Dose Quality Factor Research Articles

Treatment-plan evaluation using the dose quality factor (DQF) for dynamic conformal arc (DCA)-based radiosurgery on patients presenting with an intracranial tumor

The aim of the present study was to find the optimum dynamic conformal arc (DCA)-based radiosurgery conditions for treatment of patients with intracranial tumors. DCA plans were generated on a commercial treatment-planning system (BrainSCAN v.5.31) for various beam-number and gantry-angle combinations by using computed tomography (CT) scans to delineate the planning target volume (PTV) and the organs at risk (OARs). To evaluate planning quality related to the various planning conditions, we analyzed the dose quality factors (DQFs) for 22 patients as a function of the number and the total angle of arcs related to the target volume, which were determined on the basis of patient-specific features. When the total angle of arcs was less than 250°, the DQF values were under 0.98 (worst group). When the total angle of arcs was more than 350 degrees, the DQF values were maximized, and the highest DQF values (best group, DQF > 0.995) occurred in the range between 50 and 120°/cm3 for the total angle/target volume condition. In this optimal range of angle/volume, the asymmetric distribution of the arcs resulted in decreased DQF values. For a relatively large target volume (more than 10 cm3), the DQF values were lower than these for a relatively small target volume (less than 10 cm3). Re-planning results showed that the planning quality could be improved using optimized planning conditions. We expect that this study will provide a basis for the evaluation of various DCA conditions prior to actual planning and treatment.

Comparative planning evaluation of intensity-modulatedradiotherapy techniques for complex lung cancer cases

Background and purpose Lung cancer treatment can be one of the most challenging fields in radiotherapy. The aim of the present study was to compare different modalities of radiation delivery based on a balanced scoring scheme for target coverage and normal tissue avoidance. Patients and methods Treatment plans were developed for 15 patients with stage III inoperable non-small cell lung cancer using 3D conformal technique and intensity-modulated radiotherapy (IMRT). Elective nodal irradiation was included for all cases to create the most challenging scenarios with large target volumes. A 2 cm margin was used around the gross tumour volume (GTV) to generate PTV2 and 1 cm margin around elective nodes for PTV1 resulting in PTV1 volumes larger than 1000 cm 3 in 13 of the 15 patients. 3D conformal and IMRT plans were generated on a commercial treatment planning system (TheraPlan Plus, Nucletron) with various combinations of beam energies and gantry angles. A ‘dose quality factor’ (DQF) was introduced to correlate the plan quality with patient specific parameters. Results A good correlation was found between the quality of the plans and the overlap between PTV1 and lungs. The patient feature factor (PFF), which is a product of several pertinent characteristics, was introduced to facilitate the choice of a particular technique for a particular patient. Conclusions This approach may allow the evaluation of different treatment options prior to actual planning, subject to validation in larger prospective data sets.

Sci‐AM2 Sat ‐ 09: Towards objective plan comparisons in radiation therapy

In recent years, various novel techniques for radiation treatment of cancer patients have been introduced to clinical practice: intensity‐modulated radiation therapy (IMRT), intensity‐modulated arc therapy (IMAT), helical tomotherapy (HT), light ions irradiation, etc. Such variety of instrumentation possibilities requires some initial comparative assessment of which particular technique would be the most beneficial for a given patient case. In clinical practice a balanced trade‐off between homogeneous and sufficient tumour irradiation and maximal sparing of sensitive structures is needed. A dose quality factor (DQF) was introduced to evaluate the plan quality for different treatment techniques based on realistic clinical requirements for target and organs at risk irradiation. A correlation between plan quality quantified by DQF with some set of patient specific features characterised by patient feature factor (PFF) is analysed in a comparative planning studies for 15 patients with stage III inoperable non‐small cell lung cancer using 3D conformal technique, IMRT and HT. For this set of patients, PFF is chosen as the product of three patient characteristics: the target complexity parameter, overlap between target and lungs, and the ratio between involved and non‐involved lungs. Future work would require validation in larger patient data sets, other disease sites and weighting of different factors of the PFF. This approach can help to select the most beneficial treatment technique prior to actual planning.

Planning evaluation of radiotherapy for complex lung cancer cases using helical tomotherapy

Lung cancer treatment is one of the most challenging fields in radiotherapy. The aim of the present study was to investigate what role helical tomotherapy (HT), a novel approach to the delivery of highly conformal dose distributions using intensity-modulated radiation fan beams, can play in difficult cases with large target volumes typical for many of these patients. Tomotherapy plans were developed for 15 patients with stage III inoperable non-small-cell lung cancer. While not necessarily clinically indicated, elective nodal irradiation was included for all cases to create the most challenging scenarios with large target volumes. A 2 cm margin was used around the gross tumour volume (GTV) to generate primary planning target volume (PTV2) and 1 cm margin around elective nodes for secondary planning target volume (PTV1) resulting in PTV1 volumes larger than 1000 cm3 in 13 of the 15 patients. Tomotherapy plans were created using an inverse treatment planning system (TomoTherapy Inc.) based on superposition/convolution dose calculation for a fan beam thickness of 25 mm and a pitch factor between 0.3 and 0.8. For comparison, plans were created using an intensity-modulated radiation therapy (IMRT) approach planned on a commercial treatment planning system (TheraplanPlus, Nucletron). Tomotherapy delivery times for the large target volumes were estimated to be between 4 and 19 min. Using a prescribed dose of 60 Gy to PTV2 and 46 Gy to PTV1, the mean lung dose was 23.8 ± 4.6 Gy. A ‘dose quality factor’ was introduced to correlate the plan outcome with patient specific parameters. A good correlation was found between the quality of the HT plans and the IMRT plans with HT being slightly better in most cases. The overlap between lung and PTV was found to be a good indicator of plan quality for HT. The mean lung dose was found to increase by approximately 0.9 Gy per percent overlap volume. Helical tomotherapy planning resulted in highly conformal dose distributions. It allowed easy achievement of two different dose levels in the target simultaneously. As the overlap between PTV and lung volume is a major predictor of mean lung dose, future work will be directed to control of margins. Work is underway to investigate the possibility of breath-hold techniques for tomotherapy delivery to facilitate this aim.