Examination of the best head tilt angle to reduce the parotid gland dose maintaining a safe level of lens dose in whole‐brain radiotherapy using the four‐field box technique

• Published in: Journal of applied clinical medical physics 2021-02, Vol.22 (2), p.49-57
• Main Authors: Shimizu, Hidetoshi, Sasaki, Koji, Aoyama, Takahiro, Tachibana, Hiroyuki, Tanaka, Hiroshi, Koide, Yutaro, Iwata, Tohru, Kitagawa, Tomoki, Kodaira, Takeshi
• Format: Article
• Language: English
• Subjects: Animal behavior; Cataracts; Dosimetry; Exocrine glands; Metastasis; parotid gland; Patients; prophylactic cranial irradiation; Radiation Oncology Physics; Radiation therapy; small cell lung cancer; whole brain
• ISSN: 1526-9914; 1526-9914
• DOI: 10.1002/acm2.13151

The parotid gland is recognized as a major‐risk organ in whole‐brain irradiation; however, the beam delivery from the left and right sides cannot reduce the parotid gland dose. The four‐field box technique using a head‐tilting device has been reported to reduce the parotid gland dose by excluding it from the radiation field. This study aimed to determine the appropriate head tilt angle to reduce the parotid gland dose in the four‐field box technique. The bilateral, anterior, and posterior beams were set for each of ten patients. The orbitomeatal plane angle (OMPA) was introduced as an indicator that expresses the head tilt angle. Next, principal component analysis (PCA) was performed to understand the interrelationship between variables (dosimetric parameters of the lens and parotid gland and OMPA). In PCA, the angle between the OMPA vector and maximum lens dose or mean parotid gland dose vector was approximately opposite or close, indicating a negative or positive correlation [r = −0.627 (p