A study of the dosimetric characteristics between different fixed-field IMRT and VMAT in early-stage primary mediastinal B-cell lymphoma

An institutional review: dosimetry comparison between simultaneous integrated boost IMRT and VMAT for prostate cancer

Purpose:

A comparative study was performed about the plan parameters and quality indices between volumetric arc therapy (VMAT) and intensity-modulated radiotherapy (IMRT) for the treatment of high-risk prostate cancer patients. The aim of this retrospective study was to compare the two methods of external beam radiotherapy IMRT and VMAT in terms of plan quality and efficacy.

Material and method:

Fifteen high-risk prostate patients were planned for radiotherapy using 6 MV photon. Three dose levels were contoured having Planning Tumour Volume 1 (PTV1 = 48 Gy), Planning Tumour Volume 2 (PTV2 = 57.6 Gy) and Planning Tumour Volume 3 (PTV3 = 60 Gy). Setup margins were given using the CHIP trial method. The prescribed PTV3 dose was 60 Gy in 20 fractions which is biologically equivalent to 74 Gy in 37 fractions using α/β = 3. In case of IMRT, seven fixed beam angles 30, 60, 105, 180, 255, 300 and 330 were used and the dose was optimised using the sliding window method. In case of rapid arc technique, one or two full arcs were used for dose optimisation while keeping all the dose constraints and other planning parameters same used in IMRT. The plan evaluation parameters and Organ at risks (OARs) doses were calculated using a dose volume histogram (DVH).

Results:

The average D2, D5, D95 and PTVmean for PTV3 were 61.22, 61.13, 58.12, 60.00 Gy and 62.41 62.24 59.53 61.12 Gy for IMRT and VMAT, respectively. The averages V60 for bladder and V30 for rectum were 22.81, 25 and 67, 65% for IMRT and VMAT, respectively. The average homogeneity index (HI), conformity index (CI) and gradient index (GI) were 1.04, 1.4833, 14.79 and 1.04, 1.704, 7.89 for IMRT and VMAT, respectively.

Conclusion:

VMAT takes less dose-delivery time and lesser number of monitoring units than IMRT, thus it compensates the intrafractional movements during dose delivery. The Dose GI in VMAT was much better than IMRT. This indicates sharper dose fall off near the normal tissue. No other major differences were observed in terms of plan evaluation parameters between IMRT and VMAT techniques. So, we conclude that VMAT technique is more efficient than IMRT in terms of plan quality and dose delivery.

A Systematic Review on Intensity Modulated Radiation Therapy for Mediastinal Hodgkin's Lymphoma

BACKGROUND

Secondary malignant neoplasms (SMNs) and cardiovascular diseases induced by chemotherapy and radiotherapy represent the main cause of excess mortality for early-stage Hodgkin lymphoma patients, especially when the mediastinum is involved. Conformal radiotherapy techniques such as Intensity-Modulated Radiation Therapy (IMRT) could allow a reduction of the dose to the organs-at-risk (OARs) and therefore limit long-term toxicity.

METHODS

We performed a systematic review of the current literature regarding comparisons between IMRT and conventional photon beam radiotherapy, or between different IMRT techniques, for the treatment of mediastinal lymphoma.

RESULTS AND CONCLUSIONS

IMRT allows a substantial reduction of the volumes of OARs exposed to high doses, reducing the risk of long-term toxicity. This benefit is conterbalanced by the increase of volumes receiving low doses, that could potentially increase the risk of SMNs. Treatment planning should be personalized on patient and disease characteristics. Dedicated techniques such as "butterfly" VMAT often provide the best trade-off.

Comparison of treatment plan quality of VMAT for esophageal carcinoma with: flattening filter beam versus flattening filter free beam

Purpose: To investigate the difference in treatment plan quality of volumetric modulated arc treatment (VMAT) for esophageal carcinoma with flattening filter beam (FF) and flattening filter free beam (FFF). Material and methods: A total of fifty-six treatment plans were generated for twenty eight esophageal carcinoma patients with flattening filter beam and flattening filter free beam, using same optimal parameters. The homogeneity index (HI) and conformal index (CI) of targets, and some special points on Dose-Volume Histogram (DVH) curves were used to compare the plan quality. The coverage volumes of 45 Gy, 30 Gy and 20 Gy outside targets (V45Gy, V30Gy and V20Gy ) were used to compare the targets peripheral dose. The MU numbers, measured delivery time and averaged dose rates were used to evaluate the delivery efficiency of treatment plans. Results: A significant decreasing in peripheral dose around targets was found using FFF beams while the dose distributions in targets were equivalent to the plans with FF beams. V45Gy, V30Gy and V20Gy were decreased by 6.46%, 88.18% and 4.40%, respectively. A significant increase in MUs and decrease in treatment time were also found in delivery test. The average MUs was increased by 21.83% and the average treatment time was reduced by down to 11.9%. Conclusions: For esophageal carcinoma, the research showed that the treatment plans with FFF beams could get comparable dose distribution in targets and could significantly reduce the peripheral dose around targets compared to the plans with FF beams.