The influence of a six degrees of freedom couch and an individual head support in patient positioning in radiotherapy of head and neck cancer.

Reproducible patient positioning is important in radiotherapy (RT) of head-and-neck cancer. We therefore compared set-up errors in head-and-neck RT resulting from three different patient positioning systems. Patients were either treated with a standard head support (SHS) and conventional treatment couch (SHS-3, n = 10), a SHS and rotational couch (SHS-6, n = 10), or an individual head support (IHS) and rotational couch (IHS-6, n = 10). Interfraction mean translation vector lenghts were significantly lower for IHS-6 compared to SHS-3 (0.8 ±â€¯0.3 mm vs. 1.4 ±â€¯0.7 mm, P = 0.001). Intrafraction displacement was comparable among cohorts. This study showed that the use of a six degrees of freedom couch combined with an IHS in head-and-neck RT resulted in better interfraction reproducibility.

Breath-hold versus mid-ventilation in SBRT of adrenal metastases.

PURPOSE: To improve local control in radiotherapy of adrenal metastases precise dose delivery without increasing toxicity is vital. Decreasing the Clinical Target Volume (CTV) - Planning Target Volume (PTV) margins by reducing breathing movement can achieve this. Few data were published concerning the effect of a breath-hold technique. This study investigates the potential of Active Breathing Control (ABC) to limit adrenal breathing movement and reduce CTV-PTV margins. METHODS: We compared adrenal gland movement in free-breathing, making use of the Mid-ventilation (MidV) technique, and with ABC. The coordinates of the adrenal glands obtained on ten phases of a free breathing 4D-CT and on several repeat inspiration ABC CT-scans were measured. Separate coordinates, the random margin component and the margin vector norm were computed and compared between the two techniques. RESULTS: We compared the two techniques in 11 patients (21 adrenal glands) and found the largest movement in the Z-direction, with values of 8.7 ±â€¯4.2 mm for MidV and 2.4 ±â€¯1.5 mm for ABC. In 71% of the cases ABC resulted in a smaller margin component than MidV, although non-significant (p ≥ 0.4). CONCLUSION: Movement of the adrenal gland is largest in the Z-direction. The mean difference in the margin vector norm between both techniques was small with large variations over the patient group, the clinical effect of these differences is unknown. Applying an individualised motion management strategy could be beneficial. If a peak-to-peak amplitude above 15 mm in the Z-direction is observed in the MidV scan we advise to examine if a breath-hold technique could reduce margins.

In vivo dosimetry with MOSFETs and GAFCHROMIC films during electron IORT for Accelerated Partial Breast Irradiation.

PURPOSE: The purpose of this study was to compare the delivered dose to the expected intraoperative radiation therapy (IORT) dose with in vivo dosimetry. For IORT using electrons in accelerated partial breast irradiation, this is especially relevant since a high dose is delivered in a single fraction. METHODS: For 47 of breast cancer patients, in vivo dosimetry was performed with MOSFETs and/or GAFCHROMIC EBT2 films. A total dose of 23.33 Gy at dmax was given directly after completing the lumpectomy procedure with electron beams generated with an IORT dedicated mobile accelerator. A protection disk was used to shield the thoracic wall. RESULTS: The results of in vivo MOSFET dosimetry for 27 patients and GAFROMIC film dosimetry for 20 patients were analysed. The entry dose for the breast tissue, measured with MOSFETs, (mean value 22.3 Gy, SD 3.4%) agreed within 1.7% with the expected dose (mean value 21.9 Gy). The dose in breast tissue, measured with GAFCHROMIC films (mean value 23.50 Gy) was on average within 0.7% (SD = 3.7%, range -5.5% to 5.6%) of the prescribed dose of 23.33 Gy. CONCLUSIONS: The dose measured with MOSFETs and GAFROMIC EBT2 films agreed well with the expected dose. For both methods, the dose to the thoracic wall, lungs and heart for left sided patents was lower than 2.5 Gy even when 12 MeV was applied. The positioning time of GAFCHROMIC films is negligible and based on our results we recommend its use as a standard tool for patient quality assurance during breast cancer IORT.

Whole breast proton irradiation for maximal reduction of heart dose in breast cancer patients.

PURPOSE: In left-sided breast cancer radiotherapy, tangential intensity modulated radiotherapy combined with breath-hold enables a dose reduction to the heart and left anterior descending (LAD) coronary artery. Aim of this study was to investigate the added value of intensity modulated proton therapy (IMPT) with regard to decreasing the radiation dose to these structures. METHODS: In this comparative planning study, four treatment plans were generated in 20 patients: an IMPT plan and a tangential IMRT plan, both with breath-hold and free-breathing. At least 97 % of the target volume had to be covered by at least 95 % of the prescribed dose in all cases. Specifically with respect to the heart, the LAD, and the target volumes, we analyzed the maximum doses, the mean doses, and the volumes receiving 5-30 Gy. RESULTS: As compared to IMRT, IMPT resulted in significant dose reductions to the heart and LAD-region even without breath-hold. In the majority of the IMPT cases, a reduction to almost zero to the heart and LAD-region was obtained. IMPT treatment plans yielded the lowest dose to the lungs. CONCLUSIONS: With IMPT the dose to the heart and LAD-region could be significantly decreased compared to tangential IMRT with breath-hold. The clinical relevance should be assessed individually based on the baseline risk of cardiac complications in combination with the dose to organs at risk. However, as IMPT for breast cancer is currently not widely available, IMPT should be reserved for patients remaining at high risk for major coronary events.