The different volume effects of small-bowel toxicity during pelvic irradiation between gynecologic patients with and without abdominal surgery: a prospective study with computed tomography-based dosimetry

Role of microbiota in radiation-induced small-bowel damage

Radiation-induced gastrointestinal damage is a common acute radiation syndrome. Previous studies have highlighted that Galectin-1 and Interleukin-6 (IL-6) are associated with flaking of small intestinal villi and intestinal radioresistance. Therefore, our goal is to study whether gut bacteria regulated by galectin-1 or IL-6 can mitigate radiation-induced small intestine damage. In this study, differences between galectin-1, sgp130-regulated and wild-type (WT) mice were analyzed by microbiome array. The effects of the Firmicutes/Bacteroidetes (F/B) ratio and the proportion of bacterial distribution at the phylum level were observed after 18 Gy whole abdomen radiation. Fecal microbiota transplantation was used to implant radioresistant gut flora into WT mice, and the number of viable small intestinal crypt foci was observed by immunohistochemistry. Fecal transplantation from galectin-1 knockout and sgp130 transgenic mice, with higher radiation resistance, into WT mice significantly increased the number of surviving small intestinal crypts. This radiation resistance, generated through gene regulation, was not affected by the F/B ratio. We initially found that the small intestinal villi of WT mice receiving radioresistant mouse fecal bacteria demonstrated better repair outcomes after radiation exposure. These results indicate the need for a focus on the identification and application of superior radioresistant bacterial strains. In our laboratory, we will further investigate specific radioresistant bacterial strains to alleviate acute side effects of radiation therapy to improve the patients' immune ability and postoperative quality of life.

Small Bowel Dose Constraints in Radiation Therapy—Where Omics-Driven Biomarkers and Bioinformatics Can Take Us in the Future

Radiation-induced gastrointestinal (GI) dose constraints are still a matter of concern with the ongoing evolution of patient outcomes and treatment-related toxicity in the era of image-guided intensity-modulated radiation therapy (IMRT), stereotactic ablative radiotherapy (SABR), and novel systemic agents. Small bowel (SB) dose constraints in pelvic radiotherapy (RT) are a critical aspect of treatment planning, and prospective data to support them are scarce. Previous and current guidelines are based on retrospective data and experts’ opinions. Patient-related factors, including genetic, biological, and clinical features and systemic management, modulate toxicity. Omic and microbiome alterations between patients receiving RT to the SB may aid in the identification of patients at risk and real-time identification of acute and late toxicity. Actionable biomarkers may represent a pragmatic approach to translating findings into personalized treatment with biologically optimized dose escalation, given the mitigation of the understood risk. Biomarkers grounded in the genome, transcriptome, proteome, and microbiome should undergo analysis in trials that employ, R.T. Bioinformatic templates will be needed to help advance data collection, aggregation, and analysis, and eventually, decision making with respect to dose constraints in the modern RT era.

Intra-abdominal Surgery and Intestinal Syndromes After Pelvic Radiation Therapy

Purpose

To determine the effects of intra-abdominal surgery on the intensities of 5 radiation-induced intestinal syndromes in survivors of pelvic cancer.

Methods and Materials

The analysis included 623 women born in 1927 or later who had survived cancer. They all had received external radiation therapy toward the pelvic area to treat gynecologic cancers. Information from 344 women who did not undergo irradiation, matched for age and residency, was also included. Main outcome measures after the surgical procedures were the intensity scores for 5 radiation-induced intestinal syndromes: urgency-tenesmus syndrome, fecal-leakage syndrome, excessive mucus discharge, excessive gas discharge, and blood discharge. The scores were based on symptom frequencies obtained from patient-reported outcomes and on factor loadings obtained from a previously reported factor analysis. Follow-up was 2 to 15 years after radiation therapy.

Results

Among survivors of cancer, intra-abdominal surgery increased the intensity of the urgency-tenesmus syndrome, the fecal-leakage syndrome, excessive gas discharge, and blood discharge but had a negligible effect on mucus discharge. Intra-abdominal surgery had an especially negative effect on the urgency-tenesmus syndrome. Although the combination of appendectomy with 1 or more other intra-abdominal surgeries resulted in the highest score for all syndromes, appendectomy alone had weak to no effect. In women who did not undergo irradiation, a similar pattern was seen, albeit with much lower scores.

Conclusions

We found intra-abdominal surgery to be a risk factor among survivors of gynecologic cancer, increasing the intensity score of 4 out of 5 radiation-induced intestinal syndromes. During radiation therapy, it may be worthwhile to pay extra attention to the dose of unwanted ionizing radiation to the intestines if the patient previously has undergone intra-abdominal surgery.

Evaluation of dosimetric predictors of toxicity after IMRT with concurrent chemotherapy for anal cancer

BACKGROUND

This study investigates the impact of dosimetric parameters on acute and late toxicity for patients with anal squamous cell carcinoma (SCC) treated with image-guided intensity modulated radiation therapy (IG-IMRT) and concurrent chemotherapy.

MATERIALS AND METHODS

Patients were enrolled in an observational cohort study between 2008 and 2013 (median follow-up 3.4 years). They were treated with standardized target and organ-at-risk (OAR) contouring, planning, and IG-IMRT. Radiotherapy dose, based on clinicopathologic features, ranged from 45 Gy to 63 Gy to gross targets and 27 Gy to 36 Gy to elective targets. Chemotherapy was concurrent 5-fluorouracil and mitomycin C (weeks 1&5). Toxicity was prospectively graded using NCI CTCAE v.3 and RTOG scales. Logistic regression was used to assess the association between dose/volume parameters (e.g small bowel V5) and corresponding grade 2 + and 3+ (G2+/3 + ) toxicities (e.g. diarrhea).

RESULTS

In total, 87 and 79 patients were included in the acute and late toxicity analyses, respectively. The most common acute G2 + toxicities were skin (dermatitis in 87 % [inguino-genital skin], 91 % [perianal skin]) and hematologic in 58 %. G2 + late anal toxicity (sphincter dysfunction), gastrointestinal toxicity, and skin toxicity were respectively experienced by 49 %, 38 %, and 44 % of patients. Statistically significant associations were observed between: G2 + acute diarrhea and small bowel V35; G2 + acute genitourinary toxicity and bladder D_0.5cc; G2 + inguino-genital skin toxicity and anterior skin V35; G2 + perianal skin toxicity and posterior skin V15; G2 + anemia and lower pelvis bone V45. D0.5 cc was significantly predictive of late toxicity (G2 + anal dysfunction, intestinal toxicity, and inguino-genital/perianal dermatitis). Maximum skin toxicity grade was significantly correlated with the requirement for a treatment break.

CONCLUSION

Statistically significant dose-volume parameters were identified and may be used to offer individualized risk prediction and to inform treatment planning. Additional validation of the results is required.

Dosimetric and Clinical Predictors for Acute and Late Gastrointestinal Toxicity Following Chemoradiotherapy of Locally Advanced Anal Cancer

AIMS

To analyse dosimetric and clinical predictors for acute and late gastrointestinal toxicity following chemoradiotherapy of anal cancer.

MATERIALS AND METHODS

Consecutive patients with locally advanced (T2 ≥4 cm - T4 or N+) anal cancer were selected from an institutional database (n = 114). All received intensity-modulated radiotherapy with concomitant 5-fluorouracil and mitomycin C. Gastrointestinal toxicity was retrospectively graded according to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 and bowel cavity, small bowel and large bowel were contoured. Dosimetric and clinical variables were tested for associations with acute grade ≥3 gastrointestinal toxicity and late grade ≥2 gastrointestinal toxicity using the Mann-Whitney test, area under receiver operating characteristic curve (AUC) and logistic regression.

RESULTS

The median follow-up was 40 months. Acute grade ≥3 gastrointestinal toxicity was seen in 51 (44.7%) of the patients; late grade ≥2 gastrointestinal toxicity was seen in 36 of the patients (39.6% of 91 patients with >1 year recurrence-free follow-up). Bowel cavity V30Gy was the best dosimetric predictor for acute gastrointestinal toxicity (AUC 0.633; P = 0.02). Large bowel V20Gy was the best dosimetric predictor for late gastrointestinal toxicity (AUC 0.698; P = 0.001) but showed no association with acute gastrointestinal toxicity. In multivariate logistic regression, increasing age was significantly associated with acute gastrointestinal toxicity; smoking and large bowel V20Gy were significantly associated with late gastrointestinal toxicity. Patients who experienced acute grade ≥3 gastrointestinal toxicity were not at an increased risk of late grade ≥2 gastrointestinal toxicity (odds ratio 1.3; P = 0.55).

CONCLUSIONS

Factors of importance for acute and late gastrointestinal toxicity were not the same. Bowel cavity V30Gy is a good metric to use for the prediction of acute gastrointestinal toxicity, but the results of our study indicate that individual large and small bowel loops need to be contoured for better prediction of late gastrointestinal toxicity. The role of the large bowel as an important organ at risk for late gastrointestinal toxicity merits further research.

Effective Organs-at-Risk Dose Sparing in Volumetric Modulated Arc Therapy Using a Half-Beam Technique in Whole Pelvic Irradiation

BACKGROUND

Although there are some controversies regarding whole pelvic radiation therapy (WPRT) due to its gastrointestinal and hematologic toxicities, it is considered for patients with gynecological, rectal, and prostate cancer. To effectively spare organs-at-risk (OAR) doses using multi-leaf collimator (MLC)'s optimal segments, potential dosimetric benefits in volumetric modulated arc therapy (VMAT) using a half-beam technique (HF) were investigated for WPRT.

METHODS

While the size of a fully opened field (FF) was decided to entirely include a planning target volume in all beam's eye view across arc angles, the HF was designed to use half the FF from the isocenter for dose optimization. The left or the right half of the FF was alternatively opened in VMAT-HF using a pair of arcs rotating clockwise and counterclockwise. Dosimetric benefits of VMAT-HF, presented with dose conformity, homogeneity, and dose-volume parameters in terms of modulation complex score, were compared to VMAT optimized using the FF (VMAT-FF). Consequent normal tissue complication probability (NTCP) by reducing the irradiated volumes was evaluated as well as dose-volume parameters with statistical analysis for OAR. Moreover, beam-on time and MLC position precision were analyzed with log files to assess plan deliverability and clinical applicability of VMAT-HF as compared to VMAT-FF.

RESULTS

While VMAT-HF used 60%-70% less intensity modulation complexity than VMAT-FF, it showed superior dose conformity. The small intestine and colon in VMAT-HF showed a noticeable reduction in the irradiated volumes of up to 35% and 15%, respectively, at an intermediate dose of 20-45 Gy. The small intestine showed statistically significant dose sparing at the volumes that received a dose from 15 to 45 Gy. Such a dose reduction for the small intestine and colon in VMAT-HF presented a significant NTCP reduction from that in VMAT-FF. Without sacrificing the beam delivery efficiency, VMAT-HF achieved effective OAR dose reduction in dose-volume histograms.

CONCLUSIONS

VMAT-HF led to deliver conformal doses with effective gastrointestinal-OAR dose sparing despite using less modulation complexity. The dose of VMAT-HF was delivered with the same beam-on time with VMAT-FF but precise MLC leaf motions. The VMAT-HF potentially can play a valuable role in reducing OAR toxicities associated with WPRT.

Unrecognized digestive toxicities of radiation therapy

The aim of this article is to review unrecognized toxicities resulting from radiation therapy of digestive neoplasms. Due to their precocious occurrence, acute toxicities are well-known by radiation oncologist, and their treatment well-established. Thus, acute toxicities will not be described in this review. We will focus on incidence, diagnosis, and management of late and uncommon toxicities occurring in the digestive tract and digestive organs. Prevention, by respecting healthy tissues constraints, is the main tool to reduce incidence of those rare complications. Nonetheless, once installed, late toxicities remain a major burden in terms of quality of life and can even be life threatening. Hence, information and education about their diagnosis and management is important.

Rectal Dose Is the Other Dosimetric Factor in Addition to Small Bowel for Prediction of Acute Diarrhea during Postoperative Whole-Pelvic Intensity-Modulated Radiotherapy in Gynecologic Patients

Simple Summary

Although the small bowel volume effect for acute diarrhea during radiotherapy has been investigated, no study has reported the influence of rectal dose. We analyzed 108 patients undergoing intensity-modulated radiotherapy after hysterectomy. Acute diarrhea was defined as onset during radiotherapy based on Common Terminology Criteria for Adverse Events (CTCAE) version 3. Both small bowel and rectum dosimetric parameters affected Grade 2 to 3 diarrhea. The high-dose volume effects on the small bowel still play an important role in postoperative intensity-modulated radiotherapy. This is the first large cohort study to demonstrate the role of both IMRT dosimetric factors of the rectum and the small bowel in acute diarrhea in gynecological patients with a previous hysterectomy. A small bowel volume of 39.6 Gy < 60 mL and a mean rectal dose of <32.75 Gy are suggested as constraints to treatment planning.

Abstract

We studied the association of rectal dose with acute diarrhea in patients with gynecologic malignancies undergoing whole-pelvic (WP) intensity-modulated radiotherapy (IMRT). From June 2006 to April 2019, 108 patients with previous hysterectomy who underwent WP IMRT were enrolled in this cohort study. WP irradiation of 39.6–45 Gy/22–25 fractions was initially delivered to the patients. Common Terminology Criteria for Adverse Events (CTCAE) version 3 was used to evaluate acute diarrhea during radiotherapy. Small bowel volume at different levels of isodose curves (Vn%) and mean rectal dose (MRD) were measured for statistical analysis. The multivariate analysis showed that the MRD ≥ 32.75 Gy (p = 0.005) and small bowel volume of 100% prescribed (V100%) ≥ 60 mL (p = 0.008) were independent factors of Grade 2 or higher diarrhea. The cumulative incidence of Grade 2 or higher diarrhea at 39.6 Gy were 70.5%, 42.2%, and 15.0% (p < 0.001) in patients with both high (V100% ≥ 60 mL and MRD ≥ 32.75 Gy), either high, and both low volume-dose factors, respectively. Strict constraints for the rectum/small bowel or image-guided radiotherapy to reduce these doses are suggested.

Evaluation of small bowel motion and feasibility of using the peritoneal space to replace bowel loops for dose constraints during intensity-modulated radiotherapy for rectal cancer

BACKGROUND

The goal of this study was to assess small bowel motion and explore the feasibility of using peritoneal space (PS) to replace bowel loops (BL) via the dose constraint method to spare the small bowel during intensity-modulated radiotherapy (IMRT) for rectal cancer.

METHODS

A total of 24 patients with rectal cancer who underwent adjuvant or neoadjuvant radiotherapy were selected. Weekly repeat CT scans from pre-treatment to the fourth week of treatment were acquired and defined as Plan, 1 W, 2 W, 3 W, and 4 W. The 4 weekly CT scans were co-registered to the Plan CT, BL and PS contours were delineated in all of the scans, an IMRT plan was designed on Plan CT using PS constraint method, and then copied to the 4 weekly CT scans. The dose-volume, normal tissue complication probability (NTCP) of the small bowel and their variations during treatment were evaluated.

RESULTS

Overall, 109 sets of CT scans from 24 patients were acquired, and 109 plans were designed and copied. The BL and PS volumes were 250.3 cc and 1339.3 cc. The V15 of BL and PS based plan of pre-treatment were 182.6 cc and 919.0 cc, the shift% of them were 28.9 and 11.3% during treatment (p = 0.000), which was less in the prone position than in the supine position (25.2% vs 32.1%, p = 0.000; 9.9% vs 14.9%, p = 0.000). The NTCPC and NTCPA based plan of pre-treatment were 2.0 and 59.2%, the shift% during treatment were 46.1 and 14.0% respectively. Majority of BL's Dmax and V15 were meet the safety standard during treatment using PS dose limit method except 3 times (3/109) of V15 and 5 times of Dmax (5/109).

CONCLUSIONS

This study indicated that small bowel motion may lead to uncertainties in its dose volume and NTCP evaluation during IMRT for rectal cancer. The BL movements were significantly greater than PS, and the prone position was significantly less than the supine position. It is feasibility of using PS to replace BL to spare the small bowel, V15 < 830 cc is the dose constraint standard.

Radiation enteritis: Diagnostic and therapeutic issues

Abdominal pelvic radiation therapy can induce acute or chronic lesions in the small bowel wall, called radiation enteritis. Treatment of acute radiation enteritis is essentially symptomatic; symptoms regress when radiation is discontinued. Conversely, late toxicity can occur up to 30 years after discontinuation of radiation therapy, posing diagnostic problems. Approximately one out of five patients treated by radiation therapy will present clinical signs of radiation enteritis, including obstruction, malabsorption, malnutrition and/or other complications. Management should be multidisciplinary, centered mainly on correction of malnutrition. Surgery is indicated in case of complications (i.e., abscess, perforation, fistula) and/or resistance to medical treatment; intestinal resection should be preferred over internal bypass. The main risk in case of iterative resections is the short bowel syndrome and the need for definitive nutritional assistance.

Dosimetric Parameters Predicting Late Small Bowel Toxicity in Patients With Rectal Cancer Receiving Neoadjuvant Chemoradiation

PURPOSE

The aim of this study was to identify dosimetric parameters that predict late small bowel (SB) toxicity after neoadjuvant long course chemoradiation (CRT) for rectal cancer.

METHODS AND MATERIALS

Four hundred eighty-six consecutive patients with locally advanced rectal cancers (clinical T3/T4 or N1/N2) who received CRT followed by surgery and had dosimetric data available for analysis were included in this study. The dose-volume relationship between small bowel irradiation and late small bowel toxicity was evaluated and a mathematical model to predict for late SB toxicity was derived.

RESULTS

Among the 486 patients with a median follow-up of 60 months from completion of radiation, 36 (7.4%) patients experienced ≥ grade 2 and 21 (4.3%) developed ≥ grade 3 late SB toxicity. A statistically significant association between the development of grade ≥3 late small bowel toxicity and the volume of small bowel irradiated was found at each dose level from 5 to 40 Gy (P < .001 for all dose volumes) in 5 Gy intervals. The average SB volume for patients who experienced grade ≥2 SB toxicity was 2149.9 cm³ and the average SB volume for patients who experienced grade ≥3 SB toxicity was 2179.9 cm³. The predicted V30 for a 5% risk for grade ≥2 SB toxicity was 101.5 cm³ and for grade ≥3 SB toxicity was 201.5 cm³. The volume of small bowel receiving at least 30 Gy (V30) was most strongly associated with grade ≥3 SB toxicity.

CONCLUSIONS

This study demonstrates the significant dose-volume relationship between volume of small bowel receiving 30 Gy (V30 Gy) and late grade ≥3 SB toxicity. When planning CRT for patients with rectal cancer, restricting V30 to <200 cm³ will be a useful guideline to minimize the 5 year grade ≥3 late SB toxicity to <5%.

Dosimetric comparison of helical tomotherapy and VMAT for anal cancer: A single institutional experience

To compare the dosimetric results of helical tomotherapy (HT) and volumetric arc therapy (VMAT) in the treatment of anal cancer. Plans were created for 20 (n = 20) patients treated for anal cancer using HT and 2 arc VMAT. Dosimetric comparison was assessed for doses to targets and organs at risk (small bowel, bladder, external genitalia, and femoral heads). Delivery time and dosimetric verification results were also compared. HT showed a higher V95% for both primary and nodal targets (V95% increase by 0.5% to 1.3%; p = ≤0.05). No differences were seen in V105%, V107%, or V110 % between techniques. HT provided better sparing of the small bowel for dose levels V30, V35, and V40 (p = 0.005, 0.001, and 0.030), but was similar at higher doses. Similarly HT provided better bladder dose at V35 only (p = 0.020). Doses to femoral heads and genitalia were similar. Delivery time was higher for the HT plans (4.58 ± 1.1 min) than VMAT (3.13 ± 0.2 minutes) (p = 0.011). Dose verification results were 99.5 ± 0.9% and 100 ± 0% (HT, n = 6) vs 95.0 ± 3.1% and 99.2 ± 0.8% (VMAT, n = 20) for global gamma criteria 3%/3 mm and 4%/4 mm, respectively. Both HT and VMAT produced high quality plans that frequently met most of the dose objectives apart from genitalia V20, V40, bladder V35, and V50. Although absolute dose differences were small, the PTV V95%, small bowel V30, V35, and V40 and bladder V35 were statistically better in the HT plans. VMAT provided a shorter delivery time by 1.45 minutes; however, our HT plans were more likely to pass tighter plan dose verification criteria than VMAT.

Stomach Dose-Volume Predicts Acute Gastrointestinal Toxicity in Chemoradiotherapy for Locally Advanced Pancreatic Cancer

AIMS

Gastrointestinal toxicity impedes dose escalation in chemoradiotherapy for hepatobiliary malignancies. Toxicity risk depends on clinical and radiotherapy metrics. We aimed to identify predictive factors using data from two prospective phase II clinical trials of locally advanced pancreatic cancer (LAPC).

MATERIALS AND METHODS

Ninety-one patients with available data from the ARCII (59.4 Gy in 33 fractions with gemcitabine, cisplatin and nelfinavir, n = 23) and SCALOP (50.4 Gy in 28 fractions with capecitabine or gemcitabine, n = 74) trials were studied. The independent variables analysed comprised age, sex, performance status, baseline symptoms, tumour size, weight loss, chemotherapy regimen and dose-volume histogram of stomach and duodenum in 5 Gy bins. The outcome measures used were Common Terminology Criteria of Adverse Events (CTCAE) grade and risk of CTCAE grade ≥2 acute upper gastrointestinal toxicity (anorexia, pain, nausea and/or vomiting). The risk of CTCAE grade ≥2 events was modelled using multivariable logistic regression and prediction of severity grade using ordinal regression.

RESULTS

CTCAE grade ≥2 symptoms occurred in 38 patients (42%). On univariate analysis, stomach V35-45Gy was predictive of risk (odds ratio 1.035, 95% confidence interval 1.007-1.063) and grade (1.023, 1.003-1.044) of toxicity. The area under the curve was 0.632 (0.516-0.747) with toxicity risk 33/66 (50%) above and 5/25 (20%) below the optimal discriminatory threshold (7.1 cm3). Using a threshold of 30 cm3, risk was 13/20 (65%) versus 25/71 (35%). The optimal multivariable logistic regression model incorporated patient sex, chemotherapy regimen and stomach V35-45Gy. Receiving gemcitabine rather than capecitabine (odds ratio 3.965, 95% confidence interval 1.274-12.342) and weight loss during induction chemotherapy (1.216, 1.043-1.419) were significant predictors for the SCALOP cohort, whereas age predicted toxicity risk in ARCII only (1.344, 1.015-1.780). Duodenum dose-volume did not predict toxicity risk or severity in any cohort.

CONCLUSIONS

In chemoradiotherapy for LAPC the volume of stomach irradiated to a moderately high dose (35-45 Gy) predicts the incidence and severity of acute toxicity. Other predictive factors can include age, sex, recent weight loss and concomitant chemotherapy agents.

Late small bowel toxicity after aggressive abdominopelvic intensity modulated radiation therapy

Purpose

We retrospectively analyzed late small bowel toxicity in patients who received abdominal or pelvic intensity modulated radiation therapy (IMRT) to the small bowel with a maximum dose greater than the generally accepted maximal tolerable dose of 45 Gy.

Methods and materials

All patients (N = 94) who received IMRT with a point dose of at least 45 Gy to tightly contoured small bowel between 2005 and 2014 at our institution were included. The median prescribed treatment dose was 70.2 Gy. The median follow-up was 20.1 months. Late small bowel toxicity was assessed using the Common Terminology Criteria for Adverse Events Version 3.0. Dosimetric variables and clinical factors were assessed for their relationship to small bowel toxicity.

Results

The median maximal small bowel point dose (D_max) was 6546.5 cGy. The estimated 5-year rates of freedom from at least grade 1, at least grade 2, and at least grade 3 late small bowel toxicity were 72.4% (95% confidence interval [CI], 60.7%-86.5%), 91.9% (95% CI, 84.1%-100%), and 93.6% (95% CI, 86.2%-100%), respectively. One patient (1.1%) developed grade 3 late toxicity, and 2 patients (2.1%) developed grade 4 late toxicity. Use of capecitabine/5-fluorouracil treatment was a significant predictor (P < 0.001) of at least grade 1 and at least grade 2 small bowel toxicity. No other clinical factors were associated with toxicity. None of the dose-volume parameters were significant predictors of small bowel toxicity.

Conclusion

It may be possible with IMRT to deliver high doses to small volumes of small bowel with low rates of significant long-term complications. Further studies should explore tolerable dose-volume relationships in cases in which aggressive abdominal or pelvic treatment may be warranted to treat the underlying malignancy.

Bag and loop small bowel contouring strategies differentially estimate small bowel dose for post-hysterectomy women receiving pencil beam scanning proton therapy

Background Small bowel (SB) dose-volume relationships established during initial computed tomography (CT) simulations may change throughout therapy due to organ displacement and motion. We investigated the impact of organ motion on SB dose-volume histograms (DVHs) in women with gynecologic malignancies treated with pencil beam scanning (PBS) proton therapy and compared PBS SB DVHs to intensity-modulated radiation therapy (IMRT). Material and methods Post-hysterectomy patients (n = 11) treated for gynecologic cancers were enrolled on an image-guided proton therapy protocol involving CT simulation with full (CTF) and empty (CTE) bladders and weekly/biweekly on-treatment scans. IMRT plans were generated for comparative analysis. SB was contoured as bowel loops or bowel bag. Wilcoxon signed-rank tests were used for matched-pair comparisons of SB, bladder, and rectum dose-volumes between CT scans and between PBS and IMRT plans. Results In PBS loops analysis, on-treatment DVH was significantly higher than CTF for doses <45 Gy (p < 0.05), and not significantly different than CTE. Specifically, V15 for loops was higher on-treatment (median 240 cm(3)) compared to CTF (median 169 cm(3), p = 0.03). In PBS bag analysis, on-treatment DVH was not significantly different from CTF across all dose ranges. Bowel bag V45 was not significantly different between on-treatment (median 540 cm(3)) and CTF (median 499 cm(3), p = 0.53). Decreasing bladder volume was associated with increasing V15 for loops and V45 for bowel bag (p < 0.005, both). Comparing PBS and IMRT, PBS resulted in significantly lower DVHs at low dose regions (<38 Gy) and higher DVHs at high dose regions (42.5-45.5 Gy) in both loops and bag analysis. IMRT plans demonstrated higher on-treatment SB loop DVHs and only minimal differences in bowel bag DVHs compared to CTF. Conclusions SB DVHs were well estimated by CTF bowel bag and underestimated by CTF loops in the setting of inconsistent bladder filling. Verifying bladder filling prior to treatment or using CTE for planning may more conservatively estimate SB dose-volume relationships.

Predicting toxicity in radiotherapy for prostate cancer

This comprehensive review addresses most organs at risk involved in planning optimization for prostate cancer. It can be considered an update of a previous educational review that was published in 2009 (Fiorino et al., 2009). The literature was reviewed based on PubMed and MEDLINE database searches (from January 2009 up to September 2015), including papers in press; for each section/subsection, key title words were used and possibly combined with other more general key-words (such as radiotherapy, dose-volume effects, NTCP, DVH, and predictive model). Publications generally dealing with toxicity without any association with dose-volume effects or correlations with clinical risk factors were disregarded, being outside the aim of the review. A focus was on external beam radiotherapy, including post-prostatectomy, with conventional fractionation or moderate hypofractionation (<4Gy/fraction); extreme hypofractionation is the topic of another paper in this special issue. Gastrointestinal and urinary toxicity are the most investigated endpoints, with quantitative data published in the last 5years suggesting both a dose-response relationship and the existence of a number of clinical/patient related risk factors acting as dose-response modifiers. Some results on erectile dysfunction, bowel toxicity and hematological toxicity are also presented.

Amifostine alleviates radiation-induced lethal small bowel damage via promotion of 14-3-3σ-mediated nuclear p53 accumulation

Amifostine (AM) is a radioprotector that scavenges free radicals and is used in patients undergoing radiotherapy. p53 has long been implicated in cell cycle arrest for cellular repair after radiation exposure. We therefore investigated the protective p53-dependent mechanism of AM on small bowel damage after lethal whole-abdominal irradiation (WAI). AM increased both the survival rate of rats and crypt survival following lethal 18 Gy WAI. The p53 inhibitor PFT-α compromised AM-mediated effects when administered prior to AM administration. AM significantly increased clonogenic survival in IEC-6 cells expressing wild type p53 but not in p53 knockdown cells. AM significantly increased p53 nuclear accumulation and p53 tetramer expression before irradiation through the inhibition of p53 degradation. AM inhibited p53 interactions with MDM2 but enhanced p53 interactions with 14-3-3σ. Knockdown of 14-3-3σ also compromised the effect of AM on clonogenic survival and p53 nuclear accumulation in IEC-6 cells. For the first time, our data reveal that AM alleviates lethal small bowel damage through the induction of 14-3-3σ and subsequent accumulation of p53. Enhancement of the p53/14-3-3σ interaction results in p53 tetramerization in the nucleus that rescues lethal small bowel damage.

Evaluating QUANTEC Small Bowel Dose-Volume Guidelines for Rectal Cancer Patients Treated Using a Couch Top Inclined Belly Board

PURPOSE

The goal of this work was to analyse small bowel (SB) dose-volume following the Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) guidelines for rectal cancer patients treated using a couch top inclined belly board (iBB). As part of this, the consistency in SB displacement was evaluated using on-treatment cone-beam computed tomographic (CBCT) imaging.

METHODS

Twenty-four patients with rectal cancer were treated on a commercially available iBB. All patients went through the standard radiochemotherapy protocol in either a pre- or postoperative setup. All patients underwent weekly CBCT imaging during the course of radiation treatment. The planning computed tomographic data sets were used to analyze the quality of SB displacement, and the CBCT data sets were used to assess the reproducibility in SB displacement during treatment. The SB dose volume was evaluated and compared with QUANTEC-recommended dose limitations. Similarly, the impact of body mass index on dose volume and SB displacement was evaluated.

RESULTS

The SB displacement was assessed respectively as "good" and "very good" by both independent evaluating radiation oncologists. The consistency of SB displacement through the course of radiation treatment was scored as "excellent" for 22 of 24 and 23 of 24 patients by both radiation oncologists, respectively. The QUANTEC recommendation was met for all patients without bowel adhesions; however, the most benefit was observed for patients with body mass index > 23 kg/m².

CONCLUSIONS

Our study has shown that QUANTEC recommendations for SB dose during rectal cancer treatment can easily be met by treating patients on a couch top iBB. This technique is robust and produces consistent SB displacement.

The different dose-volume effects of normal tissue complication probability using LASSO for acute small-bowel toxicity during radiotherapy in gynecological patients with or without prior abdominal surgery

Purpose. To develop normal tissue complication probability (NTCP) model with least absolute shrinkage and selection operator (LASSO) to analyze dose-volume effects that influence the incidence of acute diarrhea among gynecological patients with/without prior abdominal surgery. Methods and Materials. Ninety-five patients receiving gynecologic radiotherapy (RT) were enrolled. The endpoint was defined as the grade 2⁺ acute diarrhea toxicity during treatment. We obtained the range of small-bowel volume in V4 Gy to V40 Gy of dose. Results. The number of patients experiencing grade 2⁺ acute diarrhea toxicity was 23/61 (38%) in the group without abdominal surgery (group 0) and 17/34 (50%) patients with abdominal surgery (group 1). The most significant predictor was found for the logistic NTCP model with V16 Gy as the cutoff dose for group 0 and V40 Gy for group 1. Logistic regression NTCP model parameters were TV₁₀ ≈ 290 cc for V16 Gy and TV₁₀ ≈ 75 cc for V40 Gy, respectively. Conclusion. To keep the incidence of grade 2⁺ acute small-bowel toxicity below 10%, we suggest that small-bowel volume above the prescription dose (V16 Gy) should be held to <290 cc for patients without abdominal surgery, and the prescription dose (V40 Gy) should be maintained <75 cc for patients with abdominal surgery.

Technical aspects of radiation therapy for anal cancer

Historically treated with surgery, current practice recommends anal carcinoma to be treated with a combination of chemotherapy and radiation. This review will examine the anatomy, modes of disease spread and recurrence, and evaluate the existing evidence for treatment options for these tumors. An in-depth examination of specific radiation therapy (RT) techniques-such as conventional 3D-conformal RT and intensity-modulated RT-will be discussed along with modern dose constraints. RT field arrangement, patient setup, and recommended gross and clinical target volume (CTV) contours will be considered. Areas in need of further investigation, such as the role in treatment for positron emission tomography (PET) will be explored.

A randomized double-blind controlled trial: impact of probiotics on diarrhea in patients treated with pelvic radiation

BACKGROUND & AIMS

Radical radiation therapy is commonly used for treatment of pelvic cancer. Up to 80% of patients receiving radiotherapy will develop acute radiation induced diarrhea. The primary aim of this randomized double blind controlled trial is to evaluate the effect of the probiotic Bifilact(®) on moderate and severe treatment-induced diarrhea during pelvic radiation.

METHODS

Patients with pelvic cancers were treated between 2006 and 2010 at L'Hôtel-Dieu de Québec, University Health Center. Some patients had surgery before pelvic radiotherapy and some received chemotherapy. A total of 246 Patients were randomized between a placebo and either of two regiments of double strain Bifilact(®) probiotics (Lactobacillus acidophilus LAC-361 and Bifidobacterium longum BB-536): a standard dose twice a day (1.3 billion CFU) or a high dose three times a day (10 billion CFU). Patients were trained to record their digestive symptoms daily with a standardized scale and they met a registered dietician and radiation oncologist every week during treatment. The main analysis compared time to first appearance of grade ≥2-3-4 diarrhea using Kaplan-Meier curves as measured by proportion of patients without moderate and severe diarrhea.

RESULTS

229 patients were analyzed. The difference between the groups for overall grade 2-3-4 diarrhea was not statistically significant (p = 0.13). However at 60 days, the proportion of patients without moderate and severe diarrhea in the standard dose group (35%) was more than twice as high as that of the placebo group (17%) with a hazard ratio of 0.69 (p = 0.04). In patients who had surgery, the standard probiotics dose group had a better proportion of patients without very severe diarrhea than the placebo group, respectively 97% and 74% (p = 0.03). In all groups, the average number of bowel movements per day during treatment was less than 3 soft stools (p = 0.80) and the median abdominal pain less than 1 based on the National Cancer Institute scale (p = 0.23).

CONCLUSION

Standard dose of Bifilact(®) may reduce radiation induced grade 2-3-4 diarrhea at the end of the treatment of patients with pelvic cancer. In patients operated on before RT, a standard dose of probiotics may reduce radiation induced grade 4 diarrhea. Nutritional interventions by a registered dietician seemed to reduce global digestive symptoms.

TRIAL REGISTRATION

clinicaltrials.gov. Identifier NCT01839721.

Small bowel toxicity after high dose spot scanning-based proton beam therapy for paraspinal/retroperitoneal neoplasms

PURPOSE

Mesenchymal tumours require high-dose radiation therapy (RT). Small bowel (SB) dose constraints have historically limited dose delivery to paraspinal and retroperitoneal targets. This retrospective study correlated SB dose-volume histograms with side-effects after proton radiation therapy (PT).

PATIENTS AND METHODS

Between 1997 and 2008, 31 patients (mean age 52.1 years) underwent spot scanning-based PT for paraspinal/retroperitoneal chordomas (81%), sarcomas (16%) and meningiom (3%). Mean total prescribed dose was 72.3 Gy (relative biologic effectiveness, RBE) delivered in 1.8-2 Gy (RBE) fractions. Mean follow-up was 3.8 years. Based on the pretreatment planning CT, SB dose distributions were reanalysed.

RESULTS

Planning target volume (PTV) was defined as gross tumour volume (GTV) plus 5-7 mm margins. Mean PTV was 560.22 cm(3). A mean of 93.2% of the PTV was covered by at least 90% of the prescribed dose. SB volumes (cm(3)) receiving doses of 5, 20, 30, 40, 50, 60, 70, 75 and 80 Gy (RBE) were calculated to give V5, V20, V30, V40, V50, V60, V70, V75 and V80 respectively. In 7/31 patients, PT was accomplished without any significant SB irradiation (V5=0). In 24/31 patients, mean maximum dose (Dmax) to SB was 64.1 Gy (RBE). Despite target doses of >70 Gy (RBE), SB received >50 and >60 Gy (RBE) in only 61 and 54% of patients, respectively. Mean SB volumes (cm(3)) covered by different dose levels (Gy, RBE) were: V20 (n=24): 45.1, V50 (n=19): 17.7, V60 (n=17): 7.6 and V70 (n=12): 2.4. No acute toxicity ≥ grade 2 or late SB sequelae were observed.

CONCLUSION

Small noncircumferential volumes of SB tolerated doses in excess of 60 Gy (RBE) without any clinically-significant late adverse effects. This small retrospective study has limited statistical power but encourages further efforts with higher patient numbers to define and establish high-dose threshold models for SB toxicity in modern radiation oncology.

Effect of different treatment plans on irradiated small-bowel volume in gynecologic patients undergoing whole-pelvic irradiation

To evaluate the effect of different treatment plans for whole-pelvic irradiation on small-bowel volumes (SBVs) in patients with gynecologic malignancies, 40 patients were enrolled in this study. Computed tomography (CT) simulations were performed, and the small bowel of each patient was outlined manually. Treatment plans with equal-weighted (EW) and non-equal-weighted (NEW) (70% in bilateral directions) techniques of four-field and intensity-modulated radiation therapy (IMRT) were performed. The V10-V100 represented the volume (cm³) at different levels of the prescribed doses (10-100%). The V10-V100 was compared among the different treatment planning techniques, and patients who were suitable for IMRT or NEW were identified. IMRT and NEW significantly reduced the V50-V100 and V40-V60 levels compared with EW, respectively. NEW caused a significant reduction in the V30-V60 levels in patients with a BMI ≥26 kg/m². Patients with IMRT demonstrated lower V70-V100 levels compared with those with NEW. In patients with a BMI ≥26 kg/m² or an age ≥55 years, lower V20-V50 levels were noted using NEW compared with IMRT. Treatment planning with larger weighting in the bilateral directions in four-field radiotherapy reduces the low-dose SBV in patients with gynecologic malignancies, especially in those with a high BMI or the elderly. IMRT effectively reduces high-dose SBV, especially in patients with a low BMI.

Gastrointestinal radiation injury: Symptoms, risk factors and mechanisms

Ionising radiation therapy is a common treatment modality for different types of cancer and its use is expected to increase with advances in screening and early detection of cancer. Radiation injury to the gastrointestinal tract is important factor working against better utility of this important therapeutic modality. Cancer survivors can suffer a wide variety of acute and chronic symptoms following radiotherapy, which significantly reduces their quality of life as well as adding an extra burden to the cost of health care. The accurate diagnosis and treatment of intestinal radiation injury often represents a clinical challenge to practicing physicians in both gastroenterology and oncology. Despite the growing recognition of the problem and some advances in understanding the cellular and molecular mechanisms of radiation injury, relatively little is known about the pathophysiology of gastrointestinal radiation injury or any possible susceptibility factors that could aggravate its severity. The aims of this review are to examine the various clinical manifestations of post-radiation gastrointestinal symptoms, to discuss possible patient and treatment factors implicated in normal gastrointestinal tissue radiosensitivity and to outline different mechanisms of intestinal tissue injury.

Small bowel dose parameters predicting grade ≥ 3 acute toxicity in rectal cancer patients treated with neoadjuvant chemoradiation: an independent validation study comparing peritoneal space versus small bowel loop contouring techniques

PURPOSE

To determine whether volumes based on contours of the peritoneal space can be used instead of individual small bowel loops to predict for grade ≥3 acute small bowel toxicity in patients with rectal cancer treated with neoadjuvant chemoradiation therapy.

METHODS AND MATERIALS

A standardized contouring method was developed for the peritoneal space and retrospectively applied to the radiation treatment plans of 67 patients treated with neoadjuvant chemoradiation therapy for rectal cancer. Dose-volume histogram (DVH) data were extracted and analyzed against patient toxicity. Receiver operating characteristic analysis and logistic regression were carried out for both contouring methods.

RESULTS

Grade ≥3 small bowel toxicity occurred in 16% (11/67) of patients in the study. A highly significant dose-volume relationship between small bowel irradiation and acute small bowel toxicity was supported by the use of both small bowel loop and peritoneal space contouring techniques. Receiver operating characteristic analysis demonstrated that, for both contouring methods, the greatest sensitivity for predicting toxicity was associated with the volume receiving between 15 and 25 Gy.

CONCLUSION

DVH analysis of peritoneal space volumes accurately predicts grade ≥3 small bowel toxicity in patients with rectal cancer receiving neoadjuvant chemoradiation therapy, suggesting that the contours of the peritoneal space provide a reasonable surrogate for the contours of individual small bowel loops. The study finds that a small bowel V15 less than 275 cc and a peritoneal space V15 less than 830 cc are associated with a less than 10% risk of grade ≥3 acute toxicity.

Normal tissue complication probability analysis of acute gastrointestinal toxicity in cervical cancer patients undergoing intensity modulated radiation therapy and concurrent cisplatin

PURPOSE

To test the hypothesis that increased bowel radiation dose is associated with acute gastrointestinal (GI) toxicity in cervical cancer patients undergoing concurrent chemotherapy and intensity-modulated radiation therapy (IMRT), using a previously derived normal tissue complication probability (NTCP) model.

METHODS

Fifty patients with Stage I-III cervical cancer undergoing IMRT and concurrent weekly cisplatin were analyzed. Acute GI toxicity was graded using the Radiation Therapy Oncology Group scale, excluding upper GI events. A logistic model was used to test correlations between acute GI toxicity and bowel dosimetric parameters. The primary objective was to test the association between Grade ≥2 GI toxicity and the volume of bowel receiving ≥45 Gy (V(45)) using the logistic model.

RESULTS

Twenty-three patients (46%) had Grade ≥2 GI toxicity. The mean (SD) V(45) was 143 mL (99). The mean V(45) values for patients with and without Grade ≥2 GI toxicity were 176 vs. 115 mL, respectively. Twenty patients (40%) had V(45) >150 mL. The proportion of patients with Grade ≥2 GI toxicity with and without V(45) >150 mL was 65% vs. 33% (p = 0.03). Logistic model parameter estimates V50 and γ were 161 mL (95% confidence interval [CI] 60-399) and 0.31 (95% CI 0.04-0.63), respectively. On multivariable logistic regression, increased V(45) was associated with an increased odds of Grade ≥2 GI toxicity (odds ratio 2.19 per 100 mL, 95% CI 1.04-4.63, p = 0.04).

CONCLUSIONS

Our results support the hypothesis that increasing bowel V(45) is correlated with increased GI toxicity in cervical cancer patients undergoing IMRT and concurrent cisplatin. Reducing bowel V(45) could reduce the risk of Grade ≥2 GI toxicity by approximately 50% per 100 mL of bowel spared.

Radiation-induced bowel complications: laparoscopic versus open staging of gynecologic malignancy

PURPOSE

To evaluate whether the type of surgical approach used to stage gynecologic malignancies influences the risk of developing nonrectal radiation-induced intestinal injury (NRRIII) in patients who subsequently receive adjuvant radiotherapy.

METHODS

A prospectively entered database was queried for all women with either primary or recurrent gynecologic malignancy who underwent external-beam radiation therapy ± brachytherapy and who had prior abdominopelvic surgery at our institution. Univariate and multivariate analysis of variables potentially affecting the risk of developing significant bowel toxicity (defined as grade 2 or more according to Radiation Therapy Oncology Group scoring) were performed.

RESULTS

One hundred fifty-nine patients were identified. The site of primary tumor was the cervix in 61 (38%) patients and the corpus uteri in the remaining patients (98, 62%). Treatment was delivered with a combination of external-beam and intracavitary irradiation to 50 (31.4%) patients, and 109 (68.6%) patients received only external-beam irradiation. Staging procedures were performed by open surgery in 93 (58.5%) patients, whereas laparoscopy was the surgical approach of choice in 66 (41.5%) women. Fifteen patients (9.4%) developed grade 2 or greater NRRIII, at median latency of 10 months (range 3-64 months); six were diagnosed as grade 3 complications requiring surgery, and three developed grade 4 complication. Multiple regression revealed an independent protective effect of pretreatment laparoscopic staging against the risk of developing both grade ≥2 and grade ≥3 NRRIII.

CONCLUSIONS

Notwithstanding potential limitations of nonrandomized study design, our findings suggest that the benefits of minimal-access surgery used to perform staging procedures may translate into long-term reduction in radiation-induced bowel injury.

[Normal tissue tolerance to external beam radiation therapy: small bowel]

The small bowel is a hollow organ involved in the transit and absorption of food. In relation to its anatomical location, a significant amount of this organ is exposed in whole or in part to ionizing radiation in external radiotherapy during abdominal or pelvic irradiation either for primary cancers or metastasis. The acute functional changes during external beam radiation are mainly leading to diarrhea, abdominal pain and bloating. The main late side effects of irradiation of the small intestine are chronic diarrhea, malabsorption with steatorrhea, abdominal spasms, intestinal obstruction, bleeding and fistulas. The architecture of the small intestine may be considered as parallel with a significant correlation between the irradiated volume of small bowel and the likelihood of acute toxicity, whatever the dose. The literature analysis recommends to consider the volume of small bowel receiving 15 Gy (threshold of 100 to 200 cm(3)) but also 30 and 50 Gy (thresholds of 35 to 300 cm(3), depending on the level of dose considered). Modern techniques of conformal radiotherapy with modulated intensity will probably have beneficial impact on small bowel toxicity.

Intensity-modulated radiotherapy in patients with cervical cancer. An intra-individual comparison of prone and supine positioning

Background

Chemoradiation for cervical cancer patients is associated with considerable gastrointestinal toxicity. Intensity-modulated radiotherapy (IMRT) has demonstrated superiority in terms of target coverage and normal tissue sparing in comparison to conventional 3D planning in gynaecological malignancies. Whether IMRT in prone (PP) or supine position (SP) might be beneficial for cervical cancer patients remains partially unanswered.

Methods

10 patients on FIGO stage IB-III cervical cancer, 6 patients for definitive and 4 patients for adjuvant external beam pelvic RT, were planned in PP and SP using a 7-field IMRT technique. IMRT plans for PP and SP (mean dose, D_mean 50.4 Gy) were optimized in terms of PTV coverage (1^st priority) and small bowel sparing (2^nd priority). A comparison of DVH parameters for PTV, small bowel, bladder, and rectum was performed.

Results

The comparison showed a similar PTV coverage of 95% of the prescribed dose and for target conformity in IMRT plans (PP, SP). PTV, rectum and bladder volumes were comparable for PP and SP. Significantly larger volumes of small bowel were found in PP (436 cc, + 35%, p = 0.01). PP decreased the volume of small bowel at 20-50.4 Gy (p < 0.05) and increased the rectum volumes covered by doses from 10-40 Gy (p < 0.01), the V50.4 was < 5% in both treatment positions. Bladder sparing was significant better at 50.4 Gy (p = 0.03) for PP.

Conclusion

In this dosimetric study, we demonstrated that pelvic IMRT in prone position for patients with cervical cancer seems to be beneficial in reducing small bowel volume at doses ≥20 Gy while providing similar target coverage and target conformity. The use of frequent image guidance with KV (kilovolt) or MV (megavolt) computertomography can reduce set-up deviations, and treatment in prone position can be done with a higher set-up accuracy. Clinical outcome studies are needed to affirm lower toxicity.

Predictors of acute bowel toxicity in patients treated with IMRT whole pelvis irradiation after prostatectomy

PURPOSE/OBJECTIVE

Whole pelvis irradiation with IMRT (WPRT-IMRT) after prostatectomy is efficient in reducing acute toxicity: however, a number of patients still experience moderate acute bowel toxicity.

MATERIALS AND METHODS

Ninety-six patients treated with WPRT-IMRT after prostatectomy with adjuvant or salvage intent were analysed. A number of parameters were individually recovered, including the DVHs of the intestinal cavity outside PTV and of the loops referred to both the WPRT phase and the whole treatment. Correlation between clinical-dosimetric parameters and acute bowel toxicity was investigated by logistic analyses. Best predictive cut-off values for continuous variables were assessed by ROC curves.

RESULTS

15/96 (15.6%) Patients experienced grade 2 toxicity (no grade 3). Best dose-volume predictors were the fraction of loops receiving more than 45, 50 and 55 Gy (respectively, V45TL ≥ 50cc, V50TL ≥ 13cc, V55TL ≥ 3cc; p-values ranging from 0.005 to 0.027). Age, GU acute toxicity, rectal acute toxicity and time between prostatectomy and IMRT were also predictors of acute bowel toxicity. Multivariate analysis showed that the most predictive independent parameters were age (OR: 1.13; 95%CI: 1.02-1.25; p=0.021) and V50TL (≥ 13cc, OR: 8.2; 95%CI: 1.7-40; p=0.009).

CONCLUSIONS

The risk of moderate acute uGI toxicity during WPRT-IMRT for post-operatively treated patients increases with age; the risk is substantially reduced in patients with small overlap between PTV and loops.

Radiation dose-volume effects in the stomach and small bowel

Published data suggest that the risk of moderately severe (>or=Grade 3) radiation-induced acute small-bowel toxicity can be predicted with a threshold model whereby for a given dose level, D, if the volume receiving that dose or greater (VD) exceeds a threshold quantity, the risk of toxicity escalates. Estimates of VD depend on the means of structure segmenting (e.g., V15 = 120 cc if individual bowel loops are outlined or V45 = 195 cc if entire peritoneal potential space of bowel is outlined). A similar predictive model of acute toxicity is not available for stomach. Late small-bowel/stomach toxicity is likely related to maximum dose and/or volume threshold parameters qualitatively similar to those related to acute toxicity risk. Concurrent chemotherapy has been associated with a higher risk of acute toxicity, and a history of abdominal surgery has been associated with a higher risk of late toxicity.

Predicting grade 3 acute diarrhea during radiation therapy for rectal cancer using a cutoff-dose logistic regression normal tissue complication probability model

PURPOSE

Understanding the dose-volume relationship of small bowel irradiation and severe acute diarrhea may help reduce the incidence of this side effect during adjuvant treatment for rectal cancer.

METHODS AND MATERIALS

Consecutive patients treated curatively for rectal cancer were reviewed, and the maximum grade of acute diarrhea was determined. The small bowel was outlined on the treatment planning CT scan, and a dose-volume histogram was calculated for the initial pelvic treatment (45 Gy). Logistic regression models were fitted for varying cutoff-dose levels from 5 to 45 Gy in 5-Gy increments. The model with the highest LogLikelihood was used to develop a cutoff-dose normal tissue complication probability (NTCP) model.

RESULTS

There were a total of 152 patients (48% preoperative, 47% postoperative, 5% other), predominantly treated prone (95%) with a three-field technique (94%) and a protracted venous infusion of 5-fluorouracil (78%). Acute Grade 3 diarrhea occurred in 21%. The largest LogLikelihood was found for the cutoff-dose logistic regression model with 15 Gy as the cutoff-dose, although the models for 20 Gy and 25 Gy had similar significance. According to this model, highly significant correlations (p <0.001) between small bowel volumes receiving at least 15 Gy and toxicity exist in the considered patient population. Similar findings applied to both the preoperatively (p = 0.001) and postoperatively irradiated groups (p = 0.001).

CONCLUSION

The incidence of Grade 3 diarrhea was significantly correlated with the volume of small bowel receiving at least 15 Gy using a cutoff-dose NTCP model.

Dose-volume relationships for acute bowel toxicity in patients treated with pelvic nodal irradiation for prostate cancer

PURPOSE

To find correlation between dose-volume histograms (DVHs) of the intestinal cavity (IC) and moderate-severe acute bowel toxicity in men with prostate cancer treated with pelvic nodal irradiation.

METHODS AND MATERIALS

The study group consisted of 191 patients with localized prostate cancer who underwent whole-pelvis radiotherapy with radical or adjuvant/salvage intent during January 2004 to November 2007. Complete planning/clinical data were available in 175 of these men, 91 of whom were treated with a conventional four-field technique (50.4 Gy, 1.8 Gy/fraction) and 84 of whom were treated with IMRT using conventional Linac (n = 26, 50.4 Gy, 1.8 Gy/fraction) or Helical TomoTherapy (n = 58, 50-54 Gy, 1.8-2 Gy/fraction). The IC outside the planning target volume (PTV) was contoured and the DVH for the first 6 weeks of treatment was recovered in all patients. The correlation between a number of clinical and DVH (V10-V55) variables and toxicity was investigated in univariate and multivariate analyses. The correlation between DVHs for the IC outside the PTV and DVHs for the whole IC was also assessed.

RESULTS

Twenty-two patients experienced toxicity (3/22 in the IMRT/tomotherapy group). Univariate analyses showed a significant correlation between V20-V50 and toxicity (p = 0.0002-0.001), with a higher predictive value observed for V40-V50. Previous prostatectomy (p = 0.066) and abdominal/pelvic surgery (p = 0.12) also correlated with toxicity. Multivariate analysis that included V45, abdominal/pelvic surgery, and prostatectomy showed that the most predictive parameters were V45 (p = 0.002) and abdominal/pelvic surgery (p = 0.05, HR = 2.4)

CONCLUSIONS

Our avoidance IMRT approach drastically reduces the incidence of acute bowel toxicity. V40-V50 of IC and, secondarily, previous abdominal/pelvic surgery were the main predictors of acute bowel toxicity.

Aminoguanidine alleviates radiation-induced small-bowel damage through its antioxidant effect

PURPOSE

To evaluate the effect and its mechanism of aminoguanidine (AG) on small-bowel protection after whole-abdominal irradiation (WAI) in rats.

METHODS AND MATERIALS

Male Sprague-Dawley rats (300-400 g) subjected to 12 Gy WAI were used for the study. Aminoguanidine at a dose of 50-800 mg/kg was administered by the gavage route 2 h before WAI. Mucosal damage of small bowel was evaluated by the grade of diarrhea and crypt survival; oxidative stress was determined by the level of 8-hydroxy 2'-deoxyguanosine (8-OHdG) with immunohistochemistry (IHC). Nitrosative stress was evaluated by the expression of inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine (3-NT) with IHC, and systemic and portal vein NOx (nitrite + nitrate) levels were measured and compared with and without AG treatment after WAI.

RESULTS

Aminoguanidine showed a dose-dependent effect against WAI-induced diarrhea. Aminoguanidine at a dose of 400 mg/kg had the best protective effect, from 92% to 17% (p = 0.002). Aminoguanidine increased crypt survival from 23% to 46% (p = 0.003). It also significantly attenuated 8-OHdG expression but not 3-NT and iNOS expression at both 4 and 8 h after 12-Gy WAI. Aminoguanidine did not alter the portal vein NOx levels 4 and 8 h after 12-Gy WAI.

CONCLUSION

Aminoguanidine has a radioprotective effect against radiation-induced small-bowel damage due to its antioxidant effect but not inhibition of nitric oxide production. Dietary AG may have a potentially protective effect on the small intestine of patients subjected to pelvic and abdominal radiotherapies.

Conformity index: a review

We present a critical analysis of the conformity indices described in the literature and an evaluation of their field of application. Three-dimensional conformal radiotherapy, with or without intensity modulation, is based on medical imaging techniques, three-dimensional dosimetry software, compression accessories, and verification procedures. It consists of delineating target volumes and critical healthy tissues to select the best combination of beams. This approach allows better adaptation of the isodose to the tumor volume, while limiting irradiation of healthy tissues. Tools must be developed to evaluate the quality of proposed treatment plans. Dosimetry software provides the dose distribution in each CT section and dose-volume histograms without really indicating the degree of conformity. The conformity index is a complementary tool that attributes a score to a treatment plan or that can compare several treatment plans for the same patient. The future of conformal index in everyday practice therefore remains unclear.