[Inverse radiotherapy planning]

Application and progress of artificial intelligence in radiation therapy dose prediction

Radiation therapy (RT) nowadays is a main treatment modality of cancer. To ensure the therapeutic efficacy of patients, accurate dose distribution is often required, which is a time-consuming and labor-intensive process. In addition, due to the differences in knowledge and experience among participants and diverse institutions, the predicted dose are often inconsistent. In last several decades, artificial intelligence (AI) has been applied in various aspects of RT, several products have been implemented in clinical practice and confirmed superiority. In this paper, we will review the research of AI in dose prediction, focusing on the progress in deep learning (DL).

Lack of Relevant Haemogram Changes During Percutaneous Radiotherapy of Localised Prostate Cancer

BACKGROUND/AIM

In percutaneous radiotherapy dose-distribution and volumetric-load of normal tissue varies in different radiation-techniques. Haematotoxicity may lead to deficiencies of the immune and blood system or to secondary malignancies. Therefore, regular blood-counts are carried out during fractionated radiotherapy. The aim was to investigate patient haemogram courses during radiotherapy of localised prostate-cancer treated with different radiation-techniques (n=3).

PATIENTS AND METHODS

In this prospective study, blood count changes were examined during fractionated radiotherapy (3D-conformal-RT/step-and-shoot-IMRT/helical-IMRT) on the prostate-region in localised prostate-cancer cases (n=50).

RESULTS

The whole patient group displayed a small but significant reduction in leukocytes. This reduction was higher in the two IMRT groups compared to the 3D-group but without any case of leukopenia. Haemoglobin- or thrombocyte-levels did not significantly change.

CONCLUSION

Regardless of the delivery mode used, localised fractionated irradiation of prostate region did not cause any clinically relevant haemogram changes in this study. These findings question the necessity of regular blood counts during fractionated radiotherapy of the prostate region for patients without any risk factors.

Photodynamic therapy for prostate cancer - A narrative review

This article is a review of approaches to treatment of low and high-grade prostate cancer including a discussion of active treatment vs. active surveillance for patients with low-grade prostate cancer. In particular, we will review PDT as an option for active treatment of low-grade prostate cancer considered in light of recent clinical trials. The mechanism and clinical methods of PDT application and the key points from clinical trials using PDT for prostate cancer with the photosensitizers m-tetrahydroxyphenyl chloride, protoporphyrin IX, motexafin lutetium, padoporfin, and padeliporfin between the years 2002 and 2017 are reviewed. Recently developed methodologies for photodynamic prostate cancer treatment that are in the experimental stage, photodynamic diagnosis, fluorescence guided resection, and PSMA-targeted PDT will also be discussed.

Inversely Planned Intensity Modulated Radiotherapy of the Breast Including the Internal Mammary Chain: A Plan Comparison Study

The aim of this paper is to evaluate the benefit of inversely planned intensity modulated radiotherapy (IMRT) in the adjuvant irradiation of breast cancer when internal mammary lymph nodes are included in the treatment volume. 20 patients treated with 3D-planned conventional radiotherapy (CRT) following breast conserving surgery were included in the study. We chose 10 patients with left-sided and 10 patients with right-sided tumors. All treatment volumes included the internal mammary chain. For plan comparison to the applied CRT plan an inverse IMRT-plan in ‘step-and-shoot’-technique was calculated.

For all patients IMRT resulted in an improved conformity of dose distribution to the target volume compared to CRT (mean COIN95: 0.798 vs. 0.514 with COIN95 = C1* C2 (C1= fraction of CTV that is covered by > 95% of the prescribed dose and C2 = volume of CTV that is covered by > 95% of the prescribed dose/total volume that is covered by > 95% of the prescribed dose). In all cases with matching adjacent beams, the homogeneity in the target volume was improved. The volume of the ipsilateral lung irradiated with a dose higher than 20 Gy was reduced with IMRT from 24.6% to 13.1% compared to CRT. For left-sided target volume the heart volume with a dose higher than 30 Gy was reduced from 6.2% to 0.2%.

The presented plan comparison study for irradiation of the breast and the parasternal lymph nodes showed a substantial improvement of the dose distribution by inversely planned IMRT compared to CRT. This is visible for the target volume, the ipsilateral lung and, in case of left-sided target volume, the heart. Despite an increase in integral dose to the entire normal tissue, the application of IMRT might be clinically advantageous in cases where no satisfying dose distribution can be obtained by CRT.

Inverse treatment planning for spinal robotic radiosurgery: an international multi-institutional benchmark trial

Stereotactic radiosurgery (SRS) is the accurate, conformal delivery of high‐dose radiation to well‐defined targets while minimizing normal structure doses via steep dose gradients. While inverse treatment planning (ITP) with computerized optimization algorithms are routine, many aspects of the planning process remain user‐dependent. We performed an international, multi‐institutional benchmark trial to study planning variability and to analyze preferable ITP practice for spinal robotic radiosurgery. 10 SRS treatment plans were generated for a complex‐shaped spinal metastasis with 21 Gy in 3 fractions and tight constraints for spinal cord (V14Gy<2 cc, V18Gy<0.1 cc) and target (coverage >95%). The resulting plans were rated on a scale from 1 to 4 (excellent‐poor) in five categories (constraint compliance, optimization goals, low‐dose regions, ITP complexity, and clinical acceptability) by a blinded review panel. Additionally, the plans were mathematically rated based on plan indices (critical structure and target doses, conformity, monitor units, normal tissue complication probability, and treatment time) and compared to the human rankings. The treatment plans and the reviewers' rankings varied substantially among the participating centers. The average mean overall rank was 2.4 (1.2‐4.0) and 8/10 plans were rated excellent in at least one category by at least one reviewer. The mathematical rankings agreed with the mean overall human rankings in 9/10 cases pointing toward the possibility for sole mathematical plan quality comparison. The final rankings revealed that a plan with a well‐balanced trade‐off among all planning objectives was preferred for treatment by most participants, reviewers, and the mathematical ranking system. Furthermore, this plan was generated with simple planning techniques. Our multi‐institutional planning study found wide variability in ITP approaches for spinal robotic radiosurgery. The participants', reviewers', and mathematical match on preferable treatment plans and ITP techniques indicate that agreement on treatment planning and plan quality can be reached for spinal robotic radiosurgery.

PACS number(s): 87.55.de

Long term results of postoperative Intensity-Modulated Radiation Therapy (IMRT) in the treatment of Squamous Cell Carcinoma (SCC) located in the oropharynx or oral cavity

BACKGROUND

To report our long-term results with postoperative intensity-modulated radiation therapy (IMRT) in patients suffering from squamous-cell carcinoma (SCC) of the oral cavity or oropharynx.

METHODS

Seventy five patients were retrospectively analyzed. Median age was 58 years and 84 % were male. 76 % of the primaries were located in the oropharynx. Surgery resulted in negative margins (R0) in 64 % of the patients while 36 % suffered from positive margins (R1). Postoperative stages were as follows: stage 1:4 %, stage 2:9 %, stage 3:17 %, stage 4a:69 % with positive nodes in 84 %. Perineural invasion (Pn+) and extracapsular extension (ECE) were present in 7 % and 29 %, respectively. All patients received IMRT using the step-and-shoot approach with a simultaneously integrated boost (SIB) in 84 %. Concurrent systemic therapy was applied to 53 patients, mainly cisplatin weekly.

RESULTS

Median follow-up was 55 months (5-150). 13 patients showed locoregional failures (4 isolated local, 4 isolated neck, 5 combined) transferring into 5-year-LRC rates of 85 %. Number of positive lymph nodes (n > 2) and presence of ECE were significantly associated with decreased LRC in univariate analysis, but only the number of nodes remained significant in multivariate analysis. Overall treatment failures occurred in 20 patients (9 locoregional only, 7 distant only, 4 combined), transferring into 3-and 5-year-FFTF rates of 77 % and 75 %, respectively. The 3-and 5-year-OS rates were 80 % and 72 %, respectively. High clinical stage, high N stage, number of positive nodes (n > 2), ECE and Pn1 were significantly associated with worse FFTF and OS in univariate analysis, but only number of nodes remained significant for FFTF in multivariate analysis. Maximum acute toxicity was grade 3 in 64 % and grade 4 in 1 %, mainly hematological or mucositis/dysphagia. Maximum late toxicity was grade 3 in 23 % of the patients, mainly long-term tube feeding dependency.

CONCLUSION

Postoperative IMRT achieved excellent LRC and good OS with acceptable acute and low late toxicity rates. The number of positive nodes (n > 2) was a strong prognostic factor for all endpoints in univariate and the only significant factor for LRC and FFTF in multivariate analysis. Patients with feeding tubes due to postoperative complications had an increased risk for long-term feeding tube dependency.

In vivo measurement of dose distribution in patients' lymphocytes: helical tomotherapy versus step-and-shoot IMRT in prostate cancer

In radiotherapy, in vivo measurement of dose distribution within patients' lymphocytes can be performed by detecting gamma-H2AX foci in lymphocyte nuclei. This method can help in determining the whole-body dose. Options for risk estimations for toxicities in normal tissue and for the incidence of secondary malignancy are still under debate. In this investigation, helical tomotherapy (TOMO) is compared with step-and-shoot IMRT (SSIMRT) of the prostate gland by measuring the dose distribution within patients' lymphocytes. In this prospective study, blood was taken from 20 patients before and 10 min after their first irradiation fraction for each technique. The isolated leukocytes were fixed 2 h after radiation. DNA double-stranded breaks in lymphocyte nuclei were stained immunocytochemically using anti-gamma-H2AX antibodies. Gamma-H2AX foci distribution in lymphocytes was determined for each patient. Using a calibration line, dose distributions in patients' lymphocytes were determined by studying the gamma-H2AX foci distribution, and these data were used to generate a cumulative dose-lymphocyte histogram (DLH). Measured in vivo (DLH), significantly fewer lymphocytes indicated low-dose exposure (<40% of the applied dose) during TOMO compared with SSIMRT. The dose exposure range, between 45 and 100%, was equal with both radiation techniques. The mean number of gamma-H2AX foci per lymphocyte was significantly lower in the TOMO group compared with the SSIMRT group. In radiotherapy of the prostate gland, TOMO generates a smaller fraction of patients' lymphocytes with low-dose exposure relative to the whole body compared with SSIMRT. Differences in the constructional buildup of the different linear accelerator systems, e.g. the flattening filter, may be the cause thereof. The influence of these methods on the incidence of secondary malignancy should be investigated in further studies.

Intensity modulated radiotherapy (IMRT) combined with concurrent but not adjuvant chemotherapy in primary nasopharyngeal cancer - a retrospective single center analysis

Background

We report our experience in 49 consecutive patients with nasopharyngeal carcinoma who were treated by Intensity-modulated radiation therapy (IMRT) combined with simultaneous but not adjuvant chemotherapy (CHT).

Methods

The medical records of 49 patients with histologically proven primary nasopharygeal carcinoma treated with IMRT and concurrent platin-based CHT (predominantly cisplatin weekly) were retrospectively reviewed. The majority of patients showed advanced clinical stages (stage III/IV:72%) with undifferentiated histology (82%). IMRT was performed in step-and-shoot technique using an integrated boost concept in 84%. In this concept, the boost volume covered the primary tumor and involved nodes with doses of 66–70.4 Gy (single dose 2.2 Gy). Uninvolved regional nodal areas were covered with doses of 54–59.4 Gy (median single dose 1.8 Gy). At least one parotid gland was spared. None of the patients received adjuvant CHT.

Results

The median follow-up for the entire cohort was 48 months. Radiation therapy was completed without interruption in all patients and 76% of the patients received at least 80% of the scheduled CHT. Four local recurrences have been observed, transferring into 1-, 3-, and 5-year Local Control (LC) rates of 98%, 90% and 90%. One patient developed an isolated regional nodal recurrence, resulting in 1-, 3-, and 5-year Regional Control (RC) rates of 98%. All locoregional failures were located inside the radiation fields. Distant metastases were found in six patients, transferring into 1-, 3, and 5-year Distant Control (DC) rates of 92%, 86% and 86%. Progression free survival (PFS) rates after 1, 3 and 5 years were 86%, 70% and 69% and 1-, 3- and 5-year Overall Survival (OS) rates were 96%, 82% and 79%. Acute toxicity ≥ grade III mainly consisted of dysphagia (32%), leukopenia (24%), stomatitis (16%), infection (8%) and nausea (8%). Severe late toxicity (grade III) was documented in 18% of the patients, mainly as xerostomia (10%).

Conclusion

Concurrent chemoradiation without the addition of adjuvant chemotherapy cycles using IMRT with an integrated boost concept yielded good disease control and overall survival in patients suffering from primary nasopharyngeal cancer with acceptable acute side effects and limited rates of late toxicity.

Intensity modulated or fractionated stereotactic reirradiation in patients with recurrent nasopharyngeal cancer

PURPOSE

To report our experience with intensity-modulated or stereotactic reirradiation in patients suffering from recurrent nasopharyngeal carcinoma

PATIENTS AND METHODS

The records of 17 patients with recurrent nasopharygeal carcinoma treated by intensity-modulated (n = 14) or stereotactic (n = 3) reirradiation in our institution were reviewed. Median age was 53 years and most patients (n = 14) were male. The majority of tumors showed undifferentiated histology (n = 14) and infiltration of intracranial structures (n = 12). Simultaneous systemic therapy was applied in 8 patients. Initial treatment covered the gross tumor volume with a median dose of 66 Gy (50-72 Gy) and the cervical nodal regions with a median dose of 56 Gy (50-60 Gy). Reirradiation was confined to the local relapse region with a median dose of 50.4 Gy (36-64Gy), resulting in a median cumulative dose of 112 Gy (91-134 Gy). The median time interval between initial and subsequent treatment was 52 months (6-132).

RESULTS

The median follow up for the entire cohort was 20 months and 31 months for survivors (10-84). Five patients (29%) developed isolated local recurrences and three patients (18%) suffered from isolated nodal recurrences. The actuarial 1- and 2-year rates of local/locoregional control were 76%/59% and 69%/52%, respectively. Six patients developed distant metastasis during the follow up period. The median actuarial overall survival for the entire cohort was 23 months, transferring into 1-, 2-, and 3-year overall survival rates of 82%, 44% and 37%. Univariate subset analyses showed significantly increased overall survival and local control for patients with less advanced rT stage, retreatment doses > 50 Gy, concurrent systemic treatment and complete response. Severe late toxicity (Grad III) attributable to reirradiation occurred in five patients (29%), particularly as hearing loss, alterations of taste/smell, cranial neuropathy, trismus and xerostomia.

CONCLUSION

Reirradiation with intensity-modulated or stereotactic techniques in recurrent nasopharyngeal carcinoma is feasible and yields encouraging results in terms of local control and overall survival in patients with acceptable toxicity in patients with less advanced recurrences. However, the achievable outcome is limited in patients with involvement of intracranial structures, emphasising the need for close monitoring after primary therapy.

IMRT reirradiation with concurrent cetuximab immunotherapy in recurrent head and neck cancer

PURPOSE

In this retrospective investigation, the outcome and toxicity after reirradiation with concurrent cetuximab immunotherapy of recurrent head and neck cancer (HNC) in patients who had contraindications to platinum-based chemotherapy were analyzed.

MATERIALS AND METHODS

Ten patients with locally advanced recurrent HNC were retrospectively evaluated. In 9 cases, histology was squamous cell carcinoma, in one case adenoid cystic carcinoma. External beam radiotherapy was part of the initial treatment in all cases. Reirradiation was carried out using step-and-shoot intensity-modulated radiotherapy (IMRT) with a median dose of 50.4 Gy. Cetuximab was applied as loading dose (400 mg/m(2)) 1 week prior to reirradiation and then weekly concurrently with radiotherapy (250 mg/m(2)).

RESULTS

The median overall survival time after initiation of reirradiation was 7 months; the 1-year overall survival (OS) rate was 40%. Local failure was found in 3 patients, resulting in a 1-year local control (LC) rate of 61%. The 1-year locoregional control (LRC) rate was 44%, while the 1-year distant metastasis-free survival (DMFS) was 75%. Acute hematological toxicity was not observed in the group. Severe acute toxicity included one fatal infield arterial bleeding and one flap necrosis. Severe late toxicities were noted in 2 patients: fibrosis of the temporomandibular joint in 1 patient and stenosis of the cervical esophagus in another.

CONCLUSIONS

IMRT reirradiation with concurrent cetuximab immunotherapy in recurrent HNC is feasible with acceptable acute toxicity. Further investigations are necessary to determine the clinical role of this therapy concept.

Intensity modulated radiotherapy (IMRT) in benign giant cell tumors--a single institution case series and a short review of the literature

BACKGROUND

Giant cell tumors are rare neoplasms, representing less than 5% of all bone tumors. The vast majority of giant cell tumors occurs in extremity sites and is treated by surgery alone. However, a small percentage occurs in pelvis, spine or skull bones, where complete resection is challenging. Radiation therapy seems to be an option in these patients, despite the lack of a generally accepted dose or fractionation concept. Here we present a series of five cases treated with high dose IMRT.

PATIENTS AND METHODS

From 2000 and 2006 a total of five patients with histologically proven benign giant cell tumors have been treated with IMRT in our institution. Two patients were male, three female, and median age was 30 years (range 20-60). The tumor was located in the sacral region in four and in the sphenoid sinus in one patient. All patients had measurable gross disease prior to radiotherapy with a median size of 9 cm. All patients were treated with IMRT to a median total dose of 64 Gy (range 57.6 Gy to 66 Gy) in conventional fractionation.

RESULTS

Median follow up was 46 months ranging from 30 to 107 months. Overall survival was 100%. One patient developed local disease progression three months after radiotherapy and needed extensive surgical salvage. The remaining four patients have been locally controlled, resulting in a local control rate of 80%. We found no substantial tumor shrinkage after radiotherapy but in two patients morphological signs of extensive tumor necrosis were present on MRI scans. Decline of pain and/or neurological symptoms were seen in all four locally controlled patients. The patient who needed surgical salvage showed markedly reduced pain but developed functional deficits of bladder, rectum and lower extremity due to surgery. No severe acute or late toxicities attributable to radiation therapy were observed so far.

CONCLUSION

IMRT is a feasible option in giant cells tumors not amendable to complete surgical removal. In our case series local control was achieved in four out of five patients with marked symptom relief in the majority of cases. No severe toxicity was observed.

Intensity modulated radiotherapy (IMRT) in patients with carcinomas of the paranasal sinuses: clinical benefit for complex shaped target volumes

INTRODUCTION

The aim of the study was to evaluate the clinical outcome of intensity modulated radiotherapy (IMRT) in 46 patients with paranasal sinus tumors with special respect to treatment-related toxicity.

PATIENTS AND METHODS

We treated 46 patients with histologically proven tumors of the paranasal sinuses with IMRT. Histological classification included squamous cell carcinoma in 6, adenocarcinoma in 8, adenoidcystic carcinoma in 20 and melanoma in 8 patients, respectively. Six patients had been treated with RT during initial therapy after primary diagnosis, and IMRT was performed for the treatment of tumor progression as re-irradiation.

RESULTS

Overall survival rates were 96% at 1 year, 90% at 3 years. Calculated from the initiation of IMRT as primary radiotherapy, survival rates at 1 and 3 years were 95% and 80%. In six patients IMRT was performed as re-irradiation, and survival rate calculated from re-irradiation was 63% at 1 year. Local control rates were 85% at 1, 81% at 2 and 49% at 3 years after primary RT and 50% at 1 year after re-irradiation. Distant metastases-free survival in patients treated with IMRT as primary RT was 83% after 1 and 64% after 3 years. For patients treated as primary irradiation with IMRT, the distant control rate was 83% at 1 year and 0% at 2 years. No severe radiation-induced side-effects could be observed.

CONCLUSION

IMRT for tumors of the paranasal sinuses is associated with very good tumor control rates. Treatment-related acute and long-term toxicity can be minimized as compared to historical results with conventional RT.

Two-dimensional ionization chamber arrays for IMRT plan verification

In this paper we describe a concept for dosimetric treatment plan verification using two-dimensional ionization chamber arrays. Two different versions of the 2D-ARRAY (PTW-Freiburg, Germany) will be presented, a matrix of 16 x 16 chambers (chamber cross section 8 mm x 8 mm; the distance between chamber centers, 16 mm) and a matrix of 27 x 27 chambers (chamber cross section 5 mm x 5 mm; the distance between chamber centers is 10 mm). The two-dimensional response function of a single chamber is experimentally determined by scanning it with a slit beam. For dosimetric plan verification, the expected two-dimensional distribution of the array signals is calculated via convolution of the planned dose distribution, obtained from the treatment planning system, with the two-dimensional response function of a single chamber. By comparing the measured two-dimensional distribution of the array signals with the expected one, a distribution of deviations is obtained that can be subjected to verification criteria, such as the gamma index criterion. As an example, this verification method is discussed for one sequence of an IMRT plan. The error detection capability is demonstrated in a case study. Both versions of two-dimensional ionization chamber arrays, together with the developed treatment plan verification strategy, have been found to provide a suitable and easy-to-handle quality assurance instrument for IMRT.

[Imaging of sacral chordoma: comparison between MRI and CT]

AIM

Sacral chordoma is a primarily benign tumor with a high tendency to recur. A correct definition of tumor volume is a significant prognostic factor. We compared the value of CT and MRI in diagnosing a sacral chordoma.

METHODS

31 patients with a histologically proven sacral chordoma were included in this study. Following parameters were analyzed by two independent radiologists: septation, signs of blood and ossification in the tumor tissue, contrast enhancement, maximal tumor diameter, infiltration of the soft tissue, the dural salc and the cauda equina and multifocality.

RESULTS

In CT all chordomas showed a hypodensity to the normal tissue and in MRI a hyperintensity on T2w images with a low level of contrast enhancement. On the basis of the more precise soft tissue contrast of MRI compared with CT, MRI was significantly more accurate in all tested parameters (p <0.05) besides in detecting tumor ossification. In CT tumor volume was frequently underestimated.

CONCLUSION

MRI in sacral chordoma is an essential tool in the pretherapeutic diagnostic regimen and in a state of relapse.

Number and Orientation of Beams in Inversely Planned Intensity-Modulated Radiotherapy of the Female Breast and the Parasternal Lymph Nodes

Intensity-modulated radiotherapy (IMRT) provides better sparing of normal tissue. We evaluated the optimum beam configuration for IMRT based on inverse treatment planning in adjuvant radiotherapy for breast cancer in a case of left-sided tumor. In addition to radiotherapy planning with the conventional technique of tangential wedged 6-MV photon beams and an oblique 15-MeV electron beam, we performed inversely planned IMRT with the step-and-shoot-technique. Dose calculation was carried out using the treatment planning system Virtuos with the inverse optimization module KonRad adapted to it. IMRT plans were generated for 2 to 16 beams. The results were compared with conventional techniques. For a maximum treatment time of 20 minutes, it is shown that IMRT with 12 modulated photon beams and 7 intensity steps is best suited for treatment in the presented case. Compared with a conventional technique with photons combined with electrons, dose conformality and homogeneity of the planning target volume was increased. The mean heart dose was reduced from 9.1 Gy to 6.1 Gy. The volume of heart irradiated with a dose higher than 30 Gy was reduced from 7.6% to 1.9%, and the volume of the left lung from 13.6% to 11.5% as well. Inverse optimization for IMRT with multiple beams is feasible in the adjuvant treatment of breast cancer. Because of the reduction of the high-dose area of a substantial cardiac volume, it is superior to conventional techniques in cases where the parasternal lymph nodes should be integrated into the target volume. Here, a clinical advantage might be detectable.

[Use of a two-dimensional ionization chamber array for quality assurance in medical linear accelerators]

Two-dimensional dosimetry measurements are an important tool of Quality Assurance in modern radiotherapy techniques, such as the Intensity Modulated Radiation Therapy (IMRT). Common procedures are usually based on the use of films or semiconductor arrays as dosimeters. This paper presents our experience with a two-dimensional ionization-chamber array. The methods presented here allow the daily use of the array for a constancy check of the accelerator. It is also shown that the position of the individual leafs of the multi-leaf collimator (MLC) can be verified to within +/- 1 mm of their calibration. A procedure for the measurements is described and discussed.

Stereotactic intensity modulated radiation therapy and inverse treatment planning for tumors of the head and neck region: clinical implementation of the step and shoot approach and first clinical results

PURPOSE/OBJECTIVE

The aim of this analysis is to evaluate the feasibility of inverse treatment planning and intensity modulated radiation therapy (IMRT) for head and neck cancer in daily clinical routine. A step and shoot IMRT approach was developed which allows the treatment of large target volumes without the need to use a split beam technique. By using the IMRT approach better protection of different organs at risk in the head and neck region may be achieved and an escalation of the dose in the tumor should be possible. We evaluated the feasibility of the treatment technique and the patient tolerance to the treatment. First clinical results are reported.

MATERIALS AND METHODS

Between 1999 and 2002, 48 patients with a carcinoma of the head and neck region were treated with curative intention. All patients were treated in a patient-specific Scotch-Cast mask. Patients who required treatment of the lymph node levels I-VI, were additionally positioned by a vacuum pillow in order to immobilize the upper part of the thorax. For inverse treatment planning, the software module KonRad was used which was integrated into the VIRTUOS planning system. Each treatment plan was verified using quantitative film dosimetry in a head and neck phantom. The step and shoot IMRT technique with a multileaf collimator integrated in a Primus (Siemens) accelerator was used for treatment. For all target volumes the whole target including the lymph nodes were covered completely by the IMRT treatment.

RESULTS

The mean total dose for the target volumes of macroscopic disease ranged between 63.0 and 64.1 Gy. The mean total dose of microscopic disease ranged between 55.2 and 60.1 Gy. The mean percentage of planning target volume receiving <90% of the prescribed dose ranged between 3.0 and 11.5%. For the treatment, the median number of beams was seven (range: five to nine). The time to deliver the treatment ranged between 9 and 18 min. The results of the verification revealed a mean deviation between measured and calculated absolute doses for the 48 patients of 0.1+/-1.4%. Including the phantom verification the IMRT treatment of the patients could be started approximately after five working days. The treatment was well tolerated by all patients. The 2-year actuarial overall survival was 92% and the 2-year actuarial local control rate was 93%. According to the Radiation Therapy Oncology Group (RTOG), no higher acute toxicity than Grade 3 was seen. Observation of the late effects revealed only one transient Grade 4 toxicity of the bone and only four patients had a xerostomia higher than Grade 1.

CONCLUSION

The use of an inversely-planned and intensity-modulated step and shoot approach is feasible in clinical routine for head and neck tumors. Treatment could be applied as planned and no increased toxicity was found. Compared to other IMRT approaches for the head and neck region the used technique allows the treatment of the primary tumor and the lymph nodes level I-VI with only one intensity modulated treatment volume. The presented technique avoids to match conventional radiotherapy fields and IMRT fields, and therefore, reduce the risk of overdosage or underdosage at the matching line. Compared to conventional treatment techniques IMRT shows advantages in tumor dose and dose at the organs at risk.

Intensity-modulated radiotherapy of the female breast

Current methods for intensity-modulated radiotherapy (IMRT) in breast cancer use forward planning based on equivalent radiological path length to design intensity modulated tangential beams. Compared to conventional tangential techniques, dose reduction of organs at risk is limited using these techniques. We developed a method for intensity modulation of multiple beams for adjuvant radiotherapy of breast cancer by application of a virtual bolus defined on CT for inverse optimization. This method enables multibeam IMRT, which provides improved sparing of lung and heart tissue. In this paper, we present the general aspects of this approach and an evaluation of the optimum beam configuration for IMRT based on inverse treatment planning. We compared this method to conventional techniques. Different clinical examples illustrate the possible indications and feasibility of this new approach. This method is superior to conventional techniques because of the reduction of high-dose area of a substantial cardiac volume in those cases where the parasternal lymph nodes are part of the target volume.

[Design of an inverse planning system for radiotherapy using linear optimization]

Our approach shows that inverse planning for intensity-modulated beams in radiotherapy can be solved efficiently by the mathematical method of linear optimization. The completeness property of this method guarantees that calculated treatment plans fulfill the dose constraints given by the oncologist. Techniques developed by our group can also avoid the possible infeasibility caused by a physically impossible dose distribution. In contrast to other optimization methods, the simplex algorithm used for linear optimization allows a very high optimization speed, i.e., very short planning cycles. These preconditions were integrated in the development of the software system MIPART ("Munich Inverse Planning And Radiotherapy Treatment"). The object-oriented software architecture of MIPART achieves a maximum of extensibility and flexibility. Our clinical tests show that MIPART can be easily integrated in the clinical routine in spite of the complexity of data in the field of intensity-modulated radiotherapy. Moreover, qualitatively better treatment plans can be generated than in conventional treatment planning, especially in complicated cases.

[Intensity modulated radiotherapy (IMRT) with compensators]

The irradiation with intensity-modulated fields is possible with static as well as dynamic methods. In our university hospital, the intensity-modulated radiotherapy (IMRT) with compensators was prepared and used for the first time for patient irradiation in July 2001. The compensators consist of a mixture of tin granulate and wax, which is filled in a milled negative mould. The treatment planning is performed with Helax-TMS (MDS Nordion). An additional software is used for editing the modulation matrix ("Modifix"). Before irradiation of the first patient, extensive measurements have been carried out in terms of quality assurance of treatment planning and production of compensators. The results of the verification measurements have shown that IMRT with compensators possesses high spatial and dosimetric exactness. The calculated dose distributions are applied correctly. The accuracy of the calculated monitor units is normally better than 3%; in small volumes, further dosimetric inaccuracies between calculated and measured dose distributions are mostly less than 3%. Therefore, the compensators contribute to the achievement of high-level IMRT even when apparatuses without MLC are used. This paper describes the use of the IMRT with compensators, presents the limits of this technology, and discusses the first practical experiences.

Dose optimization via index-dose gradient minimization

This paper presents an iterative optimization algorithm based on gradient minimization of index dose, defined as the product of physical dose and a numerical index. Acting as a template the index distribution is designed to represent the dosimetry that meets the dose volume histogram-based optimization objectives. The treatment dosimetry is optimized when the uniformity of the index-dose distribution is maximized. Prior to optimization the user can select all or only some of the beams to be intensity modulated. The remaining unmodulated beams can be either open or wedged photon beams, electron beams, or beams of previous treatments. The optimization result and treatment delivery efficiency can often be enhanced by including not only the IM photon beams but also all suitable fixed-beams available on the linac in the treatment plan. In addition, the doses from previous treatments can also be considered in the optimization of current treatment. Five clinical examples with different complexities in optimization objective are presented. The effects of two nonoptimization variables, beam setup and initial beam weights, on the quality of the dose optimization are also presented. The results are analyzed in terms of isodose distribution, dose volume histograms, and a dose optimization quality factor. The optimization algorithm, implemented in our in-house TPS PLanUNC, has been used in clinical application since 1996. The primary advantages of our optimization algorithm include computational efficiency, intensity modulation selection choice, and performance reliability for a wide range of clinical beam setups and optimization objectives.

Compensators for IMRT--an investigation in quality assurance

Intensity modulated radiotherapy (IMRT) allows dose distributions which adequately consider organs at risk (OAR) and dose homogeneity to the target volume. This is practically reached by conforming the beam profiles to the shape of the planning target volume (PTV), by shaping the fluence with multileaf collimators (MLC) or compensators. Though compensator production is time consuming and seems less convenient than the use of MLC, compensators offer much easier quality assurance. In this study the effects of certain simplifications of compensator production were studied. Compensators were produced and ionization chamber measurements in a water phantom and film measurements in a solid phantom were performed to verify the compensators. The results of the measurements were compared to the fluence distributions given by the planning system. The measurements were meant to show how realistic the investigated simplifications were, and to reveal a suitable and reliable testing method for compensators. Monte-Carlo calculations employing the EGS 4 Code were further performed to support the measurements.