Feasibility of hybrid TomoHelical- and TomoDirect-based volumetric gradient matching technique for total body irradiation

A novel AP/PA total body irradiation technique using abutting IMRT fields at extended SSD

PURPOSE

To develop a Total Body Irradiation (TBI) technique using IMRT at extended SSD that can be performed in any size Linac room.

METHODS

Patients studied were placed on a platform close to the floor, directly under the gantry with cranial-caudal axis parallel to the gantry rotation plane and at SSD ∼200 cm. Two abutting fields with the same external isocenter at gantry angles of ±21˚, collimator angle of 90˚, and field size of 25 × 40 cm2 are employed for both supine and prone positions. An iterative optimization algorithm was developed to generate a uniform dose at the patient mid-plane with adequate shielding to critical organs such as lungs and kidneys. The technique was validated in both phantom and patient CT images for treatment planning, and dose measurement and QA were performed in phantom.

RESULTS

A uniform dose distribution in the mid-plane within ±5% of the prescription dose was reached after a few iterations. This was confirmed with ion-chamber measurements in phantom. The mean dose to lungs and kidneys can be adjusted according to clinical requirements and can be as low as ∼25% of the prescription dose. For a typical prescription dose of 200 cGy/fraction, the total MU was ∼2400/1200 for the superior/inferior field. The overall treatment time for both supine/prone positions was ∼54 min to meet the maximum absorbed dose rate criteria of 15 cGy/min. IMRT QA with portal dosimetry shows excellent agreement.

CONCLUSIONS

We have developed a promising TBI technique using abutting IMRT fields at extended SSD. The patient is in a comfortable recumbent position with good reproducibility and less motion during treatment. An additional benefit of this technique is that full 3D dose distribution is available from the TPS with a DVH summary for organs of interest. The technique allows precise sparing of lungs and kidneys and can be executed in any linac room.

Hybrid Tomo-Helical and Tomo-Direct radiotherapy for localized prostate cancer

PURPOSE

The aim of the study is to present a new planning approach to provide better planning target volume (PTV) coverage and reduce bladder and rectum dose with hybrid Tomo-Helical (TH)/Tomo-Direct (TD) radiotherapy (RT) for localized prostate cancer (LPC).

METHODS

Twenty-five LPC patients were included in this retrospective study. TH plans, TD plans, and hybrid TH/TD plans were created. Lateral beams were used for the hybrid TD plan and the prescribed dose was 70 Gy in 28 fractions (hybrid plans were combined 45 Gy/ 18 fxs for TH and 25 Gy/10 fxs for TD). Doses of PTV (D2%, D98%, D50%, homogeneity index (HI), conformity index (CI), coverage) and organs at risk (OARs) (V50%, V35%, V25%, V5%, and V95%) were analyzed. The Wilcoxon signed-rank test was used to analyze the difference in dosimetric parameters. p-Value < 0.05 was considered statistically significant.

RESULTS

TH plans showed better CI, and target coverage (p < 0.01) than TD and hybrid plans in all patient plan evaluations. However, TD plans D2%, D98%, and D50% doses were better than TH and hybrid plans. The HI values were similar between the three plans. Significant reductions in bladder and rectum V50%, V35%, and V25% doses (p < 0.001) were observed with hybrid plans compared to TH and TD. Penile bulb V95% and bowel V5% doses were better in the hybrid plans. Left and right femoral head V5% doses were higher in the hybrid plan compared to others (p < 0.001).

CONCLUSION

Concurrently hybrid TH/TD RT plan can be a good option to reduce the doses of the rectum and bladder in the RT of LPC.

The effects of rotational setup errors in total body irradiation using helical tomotherapy

Purpose

Helical tomotherapy (HT) is a form of intensity‐modulated radiation therapy that is employed in total body irradiation (TBI). Because TBI targets the whole body, accurate setup positioning at the edge of the treatment volume is made difficult by the whole‐body rotational posture. The purpose of this study is to clarify the tolerance for rotational setup error (SE) in the vertical direction. In addition, we perform a retrospective analysis of actually irradiated dose distributions using previous patients’ irradiation data.

Methods

To clarify the effects of rotational SE on the dose distribution, the planned CT images of 10 patients were rotated by 1–5° in the vertical (pitch) direction to create a pseudo‐rotational SE image. Then, the effect of the magnitude of the rotational SE on the dose distribution was simulated. In addition, the irradiated dose to the patients was analyzed by obtaining recalculated dose distributions using megavoltage CT images acquired before treatment.

Results

The simulation results showed that the average value of the lung volume receiving at least 10 Gy did not exceed the allowable value when the SE value was ≤2°. When the rotational SE was ≤3°, it was possible to maintain the clinical target volume dose heterogeneity within ±10% of the prescribed dose, which is acceptable according to the guidelines. A retrospective analysis of previous patients’ irradiation data showed their daily irradiation dose distribution. The dose to the clinical target volume was reduced by up to 3.4% as a result of the residual rotational SE. Although whole‐course retrospective analyses showed a statistically significant increase in high‐dose areas, the increase was only approximately 1.0%.

Conclusions

Dose errors induced by rotational SEs of ≤2° were acceptable in this study.

Total body irradiation of bone marrow transplant using helical TomoTherapy with a focus on the quality of dose contribution at junction target volumes

PURPOSE

Total body irradiation (TBI) can be safely delivered on TomoTherapy (Accuray, Sunnyvale, CA, USA) in both pediatric and adult patients with proper imaging and planning despite the length constraint of 135 cm. To overcome this limitation, two CT (Computed Tomography) scans (CT1& CT2) are taken in patients above 135 cm in height. Adequate junction dose coverage is important in TBI. Presently, there is no clinical report with a focus on the quality of dose distribution at the CT junction in view of the guidelines on quality of coverage from the RTOG. Hence, our main objectives were to evaluate the dose distribution and quality of coverage at the junction in 16 patients who received TBI using TomoTherapy.

METHODS

PTV(upper) and PTV(lower) along with a junction were created on CT1 and CT2, respectively. Subsequently, the 10 cm junction in the thigh region was divided into five target volumes of 2 cm thickness with dose prescription ranging from 10 to 90% to deliver a total dose equal to 100% when fused.

RESULTS

The D₅₀ was equal to the prescribed dose in most of the cases ranging from 99.5 to 104% for PTV(upper), 100-103% for PTV(lower), and 99.5-108% for junctional PTVs (1PTV, 2PTV, 3PTV, 4PTV, and 5PTV). The average D₉₅ doses from PTV(upper) and PTV(lower) were 97 ± 1.4% and 96.7 ± 1.08%, respectively. The average D₉₅ doses for 1PTV, 2PTV, 3PTV, 4PTV, and 5PTV were 96.1 ± 1.88%, 91.6 ± 1.82%, 87.3 ± 1.5%, 91.6 ± 1.4%, and 96.2 ± 1.5% respectively. Q_RTOG values ranged between 0.85 and 1.05 and were in concordance with RTOG guidelines.

CONCLUSION

Since junction-based planning was required for most TBI patients, it is essential to evaluate the quality of dose coverage in the junction for better TBI plans.

A dosimetric evaluation of a novel technique using abutted radiation fields for myeloablative total body irradiation

Background:

The present study reports myeloablative total body irradiation (TBI) on an isocentrically mounted linac by laying the patient on the floor and management of abutting radiation fields and partial shielding of lungs. Dosimetrical efficacy of this novel technique was evaluated.

Materials and methods:

In this retrospective study, dosimetrical parameters from TBI plans on whole-body CT scans of 46 patients were analysed. The prescribed dose to TBI was 12 Gy in six fractions delivered over a period of 3 days for myeloablative conditioning. TrueBeam STx platform Linac (Varian Medical Systems Inc., Palo Alto, CA, USA) was used to deliver opposing fields. Radiation fields were abutted to form a single large field using an arithmetic formula at source-to-skin-distance of 210 cm.

Results:

Discrepancies in dose calculated by treatment planning system were within 1·6% accuracy, and dose profile at the junction of abutting radiation fields was reproduced within 3·0% accuracy. The real treatment time for each patient was ~30 minutes/fraction. Monitor unit was weighted for multiple sub-fields to achieve dose homogeneity within 5·0% throughout the whole body, and the mean dose to lung was ≤10 Gy.

Conclusion:

Our abutting radiation field technique for myeloablative TBI is feasible in any existing linac bunker. ‘Island-blocking’ is feasible in this technique using multi-leaf collimator. This technique is cost-effective as it does not require any costly equipment than the readily available equipment in any radiotherapy facility. In general, TBI requires laborious planning procedures and spacious linac bunkers; this novel technique has the potential to change previously held notions.

Total marrow and lymphoid irradiation with helical tomotherapy: a practical implementation report

Purpose

To standardize the technique; evaluate resources requirements and analyze our early experience of total marrow and lymphoid irradiation (TMLI) as part of the conditioning regimen before allogenic bone marrow transplantation using helical tomotherapy.

Materials and Methods

Computed tomography (CT) scanning and treatment were performed in head first supine (HFS) and feet first supine (FFS) orientations with an overlap at mid-thigh. Patients along with the immobilization device were manually rotated by 180° to change the orientation after the delivery of HFS plan. The dose at the junction was contributed by a complementary dose gradient from each of the plans. Plan was to deliver 95% of 12 Gy to 98% of clinical target volume with dose heterogeneity <10% and pre-specified organs-at-risk dose constraints. Megavoltage-CT was used for position verification before each fraction. Patient specific quality assurance and in vivo film dosimetry to verify junction dose were performed in all patients.

Results

Treatment was delivered in two daily fractions of 2 Gy each for 3 days with at least 8-hour gap between each fraction. The target coverage goals were met in all the patients. The average person-hours per patient were 16.5, 21.5, and 25.75 for radiation oncologist, radiation therapist, and medical physicist, respectively. Average in-room time per patient was 9.25 hours with an average beam-on time of 3.32 hours for all the 6 fractions.

Conclusion

This report comprehensively describes technique and resource requirements for TMLI and would serve as a practical guide for departments keen to start this service. Despite being time and labor intensive, it can be implemented safely and robustly.

Intensity-modulated radiation therapy for multiple targets with tomotherapy using multiple sets of static ports from different angles

BACKGROUND

To treat multiple targets separated in the craniocaudal direction within a short time, we invented a new technique using multiple static-port tomotherapy with the dynamic-jaw mode and named it the pseudo-DJDC (pDJDC) technique. We compared the pDJDC plans and helical tomotherapy plans using the dynamic-jaw mode (HDJ) for multiple targets. In the pDJDC plans, we used a beam set with 2-7 ports to the targets at the same level in the craniocaudal direction, and employed another beam set for other targets using different port angles (9-12 angles in total).

METHODS

In seven patients, two plans using the pDJDC and HDJ techniques were compared. For multiple targets (n = 2-6), 20-60 Gy in 2- to 7.5-Gy fractions were prescribed for the planning target volumes at D50%. The conformity index, uniformity index (D5%/D95%), dose distribution in the lung, and treatment time were evaluated.

RESULTS

The median conformity index of all seven patients was 3.0 for the pDJDC plans and 2.4 for the HDJ plans (P = 0.031). The median uniformity indices of the planning target volume (n = 25) for the two plans were 1.048 and 1.057, respectively (P = 0.10). For five patients with thoracic targets, the median mean lung doses were 2.6 Gy and 2.4 Gy, respectively (P = 0.63). The median V5Gy and V20Gy of the lungs in the five patients were 11.8% and 8.5% (P = 0.63), and 1.6% and 2.1% (P = 0.31), respectively. The pDJDC plans reduced the treatment time by 48% compared to the HDJ plans (median: 462 and 884 sec, respectively, P = 0.031).

CONCLUSION

The pDJDC technique allows treatment of multiple targets in almost half the time of the HDJ technique. The pDJDC plans were comparable to the HDJ plans in dose distribution, although the conformity index deteriorated.