Developing an adaptive radiation therapy strategy for nasopharyngeal carcinoma

Abstract

Adaptive radiotherapy (ART) has recently been introduced to restore the planned dose distribution by accounting for the anatomic changes during treatment. By quantifying the anatomic changes in nasopharyngeal carcinoma (NPC) patients, this study aimed to establish an ART strategy for NPC cases. A total of 30 NPC patients treated with helical tomotherapy were recruited. In the pretreatment megavoltage CT images, the anatomic changes of the posterolateral wall of nasopharynx (P-NP), neck region and parotid glands were measured and assessed. One-way repeated measure ANOVA was employed to define threshold(s) at any time-point. The presence of a threshold(s) would indicate significant anatomical change(s) such that replanning should be suggested. A pragmatic schedule for ART was established by evaluating the threshold for each parameter. Results showed the P-NP, parotid gland and neck volumes demonstrated significant regressions over time. Respectively, the mean loss rates were 0.99, 1.35, and 0.39 %/day, and the mean volume losses were 35.70, 47.54 and 11.91% (all P < 0.001). The parotid gland shifted medially and superiorly over time by a mean of 0.34 and 0.24 cm, respectively (all P < 0.001). The neck region showed non-rigid posterior displacement, which increased from upper to lower neck. According to the threshold occurrences, three replans at 9th, 19th and 29th fractions were proposed. This ART strategy was able to accommodate the dosimetric consequences due to anatomic deviation over the treatment course. It is clinically feasible and would be recommended for centers where an adaptive planning system was not yet available.

Optimal adaptive IMRT strategy to spare the parotid glands in oropharyngeal cancer

“…While different numbers of replannings aimed at sparing the PG have been investigated in the literature, the optimal timing of these replannings has not been thoroughly assessed [8,13,15,16,[25][26][27][28][29][30][31][32][33][34]. The endpoint of these studies was the quantification of the dosimetric benefit of sparing the PG, while keeping or even increasing the minimum dose in the PTV, using different CT-based IMRT replanning scenarios.…”

“…Different ART scenarios have been investigated and compared to a classical non-ART scenario with varying numbers and timings tested: one replanning performed either mid treatment [13], at week 2 [14] or at a patient-specific time based on weight loss or tumor shrinkage [10], two replannings at weeks 2 and 4 [13,15], three replannings at the 9th, 19th, and 29th fractions [16], and, the most extensive ART strategy, six weekly replannings [8,13]. All these studies show that ART results in a decrease in the PG mean dose.…”

A longitudinal evaluation of early anatomical changes of parotid gland in intensity modulated radiotherapy of nasopharyngeal carcinoma patients with parapharyngeal space involvement

“…If this happens, the gland may enter into the high‐dose zone that is designed to cover the planning target volume (PTV). As a result, the parotid gland will receive a much higher than the planned dose . Since the parotid gland accounts for 60–65% of total saliva production, high dose to this organ can further increase the risk of xerostomia .…”

“…As a result, the parotid gland will receive a much higher than the planned dose. 12,13 Since the parotid gland accounts for 60-65% of total saliva production, high dose to this organ can further increase the risk of xerostomia. 14 In order to solve this problem, adaptive radiotherapy has been suggested in which the treatment plan is modified based on the tumour response and anatomical changes of OARs during a radiotherapy course.…”

Replanning Criteria and Timing Definition for Parotid Protection-Based Adaptive Radiation Therapy in Nasopharyngeal Carcinoma

“…The timing of replanning is a controversial topic in parotid protection-based ART in head and neck cancer. Someone recommended replanning when it became obvious that a tumor had shrunk, weight loss had occurred, or skin separation had reduced [7,11,12,[21][22][23], while others believe that replanning should be performed when a specific fraction has been reached [26][27][28]. Our precious study found that parotid volume variation presented a linear pattern throughout IMRT of NPC realized by HT technique, and the rate of volume variation reached its peak at the 16th fraction and then decreased gradually, suggesting that replanning is appropriate in the fourth week [14].…”