.0% (±4.9%), while for intensity‐modulated radiotherapy and volumetric‐modulated arc therapy treatments the mean dose difference was −3.0 (±5.3%) and −2.5 (±5.2%), respectively. In addition, root cause analyses were conducted on the in vivo dosimetry measurements of two breast cancer treatment techniques, as well as prostate treatments with intensity‐modulated radiotherapy and volumetric‐modulated arc therapy. During the breast study, the dose differences of breast treatments in supine position were correlated to patient setup and EPID positioning errors. Based on these observations, an automatic image shift correction algorithm is developed by DOSIsoft S.A. The prostate study revealed that beams and arcs with out‐of‐tolerance in vivo dosimetry results tend to have more complex modulation and a lower exposure of the points of interest. The statistical studies indicate that in vivo dosimetry with EPIgray has been successfully implemented for classical and complex techniques in clinical routine at our institution. The additional breast and prostate studies exhibit the prospects of EPIgray as an easy supplementary quality assurance tool. The validation, the automatization, and the reduction of false‐positive results represent an important step toward adaptive radiotherapy with EPIgray.PACS number(s): 87.53.Bn, 87.55.Qr, 87.56.Fc, 87.57.uq