Abstract
BackgroundThe advent of IMRT and image-guided radiotherapy (IGRT) in combination with involved-field radiotherapy (IF-RT) in inoperable non-small-cell lung cancer results in a decreased incidental dose deposition in elective nodal stations. While incidental nodal irradiation is considered a relevant by-product of 3D-CRT to control microscopic disease this planning study analyzed the impact of IMRT on dosimetric parameters and tumor control probabilities (TCP) in elective nodal stations in direct comparison with 3D-CRT.Methods and materialsThe retrospective planning study was performed on 41 patients with NSCLC (stages II-III). The CTV was defined as the primary tumor (GTV + 3 mm) and all FDG-PET-positive lymph node stations. As to the PTV (CTV + 7 mm), both an IMRT plan and a 3D-CRT plan were established. Plans were escalated until the pre-defined dose-constraints of normal tissues (spinal cord, lung, esophagus and heart) were reached. Additionally, IMRT plans were normalized to the total dose of the corresponding 3D-CRT. For two groups of out-of-field mediastinal node stations (all lymph node stations not included in the CTV (LNall_el) and those directly adjacent to the CTV (LNadj_el)) the equivalent uniform dose (EUD) and the TCP (for microscopic disease a D50 of 36.5 Gy was assumed) for the treatment with IMRT vs 3D-CRT were calculated.ResultsIn comparison, a significantly higher total dose for the PTV could be achieved with the IMRT planning as opposed to conventional 3D-CRT planning (74.3 Gy vs 70.1 Gy; p = 0.03). In identical total reference doses, the EUD of LNadj_el is significantly lower with IMRT than with 3D-CRT (40.4 Gy vs. 44.2 Gy. P = 0.05) and a significant reduction of TCP with IMRT vs 3D-CRT was demonstrated for LNall_el and LNadj_el (12.6 % vs. 14.8 %; and 23.6 % vs 27.3 %, respectively).ConclusionsIn comparison with 3D-CRT, IMRT comes along with a decreased EUD in out-of-field lymph node stations. This translates into a statistically significant decrease in TCP-values. Yet, the combination of IF-RT and IMRT leads to a significantly better sparing of normal tissues and higher total doses whereas the potential therapeutic drawback of decreased incidental irradiation of elective lymph nodes is moderate.
Highlights
The advent of intensity modulated radiotherapy (IMRT) and image-guided radiotherapy (IGRT) in combination with involved-field radiotherapy (IF-RT) in inoperable non-small-cell lung cancer results in a decreased incidental dose deposition in elective nodal stations
Given the fact that IMRT is of additional benefit with respect to dose escalation and the sparing of relevant organs at risk (OAR) [11,12,13], it is yet unclear if the high dose conformality of IMRT implies an adverse effect on tumor control probability (TCP) for microscopic disease in the “rind”-region outside the clinical target volume
Data are presented as means ± standard deviation IMRT intensity modulated radiotherapy, 3D-CRT 3D-conformal radiotherapy, Dmax maximum point dose within the defined organ at risk, V20, V10 ... percentage of volume of the defined organ at risk receiving more than the indicated dose *Test for statistical significance performed for IMRTnorm vs. 3D-CRT
Summary
The advent of IMRT and image-guided radiotherapy (IGRT) in combination with involved-field radiotherapy (IF-RT) in inoperable non-small-cell lung cancer results in a decreased incidental dose deposition in elective nodal stations. Given the fact that IMRT is of additional benefit with respect to dose escalation and the sparing of relevant organs at risk (OAR) [11,12,13], it is yet unclear if the high dose conformality of IMRT implies an adverse effect on tumor control probability (TCP) for microscopic disease in the “rind”-region outside the clinical target volume This therapeutic backdrop was the incentive to perform the presented in silico-analysis, which is a head-to-head comparison of IMRT and 3DCRT in terms of dose distribution and hypothetical TCP in out-of-field mediastinal and hilar lymph node stations. It was carried out on a group of 41 patients who had participated in the ‘PET-PLAN pilot trial’, which examined the rate of isolated ‘out-of-field’ nodal failures with FDGPET based IF-RT [6]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
