Photon and Proton Dose Painting Based on Oxygen Distribution - Feasibility Study and Tumour Control Probability Assessment.

Solid tumours may present hypoxic sub-regions of increased radioresistance. Hypoxia quantification requires of clinically implementable, non-invasive and reproducible techniques as positron emission tomography (PET). PET-based dose painting strategies aiming at targeting those sub-regions may be limited by the resolution gap between the PET imaging resolution and the smaller scale at which hypoxia occurs.

Implications of the Harmonization of [F]FDG-PET/CT Imaging for Response Assessment of Treatment in Radiotherapy Planning.

The purpose of this work is to present useful recommendations for the use of [F]FDG-PET/CT imaging in radiotherapy planning and monitoring under different versions of EARL accreditation for harmonization of PET devices. A proof-of-concept experiment designed on an anthropomorphic phantom was carried out to establish the most suitable interpolation methods of the PET images in the different steps of the planning procedure. Based on PET/CT images obtained by using these optimal interpolations for the old EARL accreditation (EARL1) and for the new one (EARL2), the treatment plannings of representative actual clinical cases were calculated, and the clinical implications of the resulting differences were analyzed.

Assessment of the Probability of Tumour Control for Prescribed Doses Based on Imaging of Oxygen Partial Pressure.

In radiotherapy, hypoxia is a known negative factor, occurring especially in solid malignant tumours. Nitroimidazole-based positron emission tomography (PET) tracers, due to their selective binding to hypoxic cells, could be used as surrogates to image and quantify the underlying oxygen distributions in tissues. The spatial resolution of a clinical PET image, however, is much larger than the cellular spatial scale where hypoxia occurs.

Evolution of the hypoxic compartment on sequential oxygen partial pressure maps during radiochemotherapy in advanced head and neck cancer.

Background And Purpose: Longitudinal Positron Emission Tomography (PET) with hypoxia-specific radiotracers allows monitoring the time evolution of regions of increased radioresistance and may become fundamental in determining the radiochemotherapy outcome in Head-and-Neck Squamous Cell Carcinoma (HNSCC). The aim of this study was to investigate the evolution of the hypoxic target volume on oxygen partial pressure maps (pO-HTV) derived from FMISO-PET images acquired before and during radiochemotherapy and to uncover correlations between extent and severity of hypoxia and treatment outcome.

Material And Methods: FMISO-PET/CT images were acquired at three time points (before treatment start, in weeks two and five) for twenty-eight HNSCC patients treated with radiochemotherapy.

Impact of SBRT fractionation in hypoxia dose painting - Accounting for heterogeneous and dynamic tumor oxygenation.

Purpose: Tumor hypoxia, often found in nonsmall cell lung cancer (NSCLC), implies an increased resistance to radiotherapy. Pretreatment assessment of tumor oxygenation is, therefore, warranted in these patients, as functional imaging of hypoxia could be used as a basis for dose painting. This study aimed at investigating the feasibility of using a method for calculating the dose required in hypoxic subvolumes segmented on F-HX4 positron emission tomography (PET) imaging of NSCLC.

Accurate, robust and harmonized implementation of morpho-functional imaging in treatment planning for personalized radiotherapy.

In this work we present a methodology able to use harmonized PET/CT imaging in dose painting by number (DPBN) approach by means of a robust and accurate treatment planning system. Image processing and treatment planning were performed by using a Matlab-based platform, called CARMEN, in which a full Monte Carlo simulation is included. Linear programming formulation was developed for a voxel-by-voxel robust optimization and a specific direct aperture optimization was designed for an efficient adaptive radiotherapy implementation.

Estimation of the risk for radiation-induced liver disease following photon- or proton-beam radiosurgery of liver metastases.

Background: Radiotherapy of liver metastases is commonly being performed with photon-beam based stereotactic body radiation therapy (SBRT). The high risk for radiation-induced liver disease (RILD) is a limiting factor in these treatments. The use of proton-beam based SBRT could potentially improve the sparing of the healthy part of the liver.

Estimation of Risk of Normal-tissue Toxicity Following Gastric Cancer Radiotherapy with Photon- or Scanned Proton-beams.

Background/aim: Gastric cancer (GC) radiotherapy involves irradiation of large tumour volumes located in the proximities of critical structures. The advantageous dose distributions produced by scanned-proton beams could reduce the irradiated volumes of the organs at risk (OARs). However, treatment-induced side-effects may still appear.

Quantitative evaluation of potential irradiation geometries for carbon-ion beam grid therapy.

Purpose: Radiotherapy using grids containing cm-wide beam elements has been carried out sporadically for more than a century. During the past two decades, preclinical research on radiotherapy with grids containing small beam elements, 25 μm-0.7 mm wide, has been performed.

Non-linear conversion of HX4 uptake for automatic segmentation of hypoxic volumes and dose prescription.

Background: Tumour hypoxia is associated with increased radioresistance and poor response to radiotherapy. Pre-treatment assessment of tumour oxygenation could therefore give the possibility to tailor the treatment by calculating the required boost dose needed to overcome the increased radioresistance in hypoxic tumours. This study concerned the derivation of a non-linear conversion function between the uptake of the hypoxia-PET tracer F-HX4 and oxygen partial pressure (pO).

Development of an interlaced-crossfiring geometry for proton grid therapy.

Background: Grid therapy has in the past normally been performed with single field photon-beam grids. In this work, we evaluated a method to deliver grid therapy based on interlacing and crossfiring grids of mm-wide proton beamlets over a target volume, by Monte Carlo simulations.

Material And Methods: Dose profiles for single mm-wide proton beamlets (1, 2 and 3 mm FWHM) in water were simulated with the Monte Carlo code TOPAS.

Clinical implementation of combined modulated electron and photon beams with conventional MLC for accelerated partial breast irradiation.

Purpose: To report the clinical implementation of a novel external beam radiotherapy technique for accelerated partial breast irradiation treatments based on combined electron and photon modulated beams radiotherapy (MERT+IMRT) with conventional MLC.

Materials And Methods: A group of patients was selected to test the viability of the technique. The prescribed dose was 38.

Comparative study of the calculated risk of radiation-induced cancer after photon- and proton-beam based radiosurgery of liver metastases.

Introduction: The potential of proton therapy to improve the sparing of the healthy tissue has been demonstrated in several studies. However, even small doses delivered to the organs at risk (OAR) may induce long-term detriments after radiotherapy. In this study, we investigated the possibility to reduce the risk of radiation-induced secondary cancers with intensity modulated proton therapy (IMPT), when used for radiosurgery of liver metastases.

Comparison of gastric-cancer radiotherapy performed with volumetric modulated arc therapy or single-field uniform-dose proton therapy.

Background: Proton-beam therapy of large abdominal cancers has been questioned due to the large variations in tissue density in the abdomen. The aim of this study was to evaluate the importance of these variations for the dose distributions produced in adjuvant radiotherapy of gastric cancer (GC), implemented with photon-based volumetric modulated arc therapy (VMAT) or with proton-beam single-field uniform-dose (SFUD) method.

Material And Methods: Eight GC patients were included in this study.

Dosimetric Comparison of Plans for Photon- or Proton-Beam Based Radiosurgery of Liver Metastases.

Purpose: Radiosurgery treatment of liver metastases with photon beams has been an established method for more than a decade. One method commonly used is the stereotactic body radiation therapy (SBRT) technique. The aim of this study was to investigate the potential sparing of the organs at risk (OARs) that the use of intensity-modulated proton therapy (IMPT), instead of SBRT, could enable.

Proton Grid Therapy: A Proof-of-Concept Study.

In this work, we studied the possibility of merging proton therapy with grid therapy. We hypothesized that patients with larger targets containing solid tumor growth could benefit from being treated with this method, proton grid therapy. We performed treatment planning for 2 patients with abdominal cancer with the suggested proton grid therapy technique.