Changes in lateral dimensions of irradiated volume and their impact on the accuracy of dose delivery during radiotherapy for head and neck cancer.
OBJECTIVE
To assess changes in lateral dimensions of irradiated volume during head and neck cancer radiotherapy and to determine their impact on the accuracy of dose delivery.


METHODS
Lateral dimensions of irradiated volumes were measured in five predefined points prior to treatment and then bi-weekly. For each measurement, midline dose was calculated and verified using in vivo dosimetry. Early radiation reactions, patient weight changes and the need to modify radiotherapy accessories were also recorded. The study included 33 head and neck cancer patients irradiated using parallel opposed megavoltage fields.


RESULTS
Body mass changes during radiotherapy ranged from -18 to +4 kg (median -5). Lateral dimension changes >5 mm (range -37 to +16) occurred in 32 patients (97%). For axis measurements, the degree of lateral dimension changes were correlated with treatment field size (P = 0.022) and degree of mucositis (P = 0.017). Axis doses calculated for changed dimensions varied from those prescribed by -2.5 to +6% (median +2%). Differences larger than 5% were present in 4.8% of calculations. In 17 patients (52%), radiotherapy accessories had to be modified during treatment. The need to modify radiotherapy accessories correlated with larger treatment portals (P = 0.004), more weight loss during treatment (P = 0.01) and higher initial N stage (P = 0.04).


CONCLUSIONS
Changes of irradiated volume lateral dimensions during head and neck cancer radiotherapy may lead to considerable dose delivery inaccuracies. Watchful monitoring, corrections to calculated dose when changes observed are significant and radiotherapy accessories modification during the course of treatment are strongly recommended.
Senkus-Konefka
Elzbieta
E
Department of Oncology and Radiotherapy, Medical University of Gdańsk, Poland. elsenkus@amg.g-da.pl
Naczk
Edmund
E
Borowska
Ilona
I
Badzio
Andrzej
A
Jassem
Jacek
J
D000328:Adult; D000368:Aged; D001835:Body Weight / Q000528:radiation effects; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D052016:Mucositis / Q000209:etiology; D009929:Organ Size; D011446:Prospective Studies; D011829:Radiation Dosage; D011882:Radiotherapy, High-Energy / Q000009:adverse effects / Q000379:methods* / Q000706:statistics & numerical data*; D015203:Reproducibility of Results