Helical tomotherapy (HT) was introduced at the Greater Poland Cancer Centre (GPCC) in April 2009. Retrospective analysis included data from the treatments performed for the first 656 patients treated with HT between May 2009 and May 2012 at the GPCC. In order to evaluate the implications on daily workload and scheduling of patients, stepwise regression and time analysis for each component of the overall treatment time, such as positioning, imaging, registration, and irradiation were performed. A detailed analysis included: (1) learning curves and optimized time needed for positioning and registration; (2) relation between irradiation time and parameters used for plan creation; and (3) average time of daily imaging. The irradiation component has the highest influence on the overall treatment time (R = 0.911). The lowest influence was observed for the imaging (R = 0.670). The learning curve for positioning was 7 months while the reduction of the average daily time needed for registration was observed even after two years. The irradiation time strongly depends on the planning parameters. Changing the pitch from 0.215 to 0.287 for pelvic cancer cases decreased the average daily beam-on time per patient by about 2 minutes. Similar changes for head and neck reduced this time by 1.3 minutes. The limitation in the usage of 1 cm field width only for complex cases, lower than 10 cm in the cranio-caudal direction, reduced the beam-on time per patient by 2 minutes. The average overall treatment time decreased from 21.5 minutes per patient in the first year of the HT usage to 13.8 minutes per patient in current practice. Our current practice shows that for a group of patients including mainly those with pelvis and head and neck cancers, the HT treatment takes approximately 15 minutes per patient allowing 40 patients to be treated within 10 hours.

Aim of the studyHelical tomotherapy is one of the methods of radiotherapy. This method enables treatment implementation for a wide spectrum of clinical cases. The vast array of therapeutic uses of helical tomotherapy results directly from the method of dose delivery, which is significantly different from the classic method developed for conventional linear accelerators. The paper discusses the method of dose delivery by a tomotherapy machine. Moreover, an analysis and presentation of treatment plans was performed in order to show the therapeutic possibilities of the applied technology. Dose distributions were obtained for anaplastic medulloblastoma, multifocal metastases to brain, vulva cancer, tongue cancer, metastases to bones, and advanced skin cancer. Tomotherapy treatment plans were compared with conventional linear accelerator plans.ResultsFollowing the comparative analysis of tomotherapy and conventional linear accelerator plans, in each case we obtained the increase in dose distribution conformity manifested in greater homogeneity of doses in the radiation target area for anaplastic medulloblastoma, multifocal metastases to brain, vulva cancer, metastases to bones, and advanced skin cancer, and the reduction of doses in organs at risk (OAR) for anaplastic medulloblastoma, vulva cancer, tongue cancer, and advanced skin cancer. The time of treatment delivery in the case of a tomotherapy machine is comparable to the implementation of the plan prepared in intensity-modulated radiotherapy (IMRT) technique for a conventional linear accelerator. In the case of tomotherapy the application of a fractional dose was carried out in each case during one working period of the machine. For a conventional linear accelerator the total value of the fractional dose in the case of anaplastic medulloblastoma and metastases to bones was delivered using several treatment plans, for which a change of set-up was necessary during a fraction.ConclusionThe obtained results confirm that tomotherapy offers the possibility to obtain precise treatment plans together with the simplification of the therapeutic system.

Our study showed that for chemoradiation of oropharyngeal cancer, using daily image guidance and proper plan adaptation scheme, the current PRV margin for the SC could be reduced to 4 mm.

In this study, set-up accuracy and time consumption of different image-guidance protocols used for prostate cancer patients were compared. Set-up corrections from 60 prostate cancer patients treated on helical tomotherapy (HT) were used to simulate four types of image-guidance protocols which were based on: (i) a limited number of imaging sessions (IG-1), (ii) reduced registration tasks during daily imaging (IG-2), or (iii) and (iv) mixed methods of imaging (IG-3, IG-4). Each protocol was evaluated for three referencing scenarios based on the first fraction, first three fractions and first five fractions. Residual set-up error, the difference between the average set-up correction and the actual correction required, was used to evaluate the accuracy of each protocol. The first five fractions referencing scenario provides the highest reduction of the margins for each image-guidance protocol evaluated in this study. The first type of protocol is the shortest way to the effective correction of the systematic component of set-up error. For the second type of the protocol, the control of the residual errors is better and, as a result, the reduction of the margins is more significant than that obtained for the first one. Moreover, the second type of the protocol provides the highest accuracy of delivered dose. The result obtained for the fourth type of protocol does not decrease the calculated margins or increase their accuracy in correspondence to the no image guidance scheme. The fourth type of the protocol is not recommended as a protocol to be used to increase the conformity of the dose. The choice of the rest protocols should be validated in the context of (i) institutional practice regarding patient set-up procedure and its time consumption, (ii) acceptable balance between the amount of the dose delivered to the organ at risk and the additional imaging dose and (iii) patient anatomical conditions.

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The study showed that for radiotherapy of NCPSC, the PRV for the lenses could be defined as 2 mm. This margin does not affect the dose distribution in the PTV and effectively reduces the differences between planned and delivered doses in the lenses.

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