Comparisons of the impact of systematic uncertainties in patient setup and prostate motion on doses to the target among different plans for definitive external-beam radiotherapy for prostate cancer

• Published in: International journal of clinical oncology Vol. 13; no. 1; pp. 54 - 61
• Main Authors: Zhu, SuYu, Mizowaki, Takashi, Norihisa, Yoshiki, Takayama, Kenji, Nagata, Yasushi, Hiraoka, Masahiro
• Format: Journal Article
• Language: English
• Published: Japan Springer Japan 01.02.2008; Springer Nature B.V
• Subjects: Cancer Research; Clinical outcomes; Comparative studies; Errors; Humans; Male; Medicine; Medicine & Public Health; Motion; Oncology; Original Article; Prostate - radiation effects; Prostate cancer; Prostatic Neoplasms - radiotherapy; Radiation therapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy, Conformal; Radiotherapy, Intensity-Modulated; Surgical Oncology; Systematic uncertainties; Dynamic-arc 3D-CRT; IMRT; Prostate cancer
• ISSN: 1341-9625; 1437-7772
• DOI: 10.1007/s10147-007-0724-4

Background We aimed to compare the impact of systematic uncertainties in patient setup and prostate motion on three different external-beam radiotherapy protocols for prostate cancer. Methods To simulate possible near-maximum systematic errors, the isocenter position was shifted to eight points with ±1.65 SD of the integrated uncertainty value along each axis that was expected to include 5%-95% of the total systematic uncertainties in each direction. Five cases were analyzed for the three plans: an old three-dimensional conformal radiotherapy (3D-CRT) protocol (four-field plus dynamic arc), a new 3D-CRT protocol (dynamic arc), and an intensity-modulated radiotherapy (IMRT) protocol, respectively. Results The averaged percentage volume covered by more than 95% of the prescription dose (V95) of the clinical target volume (CTV) for the original plans was 100% for all protocols. After simulating the errors, V95 of the CTV for IMRT cases was maintained at 100%. On the other hand, these values for the new and old 3D-CRT protocols were 93.1% and 63.2%, respectively. The values for the percentage prescription dose received by at least 95% volume (D95) of the CTV for the original plans were 100%, 98.4%, and 97.6% for the IMRT, new 3D-CRT, and old 3D-CRT plans, respectively. However, when the effects of the systematic errors were taken into consideration, the net decreases in the D95 values were 0.3%, 4.3%, and 8.1%, respectively. Conclusion The current IMRT protocol is considered to successfully compensate for systematic uncertainties. In contrast, the multi-leaf collimator (MLC) margins set for the old 3D-CRT protocol were not enough to ensure the actual delivery of the prescription dose to the CTV. Therefore, it is very important to include these issues in the plan design in the interpretation of clinical outcomes.