Automatic learning-based beam angle selection for thoracic IMRT.

Currently, intensity-modulated radiation therapy (IMRT) is commonly used in radiotherapy clinics. However, designing a treatment plan with multiple beam angles depends on the experience of human planners, and is mostly achieved using a trial-and-error approach. It is preferrable but challenging to solve this issue automatically and mathematically using an optimization approach. The goal of this study is to develop a mixed-integer linear programming (MILP) approach for the beam angle optimization (BAO) of non-coplanar IMRT for liver cancer. MILP models for the BAO of both coplanar and non-coplanar IMRT treatment plans were developed. The beam angles of the IMRT plans were first selected by the MILP model built using mathematical optimization software. Next, the IMRT plans with the selected beam angles was created in a commercial treatment planning system. Finally, the fluence map and dose distribution of the IMRT plans were generated under pre-defined dose-volume constraints. The IMRT plans of 10 liver cancer patients previously treated at our institute were used to assessed the proposed MILP models. For each patient, both coplanar and non-coplanar IMRT plans with beam angles optimized by the MILP models were compared with the IMRT plan clinically approved by physicians. The MILP model-guided IMRT plans showed reduced doses for most of the organs at risk (OARs). Compared with the IMRT plans clinically approved by physicians, the doses for the spinal cord (28.5 vs. 36.1, P=0.001<0.05) and liver (27.6 vs. 29.1, P=0.005<0.05) decreased significantly in the IMRT plans with non-coplanar beams selected by the MILP models. The MILP model is an effective tool for the BAO in coplanar and non-coplanar IMRT treatment planning. It facilitates the automation of IMRT treatment planning for current high-precision radiotherapy.

Potential for Dose-escalation in the Post-prostatectomy Setting with Intensity Modulated Radiation Therapy: A Dosimetric Study using EORTC Consensus Guidelines for Target Volume Contours

Purpose: To evaluate the dosimetric characteristics of intensity-modulated radiotherapy (IMRT) treatment plan with beam angle optimization. Methods: Ten post-operation patients with cervical cancer were included in this analysis. Two IMRT plans using seven beams were designed in each patient. A standard coplanar equi-space beam angles were used in the first plan (plan 1), whereas the selection of beam angle was optimized by beam angle optimization algorithm in Varian Eclipse treatment planning system for the same number of beams in the second plan (plan 2). Two plans were designed for each patient with the same dose-volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and total MU were compared. Results: For conformity and homogeneity in PTV, no statistically differences were observed in the two plans. For the mean dose in bladder, plan 2 were significantly lower than plan 1(p<0.05). No statistically significant differences were observed between two plans for the mean doses in rectum, left and right femur heads. Compared with plan1, the average monitor units reduced 16% in plan 2. Conclusion: The IMRT plan based on beam angle optimization for cervical cancer could reduce the dose delivered to bladder and also reduce MU. Therefore there were some dosimetric advantages in the IMRT plan with beam angle optimization for cervical cancer.

To prospectively compare volumetric intensity-modulated arc therapy (VMAT) and conventional intensity-modulated radiation therapy (IMRT) in coverage of planning target volumes and avoidance of multiple organs at risk (OARs) in patients undergoing definitive chemoradiotherapy for advanced (stage III or IV) squamous cell cancer of the head and neck. Computed tomography scans of 20 patients with advanced tumors of the larynx, naso-, oro- and hypopharynx were prospectively planned using IMRT (7 field) and VMAT using two arcs. Calculated doses to planning target volume (PTV) and OAR were compared between IMRT and VMAT plans. Dose-volume histograms (DVH) were utilized to obtain calculated doses to PTV and OAR, including parotids, cochlea, spinal cord, brainstem, anterior tongue, pituitary and brachial plexus. DVH's for all structures were compared between IMRT and VMAT plans. In addition the plans were compared for dose conformity and homogeneity. The final treatment plan was chosen by the treating radiation oncologist. VMAT was chosen as the ultimate plan in 18 of 20 patients (90%) because the plans were thought to be otherwise clinically equivalent. The IMRT plan was chosen in 2 of 20 patients because the VMAT plan produced concentric irradiation of the cord which was not overcome even with an avoidance structure. For all patients, VMAT plans had a lower number of average monitor units on average (MU = 542.85) than IMRT plans (MU = 1612.58) (P < 0.001). Using the conformity index (CI), defined as the 95% isodose volume divided by the PTV, the IMRT plan was more conformal with a lower conformity index (CI = 1.61) than the VMAT plan (CI = 2.00) (P = 0.003). Dose homogeneity, as measured by average standard deviation of dose distribution over the PTV, was not different with VMAT (1.45 Gy) or IMRT (1.73 Gy) (P = 0.069). There were no differences in sparing organs at risk. In this prospective study, VMAT plans were chosen over IMRT 90% of the time. Compared to IMRT, VMAT plans used only one third of the MUs, had shorter treatment times, and similar sparing of OAR. Overall, VMAT provided similar dose homogeneity but less conformity in PTV irradiation compared to IMRT. This difference in conformity was not clinically significant.

Objective To compare the treatment effects,dosimetry,and toxicities to organs at risk of intensity-modulated radiation therapy (IMRT) and 3-dimentional conformal radiotherapy (3DCRT) plans for cervical carcinoma patients with recurrence and metastasis. Methods 62 cervical carcinoma patients with recurrence and metastasis were analyzed retrospectively, and divided into two groups including intensitymodulated radiation therapy group (n=29) and 3-dimentional conformal radiotherapy group (n=32).Patients were performed with 6 MV-X ray.The regimen was 1.8-2.2 Gy/f,1 f/d,18-33 times in total.Prescribed dose was 40-60 Gy and median dose was 52.8 Gy. At the same time for the IMRT group 29 cases were performed with 3DCRT, which was designed using the same prescribed dose to compare radiation dose distributed in organs at risk (OAR).Results The maximum dose of the two plans showed that bladder and small intestine in IMRT plans were lower than that in 3DCRT (P＜0.05), showing the IMRT's protective advantage. The maximum dose of PTV in IMRT plans were significantly higher than 3DCRT (P＜0.05). In the group of IMRT plans, the overall 1-,2-,and 3-year survival rates were 65.5 ％(19/29), 42.1％(8/19), and 25.0 ％(2/8),respectively,the median survival time was 19 months,of 28 deaths,21 patients died of tumor progression,7 patients died of distant metastases.In the group of 3DCRT plans,the overall 1-,2-,and 3-year survival rates were 60.6 ％(20/33),35.0 ％(7/20),and 14.3 ％(1/7),respectively,the median survival time was 17 months,of 32 deaths, 24 patients died of tumor progression, 8 patients died of distant metastasis. There were no significant differences in overall 1-, 2-, and 3-year survival rates between the two groups (P＞0.05). The incidence rate of toxicity in the IMRT plans was significantly lower than that in the 3DCRT plans, especially for patients with Ⅰ level and Ⅱ level.Conclusion The treatment effects of the IMRT plans are better than the 3DCRT plans for cervical carcinoma patients with recurrence and metastasis. IMRT plans can improve radiation dose in tumors and reduce the dose distributed in normal issue and reduce the incidence of the side effect. Key words: Uterine cervical neoplasms; Recurrence; Neoplasm metastasis; Radiotherapy,intensity-modulated; Radiotherapy, conformal

Image Guided Radiation Therapy for Prostate IMRT: Rectum Volume Changes and Dosimetric Considerations

Purpose:To evaluate the dosimetric characteristics of intensity‐modulated radiotherapy (IMRT) treatment plan with beam angle optimization.Methods:Ten post‐operation patients with cervical cancer were included in this analysis. Two IMRT plans using seven beams were designed in each patient. A standard coplanar equi‐space beam angles were used in the first plan (plan 1), whereas the selection of beam angle was optimized by beam angle optimization algorithm in Varian Eclipse treatment planning system for the same number of beams in the second plan (plan 2). Two plans were designed for each patient with the same dose‐volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and total MU were compared.Results:For conformity and homogeneity in PTV, no statistically differences were observed in the two plans. For the mean dose in bladder, plan 2 were significantly lower than plan 1(p&lt;0.05). No statistically significant differences were observed between two plans for the mean doses in rectum, left and right femur heads. Compared with plan1, the average monitor units reduced 16% in plan 2.Conclusion:The IMRT plan based on beam angle optimization for cervical cancer could reduce the dose delivered to bladder and also reduce MU. Therefore there were some dosimetric advantages in the IMRT plan with beam angle optimization for cervical cancer.

NTCP modeling analysis of acute hematologic toxicity in whole pelvic radiation therapy for gynecologic malignancies – A dosimetric comparison of IMRT and spot-scanning proton therapy (SSPT)

Correlation of Integral Dose, White Blood Cell Counts, and Radiation Therapy Techniques for Head and Neck Cancer Patients Under Radiation Therapy

A Treatment Planning System for Intensity-Modulated Small Animal Radiotherapy Realized Using an Existing Movable Rectangular Collimator

Feasibility of dose escalation using intensity-modulated radiotherapy in posthysterectomy cervical carcinoma

&lt;p&gt;&lt;strong&gt;Purpose: &lt;/strong&gt;The purpose of this study is to analyze and compare the dosimetric parameters of three dimensional conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT) in selected non-small cell lung cancer (NSCLC) cases. &lt;strong&gt;&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;Ten patients with inoperable NSCLC were selected for this study. The 3DCRT and IMRT plans were generated for all patients following Radiation Therapy Oncology Group (RTOG) guidelines. Generated plans were then compared on the basis of planning target volume (PTV) coverage, dose delivered to organs at risk, homogeneity index (HI), and conformity index (CI) for the prescribed dose (PD) of 50 Gy in 25 fractions.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;The mean D&lt;sub&gt;95 &lt;/sub&gt;and D&lt;sub&gt;99 &lt;/sub&gt;(dose to the 95% and 99% volume) for the PTV were found better in the 3DCRT plans compared to the ones in the IMRT plans. On an average, the volume receiving 20 Gy (V&lt;sub&gt;20&lt;/sub&gt;) of contralateral lung was 2.91% and 3.03% in the 3DCRT and IMRT plans, respectively. The D&lt;sub&gt;mean&lt;/sub&gt; of contralateral lung was 3.17 Gy (3DCRT) versus 4.2 Gy (IMRT), whereas the D&lt;sub&gt;mean&lt;/sub&gt; of ipsilateral lung was 12.69 Gy (3DCRT) and 13.82 Gy (IMRT). The V&lt;sub&gt;20&lt;/sub&gt; of ipsilateral lung was found to be slightly lower in the 3DCRT (25.67%) when compared to the IMRT (30.50%). The dose to the heart was comparable in the 3DCRT and IMRT plans (mean dose: 4.42 Gy versus 4.48 Gy; D&lt;sub&gt;33&lt;/sub&gt;: 3.77 Gy versus and 4.02 Gy). For the spinal cord, the D&lt;sub&gt;max &lt;/sub&gt;was found to be lower in the 3DCRT plans (18.40 Gy) when compared to the IMRT plans (25.49 Gy). The HI was 1.08 versus 1.41 in the 3DCRT and IMRT plans, respectively. The CI was identical (1.67) in both sets of plans.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusion: &lt;/strong&gt;Based on the results of this study, the PTV coverage was found to be slightly better in the 3DCRT plans when compared to the one in the IMRT plans. On average, the dose to the organs at risk were found to be comparable.&lt;/p&gt;

Purpose: To study the feasibility of adaptive intensity-modulated radiation therapy (IMRT) using field aperture re-optimization on a new CT set showing target volume change and to evaluate its potential clinical benefit. Method and Materials: A lung cancer patient who had a significant change of target volume during treatment with helical tomotherapy and required a plan adaptation was selected for the study. Two CT scans were performed: one was taken before radiotherapy, and the other was taken after 21 treatment fractions. A six-field step-and-shoot IMRT plan was generated on the initial CT and transferred to the second CT after image registration. The MLC segment field apertures and weights were re-optimized using direct machine parameter optimization (DMPO) for 10 iterations in Pinnacle inverse planning system on the second CT set. The dose distributions and dose volume histograms were compared between the original and the adaptive plans for both helical tomotherapy and the six-field IMRT plan to evaluate the potential benefit of adaptation. The method is also applied to a clinical case by propagating contours from planning CT to daily MVCTs and calculating cumulative dose distributions based on a deformable model using both non-adapted and daily-adapted IMRT plans. Results: Both the adaptive helical tomotherapy and six-field IMRT plans give dose distributions that yield better dose coverage of target volumes and spare more healthy lung tissue compared to the original plans for the clinical case studied. Re-optimization of the six-field step-and-shoot IMRT plan only required 5 minutes using DMPO. The time required for the whole IMRT adaptation process including contour propagation will also be reported. Conclusion: An IMRT plan can be adapted very quickly using field aperture re-optimization based on the new CT images with contours adjusted to reflect changes in gross tumor volume and sensitive structures.

Radiotherapy of the posterior fossa for medulloblastoma treatment can induce ototoxicity, especially when combined with cisplatin chemotherapy. Sensorineural hearing loss can be severe enough to cause permanent disability, which may compromise cognitive development in paediatric patients. This study evaluates the sparing of the cochlea in conventional radiotherapy, three-dimensional conformal radiotherapy (3D-CRT), and intensity-modulated radiotherapy (IMRT). CT scans of three patients were used to plan posterior fossa radiotherapy using coplanar beam arrangements. The posterior fossa and the cochlea were contoured as well as other organs-at-risk (non-posterior fossa brain, lenses, optic nerves, pituitary and cervical spinal cord). Three treatment plans were compared: conventional two-dimensional treatment (parallel-opposed lateral pair); 3D-CRT (two wedged posterior oblique fields); and a four-field coplanar IMRT plan. 3D-CRT and IMRT reduced cochlear doses to less than 70% of the mean target dose. These plans also reduced dose to the non-posterior fossa brain and cervical spinal cord. IMRT showed no advantage over 3D-CRT in sparing the optic nerves and lenses, compared with 3D-CRT. Normal tissue doses were higher in both conformal techniques than in the IMRT plans. Conformal techniques reduced the dose to the cochlea, non-posterior fossa brain and cervical spinal cord. The small size and proximity to the planning target volume (PTV) of the cochlea limited the effectiveness of the IMRT plan. Coplanar 3D-CRT was judged superior to coplanar IMRT, particularly in children, because it achieved adequate sparing of the cochlea and anterior cranial structures, such as the lenses and optic nerves, without compromising the dose to the posterior fossa.

Purpose: To perform efficient quality control (QC) of intensity‐modulated radiotherapy (IMRT) plans of gynecological (GYN) cancer in clinical trials. Methods: Plan QC is a necessary component in clinical trials that requires much time and effort. IMRT plans from the INTERTECC clinical trial for the treatment of intact cervix cancer patients have been used to evaluate a plan QC tool. The CT image, organ and target contours, and the clinical IMRT plan were imported into a GPU‐based treatment re‐planning system that was originally designed to perform online adaptive radiotherapy. The clinical plan was considered as the reference plan and the re‐planning system automatically created a new plan. The objective for re‐planning was to reduce dose of organs‐at‐risk (OARs) and to get a more uniform dose in the PTV with respect to the reference plan. After performing automatic re‐planning on each plan, we compared the new and the reference DVH curves in terms of the treatment planning goals specified in the clinical trial protocol. Results: Data from 12 patients was retrospectively analyzed. Results showed that DVH curves of the automatic plan satisfy the specified clinical constraints more frequently than the actual clinical plans. DVH for the PTV of the new plan was in most cases similar to the clinical plans, indicating good quality PTV coverage. In 2 out of the 12 cases the QC tool could achieve a PTV hotspots reduction of 11% and 10% respectively. For most patients, lower doses in OARs were achieved after re‐planning, except in those plans where there was overlap between OARs and PTV. Re‐planning takes less than 1 min for each case. Conclusion: We have proved the feasibility of efficient IMRT plan QC in clinical trials for patients with GYN cancer. Varian Medical Systems through a Master Research Agreement