The Dosimetric Impact of Prostate Rotations During Electromagnetically Guided External-Beam Radiation Therapy

• Published in: International journal of radiation oncology, biology, physics Vol. 85; no. 1; pp. 230 - 236
• Main Authors: Amro, Hanan, PhD, Hamstra, Daniel A., MD, Mcshan, Daniel L., PhD, Sandler, Howard, MD, Vineberg, Karen, CMD, Hadley, Scott, PhD, Litzenberg, Dale, PhD
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-01-2013
• Subjects: Electromagnetic Fields; Hematology, Oncology and Palliative Medicine; Humans; Male; METRICS; Movement; PATIENTS; PLANNING; PROSTATE; Prostate - anatomy & histology; Prostate - radiation effects; Prostatic Neoplasms - pathology; Prostatic Neoplasms - radiotherapy; RADIATION DOSES; Radiology; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy, Image-Guided - methods; Radiotherapy, Intensity-Modulated - methods; ROTATION; Tumor Burden
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/j.ijrobp.2012.03.020

Purpose To study the impact of daily rotations and translations of the prostate on dosimetric coverage during radiation therapy (RT). Methods and Materials Real-time tracking data for 26 patients were obtained during RT. Intensity modulated radiation therapy plans meeting RTOG 0126 dosimetric criteria were created with 0-, 2-, 3-, and 5-mm planning target volume (PTV) margins. Daily translations and rotations were used to reconstruct prostate delivered dose from the planned dose. D95 and V79 were computed from the delivered dose to evaluate target coverage and the adequacy of PTV margins. Prostate equivalent rotation is a new metric introduced in this study to quantify prostate rotations by accounting for prostate shape and length of rotational lever arm. Results Large variations in prostate delivered dose were seen among patients. Adequate target coverage was met in 39%, 65%, and 84% of the patients for plans with 2-, 3-, and 5-mm PTV margins, respectively. Although no correlations between prostate delivered dose and daily rotations were seen, the data showed a clear correlation with prostate equivalent rotation. Conclusions Prostate rotations during RT could cause significant underdosing even if daily translations were managed. These rotations should be managed with rotational tolerances based on prostate equivalent rotations.