Dataset Information

IMPT versus VMAT for Pelvic Nodal Irradiation in Prostate Cancer: A Dosimetric Comparison.

ABSTRACT: Purpose:To compare dosimetric data of the organs at risk (OARs) and clinical target volumes (CTVs) between intensity-modulated proton therapy (IMPT) and volumetric-modulated arc therapy (VMAT) for patients undergoing prostate and elective, pelvic lymph node radiotherapy in the setting of unfavorable, intermediate and high-risk prostate carcinoma. Methods and Materials:A study of moderately hypofractionated proton therapy (6750 centigray [cGy] in 25 fractions) is in progress for unfavorable, intermediate and high-risk prostate cancer where treatment includes an elective pelvic nodal CTV (4500 cGy in 25 fractions). Ten consecutively accrued patients were the subjects for dose-volume histogram comparison between IMPT and VMAT. Two treatment plans (IMPT and VMAT) were prepared for each patient with predefined planning objectives for target volumes and OARs. The IMPT plans were prepared with 2 lateral beams and VMAT plans with 2 arcs. Results:The CTV coverage was adequate for both plans with 99% of CTVs receiving ??100% of the prescription doses. Mean doses to the bladder, rectum, large bowel, and small bowel were lower with IMPT versus VMAT. Mean femoral head dose was greater with IMPT. The percentage of volumes of rectum receiving ??47.5 Gy, large bowel receiving ? 27.5 Gy, small bowel receiving ??30 Gy, and bladder receiving ??37.5 Gy was less with IMPT versus VMAT, largely because of reduction in the low-dose "bath" associated with VMAT. Conclusions:In the setting of prostate and elective, pelvic nodal radiotherapy for prostate cancer, IMPT can significantly reduce the dose to OARs, in comparison to VMAT, and provide adequate target coverage.

SUBMITTER: Whitaker TJ

PROVIDER: S-EPMC6874187 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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IMPT versus VMAT for Pelvic Nodal Irradiation in Prostate Cancer: A Dosimetric Comparison.

Whitaker Thomas J TJ Routman David M DM Schultz Heather H Harmsen William S WS Corbin Kimberly S KS Wong William W WW Choo Richard R

International journal of particle therapy 20190321 3

<h4>Purpose</h4>To compare dosimetric data of the organs at risk (OARs) and clinical target volumes (CTVs) between intensity-modulated proton therapy (IMPT) and volumetric-modulated arc therapy (VMAT) for patients undergoing prostate and elective, pelvic lymph node radiotherapy in the setting of unfavorable, intermediate and high-risk prostate carcinoma.<h4>Methods and materials</h4>A study of moderately hypofractionated proton therapy (6750 centigray [cGy] in 25 fractions) is in progress for un ...[more]

PMID: 31788504

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Project description:Volumetric-modulated arc therapy (VMAT) is emerging as a leading technology in treating early-stage, non-small cell lung cancer (NSCLC) with stereotactic ablative radiotherapy (SABR). However, two other modalities capable of deliver-ing intensity-modulated radiation therapy (IMRT) include fixed-beam and helical TomoTherapy (HT). This study aims to provide an extensive dosimetric compari-son among these various IMRT techniques for treating early-stage NSCLC with SABR. Ten early-stage NSCLC patients were retrospectively optimized using three fixed-beam techniques via nine to eleven beams (high and low modulation step-and-shoot (SS), and sliding window (SW)), two VMAT techniques via two partial arcs (SmartArc (SA) and RapidArc (RA)), and three HT techniques via three different fan beam widths (1 cm, 2.5 cm, and 5 cm) for 80 plans total. Fixed-beam and VMAT plans were generated using flattening filter-free beams. SS and SA, HT treatment plans, and SW and RA were optimized using Pinnacle v9.1, Tomoplan v.3.1.1, and Eclipse (Acuros XB v11.3 algorithm), respectively. Dose-volume histogram statistics, dose conformality, and treatment delivery efficiency were analyzed. VMAT treatment plans achieved significantly lower values for contralat-eral lung V5Gy (p ? 0.05) compared to the HT plans, and significantly lower mean lung dose (p < 0.006) compared to HT 5 cm treatment plans. In the comparison between the VMAT techniques, a significant reduction in the total monitor units (p = 0.05) was found in the SA plans, while a significant decrease was observed in the dose falloff parameter, D2cm, (p = 0.05), for the RA treatments. The maximum cord dose was significantly reduced (p = 0.017) in grouped RA&SA plans com-pared to SS. Estimated treatment time was significantly higher for HT and fixed-beam plans compared to RA&SA (p < 0.001). Although, a significant difference was not observed in the RA vs. SA (p = 0.393). RA&SA outperformed HT in all parameters measured. Despite an increase in dose to the heart and bronchus, this study demonstrates that VMAT is dosimetrically advantageous in treating early-stage NSCLC with SABR compared to fixed-beam, while providing significantly shorter treatment times.

Project description:BackgroundTraditional clinical target volume (CTV) definition for pelvic radiotherapy in prostate cancer consists of large volumes being treated with homogeneous doses without fully utilizing information on the probability of microscopic involvement to guide target volume design and prescription dose distribution.MethodsWe analyzed patterns of nodal involvement in 75 patients that received RT for pelvic and paraaortic lymph node metastases (LNs) from prostate cancer in regard to the new NRG-CTV recommendation. Non-rigid registration-based LN mapping and weighted three-dimensional kernel density estimation were used to visualize the average probability distribution for nodal metastases. As independent approach, the mean relative proportion of LNs observed for each level was determined manually and NRG and non-NRG levels were evaluated for frequency of involvement. Computer-automated distance measurements were used to compare LN distances in individual patients to the spatial proximity of nodal metastases at a cohort level.Results34.7% of patients had pelvic LNs outside NRG-consensus, of which perirectal was most common (25.3% of all patients) followed by left common iliac nodes near the left psoas major (6.7%). A substantial portion of patients (13.3%) had nodes at the posterior edge of the NRG obturator level. Observer-independent mapping consistently visualized high-probability hotspots outside NRG-consensus in the perirectal and left common iliac regions. Affected nodes in individual patients occurred in highly significantly closer proximity than at cohort-level (mean distance, 6.6 cm vs. 8.7 cm, p < 0.001).ConclusionsBased on this analysis, the common iliac level should extend to the left psoas major and obturator levels should extend posteriorly 5 mm beyond the obturator internus. Incomplete coverage by the NRG-consensus was mostly because of perirectal involvement. We introduce three-dimensional kernel density estimation after non-rigid registration-based mapping for the analysis of recurrence data in radiotherapy. This technique provides an estimate of the underlying probability distribution of nodal involvement and may help in addressing institution- or subgroup-specific differences. Nodal metastases in individual patients occurred in highly significantly closer proximity than at a cohort-level, which supports that personalized target volumes could be reduced in size compared to a "one-size-fits-all" approach and is an important basis for further investigation into individualized field designs.

Project description:To cover the microscopic tumor spread in squamous cell carcinoma of the esophagus (SCC), longitudinal margins of 3-4 cm are used for radiotherapy (RT) protocols. However, smaller margins of 2-3 cm might be reasonable when advanced diagnostic imaging is integrated into target volume delineation. Purpose of this study was to compare the dose distribution and deposition to the organs at risk (OAR) for different longitudinal margins using a DVH- and NTCP-based approach.Ten patients with SCC of the middle or lower third were retrospectively selected. Three planning target volumes (PTV) with longitudinal margins of 4 cm, 3 cm and 2 cm and an axial margin of 1.5 cm to the gross target volume (GTV) were defined for each patient. For each PTV two treatment plans with total doses of 41.4 Gy (neoadjuvant treatment) and 50.4 Gy (definite treatment) were calculated. Dose to the lungs, heart, myelon and liver were then evaluated and compared between different PTVs.When using a longitudinal margin of 3 cm instead of 4 cm, all dose parameters (Dmin, Dmean, Dmedian and V5-V35), except Dmax could be significantly reduced for the lungs. Regarding the heart, a significant reduction was seen for Dmean and V5, but not for Dmin, Dmax, Dmedian and V10-V35. When comparing a longitudinal margin of 4 cm to a longitudinal margin of 2 cm, a significant difference was calculated for Dmin, Dmean, Dmedian and V5-V35 of the lungs and for Dmax, Dmean and V5-V35 of the heart. Nevertheless, no difference was seen for median heart dose. An additional dose reduction for V10 of the heart was achieved for definite treatment plans when using a longitudinal margin of 3 cm. The NTCP-based risk of pneumonitis was significantly reduced by a margin reduction to 2 cm for neoadjuvant and definite treatment plans.Reduction of longitudinal margins from 4 cm to 3 cm can significantly reduce the dose to lungs and Dmean of the heart. Despite clinical benefit and oncologic outcome remain unclear, reduction of the longitudinal margins might provide the opportunity to reduce side effects of chemoradiation (CRT) for SCC in upcoming studies.

Project description:BackgroundInter-fractional variation in urinary bladder volumes during the course of radiotherapy (RT) for prostate cancer causes deviations between planned and delivered doses. This study compared planned versus daily cone-beam CT (CBCT)-based spatial bladder dose distributions, for prostate cancer patients receiving local prostate treatment (local treatment) versus prostate including pelvic lymph node irradiation (pelvic treatment).Material and methodsTwenty-seven patients (N = 15 local treatment; N = 12 pelvic treatment) were treated using daily image-guided RT (1.8 Gy@43-45 fx), adhering to a full bladder/empty rectum protocol. For each patient, 9-10 CBCTs were registered to the planning CT, using the clinically applied translations. The urinary bladder was manually segmented on each CBCT, 3 mm inner shells were generated, and semi and quadrant sectors were created using axial/coronal cuts. Planned and delivered DVH metrics were compared across patients and between the two groups of treatment (t-test, p < .05; Holm-Bonferroni correction). Associations between bladder volume variations and the dose-volume histograms (DVH) of the bladder and its sectors were evaluated (Spearman's rank correlation coefficient, rs).ResultsBladder volumes varied considerably during RT (coefficient of variation: 16-58%). The population-averaged planned and delivered DVH metrics were not significantly different at any dose level. Larger treatment bladder volumes resulted in increased absolute volume of the posterior/inferior bladder sector receiving intermediate-high doses, in both groups. The superior bladder sector received less dose with larger bladder volumes for local treatments (rs ± SD: -0.47 ± 0.32), but larger doses for pelvic treatments (rs ± SD: 0.74 ± 0.24).ConclusionsSubstantial bladder volume changes during the treatment course occurred even though patients were treated under a full bladder/daily image-guided protocol. Larger bladder volumes resulted in less bladder wall spared at the posterior-inferior sector, regardless the treatment received. Contrary, larger bladder volumes meant larger delivered doses to the superior bladder sector for pelvic RT but smaller doses for local treatments.

Dataset Information

IMPT versus VMAT for Pelvic Nodal Irradiation in Prostate Cancer: A Dosimetric Comparison.

Publications

IMPT versus VMAT for Pelvic Nodal Irradiation in Prostate Cancer: A Dosimetric Comparison.

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