Volumetric and Dosimetric Assessment by Cone-Beam Computed Tomography Scans in Head and Neck Radiation Therapy: A Monitoring in Four Phases of Treatment

Abstract

Due to the anatomical changes frequently occurring during the course of head and neck (H&N) cancer radiotherapy, the dose distribution, which was actually delivered to the patient, might significantly differ from that planned. The aim of this paper is to investigate these volumetric changes and the resulting dosimetric implications on organs at risk (OARs) and clini- and 25 th CBCT (13.3%) but it complied with dose constraint. The differences observed for the spinal cord and mandible maximum doses were not clinically relevant. In conclusion, the dosimetric analysis on CBCT can help clinicians to monitor treatment progress and to evaluate whether and when a new plan is necessary. The main benefit of replanning could be to preserve the parotids and our data support the hypothesis that the 3 rd week of radiotherapy should be a check point for parotids.

Identifying patients who may benefit from adaptive radiotherapy: Does the literature on anatomic and dosimetric changes in head and neck organs at risk during radiotherapy provide information to help?

“…Clear swelling of the larynx and pharyngeal constrictor muscles was found by Ricchetti et al [53] at week seven of radiotherapy. Swelling of the larynx was also reported by Cozzolino et al [66], five weeks after the start of radiotherapy. Popovtzer et al [52] observed a thickness change of +111% in parts of the pharyngeal constrictors that received more than 50 Gy, three months post chemoradiation.…”

“…Sanguineti et al [62] studied weekly CT scans of eighty-five patients and concluded that the PG shrinkage is not linear (PGs shrunk most during the first half of treatment). Thirty-eight papers reported on PG anatomic changes [2,4,6,7,9,12,13,[15][16][17][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45]47,48,50,53,56,57,59,60,[62][63][64][65][66]. The most common reported anatomic changes were volume loss (Table S1) and medial shifts of the PGs [17,[32][33][34]37,42,44,45,48,51,...…”

“…Twenty-six papers described both anatomic and dosimetric changes during the course of radiation [2,4,6,[11][12][13][15][16][17]31,34,36,38,39,[41][42][43][44]46,48,54,59,61,63,65,66]. Two studies reported on dosimetric changes without referring to anatomic changes [18,51].…”

“…A number of authors reported on changes in maximum doses or D 1% to the brainstem [2,6,15,16,18,31,34,[41][42][43]59] and the spinal cord [2,6,11,13,15,16,18,31,34,36,[41][42][43]59,66] during the course of treatment (results are listed in Table S3). Zhao et al [6] found the highest dose increase in D 1% of the spinal cord and the brainstem of on average 0.20 and 0.09 Gy per fraction, which would result in an accumulated excess dose of 5.6 and 2.5 Gy, respectively, for the entire treatment course.…”

Dosimetric effect of body contour changes for prostate and head and neck volumetric modulated arc therapy plans

“…While some of the patients had 95% or 93% isodose line shifts less than 1 mm due to 1 cm uniform body contour change, some of the patients had 95% or 93% isodose line shifts more than 4 mm. This may explain the fact that although there was literature claiming the target coverage was affected by anatomical changes (e.g., weight loss), others showed that anatomical changes had minimal effect on target coverage …”