Dosimetric evaluation of three adaptive strategies for prostate cancer treatment including pelvic lymph nodes irradiation. Issue 12 (13th November 2015)

• Record Type: Journal Article
• Authors: Cantin, Audrey; Gingras, Luc; Lachance, Bernard; Foster, William; Goudreault, Julie; Archambault, Louis
• Is Part Of: Medical physics. Volume 42:Issue 12(2015)
• Page Start: 7011
• Page End: 7021
• Publication Date: 2015-11-13
• Subjects: biomechanics -- cancer -- computerised tomography -- dosimetry -- image registration -- medical image processing -- radiation therapy; Dose‐volume analysis -- Computed tomography -- Registration -- Cancer -- Movement and locomotion; Computerised tomographs -- Radiation therapy -- Biological material, e.g. blood, urine; Haemocytometers -- Digital computing or data processing equipment or methods, specially adapted for specific applications -- Image data processing or generation, in general -- Scintigraphy; adaptive radiotherapy -- image guided radiation therapy -- prostate cancer -- intensity‐modulated radiation therapy -- treatment planning; Cone beam computed tomography -- Medical imaging -- Anatomy -- Gold -- Dosimetry -- Intensity modulated radiation therapy -- Radiation treatment -- Cancer -- Adaptive methods; Medical physics -- Periodicals; Medical physics; Geneeskunde; Natuurkunde; Toepassingen; Biophysics; Periodicals; Periodicals; Electronic journals; 610.153
• DOI: 10.1118/1.4935529
• Languages: English
• ISSNs: 0094-2405

Abstract

Abstract : Purpose: The movements of the prostate relative to the pelvic lymph nodes during intensity‐modulated radiation therapy treatment can limit margin reduction and affect the protection of the organs at risk (OAR). In this study, the authors performed an analysis of three adaptive treatment strategies that combine information from both bony and gold marker registrations. The robustness of those treatments against the interfraction prostate movements was evaluated. Methods: A retrospective study was conducted on five prostate cancer patients with 7–13 daily cone‐beam CTs (CBCTs). The clinical target volumes (CTVs) consisting of pelvic lymph nodes, prostate, and seminal vesicles as well as the OARs were delineated on each CBCT and the initial CT. Three adaptive strategies were analyzed. Two of these methods relied on a two‐step patient positioning at each fraction. First step: a bony registration was used to deliver the nodal CTV prescription. Second step: a gold marker registration was then used either to (1) complete the dose delivered to the prostate (complement); (2) or give almost the entire prescription to the prostate with a weak dose gradient between the targets to compensate for possible motions (gradient). The third method (COR) used a pool of precalculated plans based on images acquired at previous treatment fractions. At each new fraction, a plan is selected from that pool based on the daily position of prostate center‐of‐mass. The dosimetric comparison was conducted and results are presented with and without the systematic shift in the prostate position on the CT planning. The adaptive strategies were compared to the current clinical standard where all fractions are treated with the initial nonadaptive plan. Results: The minimum daily prostate D 95% is improved by 2%, 9%, and 6% for the complement, the gradient, and the COR approaches, respectively, compared to the nonadaptive method. The average nodal CTV D 95% remains constant across the strategies, except for the gradient approach where a reduction of 7% is observed. However, a correction of the systematic shift reduced the problem, and the adaptive strategies remain robust against the prostate movement across the fraction. The bladder V 55Gy is reduced by 35% on average for the adaptive strategies. Conclusions: Because they offer increased CTV coverage and OAR sparing, adaptive methods may be suitable candidates for simple and efficient adaptive treatment strategies for prostate cancer. Margin reduction and systematic error correction in the prostate position improve the protection of the OAR and the dose coverage. A cumulative dose to simulate a complete treatment would show real effects and allow a better comparison between each method.