A case report of radiotherapy for head and neck cancer in a pregnant woman: dosimetric optimization and in vivo dosimetry

Abstract

Background

Radiotherapy during pregnancy is a rare and ethically complex requiring careful management of fetal exposure. Although peripheral doses from head and neck radiotherapy are typically low, fetal irradiation carries a potential developmental or carcinogenic risk. Accurate dose estimation and optimization are essential when radiotherapy cannot be postponed.

Case presentation

A 27-year-old woman, 26 weeks pregnant, required adjuvant radiotherapy for a left parotid adenoid cystic carcinoma (pT4a N3b, R1). To minimize fetal exposure, a one-month pre-treatment period was dedicated to dosimetric optimization. Three clinically equivalent VMAT plans were compared using different collimator angles (15°/345°, 80°/30°, and 80°/100°). Out-of-field dose measurements were assessed using a calibrated ionization chamber positioned in a slab phantom at varying depths and distances simulating fetal position and progression of pregnancy. All plan showed low out-of-field dose, below 100 mGy. The plan with 80°/100° collimator angles (Popt2) consistently showed the lowest out-of-field dose and was therefore selected for treatment. A lead apron was added during treatment. In vivo dosimetry was performed using radiophotoluminescent (RPL) detectors placed weekly under the lead apron at the uterine fundus projection. Over 10 monitored fractions, single-session doses averaged 1.25 mGy, and cumulative five-session doses reached 5.9–6.7 mGy. Total extrapolated fetal dose was approximately 41.0 mGy, closely matching the phantom-based estimate of 31.1 mGy.

Conclusions

This unprecedented case in our institution demonstrates the feasibility of safely delivering radiotherapy during pregnancy through multidisciplinary coordination and meticulous dose management. Phantom-based optimization and in vivo dosimetry confirmed that the fetal dose remained below the 100 mGy threshold set by international guidelines for deterministic effects. The patient completed treatment without complications and delivered a healthy infant at term. This experience provided the foundation for a standardized dosimetric approach within our institution for future cases involving pregnancy and radiotherapy.

Background

Radiotherapy during pregnancy is rare and presents significant ethical and technical challenges dure to fetal radiation exposure. The nature of these effects depends on both the dose level and the stage of pregnancy [1]. Although postponing treatment until after delivery is preferable whenever possible, radiotherapy can be administered during pregnancy under certain conditions. The International Commission on Radiological Protection (ICRP) has established that, for an absorbed dose below 100  mGy, no risk to fetal development is expected [2] and medical termination of pregnancy is not justified regarding radiation risks. Nevertheless, fetal dose optimization remains essential, as stochastic risks may exist even at low exposure levels.