Comparison of calculated dose distributions reported as dose-to-water and dose-to-medium for intensity-modulated radiotherapy of nasopharyngeal cancer patients

Ðeni Smilović Radojčić; Manda Švabić Kolacio; Milan Radojčić; David Rajlić; Božidar Casar; Dario Faj; Slaven Jurković

doi:10.1016/j.meddos.2017.11.008

Comparison of calculated dose distributions reported as dose-to-water and dose-to-medium for intensity-modulated radiotherapy of nasopharyngeal cancer patients

Med Dosim. 2018;43(4):363-369. doi: 10.1016/j.meddos.2017.11.008. Epub 2018 Jan 4.

Authors

Ðeni Smilović Radojčić¹, Manda Švabić Kolacio¹, Milan Radojčić², David Rajlić¹, Božidar Casar³, Dario Faj⁴, Slaven Jurković⁵

Affiliations

¹ Medical Physics Department, University Hospital Rijeka, Rijeka, Croatia.
² Clinic for Radiotherapy and Oncology, University Hospital Rijeka, Rijeka, Croatia.
³ Department of Radiation Physics, Institute of Oncology, Ljubljana, Slovenia.
⁴ Faculty of Medicine, University of Osijek, Osijek, Croatia; Faculty of Dental Medicine and Health, University of Osijek, Osijek, Croatia.
⁵ Medical Physics Department, University Hospital Rijeka, Rijeka, Croatia; Department of Physics, Faculty of Medicine, University of Rijeka, Rijeka, Croatia. Electronic address: slaven.jurkovic@medri.uniri.hr.

PMID: 29306538
DOI: 10.1016/j.meddos.2017.11.008

Abstract

Advanced dose calculation algorithms for radiation therapy treatment planning can report external beam photon dose 2-sided, in terms of dose-to-medium (D_m) and dose-to-water (D_w). The purpose of our study was to determinate the effect of D_w and D_m reporting modes built in Elekta Monaco treatment planning system on intensity-modulated radiotherapy dose distributions for patients with nasopharyngeal cancer. For 13 patients involved in this retrospective study, 2 plans were created: 1 using D_w and another according to D_m reporting mode. Treatment plans were normalized such that 100% planning target volume should be covered by 95% of prescribed dose. Dose-volume constraints were assigned according to international standards. The comparison between dose distributions was performed evaluating quantities important for respective volumes of interest. For target volumes, heterogeneity index and conformity index methodology were used along with the maximum dose concept. Also, for the comparisons over particular organ at risk, maximum dose or mean dose as well as dose-volume concepts were used. For all target volumes and majority of organs at risk, the differences between 2 reporting modes are statistically insignificant, but this is not the case for bony structured organs at risks: mandible and cochlea. It was observed that D_w is higher than D_m with mean difference of 9.91% (p = 0.000009) of the mandible volume covered with 70 Gy. The same trend was observed for left and right cochlea with difference in mean dose of 8.74% (p = 0.037) and 6.87% (p = 0.029), respectively. The comparative analysis of dosimetric parameters in this study shows that the selection of reporting modes in Monaco treatment planning system can produce dose differences up to 15% in high-density volumes such as mandible and cochlea, which might have clinical consequences.

Keywords: Dose reporting modes; IMRT; Nasopharyngeal cancer patient; Treatment planning.

Publication types

Comparative Study

MeSH terms

Cochlea / radiation effects
Humans
Mandible / radiation effects
Nasopharyngeal Neoplasms / radiotherapy*
Organs at Risk
Radiotherapy Dosage
Radiotherapy, Intensity-Modulated / adverse effects
Radiotherapy, Intensity-Modulated / methods*
Retrospective Studies