Which nasopharyngeal cancer patients need adaptive radiotherapy?

Abstract

BackgroundAdaptive radiotherapy (ART) has potential benefits in patients with nasopharyngeal cancer (NPC). This retrospective study aimed to identify the factors favoring ART.Materials and methodsForty NPC patients were retrospectively included in this study. All patients received two-phase, volumetric modulated arc radiotherapy (VMAT) and underwent a second computed tomography (CT) for the phase II ART. We generated phantom, non-ART plans by a hybrid method for comparison with ART plans. A paired t-test was used to evaluate the dose differences between these two plans. A subgroup analysis through a paired t-test was used to evaluate the factors favoring ART.ResultsThe second CT images were captured at the median 22 fractions. The median total dose of the planning target volume-one (PTV-1) was 72 Gy, and the phase II dose was 16 Gy. The volumes of the ipsilateral parotid gland (23.2 vs. 19.2 ml, p < 0.000), contralateral parotid gland (23.0 vs. 18.4 ml, p < 0.000), clinical target volume-1 (CTV-1, 32.2 vs. 20.9 ml, p < 0.000), and PTV-1 (125.8 vs. 107.3 ml, p < 0.000) all shrunk significantly between these two CT simulation procedures. Among the nearby critical organs, only the ipsilateral parotid gland displayed significant dose reduction by the ART plan (5.3 vs. 6.0 Gy, p = 0.004). Compared to the phantom plan, the ART could significantly improve the PTV-1 target volume coverage of D98 (15.4 vs. 12.3 Gy, p < 0.000). Based on the D98 of PTV-1, the factors of a large initial weight (> 60 kg, p < 0.000), large body mass index (BMI) (> 21.5, p < 0.000), obvious weight loss (> 2.8 kg, p < 0.000), concurrent chemoradiotherapy (p < 0.000), and stages III–IV (p < 0.000) favored the use of ART.ConclusionsART could significantly reduce the mean dose to the ipsilateral parotid gland. ART has dosimetrical benefit for patients with a heavy initial weight, large BMI, obvious weight loss, concurrent chemoradiotherapy, and cancer in stages III–IV.

Radiotherapy for Head and Neck Cancer: Evaluation of Triggered Adaptive Replanning in Routine Practice

“…All three cases received chemotherapy in addition to radiotherapy (2 had cisplatin 100 mg/m 2 and 1 had carboplatin with previous induction chemotherapy). The mean fraction for rescan CT was 21 (range, [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. No other primaries were found to be correlated with need for ART ( Table 3).…”

“…There is limited data to identify the candidates most likely to benefit from ART (11,26,27). Brown et al stated having more advanced nodal disease, nasopharyngeal primary, being treated with tomotherapy and VMAT compared to IMRT are the factors contributing to re-planning (11).…”

Adaptive radiotherapy for head and neck cancer

“…Most authors advocate for re-planning when these constraints (spinal cord max dose < 45-48 Gy and brainstem max dose < 54 Gy) are breached during radiotherapy. However, studies do not consistently report overdosing of the spinal cord or brainstem with some reporting significant increases in the max dose throughout radiotherapy [8,10,11,19,24,42] and some noting no change [20,40,43,44]. In a prospective cohort study of 22 patients with HNSCC where re-planning was triggered by underdosage of the target volumes (CTV coverage < 95%), overdosage of the parotids (mean dose > 26 Gy), or overdosage of the spinal cord (max dose > 45 Gy) [15], the spinal cord max dose reached the threshold for triggering A-ART in only 3 of 22 patients, whereas parotid gland overdosages occurred in 3 right and 5 left parotids, and CTV undercoverage in 7 instances.…”

“…A negative dosimetric change means that it decreased in the dose received (e.g. -10% indicates a 10% decrease in mean parotid dose) "-"information was either not available or was not directly comparable to other volumetric/dosimetric data reported and thus not included " NS " parotid side was not specified "* "parotid side (left or right) was specified; however, ipsilateral and contralateral designation were not specified " Ipsi "ipsilateral parotid [11,24,42] and with several series failing to show a significant overdosage of this structure [20,40,43,44]; clinically significant deviations may only occur in a minority of patients. The effect of adaptive re-planning on the efficacy and tolerability of postoperative radiation for HNSCC is less clear, given the scarcity of data in this cohort.…”

Emerging radiotherapy technologies and trends in nasopharyngeal cancer

“…Tijssen et al [63] published a comprehensive commissioning protocol for the installation of such machines. Adaptive planning for NPC patients has been shown to significantly reduce the dose to the ipsilateral parotid gland [64]. Chuter et al [65] showed that it was feasible for an MR-linear accelerator to utilize current off-line strategies for adaptive planning for head and neck cancers.…”