Dose differences in intensity‐modulated radiotherapy plans calculated with pencil beam and Monte Carlo for lung SBRT

Abstract

For patients with medically inoperable early‐stage non‐small cell lung cancer (NSCLC) treated with stereotactic body radiation therapy, early treatment plans were based on a simpler dose calculation algorithm, the pencil beam (PB) calculation. Because these patients had the longest treatment follow‐up, identifying dose differences between the PB calculated dose and Monte Carlo calculated dose is clinically important for understanding of treatment outcomes. Previous studies found significant dose differences between the PB dose calculation and more accurate dose calculation algorithms, such as convolution‐based or Monte Carlo (MC), mostly for three‐dimensional conformal radiotherapy (3D CRT) plans. The aim of this study is to investigate whether these observed dose differences also exist for intensity‐modulated radiotherapy (IMRT) plans for both centrally and peripherally located tumors. Seventy patients (35 central and 35 peripheral) were retrospectively selected for this study. The clinical IMRT plans that were initially calculated with the PB algorithm were recalculated with the MC algorithm. Among these paired plans, dosimetric parameters were compared for the targets and critical organs. When compared to MC calculation, PB calculation overestimated doses to the planning target volumes (PTVs) of central and peripheral tumors with different magnitudes. The doses to 95% of the central and peripheral PTVs were overestimated by 9.7%±5.6% and 12.0%±7.3%, respectively. This dose overestimation did not affect doses to the critical organs, such as the spinal cord and lung. In conclusion, for NSCLC treated with IMRT, dose differences between the PB and MC calculations were different from that of 3D CRT. No significant dose differences in critical organs were observed between the two calculations.PACS number: 87.53.Ly

Dosimetric differences between local failure and local controlled non‐small cell lung cancer patients treated with stereotactic body radiotherapy: A matched‐pair study

“…One of the planning factors is the algorithm used for dose calculation. Previous studies have shown that the use of PB dose results in an over‐estimation of the actual planned dose by approximately 10% . To evaluate the potential impact of tumour underdosing with PB calculation for local failure, we performed a matched‐pair study in which patients with and without local failure were paired and matched for other clinical factors in a population all treated with a dose of 50 Gy in five fractions using the same treatment planning and delivery technique.…”

“…Previous studies have shown that the use of PB dose results in an over-estimation of the actual planned dose by approximately 10%. [9][10][11][12][13][14][15] To evaluate the potential impact of tumour underdosing with PB calculation for local failure, we performed a matched-pair study in which patients with and without local failure were paired and matched for other clinical factors in a population all treated with a dose of 50 Gy in five fractions using the same treatment planning and delivery technique. Cases of local failure were successfully matched to control subjects while accounting for similar lengths of follow-up time and similar clinical features.…”

“…In particular, the inaccuracy of early dose calculation algorithms such as pencil beam (PB) relative to modern methods could have led to lower doses delivered in some cases, resulting in a potentially higher risk of local failure. Studies have shown significant differences in target dose coverage between the clinical plans calculated with pencil beam (PB) algorithms and recalculated plans with more accurate algorithms, such as superposition‐convolution based or Monte Carlo (MC) algorithms . Our institution has over a decade of experience with SBRT treatment for NSCLC with excellent local control rate .…”

“…Studies have shown significant differences in target dose coverage between the clinical plans calculated with pencil beam (PB) algorithms and recalculated plans with more accurate algorithms, such as superposition-convolution based or Monte Carlo (MC) algorithms. [9][10][11][12][13][14][15] Our institution has over a decade of experience with SBRT treatment for NSCLC with excellent local control rate. 5,16 Our initial planning approach utilised PB dose calculation with the BrainLAB iPlan system (BrainLAB AG, Feldkirchen, Germany).…”

Verification of dose profiles generated by the convolution algorithm of the gamma knife® radiosurgery planning system

“…Both studies suggest that the dose‐calculation algorithm should be transitioned from TMR10 to convolution. Prior to this transition, however, the accuracy of the convolution algorithm of the LGP should be verified although the convolution algorithm has been extensively employed and verified in external beam radiotherapies . In this study, we assessed the accuracy of the absolute dose distributions that were obtained with the convolution algorithm of the LGP version 10.1.…”