Can a total body irradiation technique be fast and reproducible?

Preclinical validation and treatment of volumetric modulated arc therapy based total bone marrow irradiation in Halcyon™ ring gantry linear accelerator

AIM

This study aims​ to report preclinical validation, and the first clinical treatment of total bone marrow irradiation (TMI) and total bone marrow and lymph nodal irradiation (TMLI) using Volumetric modulated arc therapy in Halcyon-E ring gantry linear accelerator. Preclinical validation includes simulation, planning, patient-specific QA, and dry run.

MATERIAL AND METHOD

Four patients, two female and two male, with body weights of 116 kg, 52 kg, 64 kg, and 62 kg; with two with chronic myeloid leukemia, one each with acute lymphoblastic leukemia and acute myeloid leukemia (AML) were simulated and planned for TMI/TMLI. Patients were immobilized with a full-body vacuum bag. Head first supine (HFS) and Feet first supine (FFS) CT scans were acquired from head to knee and knee to toe. Planning target volume (PTV) was created with a uniform margin of 6 mm over the total bone marrow/bone marrow + lymph nodes. HFS and FFS PTVs were optimized independently using 6MV unflatten energy for 12 Gy in 6 fractions. Plans were merged to create the resultant dose distribution using a junction bias dose matching technique. The total number of isocenters was ≤ 10 per CT set, and two to four full arcs were used for each isocenter. A junction dose gradient technique was used for dose feathering between arcs between adjacent isocenters.

RESULT

Only one female patient diagnosed as AML received the TMLI treatment, while the other three patients dropped out due to clinical complications and comorbidities that developed in the time between simulation and treatment. The result presented has been averaged over all four patients. For PTV, 95% dose was normalised to 95% volume, PTV_V107% receiving 3.3 ± 3.1%. Total lung mean and V12Gy were 1048.6 ± 107.1 cGy and 19.5 ± 12.1%. Maximum lens doses were 489.5 ± 35.5 cGy (left: L) and 497 ± 69.2 cGy (right: R). The mean cardiac and bilateral kidney doses were 921.75 ± 89.2 cGy, 917.9 ± 63.2 cGy (L), and 805.9 ± 9.7 cGy (R). Average Monitor Unit was 7738.25 ± 1056.6. The median number of isocenters was 17(HFS+FFS), average MU/Dose (cGy) ratio per isocenter was 2.28 ± 0.3.

CONCLUSION

Halcyon-E ring gantry linear accelerator capable of planning and delivering TMI/TMLI.​​.

Feasibility study of volumetric modulated arc therapy with Halcyon™ linac for total body irradiation

Background

The use of total body irradiation (TBI) with linac-based volumetric modulated arc therapy (VMAT) has been steadily increasing. Helical tomotherapy has been applied in TBI and total marrow irradiation to reduce the dose to critical organs, especially the lungs. However, the methodology of TBI with Halcyon™ linac remains unclear. This study aimed to evaluate whether VMAT with Halcyon™ linac can be clinically used for TBI.

Methods

VMAT planning with Halcyon™ linac was conducted using a whole-body computed tomography data set. The planning target volume (PTV) included the body cropped 3 mm from the source. A dose of 12 Gy in six fractions was prescribed for 50% of the PTV. The organs at risk (OARs) included the lens, lungs, kidneys, and testes.

Results

The PTV D_98%, D_95%, D_50%, and D_2% were 8.9 (74.2%), 10.1 (84.2%), 12.6 (105%), and 14.2 Gy (118%), respectively. The homogeneity index was 0.42. For OARs, the D_mean of the lungs, kidneys, lens, and testes were 9.6, 8.5, 8.9, and 4.4 Gy, respectively. The V_12Gy of the lungs and kidneys were 4.5% and 0%, respectively. The D_max of the testes was 5.8 Gy. Contouring took 1–2 h. Dose calculation and optimization was performed for 3–4 h. Quality assurance (QA) took 2–3 h. The treatment duration was 23 min.

Conclusions

A planning study of TBI with Halcyon™ to set up VMAT-TBI, dosimetric evaluation, and pretreatment QA, was established.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13014-021-01959-3.

Comparison of different TBI techniques in terms of dose homogeneity - review study

Total body irradiation (TBI) is a kind of external beam radiotherapy, used in conjunction with chemotherapy with the purpose of immunosuppression. Since the target in TBI is the whole body, so achieving uniform dose distribution throughout the entire body during TBI is necessary. As recommended by AAPM dose variation must be within ±10% of the prescription dose. With the evidences from literature there is limited substantiation to consider a treatment method better than others, but with regard to the size of the treatment room, workload of the radiotherapy department and prevalent technology used within each treatment department it is recommended to make the suitable and optimum method in each department. In this work, a review study was performed on different TBI techniques with the purpose of assessment and comparison of dose distribution homogeneity in these methods.

Dose-escalated volumetric modulated arc therapy for total marrow irradiation: A feasibility dosimetric study with 4DCT planning and simultaneous integrated boost

PURPOSE

To evaluate the planning feasibility of dose-escalated total marrow irradiation (TMI) with simultaneous integrated boost (SIB) to the active bone marrow (ABM) using volumetric modulated arc therapy (VMAT), and to assess the impact of using planning organs at risk (OAR) volumes (PRV) accounting for breathing motion in the optimization.

METHODS

Five patients underwent whole-body CT and thoraco-abdominal 4DCT. A planning target volume (PTV) including all bones and ABM was contoured on each whole-body CT. PRV of selected OAR (liver, heart, kidneys, lungs, spleen, stomach) were determined with 4DCT. Planning consisted of 9-10 full 6 MV photon VMAT arcs. Four plans were created for each patient with 12 Gy prescribed to the PTV, with or without an additional 4 Gy SIB to the ABM. Planning dose constraints were set on the OAR or on the PRV. Planning objective was a PTV D_mean < 110% of the prescribed dose, a PTV V_110% < 50%, and OAR D_mean ≤ 50-60%.

RESULTS

PTV D_mean < 110% was accomplished for most plans (n = 18/20), while all achieved V_110%<50%. SIB plans succeeded to optimally cover the boost volume (median ABM D_mean = 16.3 Gy) and resulted in similar OAR sparing compared to plans without SIB (median OAR D_mean = 40-54% of the ABM prescribed dose). No statistically significant differences between plans optimized with constraints on OAR or PRV were found.

CONCLUSIONS

Adding a 4 Gy SIB to the ABM for TMI is feasible with VMAT technique, and results in OAR sparing similar to plans without SIB. Setting dose constraints on PRV does not impair PTV dosimetric parameters.

Image-guided total-body irradiation with a movable electronic portal imaging device for bone marrow transplant conditioning

INTRODUCTION

To prevent radiation pneumonitis following total body irradiation (TBI) clinicians usually use lung shield blocks. The correct position of these shields relative to the patient's lungs is usually verified via mega-voltage imaging and computed radiographic (CR) films. In order to improve this time-consuming procedure, we developed in our department a dedicated, movable, real-time imaging system for image-guided TBI.

MATERIAL & METHODS

The system consists of an electronic portal imaging device (EPID) mounted on a dedicated support whose motion along a rail can be controlled from the linac console outside the bunker room. Images are acquired online using a stand-alone console. To test the system efficacy we retrospectively analyzed data of lung blocks positioning from two groups of 10 patients imaged with EPID or CR-films, respectively.

RESULTS

The median number of portal images per fraction was 2 (range 1-5) and 1 (range 1-2) for the EPID and the CR-film system, respectively. The minimum time required for an EPID image acquisition, without interpretation and no need of patient position correction in the bunker, was 20seconds against 214seconds for the CR-film. Lung shielding positioning in the right-left and superior-inferior directions was improved using the EPID system (p<0.01).

CONCLUSIONS

Compared to CR-films, our movable real-time imaging EPID system is a simple technical solution able to reduce the minimum imaging time for lung shielding by a factor of 10. With the increased possibility to acquire more images as compared to CR-film system the EPID system has the potential to improve patient alignment, as well as patient's comfort and overall setup time.

Higher Reported Lung Dose Received During Total Body Irradiation for Allogeneic Hematopoietic Stem Cell Transplantation in Children With Acute Lymphoblastic Leukemia Is Associated With Inferior Survival: A Report from the Children's Oncology Group

PURPOSE

To examine the relationship between lung radiation dose and survival outcomes in children undergoing total body irradiation (TBI)-based hematopoietic stem cell transplantation (HSCT) for acute lymphoblastic leukemia on the Children's Oncology Group trial.

METHODS AND MATERIALS

TBI (1200 or 1320 cGy given twice daily in 6 or 8 fractions) was used as part of 3 HSCT preparative regimens, allowing institutional flexibility regarding TBI techniques, including lung shielding. Lung doses as reported by each participating institution were calculated for different patient setups, with and without shielding, with a variety of dose calculation techniques. The association between lung dose and transplant-related mortality, relapse-free survival, and overall survival (OS) was examined using the Cox proportional hazards regression model controlling for the following variables: TBI dose rate, TBI fields, patient position during TBI, donor type, and pre-HSCT minimal residual disease level.

RESULTS

Of a total of 143 eligible patients, 127 had lung doses available for this analysis. The TBI techniques were heterogeneous. The mean lung dose was reported as 904.5 cGy (standard deviation, ±232.3). Patients treated with lateral fields were more likely to receive lung doses ≥800 cGy (P < .001). The influence of lung dose ≥800 cGy on transplant-related mortality was not significant (hazard ratio [HR], 1.78; P = .21). On univariate analysis, lung dose ≥800 cGy was associated with inferior relapse-free survival (HR, 1.76; P = .04) and OS (HR, 1.85; P = .03). In the multivariate analysis, OS maintained statistical significance (HR, 1.85; P = .04).

CONCLUSIONS

The variability in TBI techniques resulted in uncertainty with reported lung doses. Lateral fields were associated with higher lung dose, and thus they should be avoided. Patients treated with lung dose <800 cGy in this study had better outcomes. This approach is currently being investigated in the Children's Oncology Group AALL1331 study. Additionally, the Imaging and Radiation Oncology Core Group is evaluating effects of TBI techniques on lung doses using a phantom.

Technical Note: Quality assurance and relative dosimetry testing of a 60 Co total body irradiator using optical imaging

PURPOSE

The aim of this study was to create an optical imaging-based system for quality assurance (QA) testing of a dedicated Co-60 total body irradiation (TBI) machine. Our goal is to streamline the QA process by minimizing the amount time necessary for tests such as verification of dose rate and field homogeneity.

METHODS

Plastic scintillating rods were placed directly on the patient treatment couch of a dedicated TBI ⁶⁰ Co irradiator. A tripod-mounted intensified camera was placed directly adjacent to the couch. Images were acquired over a 30-s period once the cobalt source was fully exposed. Real-time image filtering was used; cumulative images were flatfield corrected as well as background and darkfield subtracted. Scintillators were used to measure light-radiation field correspondence, dose rate, field homogeneity, and symmetry. Dose rate effects were measured by modifying the height of the treatment couch and scintillator response was compared to ionization chamber (IC) measurements. Optically stimulated luminesce detector (OSLD) used as reference dosimeters during field symmetry and homogeneity testing.

RESULTS

The scintillator-based system accurately reported changes in dose rate. When comparing normalized output values for IC vs scintillators over a range of source-to-surface distances, a linear relationship (R²  = 0.99) was observed. Normalized scintillator signal matched OSLD measurements with <1.5% difference during field homogeneity and symmetry testing. Beam symmetry across both axes of the field was within 2%. The light field was found to correspond to 90 ± 3% of the isodose maximum along the longitudinal and latitudinal axis, respectively. Scintillator imaging output results using a single image stack requiring no postexposure processing (needed for OSLD) or repeat manual measurements (needed for IC).

CONCLUSION

Imaging of scintillation light emission from plastic rods is a viable and efficient method for carrying out TBI ⁶⁰ Co irradiator QA. We have shown that this technique can accurately measure field homogeneity, symmetry, light-radiation field correspondence, and dose rate effects.

Effect of electron contamination on in vivo dosimetry for lung block shielding during TBI

Our institution performs in vivo verification measurement for each of our total body irradiation (TBI) patients with optically stimulated luminescent dosimeters (OSLD). The lung block verification measurements were commonly higher than expected. The aim of this work is to understand this discrepancy and improve the accuracy of these lung block verification measurements. Initially, the thickness of the lung block was increased to provide adequate lung sparing. Further tests revealed the increase was due to electron contamination dose emanating from the lung block. The thickness of the bolus material covering the OSLD behind the lung block was increased to offset the electron contamination. In addition, the distance from the lung block to the dosimeter was evaluated for its effect on the OSLD reading and found to be clinically insignificant over the range of variability in our clinic. The results show that the improved TBI treatment technique provides for better accuracy of measured dose in vivo and consistency of patient setup.

PACS number(s): 87.53.Bn, 87.53.Kn, 87.55.N‐, 87.55.Qr

An Evidence-Based Review of Total Body Irradiation

The purpose of this literature review is to investigate clinical treatment methods of total body irradiation within the context of a clinical department adopting a paediatric cohort with no existing technique. An extensive review of the literature was conducted using PubMed, Science Direct, Google Scholar, and Clinicians Knowledge Network. Articles were limited to nonhelical tomotherapy, nonparticle therapies, and those using hyperfractionated regimes. Total marrow irradiation was excluded because of national treatment and trial limitations. Of the numerous patient positioning methods present within the literature, the most comfortable and reproducible positioning methods for total body irradiation include both supine and the supine and/or prone combination. These positions increased stability and patient comfort during treatment, while also facilitating computed tomography data acquisition at the simulation stage. Ideally, dose calculations should be performed using a three-dimensional treatment planning system and quality assurance procedures that include in vivo dosimetry measurements. The available literature also suggests inhomogeneity correction factors and intensity modulation are superior to conventional open field techniques and should be implemented within developing protocols. Dynamic machine dose modulation is suggested to reduce department impact, removing the need for tissue compensators and accessory shielding devices, while providing significant improvements to treatment time and dose accuracy. Further long-term survival and intensity modulation studies are warranted, including direct comparisons of both dose modulation and treatment efficiency.

Total body irradiation with step translation and dynamic field matching

The purpose of this study is to develop a total body irradiation technique that does not require additional devices or sophisticated processes to overcome the space limitation of a small treatment room. The technique aims to deliver a uniform dose to the entire body while keeping the lung dose within the tolerance level. The technique treats the patient lying on the floor anteriorly and posteriorly. For each AP/PA treatment, two complementary fields with dynamic field edges are matched over an overlapped region defined by the marks on the body surface. A compensator, a spoiler, and lung shielding blocks were used during the treatment. Moreover, electron beams were used to further boost the chest wall around the lungs. The technique was validated in a RANDO phantom using GAFCHROMIC films. Dose ratios at different body sites along the midline ranged from 0.945 to 1.076. The dose variation in the AP direction ranged from 96.0% to 104.6%. The dose distribution in the overlapped region ranged from 98.5% to 102.8%. Lateral dose profiles at abdomen and head revealed 109.8% and 111.7% high doses, respectively, at the body edges. The results confirmed that the technique is capable of delivering a uniform dose distribution to the midline of the body in a small treatment room while keeping the lung dose within the tolerance level.

Outcome and risk factors for late-onset complications 24 months beyond allogeneic hematopoietic stem cell transplantation

OBJECTIVES

The aim of this retrospective study was to assess the incidence of late complications occurring ≥2 years after allogeneic hematopoietic stem cell transplantation (HSCT) for malignant diseases using a T-cell depletion strategy.

METHODS

Between 1984 and 2004, 142 patients were eligible for the study. Total body irradiation (TBI) was carried out in 85% of the patients and T-cell depletion in 84%.

RESULTS

Non-relapse mortality (NRM) was 3% (95% CI 0-11) at 10 years, and serious late events affected a substantial number of patients. The cumulative incidence (CI) of chronic graft-versus-host disease (cGvHD) was 30% (95% CI 23-40), and that of infectious complications was 17% (95% CI 11-23). Multivariate analysis showed a higher risk for late complications in patients with cGvHD (HR 1.9, 95% CI 1.2-3.2, P=0.011) and patients receiving methylprednisolone during conditioning (HR 1.9, 95% CI 1.1-3.3, P=0.019 1), patients with cGvHD also having a higher risk for NRM (HR 13.2, 95% CI 1.2-143, P=0.03), as well as those receiving steroids for >3 months (HR 40.3, 95% CI 2.3-718, P=0.02) and those receiving antithymocyte globulin (HR 9.6, 95% CI 0.8-68, P=0.024).

CONCLUSIONS

A significant proportion of long-term survivors of HSCT had late complications. cGvHD remained an important risk factor for late complications despite T-cell depletion resulting in immunosuppression and infectious complications.

Implementation of a lateral total body irradiation technique with 6 MV photons: The University of Texas Health Science Center in San Antonio experience

Purpose: Total body irradiation (TBI) involves delivery of marrow-ablative or suppressive dose to the entirety of the marrow habitus. In its current practice, TBI often involves positioning the patient in an uncomfortable upright body position for extended periods of time while delivering radiation dose via anteroposterior/posterioanterior (AP/PA) fields. In an effort to maximize reproducibility and patient comfort, especially for paediatric patients, a supine lateral total body irradiation (LTBI) protocol was implemented as preparatory regimen for bone marrow transplant.

Methods and Materials: One hundred and forty-five patient charts were reviewed. Patients were treated in supine position with hands clasped over the upper abdomen in a comfortable position. They were placed in a methylcrylate body box and irradiated with opposed lateral fields at extended distance of 350 cm to the midplane of the patient. Each field delivered 100 cGy with a midplane dose of 200 cGy per fraction. Dose regimes varied from 200 to 1,200 cGy total doses. Custom lead compensating filters were utilized. A 6 MV photon beam produced by a Varian Clinac 600c linear accelerator was applied. In vivo thermoluminescent dosimeter (TLD) readings were taken for anatomical regions of interest (ROI). TLDs were placed in each ROI under a 1.5-cm-thick bolus for maximum dose build-up.

Results and Conclusion: The resulting data demonstrate a dosimetric variability of anatomical ROI from reference prescription dose of less than 3%. LTBI has been used for more than ten years in our institution and produced favourable results for more than 100 patients. We suggest this LTBI approach to facilitate successful treatment of children who require TBI while maintaining dose uniformity as recommended by the American Association of Physicists in Medicine Report 17.

[Total body irradiation: present and future]

Total body irradiation (TBI) has an established role as preparative regimen for bone-marrow transplantation in the treatment of hematological malignancies. Many randomized trials demonstrated that the clinical outcomes obtained from the association of TBI and cyclophosphamide are equivalent, or, sometimes, better than those based on chemotherapeutic agents. Despite the therapeutic progress of the last years, and the consequent improvement in the overall survival, this preparative regimen remains always associated with a relatively high rate of acute and late toxicity. In this article, we review the actual indications of TBI in clinical practice, and analyze the technological progress in this domain. We focus on the hypothesis that a selective irradiation of the hematopoietic or lymphoid organs is actually possible with intensity-modulated radiotherapy. Technical limits and preliminary results in terms of acute and late toxicities of intensity-modulated TBI are analyzed. With these new technologies, treatment-related toxicity is not anymore a major limiting factor in the preparative regimens for bone-marrow transplantation, allowing for a larger spectrum of TBI indications, a possible extension to patients older than 50 years, or a dose escalation. Preliminary results warrant, however, further evaluation in clinical trials to better assess the impact of this new approach on disease control and the long-term toxicity.

Renal insufficiency in patients with hematologic malignancies undergoing total body irradiation and bone marrow transplantation: a prospective assessment

PURPOSE

Patients with malignant hematologic disorders undergoing bone marrow transplantation (BMT) may develop renal insufficiency. A study was undertaken to assess prospectively the subclinical renal function changes with radioisotopic methods in patients undergoing BMT for hematologic malignancies.

METHODS AND MATERIALS

We studied 71 patients with normal renal function undergoing BMT for various hematologic malignancies, mostly leukemias. Conditioning included chemotherapy and 12 Gy (45 patients) or 13.5 Gy (26 patients) fractionated total-body irradiation (TBI). In 21 patients receiving 12 Gy TBI, the kidney dose was limited to 10 Gy using partial transmission blocks fabricated after renal opacification with nonionic, hypo-osmolar contrast medium. The glomerular filtration rate (GFR) and effective renal plasmatic flow (ERPF) were determined radioisotopically before conditioning and at 4, 12, and 18 months, using (51)Cr ethylene-diamine-tetra-acetic acid and (131)I ortho-iodo-hippurate, respectively. Renal insufficiency was defined as a decrease of >/=30% in GFR or ERPF compared with the baseline values. The potential influence of patient- and treatment-related variables on renal dysfunction was assessed.

RESULTS

At 4 (early) and 12-18 (late) months, a >/=30% GFR drop was observed in 54% and 49% of patients and a >/=30% ERPF drop in 44% and 34% of patients, respectively. After stepwise logistic analysis, a GFR reduction at 4 months correlated significantly with age (<40 years old, worse), TBI using kidney blocks (partial kidney shielding to 10 Gy was associated with a higher rate of renal dysfunction at 4 months compared with the full TBI dose), and days of aminoglycoside/vancomycin use. An ERPF drop at 4 months was independently related with the days of amphotericin use and days of prostaglandin E(1) use (prophylaxis against hepatic venoocclusive disease). A GFR and ERPF reduction at 12-18 months correlated with days of amphotericin use and days of prostaglandin E(1) use, respectively.

CONCLUSION

Early post-BMT renal dysfunction is associated with the administration of potentially nephrotoxic drugs. An inverse correlation with the prescribed TBI dose was observed; patients whose kidneys received 10 Gy through the use of partial shielding blocks had significantly greater renal dysfunction at 4 months. The administration of potentially nephrotoxic contrast agents used in radiotherapy treatment planning may be responsible for the latter observation. Prostaglandin E(1) use correlated with a significant reduction in ERPF at both 4 and 12-18 months.

Renal toxicity after total body irradiation

PURPOSE

To evaluate the incidence of renal dysfunction after total body irradiation (TBI).

METHODS AND MATERIALS

Between 1990 and 1997, 64 patients (median age 50 years) received TBI as part of the conditioning regimen before bone marrow transplantation (BMT). Five patients with abnormal renal function at the beginning of treatment or with incomplete data were excluded. All patients received a total of 12 Gy (6 fractions twice daily for 3 consecutive days) prescribed to the peak lung dose (corrected for lung transmission) at a dose rate of 7.5 cGy/min. Renal shielding was not used. Renal dysfunction was assessed on the basis of the serum creatinine levels measured at the start and end of TBI and at 6, 12, 18, and 24 months after completion of BMT. Cox proportional hazard analysis was used to evaluate the various factors known to affect renal function.

RESULTS

Only 4 patients had elevated serum creatinine levels at 12 months and subsequently only 2 of the 33 surviving patients had persistent elevated renal serum creatinine levels 24 months after BMT. A fifth patient developed proteinuria and mildly elevated serum creatinine levels at 2.5 years. In 2 patients, the elevation coincided with disease relapse and normalized once remission was achieved. In the third patient, the elevation in serum creatinine levels coincided with relapse of multiple myeloma and the presence of Bence-Jones proteinuria. The fourth patient was the only patient who developed chronic renal failure secondary to radiation nephritis at 2 years. The etiology of the fifth patient's rise in creatinine was unknown, but may have been secondary to radiation nephritis. On univariate analysis, but not on multivariate analysis, a significant correlation was found between TBI-related renal dysfunction and hypertension before and after BMT.

CONCLUSION

A dose of 12 Gy at 2 Gy/fraction resulted in only 1 case of radiation nephritis in the 59 patients studied 24 months after the completion of TBI and BMT.

Dose compensation of the total body irradiation therapy

The aim of the study is to improve dose uniformity in the body by the compensator-rice and to decrease the dose to the lung by the partial lung block. Rando phantom supine was set up to treat bilateral fields with a 15 MV linear accelerator at 415cm treatment distance. The experimental procedure included three parts. The first part was the bilateral irradiation without rice compensator, and the second part was with rice compensator. In the third part, rice compensator and partial lung block were both used. The results of thermoluminescent dosimeters measurements indicated that without rice compensator the dose was non-uniform. Contrarily, the average dose homogeneity with rice compensator was measured within +/- 5%, except for the thorax region. Partial lung block can reduce the dose which the lung received. This is a simple method to improve the dose homogeneity and to reduce the lung dose received. The compensator-rice is cheap, and acrylic boxes are easy to obtain. Therefore, this technique is suitable for more studies.

Total body irradiation before allogeneic bone marrow transplantation: is more dose better?

PURPOSE

This study was performed to retrospectively assess the potential influence of total-body irradiation (TBI) dose on overall survival in patients undergoing allogeneic bone-marrow transplants (BMT) for hematologic malignancies.

METHODS AND MATERIALS

Between October 1984 and December 1996, 116 patients were conditioned with high-dose chemotherapy and fractionated TBI before allogeneic BMT. The median age was 34 years (range 3-60). The TBI dose was given in 6 fractions, twice-a-day, over 3 days before BMT. The total dose was 10 Gy in 24 patients, 12 Gy in 66 patients, and 13.5 Gy in 26 patients.

RESULTS

TBI dose was inversely correlated with overall survival. Five-year survival was 62% for patients conditioned with 10 Gy, 55% for patients conditioned with 12 Gy, and 46% for patients conditioned with 13.5 Gy. Age at BMT was also independently correlated with survival, with the best outcome for patients < 40 years old.

CONCLUSION

A TBI dose (fractionated) > 10 Gy may not necessarily be associated with a better outcome in patients undergoing allogeneic bone-marrow transplant for hematologic malignancies.

Set-up verification using portal imaging; review of current clinical practice

In this review of current clinical practice of set-up error verification by means of portal imaging, we firstly define the various types of set-up errors using a consistent nomenclature. The different causes of set-up errors are then summarized. Next, the results of a large number of studies regarding patient set-up verification are presented for treatments of patients with head and neck, prostate, pelvis, lung and breast cancer, as well as for mantle field/total body treatments. This review focuses on the more recent studies in order to assess the criteria for good clinical practice in patient positioning. The reported set-up accuracy varies widely, depending on the treatment site, method of immobilization and institution. The standard deviation (1 SD, mm) of the systematic and random errors for currently applied treatment techniques, separately measured along the three principle axes, ranges from 1.6-4.6 and 1.1-2.5 (head and neck), 1.0-3.8 and 1.2-3.5 (prostate), 1.1-4.7 and 1.1-4.9 (pelvis), 1.8-5.1 and 2.2-5.4 (lung), and 1.0-4.7 and 1.7-14.4 (breast), respectively. Recommendations for procedures to quantify, report and reduce patient set-up errors are given based on the studies described in this review. Using these recommendations, the systematic and random set-up errors that can be achieved in routine clinical practice can be less than 2.0 mm (1 SD) for head and neck, 2.5 mm (1 SD) for prostate, 3.0 mm (1 SD) for general pelvic and 3.5 mm (1 SD) for lung cancer treatment techniques.

A variable speed translating couch technique for total body irradiation

We have developed a variable speed translating patient couch system for the delivery of total body irradiation (TBI). For a whole body Rando-type phantom, dose variation at mid-plane relative to the prescription point (navel) can be as high as 15% (neck or legs) with a constant velocity. By taking into account variations in body thickness, the intensity modulation radiation therapy, resulting from variable velocities, effectively delivers a uniform dose distribution at mid plane. The couch control user interface, technical aspects and dose planning optimization procedure for determining velocity distribution are described.

The clinical application of dynamic shielding and imaging in moving table total body irradiation

The moving table technique for total body irradiation (MTT TBI) has some advantages in regard to dose homogeneity, patient positioning and comfort. However, divergence of the radiation field coupled with patient motion necessitates corresponding motion of the shielding blocks and verification film so that penumbra is minimized. MTT TBI system is presented, together with dose calculations, incorporating moving trays for shields and film to ensure dose delivery with minimal penumbra of the blocked field.

In vivo dosimetry during external photon beam radiotherapy

In this critical review of the current practice of patient dose verification, we first demonstrate that a high accuracy (about 1-2%, 1 SD) can be obtained. Accurate in vivo dosimetry is possible if diodes and thermoluminescence dosimeters (TLDs), the main detector types in use for in vivo dosimetry, are carefully calibrated and the factors influencing their sensitivity are taken into account. Various methods and philosophies for applying patient dose verification are then evaluated: the measurement of each field for each fraction of each patient, a limited number of checks for all patients, or measurements of specific patient groups, for example, during total body irradiation (TBI) or conformal radiotherapy. The experience of a number of centers is then presented, providing information on the various types of errors detected by in vivo dosimetry, including their frequency and magnitude. From the results of recent studies it can be concluded that in centers having modern equipment with verification systems as well as comprehensive quality assurance (QA) programs, a systematic error larger than 5% in dose delivery is still present for 0.5-1% of the patient treatments. In other studies, a frequency of 3-10% of errors was observed for specific patient groups or when no verification system was present at the accelerator. These results were balanced against the additional manpower and other resources required for such a QA program. It could be concluded that patient dose verification should be an essential part of a QA program in a radiotherapy department, and plays a complementary role to treatment-sheet double checking. As the radiotherapy community makes the transition from the conventional two-dimensional (2D) to three-dimensional (3D) conformal and intensity modulated dose delivery, it is recommended that new treatment techniques be checked systematically for a few patients, and to perform in vivo dosimetry a few times for each patient for situations where errors in dose delivery should be minimized.

Partial lung shield for TBI

In this study, AP/PA setup was used with a 4 MV linear accelerator. The prescribed dose is 1000 cGy, with a dose per fraction of 200 cGy. One of the simplest lung dose determinations is the nomograph relating dose correction factor and patient thickness. To save time in taking port film in every treatment, lung block is used in alternating fashion: anterior blocks are used in the second and fourth fraction and posterior block is used in the third and fifth fraction. If we set the average correction factor for the lower density lung to 1.18, the six open fields will deliver an average of 708 cGy to the lung. To limit the lung dose to 10 Gy, each blocked field should deliver 73 cGy. Measurements showed that a thickness of slightly less than 1 cm of cerrobend provides approximately 65% transmission, which approximates the desired 73% broad beam transmission. The proper transmission of the partial lung shield is verified by measurements made for the patients with diodes placed at the entrance and the exit side of the lung. While we describe a particular setup, the procedure can be modified to accommodate different dose fraction. There are many ways to deliver the TBI dose, and the method of constructing the partial lung shield described here is one of the many methods that may be used to limit the dose to the lung.

Midplane dose determination during total body irradiation using in vivo dosimetry

BACKGROUND AND PURPOSE

During TBI techniques an accurate determination of the dose distribution is very difficult when using commercial treatment planning systems. In order to determine the midplane dose, an algorithm was developed based on the use of in vivo dosimetry.

MATERIALS AND METHODS

Scanditronix EDP-30 diodes were placed at the entrance and the exit surface for in vivo dosimetry. The proposed algorithm was validated firstly in a regular and homogeneous phantom of different thickness with an ionization chamber and TL dosimeters and secondly in an Alderson anthropomorphic phantom with TL dosimeters. In this study, in vivo measurements were evaluated in 60 patients and furthermore, in 20 of them, the midplane dose calculated with this algorithm was compared with the method described by Rizzotti A, Compri C, Garusi GF. Dose evaluation to patients irradiated by 60Co beams, by means of direct measurement on the incident and on the exit surfaces. Radiother. Oncol. 1985;3:279-283.

RESULTS

No differences were found between the two methods. The differences between dose values calculated with both methods and dose values measured with the ionization chamber and TL dosimeters were within +/-22% and +/-4%, respectively, in the regular and homogeneous phantom and within +/-2% in the Alderson phantom. The algorithm was useful in calculating the midplane dose when heterogeneities as lungs were present. Even when partial transmission blocks were used to reduce the dose to the lungs, the algorithm with modified correction factors gave a midplane lung dose in the Alderson phantom within 1.3% of the measurements with TL dosimeters. For 360 patients' measurements in each A-P and P-A field, the relative deviations were analyzed between the measured and calculated entrance, exit dose and midplane dose and the prescribed dose, always applying the temperature correction factor. These deviations at the entrance dose were within +/-4%. Greater deviations were found for the exit dose measurements. Deviations larger than +/-10% corresponded in general to obese patients, with a thickness over 25 cm. The relative deviations between the total received and prescribed midplane doses in 60 patients were within +/-3%.

CONCLUSIONS

The results indicate excellent correspondence between the total prescribed and calculated midplane doses using this algorithm while also no significant differences were found when the Rizzotti method was used. Comparison between doses measured with TL dosimeters in the core of Alderson phantom lungs and doses calculated from in vivo measurements showed that the proposed algorithm could be used in the presence of heterogeneities even when partial transmission blocks were used. The temperature correction factor must be applied in order to avoid a 2-3% dose overestimation.

In vivo diode dosimetry for total marrow irradiation

PURPOSE

To describe a method and evaluate the efficacy of using a p-type silicon diode as an alternative to thermoluminescent dosimeters for verifying the accuracy of total marrow irradiation setups and calculations.

METHODS AND MATERIALS

A calibration factor has been measured for a 6 MV photon beam incident horizontally onto a polystyrene phantom inside an in-house built total marrow irradiation stand. Signal responses due to positioning and orientation of the diode with respect to the source were compared to a 0.6 cc cylindrical ionization chamber inside a polystyrene phantom. Procedures for predicting the diode reading and taking entrance measurements have been developed and action levels established to determine causes for discrepancies when ratios between predicted and actual values fell outside a +/- 5% tolerance range. Measurements were taken at the skin surface over the umbilicus calculation point for alternating 1.5 Gy anterior and posterior fractions given bidaily over a 3-day period.

RESULTS

A total of 137 measurements taken from January to September 1994 for 23 patients were analyzed using a frequency histogram. The histogram indicated a mean reading of 1.002 +/- 2.6, and that three of the measurements fell outside the 5% tolerance. Investigation into the cause of the discrepancies showed that the diode had been improperly placed one time and that further patient immobilization needs to be considered.

CONCLUSION

It is possible to use a diode as an in vivo dosimeter for a total marrow irradiation technique. The ease of implementation and immediate readouts make a diode system preferable to a thermoluminescent system for identifying systematic errors and verifying treatment configurations and monitor unit calculations.

Calibration of semiconductor detectors for dose assessment in total body irradiation

The aim of this paper is to discuss the measurements carried out to implement 'in vivo dosimetry' with EDP-30 diodes in total body irradiation (TBI) techniques. Exit calibrations and calibrations behind cerrobend protection blocks showed the importance of calibrating diodes in all relevant clinical conditions. Special attention was given to calibration of diodes behind cerrobend blocks. Dependence of the calibration factors on the thickness of the shielding blocks was, therefore, studied. This dependence was again studied after adding a wax cap to the diode and when the ionisation chamber was placed at the same depth as the measuring point of the diode. Temperature dependence in diode sensitivity and dependence on accumulated dose for diodes response and for temperature correction factors were also examined.

Total body irradiation with translation method

Total body irradiation (TBI) using translation method has been applied in 20 patients prior to bone marrow transplantation (BMT). This paper describes the technique of irradiation as well as the results of in vivo dosimetry in patients undergoing TBI. According to our experience, the translation technique is comfortable for patient and provides homogeneous dose distribution over the whole body.