278P - Serial assessment of parotid volume changes during radical chemoradiation of locally advanced head and neck cancer: Its implications in practice of adaptive radiotherapy

Background

Radical chemoradiation (CTRT) is the standard of care in locally advanced head and neck cancer (LAHNC). For mitigating the normal tissue toxicity, many techniques have been explored and utilized, including IMRT and adaptive radiotherapy (ART). Significant anatomical variations occur during CTRT due to weight loss and tumor and normal tissue changes. In the present study, serial changes in parotid volumes were assessed with weekly scans along with dosimetric correlation.

Methods

This prospective, single-institutional study, included 12 patients with LA HNC receiving CTRT. All underwent CT simulation (CT sim) followed by weekly rescans from week 1 to 6. Target volumes and organs at risk, including right & left parotids (RP & LP) were recontoured in all rescans after fusion with the CT sim. Dose overlay was done in each rescan to generate a hybrid plan to study corresponding dosimetric variations. Volume changes in parotids were reported as percentage change from the baseline.

Results

In CT sim, right parotid volumes (RPV) ranged from 15.7 - 44.2 cc (mean - 24.1 SD – 7.9) and left parotid volume (LPV) from 12.2 - 47.1 cm³ (mean 22.8, SD -9.9). Mean % reduction in RPV in week 1, 2, 3, 4, 5 and 6 were 14.2% (p=0.003), 17.1% (p=0.007), 21.8% (p < 0.001), 25.6% (p < 0.001), 30% (p < 0.001), 32.1% (p < 0.001) respectively. Mean % reduction in LPV in week 1, 2, 3, 4, 5 and 6 were 8.9% (p=0.016), 14.5% (p=0.012), 17.7% (p=0.001), 20.1% (p=0.002), 24.9% (p < 0.001), 28.9% (p < 0.001) respectively. LP D mean showed a significant increase in week 3 (4.6% from baseline, p=0.019) and week 6 (7.6% from baseline, p=0.034). Both parotids showed a significant reduction in V26 Gy with 12.3%, 15.1%, 18.9%, 22.9%, 25.7%, 27.0%, respectively, from week 1 to 6 in RP and 7.3%, 15.7%, 13.8%, 16.8%, 20.8%, 24.1%, respectively, in LP.

Conclusions

Parotid volume shrinkage started from the 1st week. At the end of CTRT, there was 30-32% reduction in volume. V26 Gy of both parotids showed significant reduction during CTRT. Studies focusing on parotid volume changes shows wide variations in volume reduction ranging from 13% to 50% at the end of treatment. These parotid volume changes during RT need to be incorporated while doing ART in LAHNC.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Uttarakhand.

Funding

Has not received any funding.

Disclosure

All authors have declared no conflicts of interest.