Potential proton and photon dose degradation in advanced head and neck cancer patients by intratherapy changes

Abstract

PurposeEvaluation of dose degradation by anatomic changes for head‐and‐neck cancer (HNC) intensity‐modulated proton therapy (IMPT) relative to intensity‐modulated photon therapy (IMRT) and identification of potential indicators for IMPT treatment plan adaptation.MethodsFor 31 advanced HNC datasets, IMPT and IMRT plans were recalculated on a computed tomography scan (CT) taken after about 4 weeks of therapy. Dose parameter changes were determined for the organs at risk (OARs) spinal cord, brain stem, parotid glands, brachial plexus, and mandible, for the clinical target volume (CTV) and the healthy tissue outside planning target volume (PTV). Correlation of dose degradation with target volume changes and quality of rigid CT matching was investigated.ResultsRecalculated IMPT dose distributions showed stronger degradation than the IMRT doses. OAR analysis revealed significant changes in parotid median dose (IMPT) and near maximum dose (D 1ml) of spinal cord (IMPT, IMRT) and mandible (IMPT). OAR dose parameters remained lower in IMPT cases. CTV coverage (V 95%) and overdose (V 107%) deteriorated for IMPT plans to (93.4 ± 5.4)% and (10.6 ± 12.5)%, while those for IMRT plans remained acceptable. Recalculated plans showed similarly decreased PTV conformity, but considerable hotspots, also outside the PTV, emerged in IMPT cases. Lower CT matching quality was significantly correlated with loss of PTV conformity (IMPT, IMRT), CTV homogeneity and coverage (IMPT). Target shrinkage correlated with increased dose in brachial plexus (IMRT, IMPT), hotspot generation outside the PTV (IMPT) and lower PTV conformity (IMRT).ConclusionsThe study underlines the necessity of precise positioning and monitoring of anatomy changes, especially in IMPT which might require adaptation more often. Since OAR doses remained typically below constraints, IMPT plan adaptation will be indicated by target dose degradations.

Systematic review and meta‐analysis of the impact of dosimetry to dysphagia and aspiration related structures

“…Blanchard et al have recently shown in their facility that IMPT can lead to reduce reliance on feeding tubes and weight loss at a median time point of 32 months post radiotherapy. Similarly, IMPT can reduce the radiation dose to the healthy surrounding tissue including DARS . In the case of IMPT, there may be a higher requirement of replanning as a result of anatomical changes in a similar way to the methodology described in Berwouts et al…”

Three discipline collaborative radiation therapy special debate: All head and neck cancer patients with intact tumors/nodes should have scheduled adaptive replanning performed at least once during the course of radiotherapy

“…How can you fully realize the potential of these technologies without ART? For example, proton therapy distributions are much less robust than photon therapy in the presence of anatomical variation . The clinical viability of a technology such as the MR‐LINAC is completely dependent on the ability to adapt plans when anatomical changes are seen .…”

Assessing Novel Drugs and Radiation Technology in the Chemoradiation of Oropharyngeal Cancer

“…The issue of standardising CTV delineation is as relevant with IMPT, notwithstanding the unique treatment planning aspects for IMPT target volumes which cannot be based on geometric margin expansion alone, owing to increased range uncertainty with resultant increased sensitivity to set-up and anatomical changes. Degradation of the dose distribution for both the target volumes and OARs can be proportionately worse for IMPT compared to IMRT over the entire course of treatment, resulting in less than anticipated therapeutic benefits for IMPT [ 16 , 17 ]. Studies evaluating robust planning parameters specific to oropharyngeal cancer have recently emerged and robustness settings do influence the dose to OARs with possible clinical impact [ 18 , 19 ].…”