The dosimetric consequences of inter-fractional patient movement on three classes of intensity-modulated delivery techniques in breast radiotherapy

A serial 4DCT study to quantify range variations in charged particle radiotherapy of thoracic cancers

Weekly serial 4DCT scans were acquired under free breathing conditions to assess water-equivalent path length (WEL) variations due to both intrafractional and interfractional changes in tissue thickness and density and to calculate proton dose distributions resulting from anatomical variations observed in serial 4DCT. A template of region of interests (ROIs) was defined on the anterior-posterior (AP) beam's eye view, and WEL measurements were made over these ROIs to quantify chest wall thickness variations. Interfractional proton dose distributions were calculated to assess changes in the expected dose distributions caused by range variations. Mean intrafractional chest wall WEL changes during respiration varied by: -4.1 mm (<-10.2 mm), -3.6 mm (<-7.1 mm), -3.2 mm (<-5.6 mm) and -2.5 mm (<-5.1 mm) during respiration in the ITV, upper, middle and lower lung regions, respectively. The mean interfractional chest wall WEL variation at Week 6 decreased by -4.0 mm (<-8.6 mm), -9.1 mm (<-17.9 mm), -9.4 mm (<-25.3 mm) and -4.5 mm (<-15.6 mm) in the ITV, upper, middle and lower lung regions, respectively. The variations were decomposed into anterior and posterior chest wall thickness changes. Dose overshoot beyond the target was observed when the initial boli was applied throughout the treatment course. This overshoot is due to chest wall thickness variations and target positional variations. The radiological path length can vary significantly during respiration as well as over the course of several weeks of charged particle therapy. Intrafractional/interfractional chest wall thickness changes can be a significant source of range variation in treatment of lung tumors with charged particle beams, resulting in dose distribution perturbations from the initial plan. Consideration of these range variations should be made in choosing the therapeutic charged particle beam range.

Genetic evolutionary taboo search for optimal marker placement in infrared patient setup

In infrared patient setup adequate selection of the external fiducial configuration is required for compensating inner target displacements (target registration error, TRE). Genetic algorithms (GA) and taboo search (TS) were applied in a newly designed approach to optimal marker placement: the genetic evolutionary taboo search (GETS) algorithm. In the GETS paradigm, multiple solutions are simultaneously tested in a stochastic evolutionary scheme, where taboo-based decision making and adaptive memory guide the optimization process. The GETS algorithm was tested on a group of ten prostate patients, to be compared to standard optimization and to randomly selected configurations. The changes in the optimal marker configuration, when TRE is minimized for OARs, were specifically examined. Optimal GETS configurations ensured a 26.5% mean decrease in the TRE value, versus 19.4% for conventional quasi-Newton optimization. Common features in GETS marker configurations were highlighted in the dataset of ten patients, even when multiple runs of the stochastic algorithm were performed. Including OARs in TRE minimization did not considerably affect the spatial distribution of GETS marker configurations. In conclusion, the GETS algorithm proved to be highly effective in solving the optimal marker placement problem. Further work is needed to embed site-specific deformation models in the optimization process.

Optimized Dose Coverage of Regional Lymph Nodes in Breast Cancer: The Role of Intensity-Modulated Radiotherapy

PURPOSE

To determine whether the use of intensity-modulated radiotherapy (IMRT) would lead to improved dosimetry for the breast and regional nodes.

METHODS AND MATERIALS

Ten patients with left-sided breast cancer were selected. The clinical target volume included left breast and internal mammillary (IM), supraclavicular (SC), and axillary (AX) nodes. The critical structures included heart, right and left lungs, contralateral breast, esophagus, thyroid, and humeral head. Conventional and a series of IMRT plans were generated for comparison.

RESULTS

The average heart D(3) was reduced from 31.4 +/- 18.9 with three-dimensional conformal radiotherapy (3D-CRT) to 15 +/- 7.2 Gy with 9-field (9-FLD IMRT). The average left lung D(30) was also decreased from 27.9 +/- 11.5 Gy (3D-CRT) to 12.6 +/- 8.2 Gy (9-FLD IMRT). The average contralateral breast D(2) was reduced from 4.4 +/- 5.3 Gy (3D-CRT) to 1.8 +/- 1.2 Gy (4-FLD IMRT). Esophagus D(2) was increased from 9.3 +/- 8.1 Gy (3D-CRT) to 29.4 +/- 5.4 (9-FLD IMRT); thyroid D(50) was increased from 0.9 +/- 0.6 Gy (3D-CRT) to 11.9 +/- 6.6 (9-FLD IMRT); humeral head D(2) was increased from 36.1 +/- 13.1 Gy (3D-CRT) to 39.9 +/- 6.5 (9-FLD IMRT).

CONCLUSIONS

The use of IMRT improves breast and regional node coverage while decreasing doses to the lungs, heart, and contralateral breast when compared with 3D-CRT. Doses to esophagus, thyroid, and humeral head, however, were increased with IMRT.

Irradiation du cancer du sein : incertitudes liées aux mouvements respiratoires et au repositionnement

Adjuvant Radiotherapy has been shown to significantly reduce locoregional recurrence but this advantage is associated with increased cardiovascular and pulmonary morbidities. All uncertainties inherent to conformal radiation therapy must be identified in order to increase the precision of treatment; misestimation of these uncertainties increases the potential risk of geometrical misses with, as a consequence, underdosage of the tumor and/or overdosage of healthy tissues. Geometric uncertainties due to respiratory movements or set-up errors are well known. Two strategies have been proposed to limit their effect: quantification of these uncertainties, which are then taken into account in the final calculation of safety margins and/or reduction of respiratory and set-up uncertainties by an efficient immobilization or gating systems. Measured on portal films with two tangential fields, CLD (central lung distance), defined as the distance between the deep field edge and the interior chest wall at the central axis, seems to be the best predictor of set-up uncertainties. Using CLD, estimated mean set-up errors from the literature are 3.8 and 3.2 mm for the systematic and random errors respectively. These depend partly on the type of immobilization device and could be reduced by the use of portal imaging systems. Furthermore, breast is mobile during respiration with motion amplitude as high as 0.8 to 10 mm in the anteroposterior direction. Respiratory gating techniques, currently on evaluation, have the potential to reduce effect of these movements. Each radiotherapy department should perform its own assessments and determine the geometric uncertainties with respect of the equipment used and its particular treatment practices. This paper is a review of the main geometric uncertainties in breast treatment, due to respiration and set-up, and solutions proposed to limit their impact.

Intensity-modulated Radiotherapy Planning from Limited Anatomical Information: Is Sim-CT Sufficient for Planning Women with Breast Cancer Receiving Intensity-modulated Radiotherapy?

AIMS

To investigate intensity-modulated radiotherapy (IMRT) plans for women with carcinoma of the breast, using a small number of Sim-CT slices, thus avoiding changing the patient's position and potential problems with CT capacity.

MATERIALS AND METHODS

Ten CT scans of women with breast cancer were obtained for use in the study. IMRT plans based on an open tangent pair and additional top-up segment fields were created using the full CT scan, and represented the gold standard treatment plan for comparison purposes. Five-slice CT simulator scans were artificially created by omitting intermediate slices from the full CT scans. Additionally, the intermediate CT slices were recreated via interpolation of the five slices using a standard interpolation algorithm. IMRT plans were created in the same way as for the full CT scans. To allow a suitable plan comparison to be made, the beam segments and monitor units were transferred to the full CT scans, and the dose distribution calculated.

RESULTS

The interpolated five-slice plans showed no significant difference in the volume of tissue receiving dose outside the range 95-105%, compared with the IMRT plans created using the full CT data set (1.3 +/- 2.2%, P = 0.092). In contrast, the discrete slice CT simulator plans increased by 6.3 +/- 5.4%, P = 0.0054, showing a statistically significant difference in the dose distribution produced and a clinically inferior plan.

CONCLUSIONS

Plans created using five discrete slice CT scans were inferior to full CT-derived IMRT treatment plans, and are therefore not acceptable for IMRT. However, interpolating five CT simulator slices provides adequate anatomical information to produce comparable IMRT plans to those created by full CT scans of the patient. This allows the introduction of IMRT for this patient group without the need to change treatment position to accommodate CT scanning.

Reduction of radiotherapy-induced late complications in early breast cancer: the role of intensity-modulated radiation therapy and partial breast irradiation

Radiotherapy after conservation surgery has been proven to decrease local relapse and death from breast cancer, and is now firmly established in the management of early breast carcinoma. Currently, the challenge is to optimise the therapeutic ratio by minimising treatment-related morbidity, while maintaining or improving local control and survival. The second part of this review examines the role of two approaches: intensity-modulated radiation therapy (IMRT) and partial breast irradiation, as means of improving the therapeutic ratio. Discussion of IMRT includes both inverse- and forward-planned methods: the breast usually requires minimal modulation to improve dose homogeneity, and therefore lends itself to simpler forward-planned IMRT techniques; whereas inverse-planned IMRT may be useful in selected cases. There are many dosimetry studies reporting the superiority of IMRT over conventional breast radiotherapy, but there is still a paucity of clinical data regarding patient benefit from these techniques. A critical literature review of clinical partial breast radiotherapy studies focuses on the influence of irradiated breast volume, dose and fractionation, and patient selection on normal tissue side-effects and local control. Clinical reports of partial breast irradiation show several encouraging, but some concerning results about local recurrence rates. Therefore, mature results from randomised trials comparing partial breast irradiation with whole-breast radiotherapy are required. Accurate localisation of the tumour bed and application of appropriate clinical target volumes and planning target volumes are discussed in detail, as these concepts are fundamental for partial breast irradiation.

Interfractional dose variation due to seromas in radiotherapy of breast cancer

We investigated the interfractional dose variation due to seromas in radiotherapy of breast cancer patients. For 3 patients who received seroma aspiration during the period of radiotherapy, 2 sets of computed tomography (CT) scanning images were obtained before and after seroma aspiration. Three sets of plans employing a conventional technique and an intensity-modulated radiotherapy (IMRT) technique were generated: the first set of plans was the optimal plan for the CT images before seroma aspiration, the second set was the plans that applied the treatment parameters with the first plans but used CT images obtained after seroma treatment, and the third set was the optimal plans for CT images taken after seroma treatment. From the analysis of each set of plans, we found that the patient anatomy change had little effect on the prescription dose (1-2% variation for both techniques) but had significant effects on the dose homogeneity in the treatment volume, which increased the dose inhomogeneity up to 13.9% for conventional treatment and 20.7% for IMRT treatment, respectively.

Dosimetric effects within target and organs at risk of interfractional patient mispositioning in left breast cancer radiotherapy

PURPOSE

To investigate the effects of interfraction setup uncertainties on the dose distribution within the clinical target volume (CTV) and the organs at risk (OAR) of left-sided breast cancer patients undergoing external radiotherapy.

METHODS AND MATERIALS

Interfractional setup errors were assessed by measuring surface control points displacements during 89 irradiation sessions in 4 patients, by means of opto-electronic localization. The measured position deviations were fed back to the treatment planning system for the evaluation of the corresponding dosimetric effects within CTV and OARs (lung, heart).

RESULTS

Results revealed errors above 5 mm on some of the control points, but corresponding volumetric variations were on average below 2% for both the CTV within the 95-105% dose range and the OARs receiving more than 50% and 90% of the prescribed dose. A specific sensitivity to the setup errors was found as a function of the treatment plan design, leading to isolated cases exhibiting volumetric variations of CTV and OARs exceeding 2%.

CONCLUSIONS

This study confirms the potential increase of treatment quality provided by the systematic patient position verification and highlights the role of opto-electronic position detection systems for the real-time check of patient setup errors and the evaluation of the corresponding dosimetric consequences, as a way to achieve consistent dose delivery.