Generating arbitrary one-dimensional dose profiles using rotational therapy

Total Body Irradiation and Total Skin Irradiation Techniques in Belgium and the Netherlands: Current Clinical Practice

Purpose

In 2014, a Belgian/Dutch Nederlandse Commissie voor Stralingsdosimetrie (NCS) task group was formed to develop guidelines on the clinical practice of total body irradiation (TBI) and total skin irradiation (TSI).

Methods and Materials

As a basis for these guidelines, a survey conducted among 17 Belgian and Dutch radiation oncology institutions measured the clinical practice of TBI. Four of these institutions also performed TSI. An update was performed in 2019 and 2020 because several institutions innovated their TBI techniques.

Results

As old and more recent studies have shown, clinical protocols for TBI and TSI still vary considerably between institutions.

Conclusions

New radiation therapy technologies have been introduced relatively slowly for TBI purposes.

The impact of different leaf limited accelerations on leaf-positional error of a self-developed MLC prototype

Multi-leaf collimator (MLC) provides an available approach to achieve sophisticated radiotherapy techniques and plays an important role in advanced high quality radiation therapy. Delivery accuracy of radiation therapy mainly depends on the leaf sequence generated by treatment plans and dynamic performance of MLCs. Previous studies have explored the influence of various leaf limited velocities and dose rates on the leaf-positional error. However, there is a lack of research on the influence of different leaf limited accelerations on the delivery accuracy or leaf-positional error. Confining our study to the technique of sliding window, we investigate the effect of various leaf limited accelerations in treatment plans on leaf-positional error of a self-developed MLC prototype. In order to preliminarily verify the assumption, experiments of leaf trajectories sequenced with different limited accelerations under the same displacement were performed. Thereafter, according to the principle of the sliding window technique and the prescribed intensity profile, leaf trajectories for different leaf limited accelerations from 1.0 m/s2 to 5.0 m/s2 were calculated. Conducted on the self-developed MLC prototype, the experiment results have shown that the maximum leaf-positional error can be kept within 0.5 mm while the average and RMS of the leaf-positional error vary from leaf limited accelerations. Under the proposal leaf limited acceleration of 3 m/s2, the self-developed MLC achieved the optimal dynamic performance. In conclusion, for commercial MLCs, optimal constraint for treatment plans should be investigated and determined because incorporation of reasonable servo-mechanical constraints into leaf sequencing algorithm can enhance the conformity between planned and delivered fields.

Accelerating total body irradiation with large field modulated arc therapy in standard treatment rooms without additional equipment

PURPOSE

The aim of this study was to develop a generic and ultra-efficient modulated arc technique for treatment with total body irradiation (TBI) without additional equipment in standard treatment rooms.

METHODS

A continuous gantry arc between 300° and 70° composed of 26 subarcs (5° per subarc) using a field size of 40 × 40 cm(2) was used to perform the initial beam data measurements. The profile was measured parallel to the direction of gantry rotation at a constant depth of 9 cm (phantom thickness 18 cm). Beam data were measured for single 5° subarcs, dissecting the individual contribution of each subarc to a certain measurement point. The phantom was moved to 20 measurement positions along the profile. Then profile optimization was performed manually by varying the weighting factors of all segments until calculated doses at all points were within ± 1 %. Finally, the dose distribution of the modulated arc was verified in phantom thicknesses of 18 and 28 cm.

RESULTS

The measured profile showed a relative mean dose of 99.7 % [standard deviation (SD) 0.7 %)] over the length of 200 cm at a depth of 9 cm. The measured mean effective surface dose (at a depth of 2 cm) was 102.7 % (SD 2.1 %). The measurements in the 28 cm slab phantom revealed a mean dose of 95.9 % (SD 2.9 %) at a depth of 14 cm. The mean dose at a depth of 2 cm was 111.9 % (SD 4.1 %). Net beam-on-time for a 2 Gy fraction is approximately 8 min.

CONCLUSION

This highly efficient modulated arc technique for TBI can replace conventional treatment techniques, providing a homogeneous dose distribution, dosimetric robustness, extremely fast delivery, and applicability in small treatment rooms, with no need for additional equipment.

Dose distribution homogeneity in two TBI techniques-Analysis of 208 irradiated patients conducted in Stanislaw Leszczynski Memorial Hospital, Katowice

BACKGROUND

To analyze and compare dose distribution homogeneity in selected points (especially in the chest wall region) for patients irradiated with two different TBI techniques to achieve a uniform total dose (excluding lungs area) specified in the range of 11.4-14.0 Gy.

MATERIAL AND METHODS

From August 2000 to December 2009, a group of 158 patients was treated by the use of 15 MV photon irradiation consisting of six fractions: four opposed lateral and two anterior-posterior/posterior-anterior (AP/PA). Patients were irradiated with the fraction dose of 2 Gy twice a day for 3 consecutive days. The prescribed dose to PC point (specified at intersection of the beam axis with the mid-plane of the patient irradiated laterally) was 12 Gy. Since January 2010 until closing the study, another group of 50 patients was treated according to a modified protocol. The treatment was carried out in six lateral fractions only, twice a day, for three following days and a lateral lung shield was used for a part of total irradiation time. The measurements of doses in 20 selected points of patient's body were carried out by means of MOSFET detectors.

RESULTS

The modified TBI technique allows to achieve an expected homogenous dose in the points of interest similar to that obtained by using the initial protocol. The calculated and measured in vivo doses met the specified range of 11.4-14 Gy for both applied TBI protocols.

CONCLUSIONS

Our results indicate that for all patients the homogenous dose distribution in the specified range was achieved.