scholarly journals How Sensitive is Mass-Based Inverse Optimization to IMRT Delivery Parameters?

2021 ◽  
Vol 8 (2) ◽  
Author(s):  
De Ornelas M ◽  
◽  
Mihaylov IB ◽  
Keyword(s):  
Head And Neck ◽  
Energy Optimization ◽  
Optimization Methods ◽  
Inverse Optimization ◽  
Dose Increase ◽  
Dose Volume ◽  
Step And Shoot ◽  
Two Parameters ◽  
Optimization Schemes ◽  
Number Of Segments

Purpose: To determine the sensitivity of changes to IMRT delivery parameters for mass-based optimization schemes: Dose-Mass- (DM) and Energy-based (Energy), compared to Dose-Volume-based (DV) optimization. Methods: Twelve Head-and-Neck (HN) and twelve lung cases were retrospectively optimized using DM and Energy optimization. In both optimization approaches nine equidistant, split beams were used for step-and-shoot deliverable IMRT. Changes to two parameters were investigated: the number of IMRT segments (5 and 10 per beam) and the minimum allowed segment area (2 and 6 cm²). Plans were normalized such that 95% of the PTV received the same dose. Dose Indices (DIs) were used for evaluation. For the lung cases, DIs included: 1%_cord, 33%_heart, 20% and 30%_both-lungs, and 50%_ esophagus. In the HN cases: 1%_cord, 1%_brainstem, left/right parotids_50%, 50%_larynx, and 50%_esophagus. Results: The lung cases demonstrated that the Energy plans were more sensitive to segment area; changing the segment area resulted in a statistically significant dose increase for 1%_cord, 30%_both-lungs and 50%_esophagus. Changes to the number of segments yielded on average statistically significant differences in dose to 1%_cord in Energy plans, 50%_esophagus in DM plans, and 20%_both-lungs in DV plans. When the segment area was changed, the HN cases yielded statistically significant differences in doses to 1%_cord, 1%_ brainstem, 50%_left and right parotids, and 50%_larynx for the Energy plans and 50%_larynx for DM plans. Moreover, changing the number of segments resulted in significant dose decrease for 50%_parotids and 50%_esophagus for the Energy plans and 50%_larynx for DV plans. Conclusions: This study showed that both lung and HN Energy plans exhibit larger sensitivity than DV and DM plans to changing IMRT delivery parameters, especially when increasing the minimum segment area rather than with varying the number of segments.

scholarly journals Adaptive radiotherapy for head and neck cancer reduces the requirement for rescans during treatment due to spinal cord dose

2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Louise Belshaw ◽  
Christina E. Agnew ◽  
Denise M. Irvine ◽  
Keith P. Rooney ◽  
Conor K. McGarry
Keyword(s):  
Spinal Cord ◽  
Head And Neck ◽  
Treatment Plan ◽  
Volumetric Modulated Arc Therapy ◽  
Target Volume ◽  
Adaptive Radiotherapy ◽  
Dose Increase ◽  
Volume Changes ◽  
Dose Volume Histograms ◽  
Dose Volume

Abstract Background Patients treated with radiotherapy for head and neck (H&N) cancer often experience anatomical changes. The potential compromises to Planning Target Volume (PTV) coverage or Organ at Risk (OAR) sparing has prompted the use of adaptive radiotherapy (ART) for these patients. However, implementation of ART is time and resource intensive. This study seeks to define a clinical trigger for H&N re-plans based on spinal cord safety using kV Cone-Beam Computed Tomography (CBCT) verification imaging, in order to best balance clinical benefit with additional workload. Methods Thirty-one H&N patients treated with Volumetric Modulated Arc Therapy (VMAT) who had a rescan CT (rCT) during treatment were included in this study. Contour volume changes between the planning CT (pCT) and rCT were determined. The original treatment plan was calculated on the pCT, CBCT prior to the rCT, pCT deformed to the anatomy of the CBCT (dCT), and rCT (considered the gold standard). The dose to 0.1 cc (D0.1cc) spinal cord was evaluated from the Dose Volume Histograms (DVHs). Results The median dose increase to D0.1cc between the pCT and rCT was 0.7 Gy (inter-quartile range 0.2–1.9 Gy, p < 0.05). No correlation was found between contour volume changes and the spinal cord dose increase. Three patients exhibited an increase of 7.0–7.2 Gy to D0.1cc, resulting in a re-plan; these patients were correctly identified using calculations on the CBCT/dCT. Conclusions An adaptive re-plan can be triggered using spinal cord doses calculated on the CBCT/dCT. Implementing this trigger can reduce patient appointments and radiation dose by eliminating up to 90% of additional un-necessary CT scans, reducing the workload for radiographers, physicists, dosimetrists, and clinicians.

COMBINED IRRADIATION OF PELVIS AND INGUINALNODAL REGIONS USING MODIFIED SEGMENTAL BOOST TECHNIQUE: A PROSPECTIVE STUDY.

2021 ◽  
pp. 71-75
Author(s):  
Sivaraj Kumar. S ◽  
Saravanan. S ◽  
Anbarasi. K
Keyword(s):  
Radiation Treatment ◽  
Target Coverage ◽  
Treatment Techniques ◽  
Dose Volume ◽  
Dosimetric Study ◽  
Dose Homogeneity ◽  
Step And Shoot ◽  
Imrt Planning ◽  
Different Depths ◽  
A Prospective Study

AIM: To describe a novel Modied Segmental Boost Technique (MSBT) for combined irradiation of pelvis and inguinal nodes and to compare the dosimetry of the new method with that of other traditional methods of radiation treatment and IMRT. Total 30 patients who required combined irradiation of pelvis and inguinal regi METHODS AND MATERIALS: ons are included in our study to illustrate details and advantages of MSBT. Conventional photons with enface electrons design was created rst with two opposing parallel elds and four eld box. MSBT plans are generated and patient is treated with this technique to TD 45-50Gy for 5-6 weeks duration. A step-and-shoot inverse IMRT planning was subsequently generated. For dosimetric comparison, these treatment techniques were evaluated by dose-volume histogram (DVH) of PTV and OARs. Dose proles at different depths from each treatment planning were generated for comparison. Comparing the modied segmental boost technique with conventional two oppos RESULTS: ing and four eld box technique, we have found out that the target coverage, dose homogeneity index (DHI) and femoral head sparing is superior in modied segmental boost technique compared to other conventional approaches. And also the patients had better clinical response of both primary and the nodes with minimal skin morbidity when compared with conventionally treated patients data. DHI and target coverage of MSBT was comparable with that of IMRT. CONCLUSION: To cover pelvis and inguinal/femoral nodes, MSBT is technically simple to simulate, plan, and execute. Dosimetric study has demonstrated that it achieves comparable PTV coverage compared with other approaches while at the same time signicantly sparing the surrounding OAR .It also has dose homogeneity comparable with IMRT and can be a nearer alternative for IMRT, in centers which are not having the facility and where the patient load is higher.

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