Open AccessPotential proton and photon dose degradation in advanced head and neck cancer patients by intratherapy changes
Author(s) -
Stützer Kristin,
Jakobi Annika,
BandurskaLuque Anna,
Barczyk Steffen,
Arnsmeyer Carolin,
Löck Steffen,
Richter Christian
Publication year - 2017
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1002/acm2.12189
Subject(s) - medicine , proton therapy , nuclear medicine , head and neck cancer , radiation therapy , head and neck , radiology , surgery
Purpose Evaluation 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. Methods For 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 ( OAR s) 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. Results Recalculated 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 ). Conclusions The 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.