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?

Abstract

In the last decade, many efforts have been made to characterize anatomic changes of head and neck organs at risk (OARs) and the dosimetric consequences during radiotherapy. This review was undertaken to provide an overview of the magnitude and frequency of these effects, and to investigate whether we could find criteria to identify head and neck cancer patients who may benefit from adaptive radiotherapy (ART). Possible relationships between anatomic and dosimetric changes and outcome were explicitly considered. A literature search according to PRISMA guidelines was performed in MEDLINE and EMBASE for studies concerning anatomic or dosimetric changes of head and neck OARs during radiotherapy. Fifty-one eligible studies were found. The majority of papers reported on parotid gland (PG) anatomic and dosimetric changes. In some patients, PG mean dose differences between planning CT and repeat CT scans up to 10 Gy were reported. In other studies, only minor dosimetric effects (i.e. <1 Gy difference in PG mean dose) were observed as a result of significant anatomic changes. Only a few studies reported on the clinical relevance of anatomic and dosimetric changes in terms of complications or quality of life. Numerous potential selection criteria for anatomic and dosimetric changes during radiotherapy were found and listed. The heterogeneity between studies prevented unambiguous conclusions on how to identify patients who may benefit from ART in head and neck cancer. Potential pre-treatment selection criteria identified from this review include tumour location (nasopharyngeal carcinoma), age, body mass index, planned dose to the parotid glands, the initial parotid gland volume, and the overlap volume of the parotid glands with the target volume. These criteria should be further explored in well-designed and well-powered prospective studies, in which possible relationships between anatomic and dosimetric changes and outcome need to be established.

Parotid gland radiation dose‐xerostomia relationships based on actual delivered dose for nasopharyngeal carcinoma

“…Previous studies suggested that, on average, the PG volume reduction rate was 26 ± 11% 16. In our study, the PG volume reduction rate was 13.5% and 13.2%, respectively, for patients with xerostomia and patients without xerostomia (Table 5).…”

“…This is mainly because OARs and tumor target volumes of HNC are close to each other 16. The parotid gland is the most studied organ at risk in head and neck cancer.…”

“…Hence, the dose actually delivered to the patient often differs from that of the initial plan. Charlotte et al reviewed the literature published in the last decade and pointed out that, on average, the PG mean dose increase was 2.2 ± 2.6 Gy as compared to the dose calculated on the planning CT 16. They also emphasized that the largest PG dose increase found by Chen et al and Cheng et al was 10.4 Gy in the sixth week of radiotherapy, and the largest median dose was 7.8 Gy at the 25th fraction 10, 20.…”

“…Thus, identifying patients earlier by selection criteria to spare OARs and further decrease the risk of complication will be beneficial to both patients and radiation departments. Previous studies selected patients by determining some criteria that would allow them to benefit from ART or replanning 4, 15, 16…”

“…Additionally, a significant dosimetric difference between patients with and without radiation‐induced liver disease (RILD) has been reported. Charlotte et al stated in their review that only a few articles reported the clinical relevance of dosimetric changes in terms of complications of head and neck cancer patients 16. As for dosimetric variation, the delivered dose may not correspond to the planned dose.…”