The dosimetric consequences of anatomic changes in head and neck radiotherapy patients.
BACKGROUND
To investigate anatomical response-related changes in the head and neck region during a course of radical radiotherapy and their impact on the planned dosimetry.


METHODS
The study consisted of 10 patients with primary mucosal carcinoma. Patients' nutritional requirements were managed as per departmental protocol to minimise weight loss during treatment. Kilovoltage computed tomography (CT) scans were acquired once 40 to 50 Gy had been delivered. Gross tumour volumes (GTV) and organs at risk were delineated and the initial optimised treatment plan was overlaid on the repeat CT. Comparisons were made between scans and absolute volume variations, centres of structures, dice similarity coefficients and the subsequent dosimetric impact were assessed.


RESULTS
Median weight loss at second scan was 3%. Primary and lymph node GTVs reduced by 49.9% (range 21.3-82%) and 73.7% (range 61.7-88.6%), respectively, yet continued to receive the prescribed dose. Maximum dose to spinal cord and brainstem changed minimally. Spared and un-spared parotid gland volumes reduced by median 23.5% and 20.5%, respectively, with no consistent translational displacement direction and minimal change in the mean dose.


CONCLUSIONS
Despite some significant geometric changes, nutritional management ensured patient size and shape was maintained in these consecutively selected patients and subsequently there was no apparent under-dosing of targets or over-dosing of normal structures with this technique. Further investigations which model gradual change and allow cumulative dosimetry are required to better characterise what occurs during the treatment course.
Department of Radiation Oncology, Austin Health Department of Radiation Oncology, Peter MacCallum Cancer Centre, Melbourne, Australia. rebecca.height@petermac.org
Rebecca
R
Height
Vincent
V
Khoo
Catherine
C
Lawford
Jennifer
J
Cox
Daryl Lim
DL
Joon
Aldo
A
Rolfo
Morikatsu
M
Wada
D000368:Aged; D002294:Carcinoma, Squamous Cell / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D005774:Gastrostomy; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008207:Lymphatic Metastasis / Q000000981:diagnostic imaging / Q000532:radiotherapy; D008297:Male; D008875:Middle Aged; D009303:Nasopharyngeal Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D044623:Nutrition Therapy; D010306:Parotid Gland / Q000528:radiation effects; D011879:Radiotherapy Dosage; D014057:Tomography, X-Ray Computed; D015431:Weight Loss