Linear array measurements of enhanced dynamic wedge and treatment planning system (TPS) calculation for 15 MV photon beam and comparison with electronic portal imaging device (EPID) measurements

Left breast radiotherapy - the impact of heart and lad doses to cardiovascular diseases developed eight years after treatment

Introduction/Objective. Left breast cancer patients undergoing radiotherapy are at higher risk of cardiovascular diseases (CVD), as a partial volume of the heart is anatomically close to target volume. This may cause cardiovascular diseases in the years following cancer treatment. The aim of this work was to develop a scoring system which identifies patients with increased risk of development of cardiovascular diseases, as consequence of left breast irradiation. Methods. The patients followed up in this study were treated during 2009. Eight years later, they were invited to participate in a study where they underwent a cardiology evaluation. Their current condition was statistically correlated to the doses received by their heart and left anterior descendant (LAD) artery. Results. Out of 114 patients, thirty-one women were evaluable for cardiology assessment. Out of these 31 subjects, six women were with a history of CVD before cancer treatment. Four women never developed any kind of heart associated disease, while in the other 27, newly onset CVD were diagnosed ranging from hypertension to myocardial infarction, strongly positively correlated to doses to heart and LAD (p = 0.003). Severity of developed cardiovascular toxicity was formulated through the correlation of mean heart and mean LAD doses with cardiovascular diseases developed in form of the scoring system. Conclusion. The doses to critical organs depend on patient anatomy and technique of irradiation. The cardiovascular complications are proven as consequence of radiotherapy. Scoring system based on doses received by heart and LAD is reliable tool in predicting CVD.

Dosimetric end-to-end tests in a national audit of 3D conformal radiotherapy

BACKGROUND AND PURPOSE

Independent dosimetry audits improve quality and safety of radiation therapy. This work reports on design and findings of a comprehensive 3D conformal radiotherapy (3D-CRT) Level III audit.

MATERIALS AND METHODS

The audit was conducted as onsite audit using an anthropomorphic thorax phantom in an end-to-end test by the Australian Clinical Dosimetry Service (ACDS). Absolute dose point measurements were performed with Farmer-type ionization chambers. The audited treatment plans included open and half blocked fields, wedges and lung inhomogeneities. Audit results were determined as Pass Optimal Level (deviations within 3.3%), Pass Action Level (greater than 3.3% but within 5%) and Out of Tolerance (beyond 5%), as well as Reported Not Scored (RNS). The audit has been performed between July 2012 and January 2018 on 94 occasions, covering approximately 90% of all Australian facilities.

RESULTS

The audit pass rate was 87% (53% optimal). Fifty recommendations were given, mainly related to planning system commissioning. Dose overestimation behind low density inhomogeneities by the analytical anisotropic algorithm (AAA) was identified across facilities and found to extend to beam setups which resemble a typical breast cancer treatment beam placement. RNS measurements inside lung showed a variation in the opposite direction: AAA under-dosed a target beyond lung and over-dosed the lung upstream and downstream of the target. Results also highlighted shortcomings of some superposition and convolution algorithms in modelling large angle wedges.

CONCLUSIONS

This audit showed that 3D-CRT dosimetry audits remain relevant and can identify fundamental global and local problems that also affect advanced treatments.

Verification of quality parameters for portal images in radiotherapy

Background

The purpose of the study was to verify different values of quality parameters of portal images in radiotherapy.

Materials and methods

We investigated image qualities of different field verification systems. Four EPIDs (Siemens OptiVue500aSi^®, Siemens BeamView Plus^®, Elekta iView^® and Varian PortalVision™) were investigated with the PTW EPID QC PHANTOM^® and compared with two portal film systems (Kodak X-OMAT^® cassette with Kodak X-OMAT V^® film and Kodak EC-L Lightweight^® cassette with Kodak Portal Localisation ReadyPack^® film).

Results

A comparison of the f50 and f25 values of the modulation transfer functions (MTFs) belonging to each of the systems revealed that the amorphous silicon EPIDs provided a slightly better high contrast resolution than the Kodak Portal Localisation ReadyPack^® film with the EC-L Lightweight^® cassette. The Kodak X-OMAT V^® film gave a poor low contrast resolution: from the existing 27 holes only 9 were detectable.

Conclusions

On the base of physical characteristics, measured in this work, the authors suggest the use of amorphous-silicon EPIDs producing the best image quality. Parameters of the EPIDs with scanning liquid ionisation chamber (SLIC) were very stable. The disadvantage of older versions of EPIDs like SLIC and VEPID is a poor DICOM implementation, and the modulation transfer function (MTF) values (f50 and f25) are less than that of aSi detectors.